HEAVY MECHANICAL TRADES

Transcription

1 HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1 Line C: Hydraulics Competencies C-1 to C-2

2 Ordering Crown Publications, Queen s Printer PO Box 9452 Stn Prov Govt 563 Superior St. 3rd Flr Victoria, B.C. V8W 9V7 Phone: Fax: crownpub@gov.bc.ca Web: , 2016 by Industry Training Authority This publication may not be reproduced in any form without permission by the Industry Training Authority. Contact Director, Crown Publications, Queen s Printer at Acknowledgments Heavy Mechanical Trades Project Working Group Writers: Lloyd Babcock, Bob Glover, Terry Lockhart, Roger Young Reviewers: Brian Haugen, Rene Tremblay, Paul Mottershead, Mark Scorah, Rick Cyr, Lloyd Babcock, Terry Lockhart Editor: Greg Aleknevicus Open School BC Project Manager: Solvig Norman, Christina Teskey (revisions) Production Technicians: Sharon Barker, Beverly Carstensen, Dennis Evans Art Coordination: Dennis Evans, Christine Ramkeesoon Art: Dennis Evans, Margaret Kernaghan, Max Licht Image Acknowledgments The following suppliers have kindly provided copyright permission for selected product images: Acklands-Grainger Inc. Alcoa Fastening Systems, Industrial Products SKF USA Inc. Stemco LP an EnPro Industries Ray Vaughan Every effort has been made to secure copyright permission for the images used in this document. ISBN Please note that it is always the responsibility of any person using these materials to inform him/herself about the Occupational Health and Safety Regulation pertaining to his/her work. The references to WorkSafeBC safety regulations contained within these materials do not / may not reflect the most recent Occupational Health and Safety Regulation (the current Standards and Regulation in BC can be obtained on the following website: We want your feedback! Please go to the BC Trades Modules website ( to enter comments about specific sections that require correction or modification. All submissions will be reviewed and considered for inclusion in the next revision. Disclaimer The materials in these booklets are for use by students and instructional staff and have been compiled from sources believed to be reliable and to represent best current opinions on these subjects. These manuals are intended to serve as a starting point for good practices and may not specify all minimum legal standards. No warranty, guarantee, or representation is made by the Heavy Mechanical Articulation Committee of BC, the British Columbia Industry Training Authority or the Queen s Printer of British Columbia as to the accuracy or sufficiency of the information contained in these publications. These manuals are intended to provide basic guidelines for heavy mechanical trades practices. Do not assume, therefore, that all necessary warnings and safety precautionary measures are contained in this booklet and that other or additional measures may not be required. Version 2, September 2016

3 Line C: Hydraulics Competencies C-1 to C-2 Table of Contents Competency C-1: Describe Hydraulic Systems Goals Learning Task 1: Describe the Principles of Hydraulics Self Test Learning Task 2: Describe the Basic Operation of a Hydraulic System Self Test Learning Task 3: Describe Types of Hydraulic Systems Self Test Learning Task 4: Interpret Basic Hydraulic Diagrams Self Test Competency C-2: Service Hydraulic Components Goals Learning Task 1: Describe Hydraulic Components Self Test Learning Task 2: Select Hydraulic Fluids Self Test Learning Task 3: Select Hydraulic Hoses and Fittings Self Test Learning Task 4: Assemble Hydraulic Hose and Fittings Self Test Learning Task 5: Demonstrate Safe Work Procedures Self Test Learning Task 6: Perform Scheduled Maintenance Self Test Answer Key HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1 3

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5 COMPETENCY C-1 DESCRIBE HYDRAULIC SYSTEMS C-1 DESCRIBE HYDRAULICS HEAVY MECHANICAL TRADES: LINE C HYDRAULICS

6 Goals In order to successfully service and maintain a hydraulic system, you must have a sound working knowledge of hydraulic principles. The widespread use of hydraulic systems requires that you be competent in the service and repair of systems and their components. When you have completed the Learning Tasks in this Competency, you will be able to: describe the principles of hydraulics describe the basic components of a hydraulic system describe the types of hydraulic systems interpret basic hydraulic diagrams HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1 7

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8 C-1 DESCRIBE HYDRAULICS LEARNING TASK 1 LEARNING TASK 1 Describe the Principles of Hydraulics Terminology Terminology is an important part of the Heavy Mechanical Trades. Hydraulics has its own language and terms. Actuator Flow rate Fluid Force Hydraulics Hydrodynamics Hydrostatics Mass Orifice Actuators convert hydraulic power into mechanical power. Examples of actuators are hydraulic cylinders and motors. Flow rate is a measure of a volume of fluid passing a point in a given amount of time, usually per minute. Metric: litres per minute (L/min) Imperial: gallons per minute (gpm) Fluid refers to any substance that flows. Both gases and liquids are fluids. Force is defined as a push or a pull. Metric: Newton (N) Imperial: pound (lb.) Hydraulics is the science of transmitting motion through the use of oil flow and oil pressure. Hydrodynamics is the science of transmitting motion through the movement of oil. The system is designed for high oil flow and low oil pressures. An example of this is a torque converter. Hydrostatics is the science of transmitting motion through the pressure of a confined oil. The system is designed for low oil flow and high oil pressures. Examples of this are hydraulic presses, hydraulic jacks, boom hydraulic systems, and blade hydraulic systems. Mass describes the amount of material in an object. Metric: gram, kilogram (g, Kg) Imperial: pound (lb.) Orifice is a component that restricts oil flow. They are used to create a pressure drop. HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1 9

9 LEARNING TASK 1 C-1 DESCRIBE HYDRAULICS Power Pressure Pump Torque Vacuum Velocity Work Power is work done in a unit of time. Metric: watt, kilowatt (w, Kw) Imperial: horsepower (hp) Pressure is a measure of force per unit of area. Pressure is a result of resistance to flow and generates force to move a load. Metric: Newton per square meter (N m 2 ), Pascal (Pa) Imperial: pounds per square inch (psi, lb in 2 ) Pumps convert mechanical energy to hydraulic energy (flow). Torque is a twisting force. Pumps take torque to turn and motors use the torque for the output force. Metric: Newton meter (N m) Imperial: pound feet (lb ft), pound inch (lb in) Vacuum is the absence of positive pressure (i.e., pressure that is less than atmospheric pressure). Metric: centimetres of mercury (cm-hg) Imperial: inches of mercury (in-hg) Velocity is rate of speed. Metric: metres per second (m/sec) Imperial: feet per second (ft/sec) Work is force through a distance. The object must move to do work. Metric: Newton metres (N m) Imperial: foot pounds (ft lbs), inch pounds (in lbs) 10 HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1

10 C-1 DESCRIBE HYDRAULICS LEARNING TASK 1 Advantages and Disadvantages Advantages of Hydraulic Systems Hydraulic systems have many advantages: simple and compact when compared with mechanical linkage systems the fluid that provides the operating force can be channeled in any direction have fewer moving parts than mechanical systems which reduces wear the hydraulic fluid acts as a continuous lubricant have build-in safety components in the form of relief or safety valves can apply forces in more than one direction can be constructed to multiply force and speed of application hydraulic force can be applied with control and smoothness the system is reversible Disadvantages of Hydraulic Systems There are also some disadvantages to hydraulic systems: can leak due to pressure, heat, force, or movement contamination will damage precision-made components expensive complex Fluid Characteristics The term fluid is used to refer to anything that flows. This includes both gases and liquids. The physical principles on which hydraulic systems operate are basically the same whether the system uses a gas or a liquid. The term hydraulics is used to refer only to systems that use a liquid. Fluids are substances that flow they have no shape of their own and seek their own level. Air in a container Air and liquid in a container Figure 1. Fluids in a Container HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1 11

11 LEARNING TASK 1 C-1 DESCRIBE HYDRAULICS The major difference between gases and liquids is that gases are compressible and liquids are not. To transfer motion in hydraulics, it s important to use a fluid that is not compressible. An automatic transmission uses hydraulic principles to establish shift points. Using a compressible liquid would not support consistent shift points. Gases are compressible Liquids are not compressible Figure 2. Gases Compared to Liquids Hydrodynamic and Hydrostatic Hydraulic systems have two classifications: hydrodynamic hydrostatic A hydrodynamic system is one in which the liquid is in motion. A hydrostatic system is one in which the liquid is confined under pressure. A water wheel is a hydrodynamic device because the ability of the wheel to do work comes from the motion of the fluid. For the water wheel to function, there has to be an endless supply of liquid provided by a river or stream. Heavy equipment and truck torque converters function like a water wheel. A hydraulic pump is hydrostatic because it operates using a fixed quantity of liquid that is confined inside the system. Pressure develops within the system when the movement of fluid is restricted or prevented. Heavy equipment uses confined oil under pressure to lift working attachments such as blades and buckets. Applications Hydraulic systems have replaced many mechanical components. Equipment/ trucks use many hydraulically operated devices, e.g., a cab-over cab tilt mechanism or a dump box. 12 HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1

12 C-1 DESCRIBE HYDRAULICS LEARNING TASK 1 Common applications for hydraulic systems include: brakes transmissions steering drive systems hoists working attachments Figure 3. Loader with Hydraulic Circuits Pascal s Law Pascal s Law states that pressure exerted anywhere in a confined incompressible fluid is transmitted equally in all directions throughout the fluid. French mathematician Blaise Pascal established the law in the 17th century. Pascal s Law for hydraulics states that output force is equal to fluid pressure multiplied by surface area that the pressure works against. This means that: as fluid pressure increases, output force will increase as piston surface area increases, output force will increase HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1 13

13 LEARNING TASK 1 C-1 DESCRIBE HYDRAULICS Figure 4. Different Sizes of Hydraulic Lines Figure 4 shows many different sizes, shapes, and lengths of hydraulic lines. The output force trying to stretch each line will be different from hose to hose due to the different hose sizes and pressures. However, each separate hose will have the same output force within itself no matter its shape, size, or length. Consider tires with different air pressures. As the pressure goes up, the tire will stretch to a larger diameter. The same forces are felt within hydraulic hoses as the pressure increases. Force, Pressure, and Area The words force, pressure, and area are used to describe the basic principles of hydraulics. To understand how they re related in hydraulics, you ll have to become familiar with their units of measurement in both metric and Imperial forms. Force In hydraulics, force is defined as any push or pull that s applied to an object. The metric unit of force is the Newton. The metric system considers the units of mass when calculating units of force. The metric units of mass are grams (g). However, since a gram is very small, the kilogram (Kg) is used when measuring mass. Metric: Newton, abbreviated N, is the force required to accelerate one kilogram at a rate of one metre per second per second (m/sec 2 ). Imperial: pound, abbreviated lb. 14 HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1

14 C-1 DESCRIBE HYDRAULICS LEARNING TASK 1 Pressure Pressure is the force that s applied to a specific area. Since pressure is a combination of the two factors, its units of measurement are a combination. Metric: Newtons per square metre, known as the pascal, abbreviated Pa. Because the pascal is a very low pressure, it s common to measure in kilopascals (kpa) (i.e., thousands of pascals). Imperial: pounds per square inch, abbreviated psi. Figure 5. Oil Pressure Gauge in kpa and psi Units Vacuum Vacuum occurs with pressure that is less than atmospheric pressure. When reading a vacuum, the metric units are Bars, or cm of mercury (cm-hg). Figure 6. Vacuum in Bars Figure 7. Vacuum in cm-hg The Imperial units are inches of mercury (in-hg). HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1 15

15 LEARNING TASK 1 C-1 DESCRIBE HYDRAULICS Figure 8. Vacuum in in-hg Bar Gauge kpa Gauge Psi Gauge in-hg (Absolute) in-hg (Vacuum) ATMOSPHERIC PRESSURE Figure 9. Pressure Reading Equivalents Area Area is the measure of surface space that oil pushes against. It s the measure of surface on which a force is applied. Metric: square metre, abbreviated m 2. Hydraulic pistons are rarely as large as a square metre, so it s common to see measurements that are fractions of metres. Imperial: square inches, abbreviated in HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1

16 C-1 DESCRIBE HYDRAULICS LEARNING TASK 1 Calculations When working on hydraulic systems, you must understand the different terms and how to perform calculations in either metric or Imperial units. The list below includes several calculations you ll have to perform when working with hydraulic systems: area Pascal s Law ideal mechanical advantage actual mechanical advantage hydraulic efficiency actuator stroke and volume velocity and flow rate power Area You need to know how to calculate the area of a circle since hydraulic pistons and cylinders are circular. There are two ways to calculate the area of a circle: Radius Method: Using the formula πr 2, where π (pronounced pie ) is equal to and where r is the radius of the circle. (The radius of a circle is equal to half its diameter.) Diameter Method: Using the formula D 2, where D is the diameter of the circle. Figure 10. A. Hydraulic Cylinder Figure 10. B. Cylinder Rod and Piston HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1 17

17 LEARNING TASK 1 C-1 DESCRIBE HYDRAULICS By measuring the cylinder bore diameter or the piston diameter, you can calculate the surface area on one side of the piston. Note the diameter measuring line on the cylinder bore and the piston in Figure 10A and Figure 10B. Metric Calculations of Area Radius Method 1. measure the diameter (D) of the circle 2. calculate the radius (r) by dividing the diameter by 2 3. insert the radius value into the formula: πr 2 e.g., What is the area of a piston 1.2 m wide? D = 1.2 m r = 1.2 m / 2 = 0.6 m Area = πr 2 = π(0.6) 2 = π(0.36) = 1.13 m 2 Diameter Method 1. measure the diameter (D) of the circle 2. insert the diameter value into the formula: D 2 e.g., What is the area of a piston 35 cm wide? D = 35 cm Area = D 2 = (35) 2 = = cm 2 18 HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1

18 C-1 DESCRIBE HYDRAULICS LEARNING TASK 1 Imperial Calculations of Area Radius Method 1. measure the diameter (D) of the circle 2. calculate the radius (r) by dividing the diameter by 2 3. insert the radius value into the formula: πr 2 e.g., What is the area of a piston 6 in. wide? D = 6 in. r = 6 in. / 2 = 3 in. Area = πr 2 = π(3) 2 = π(9) = in. 2 Diameter Method 1. measure the diameter (D) of the circle 2. insert the diameter value into the formula: D 2 e.g., What is the area of a piston 12 in. wide? D = 12 in. Area = D 2 = (12) 2 = = 113 in. 2 Pascal s Law Expressed mathematically, these are the relationships between force, pressure, and area: Force F Pressure = or P = Area A Force= Pressure Area or F = P A Force F Area = or A = Pressure P HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1 19

19 LEARNING TASK 1 C-1 DESCRIBE HYDRAULICS To help you remember the formulas, you can use the formula triangle (Figure 11). F P A Figure 11. Force, Pressure, and Area Triangle F (force) is always at the top and is calculated by multiplying the other two factors, P (pressure) A (area). To calculate either pressure or area, you must treat the line across the middle of the triangle as a division sign. Thus P (pressure) is F (force) divided by A (area) and A (area) is F (force) divided by P (pressure). Note: When calculating force, always use Pascals (Pa) rather than kilopascals (kpa). Metric Calculations for Pascal s Law Calculate the output force of the system shown in Figure 12: input piston diameter is 0.12 m input force is 1000 N output piston diameter is 0.20 m 1000 N? 0.12 m 0.20 m Figure HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1

20 C-1 DESCRIBE HYDRAULICS LEARNING TASK 1 First, calculate the area of the input piston: Area = D 2 = (0.12) 2 = = m 2 Now that you know the area ( m 2 ) and the force (1000 N), you can calculate the pressure using the formula: P = F/A. P = F/A P = 1000 N / m 2 P = Pa The total pressure in the system is Pa. In order to find the force on the output piston, first find its area: Area = D 2 = (0.20) 2 = = m 2 Now that you know the pressure ( Pa) and the area of the output piston ( m 2 ), calculate the output force using the formula, F = PA: F = P A F = Pa m 2 F = 2778 N The output force is 2778 N. HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1 21

21 LEARNING TASK 1 C-1 DESCRIBE HYDRAULICS Imperial Calculations for Pascal s Law Calculate the output force of the system shown in Figure 13: input piston diameter is 2 in. output piston diameter is 6 in. output force is 1800 lbs.? 1800 lbs. 2" 6" Figure 13. First, calculate the area of the output piston: D = 6 in. r = 3 in. Area = πr 2 = π(3) 2 = π9 = 28.3 in. 2 Now that you know the output force (1800 lbs.) and the area of the output piston (28.3 in. 2 ), you can calculate the total pressure in the system using the formula: P = F/A. P = F/A P = 1800 lbs. / 28.3 in. 2 P = 63.6 psi 22 HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1

22 C-1 DESCRIBE HYDRAULICS LEARNING TASK 1 In order to find the force on the input piston, first find its area: D = 2 in. r = 1 in. Area = πr 2 = π(1) 2 = π = 3.14 in. 2 Now that you know the pressure (63.6 psi) and the area of the input piston (3.14 in. 2 ), calculate the input force using the formula, F = PA: F = P A F = 63.6 psi 3.14 in. 2 F = lbs. The input force is lbs. Ideal Mechanical Advantage (IMA) The ratio of output force to input force is called mechanical advantage. Ideally, you can calculate this by comparing the surface area of the input piston to the surface area of the output piston as you did above N? 0.12 m 0.20 m Figure 14. HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1 23

23 LEARNING TASK 1 C-1 DESCRIBE HYDRAULICS The ideal mechanical advantage (IMA) is expressed as a ratio of output surface area to input surface area: output piston area is m 2 input piston area is m 2 IMA = m m 2 = This will usually be written as a ratio: 2.779:1 This means the output piston area is times as large as the input piston. The speed of the output cylinder will be times slower, but will develop times more force. The reason this is called ideal mechanical advantage (rather than just mechanical advantage ) is that it does not take into consideration losses from heat or friction. Actual Mechanical Advantage (AMA) In the real world, there will be energy losses which will result in less output force than expected. Actual mechanical advantage (AMA) is a ratio of the output force compared to the input force as determined by actual measurements N 2000 N Figure 15. Actual Input and Output Force Measurements 24 HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1

24 C-1 DESCRIBE HYDRAULICS LEARNING TASK 1 The actual mechanical advantage (AMA) is expressed as a ratio of the measured output force to the measured input force: input force is measured at 1000 N output force is measured at 2000 N AMA = 2000 N 1000 N = 2 This will usually be written as a ratio: 2:1 This means the output force is 2 times greater than the input force. Comparing the IMA with the AMA will allow you to determine hydraulic efficiency. Hydraulic Efficiency Hydraulic efficiency is a comparison of the actual mechanical advantage to the ideal mechanical advantage and is expressed as a percentage. You can use this to check the efficiency of hydraulic pumps, circuits, actuators, and systems. The basic formula for efficiency is: AMA IMA 100. e.g., If the IMA is 2.779, and the AMA is 2, the hydraulic efficiency is: Hydraulic Efficiency = AMA IMA 100 = = 72.0 Hydraulic efficiency is 72.0% and you can check this with a manual to see if it s acceptable. HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1 25

25 LEARNING TASK 1 C-1 DESCRIBE HYDRAULICS Actuator Stroke and Volume Stroke is the distance that the actuator rod moves from stop to stop cm Load 61 cm Load Figure 16. Cylinder Stroke Figure 16 shows two different cylinders with different strokes. Stroke measurements are needed to calculate cylinder volumes, cycle times, and efficiency. Stroke and Volume Calculations 1. Measure the cylinder rod stroke from stop to stop. 2. Measure the piston diameter and calculate the piston area. 3. Enter the dimensions into the formula: Cylinder Volume = Piston Area Stroke e.g., Cylinder rod stroke is 1 m Piston area is 0.02 m 2 Cylinder volume = 1 m 0.02 m 2 = 0.02 m 3 e.g., Cylinder rod stroke is 36 in. Piston area is in. 2 Cylinder volume = 36 in in. 2 = in HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1

26 C-1 DESCRIBE HYDRAULICS LEARNING TASK 1 Velocity and Flow The movement of fluid in a hydraulic system is defined by the following terms: Hydraulic flow refers to the movement of fluid and is measured as velocity and flow rate. Velocity is the average speed of a fluid past a given point measured in metres per second (m/s) or feet per second (fps). Flow rate is a measurement of the volume of fluid that passes a given point in a given period of time and is measured in litres per minute (L/ min) or in gallons per minute (gpm). Velocity of a fluid and its flow rate are closely related. In hydraulic lines of two different diameters (Figure 17), the flow rate (the amount of fluid moving past a given point in a given time) is the same. However, the different sized lines will have different velocities. 5 L/min. 5 L/min cm A 61 cm B Figure 17. Velocity of Fluid in Lines The flow rate of lines A and B is 5 L/min. The illustrated section of each line has a volume of 5 L. The fluid in line A travels 30.5 cm every minute to maintain the flow rate, while the fluid in line B travels 61 cm every minute to maintain the same flow rate. This means that the fluid in line B must move at a faster velocity than the fluid in line A. Velocity The faster the fluid moves, the greater the friction and the higher the heat. When hydraulic systems are designed, the size of the lines is carefully chosen so that the fluid travels at a speed adequate for the needs of the equipment, but not so fast that the system overheats. HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1 27

27 LEARNING TASK 1 C-1 DESCRIBE HYDRAULICS Flow Rate The relationship between the velocity of fluid and the size of hydraulic lines also applies to hydraulic cylinders. In Figure 18, the flow rate of each system is 5 L/min cm 5 L/min. A 61 cm 5 L/min. B Figure 18. Speed of the Cylinder At this rate of flow, the piston in system B will travel a greater distance (61 cm) than the piston in system A (30.5 cm). This also means that piston B will travel much faster than piston A. Given an equal rate of flow, a piston in a smaller diameter cylinder will travel further and faster than a piston in a larger diameter cylinder. With the constant flow rate into the two cylinders in Figure 18, the two cylinders will retract faster than they will extend. The cylinder rod occupies space in the cylinder causing the rod to retract faster to accommodate the oil filling at a constant rate. Volume of rod + volume of oil filling = volume of oil leaving the cylinders Also, the cylinder rod will have more output force when extending than retracting as the piston loses effective area where the rod attaches to the piston. The right side of each piston in Figure 18 has less effective area than the left side of each piston. This causes the cylinder rod to extend slower and with more force than retracting. 28 HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1

28 C-1 DESCRIBE HYDRAULICS LEARNING TASK 1 The relationship between the flow in a hydraulic system and the pressure it develops is important when trouble-shooting systems. If a hydraulic circuit is unable to lift a specified load, the problem is that the system is not developing sufficient pressure. If a hydraulic circuit is not operating at its specified speed, the problem is that it s not creating sufficient flow. Power Horsepower (hp) is the name of several units of measurement of power. Horsepower was originally defined to compare the output of steam engines with the power of draft horses in continuous operation. The unit was widely adopted to measure the output of piston engines, turbines, electric motors, and other machinery. Horsepower is also used to measure hydraulic output. Power is defined as work per unit of time. Before you can calculate horsepower, you must understand work. Work is equal to a force multiplied by a distance. An actuator extending or retracting would be performing work. Work Calculations e.g., Work = Force Distance = N 2 m = N m e.g., Work = Force Distance = 100 lbs 6.5 ft. = 650 ft lbs. Power Calculations Power is calculated as the amount of work done over a specific unit of time. The metric system uses the watt (w) as its unit of power. 1 watt is equal to 1 N m of work done over 1 sec (or 60 N m of work done over 1 minute). 1 w = 1 N m/sec The Imperial system uses horsepower (hp) as its unit of power. 1 horsepower is equal to 550 ft lbs. of work done over 1 second (or ft lbs. of work done over 1 minute). 1 hp = 550 ft lbs./sec Hydraulic power must consider flow rate, pressure of the system, and a given mathematical constant. HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1 29

29 LEARNING TASK 1 C-1 DESCRIBE HYDRAULICS Imperial Power Calculation hydraulic output power (hp) = flow rate (gpm) Pressure (psi) e.g., power = 2 gpm 1500 psi = 1.75 hp. Hydraulic Efficiency Input power will always be greater than output power. A complaint that there is low hydraulic power may indicate low power in a diesel engine. Input power requirements can be calculated if you know the system s hydraulic efficiency. Divide the output power as calculated above to get the input power. Bernoulli s Principle Bernoulli s Principle states that as the velocity of a flow increases, the pressure decreases. The simple form of Bernoulli s Principle is valid for incompressible flows (most liquid flows) and also for compressible flows (gases). Low velocity High pressure High velocity Low pressure Low velocity High pressure Direction of flow Figure 19. Bernoulli s Principle Figure 19 shows the relationship between flow speed and pressure. When the speed of the oil increases, the pressure decreases proportionally. The oil has less ability to push against the inner wall of the line as the speed of the oil increases. The area of restriction is referred to as a Venturi the Venturi may cause the pressure to drop to a vacuum (that is, less than atmospheric pressure). 30 HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1

30 C-1 DESCRIBE HYDRAULICS SELF TEST 1 SELF TEST 1 1. Match the following units of measurement with the properties they measure: a. Newton (N), kilonewton (kn) b. pound per square inch (psi) c. pound (lb.) d. pascal, kilopascal (Pa or KPa) e. gallons per minute (gpm) f. square metre (m 2 ) g. metres per second (m/s) h. square inch (sq.in. or in 2 ) i. feet per second (fps) j. litres per minute (l/min.) 1. flow rate Metric 2. pressure Imperial 3. area Imperial 4. velocity Metric 5. flow rate Imperial 6. force Metric 7. force Imperial 8. area Metric 9. velocity Imperial 10. pressure Metric 2. By definition, what does the term fluid include? a. liquids only b. gases only c. both gases and liquids d. hydraulic oil only 3. What is one of the basic principles that accounts for the effectiveness of hydraulic systems? a. compressible and can transmit force through compression b. easily vapourized c. frictionless and flow quickly d. non-compressible and transmit pressure equally in all directions 4. How is pressure calculated in a hydraulic system? a. multiply force by area (F x A) b. multiply area by force (A x F) c. divide force by area (F A) d. divide area by force (A F) HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1 31

31 SELF TEST 1 C-1 DESCRIBE HYDRAULICS 5. Using the appropriate formulas, calculate the missing values in the following diagrams. a. system pressure output force 125 lbs? 1.25 in in 2 b. input force piston area? N 4.5 cm 2? 800 kpa c. input force piston area? 2500 lbs 2.25 in 2? 250 psi 32 HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1

32 C-1 DESCRIBE HYDRAULICS SELF TEST 1 d. piston area output force 6000 N?? 5 cm kpa 6. What is the ideal mechanical advantage in question 5 diagram d? a. 2:1 b. 0.04:1 c. 200:1 d. 2000:1 HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1 33

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34 C-1 DESCRIBE HYDRAULICS LEARNING TASK 2 LEARNING TASK 2 Describe the Basic Operation of a Hydraulic System Basic System Component Hydraulic systems convert mechanical energy into hydraulic energy, which can then be directed to different devices to perform work. Figure 1 illustrates a typical circulating hydraulic system and its main components. It is a circulating system because the fluid is not confined at a working pressure throughout the whole system. Instead, fluid at atmospheric pressure is drawn from a reservoir, moves through the system, and returns to the reservoir. Reservoir Relief valve Pump Control valve Cylinder Figure 1. Basic Circulating Hydraulic System Components The main components of a hydraulic system are: reservoir pump control valve actuator connecting lines HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1 35

35 LEARNING TASK 2 C-1 DESCRIBE HYDRAULICS Reservoir The reservoir stores the oil required for the hydraulic system. The reservoir is usually 2 to 3 times larger than the pump volume. This gives the oil time to cool before re-circulating through the system. For example, a hydraulic system with a 100 L/min pump should have a L reservoir. A reservoir twice as large as the pump capacity will re-circulate the tank volume every two minutes. This helps cool the oil. A typical reservoir has the following components: filler cap air vent or breather cap oil level gauge outlet and return lines baffle intake strainer drain plug Filler Cap The filler cap is the cover of the entry point for oil. The filler hole usually has a fine screen to filter out contaminants as oil is added to the reservoir. Air Vent or Breather Cap In non-pressurized reservoirs, and in systems that use gravity to drain the oil, air must be allowed to enter the reservoir. This prevents the creation of a partial vacuum that would prevent effective flow. The air vent contains a filter that must be kept clean at all times. Pressurized systems are sealed and have no air vent. Instead, they have an air valve that is pre-set within the operating limits of the system. Caution should be used anytime you loosen a cap on a pressurized system you may get burnt with hot oil. Oil Level Gauge An oil level gauge records the level of oil without having to open the reservoir. A dipstick is another method of determining level in the reservoir. Always refer to manufacturer s specifications when checking oil levels. 36 HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1

36 C-1 DESCRIBE HYDRAULICS LEARNING TASK 2 Outlet and Return Lines Outlet and return lines are designed to enter the reservoir at points that minimize turbulence. Although the lines may enter the tank at the sides or through the top, their ends are always close to (but not on) the bottom of the tank. If they were in contact with the bottom, the pump could draw in contaminants that have settled there and the return line could stir up contaminants. Another reason to have the return line near the bottom of the tank is to prevent foaming of the oil. If you have to install additional return lines in a hydraulic system, be sure that the ends are located below the level of oil in the reservoir to avoid foaming. The end of the return line, which does not have a filter, is angled at 45. This directs the hot oil away from contaminants on the bottom of the tank and towards the side of the tank which maximizes cooling. Fill cap Breather/vent Return line Gauge Intake filter To pump Sump end Strainer Baffle Drain plug Figure 2. Suction Line, Return Line, and Baffle Baffle A baffle is situated on the bottom of the tank between the outlet line and the return line. It keeps the returning oil separate, slows its mixing with the oil about to enter the pump, and gives time for any contaminants to settle. By reducing turbulence, it also helps air escape from the oil and increases the loss of heat through conduction in the tank walls. HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1 37

37 LEARNING TASK 2 C-1 DESCRIBE HYDRAULICS Intake Strainer The intake strainer is attached directly to the end of the intake pipe. It s usually a fine screen. It operates in conjunction with the main oil filter for the system, which may also be installed in the reservoir. Drain Plug A drain plug allows all the oil to be drained from the reservoir. Some drain plugs have magnetic attachments to help remove metal chips and other very fine metallic contaminants from the oil. Hydraulic Tank Head Pressure Head pressure is defined as the weight of a fluid as a result of its depth. Very Low Low Medium High Very High Figure 3. Hydraulic Head Pressure Figure 3 demonstrates the increased pressure on lower orifices. Openings nearer to the bottom of the tank have greater head pressure. Hydraulic tanks must be designed and located on the equipment to maximize head pressure. If the pump draws oil faster than the head pressure can supply, the pump will cavitate (starve for oil) and fail. When the equipment has a pressurized hydraulic tank, head pressure of the oil will add to the air pressure in the tank to make the combined head pressure. 38 HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1

38 C-1 DESCRIBE HYDRAULICS LEARNING TASK 2 It s important that you understand the causes of pump cavitation and identify when it occurs. Pump The function of a pump is to move fluid throughout a system. The pump takes mechanical energy from an engine or electric motor and uses it to move fluid against the resistance in the system. This resistance creates the hydraulic pressure that operates the working parts of the system. Pumps work on the principle of displacement. In each sequence of its operation, the pump displaces a volume of fluid, moving it forward in the system and creating flow. That displaced fluid is then replaced by more fluid, which in turn is displaced. A non-positive displacement pump (engine water pump) operates using centrifugal force. There is no seal between the inlet and outlet, so minimal pressure is created during operation. In a positive displacement pump (hydraulic pump), the inlet side is sealed from the outlet side. The tolerances between the moving parts (gears, vanes, or pistons) and the stationary part (housing) are so fine that the fluid taken into the pump cannot escape back to the inlet. As it is moved forward to the outlet side of the pump, it encounters the resistance of the system and counteracts that resistance by developing pressure. If there were no seal between inlet and outlet, the fluid would flow back to the inlet side at the least sign of resistance. Positive displacement pumps create flow and then back the flow up to support pressure. Because the creation of pressure is essential for a hydraulic system to function, all hydraulic systems use positive displacement pumps. The ports on the hydraulic pumps are different sizes to accommodate oil flow to and from the pump. The suction side of the pump will have the largest size port as it uses head pressure to feed the pump. The outlet size will be about one quarter the size of the inlet as the pump is forcing the oil out the outlet. HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1 39

39 LEARNING TASK 2 C-1 DESCRIBE HYDRAULICS Positive Displacement Pumps Figure 4 shows three common designs of positive displacement pumps. These pumps may have fixed or variable displacement (delivery). These are: gear vane piston A 2 Pressure plate 3 Gear shaft 4 Shaft seal 5 Shaft bushing Inlet port 1 9 Check valve Outlet port 8 7 Return passage 6 Flange plate 10 Outlet oil 11 Inlet oil B 2 Rotor 3 Vane C 1 Inlet port Outlet port 4 5 Cam ring Figure 4. Basic Hydraulic Pumps There are many design variations of these three types. Each design variation has special characteristics that make it suitable for certain applications. Pump Rating Hydraulic pumps are rated in three different ways: displacement flow rating pressure rating Displacement is the volume of fluid that is swept by the pump in one cycle or revolution. 40 HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1

40 C-1 DESCRIBE HYDRAULICS LEARNING TASK 2 The greater the displacement of a pump, the more flow it can produce at a given number of revolutions per minute. Some pumps are fixed displacement and the only way to increase or decrease pump output is by changing the engine rpm (Figure 4A and Figure 4B). Other pumps are variable displacement and can change the pump output without changing the engine rpm (Figure 4C). Figure 5. Variable Displacement Pump Movement of the swashplate in Figure 5 will change pump displacement from zero to maximum. Movement of the swashplate can be done manually, hydraulically, or electrically. The displacement of pumps is rated in: Metric: cm 3, m 3, litres Imperial: in 3, gals. Oil Flow in the Pump The gear pump traps oil between the teeth and the housing. The oil travels around from the low-pressure side to the high-pressure side. Both gears trap and move the oil at the same time. One rotation of the input shaft and both gears will move the displacement volume of oil (Figure 6A). Sealing between the vane and the housing is done by the support of the shaft bearings holding the gears to a close running clearance. The high pressure on the gears will force the gears to the low-pressure side of the pump. As the bearings wear, the gears will dig into the housing on the low side. This type of pump is considered to be an unbalanced pump. The vane pump traps oil between the vanes and the ring. The oil travels around the ring from the low-pressure side to the high-pressure side (Figure 6B). The sealing of the vanes to the ring is done by centrifugal force of the vane and oil pressure behind the vane. HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1 41

41 LEARNING TASK 2 C-1 DESCRIBE HYDRAULICS The piston pump receives the oil through the slotted valve plate, into the cylinder bore cavity as the piston slides down the shoeplate/swashplate. The cylinder barrel rotates with the pistons and aligns with the slotted valve plate for oil to be pushed from the cylinder bore. The piston follows the shoeplate/swashplate and this forces the piston down the bore forcing the oil downstream (Figure 6C). The clearances between the pistons and the bores make this pump the most positive displacement pump. The oil that leaks past the pistons into the shaft area lubricates the bearings and is drained back to the tank as case drain. One rotation of the drive shaft and all the pistons will experience one stroke of displacement oil. Figure 6. A. Unbalanced Gear Pump Figure 6. B. Unbalanced Vane Pump 42 HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1

42 C-1 DESCRIBE HYDRAULICS LEARNING TASK 2 Figure 6. C. Unbalanced Piston Pump The flow rating of a pump is measured in litres per minute (L/min) or gallons per minute (gpm). The capacity of a pump is rated to deliver a certain number of litres or gallons per minute at a given speed and pressure. Actual pump flow rate is normally measured with a flow meter installed between the pump and control valves. Ideal flow rate can be calculated if you know the pump s displacement and the number of revolutions per minute. e.g., A pump is turning at 1000 rpm and has a displacement of 10 cm cm 3 = 0.01 L 0.01 L 1000 rpm = 10 L/min The pump has an ideal flow rate of 10 L/min. Pump pressure rating indicates what operating pressure the pump can withstand without damage. Adjustments made to system relief valves will control the maximum pressure of that system. If the relief valves are set beyond the pressure rating of the pump, the result may be more productivity, but the pump will prematurely fail. As a safety measure, a pump will have higher pressure and flow ratings than those actually demanded by the system. The reserve capacity usually results in longer life for the pump. HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1 43

43 LEARNING TASK 2 C-1 DESCRIBE HYDRAULICS The pump s pressure rating will depend on the type of pump, pump materials, pump clearances, and whether the pump is balanced or unbalanced. Balanced pumps must have the outlet pressure on both sides of the pumping elements to counter the forces from the oil pressure. The pump that offers this design feature is the vane type pump (Figure 7). The piston pump design offers the least internal leakage and supports the highest pressures with the highest efficiency. Figure 7. Balanced Vane Pump The energy available in a hydraulic system includes: input horsepower of the engine or electric motor that powers the pump speed of operation (the flow rate of the pump) pressure and output force A system will not be able to operate faster than the limits set by the displacement of the pump and by its top operating speed (rpm) both of which determine its flow rating. Control Valve Valves are the control mechanisms in a hydraulic system. Valves are components that contain one or more movable parts that can open, close, or limit the flow of hydraulic fluid. 44 HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1

44 C-1 DESCRIBE HYDRAULICS LEARNING TASK 2 Valves can be of three types: pressure control valves directional control valves volume (or flow) control valves Pressure Control Valves Pressure control (relief) valves are used to reduce or limit pressure. They can unload a pump (discharge it if the pressure gets too high) or set the pressure at which oil will enter a hydraulic circuit. From pump To sump Adjustment Figure 8. Direct-acting Pressure Relief Valve Pressure control valves are categorized as either direct acting or pilot operated. Direct Acting Pressure Relief The force of the oil pressure works directly on the surface area of the ball. The pressure against the ball must overcome the force of the spring holding the ball on its seat. Pilot Operated (Non-direct Acting) Pressure Relief A pilot operated pressure relief valve is designed to handle high volumes and minimize pressure override. Oil flows through the main poppet orifice and fills the cavity inside the main poppet. The light main poppet spring and the oil pressure hold the main poppet on its seat. The pilot poppet and pilot poppet spring trap the oil in the main poppet cavity (Figure 9). The oil force from the oil pressure in the main poppet cavity must overcome the pilot poppet spring force. When the pilot poppet unseats, oil bleeds out of the main poppet cavity causing the main poppet to move off its seat. This allows oil to flow to the downstream cavity. HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1 45

45 LEARNING TASK 2 C-1 DESCRIBE HYDRAULICS The upstream oil pressure is always working against the main poppet spring and the main poppet cavity oil pressure. This feature minimizes the pressure override on this valve. Drain Inlet Outlet Inlet Closed Discharge Open Figure 9. Pilot Operated Relief Valve Cracking Pressure When the pressure is high enough to move the ball off its seat, the pressure control valve is at its cracking pressure. Full Flow Pressure If the pressure control needs complete pump flow, the plunger needs to move far enough to allow all the flow past the ball (Figure 10). As the ball moves, it compresses the spring, increasing the spring pressure. As a result, the system pressure needs to increase to overcome the extra spring tension. The difference between cracking pressure and full flow pressure is pressure override. All direct acting pressure control valves experience pressure override. Pressure override is not a good feature when we need to regulate pressures at a specific level. Pilot operated relief valves are needed to handle high volumes and minimize the pressure override on complex hydraulic systems. 46 HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1

46 C-1 DESCRIBE HYDRAULICS LEARNING TASK 2 A B C Outlet Inlet Cracking pressure Figure 10. Pressure Override Full-flow pressure Normally Open Versus Normally Closed Valves Each pressure control valve will rest in either a normally open or normally closed position. A pressure control valve that is in the normally closed position will only open when the upstream oil pressure overcomes the force of the valve spring. This allows oil to move to a secondary circuit (Figure 10). A pressure control valve that is in the normally open position will only close when the downstream pressure overcomes the force of the valve spring. This restricts the oil getting into the secondary circuit (Figure 11). This is commonly used as a pressure-reducing valve for the secondary circuit. Drain Inlet port Outlet port Spool Pilot pressure Figure 11. Normally Open Valve HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1 47

47 LEARNING TASK 2 C-1 DESCRIBE HYDRAULICS Types of Pressure Control Valves relief valves unloading valves pressure-reducing valves pressure sequence valves counter balance valves brake valves Relief Valves System relief valves are normally closed and located to protect system components from damage. The system relief valves are located between the pump and the directional control valves. The system relief valve may be physically located in the pump or the directional control valve housing. However, the system relief valve must control the maximum pressure between the pump and the directional control valves. Each pump will have its own system relief valve. System relief valves can be either direct acting or pilot operated. Figure 12. System Relief Valve and Housing Circuit relief valves are normally closed and located in a working circuit, such as lift or lower circuits. These relief valves protect the cylinder s hoses and directional control valve from pressure spikes. The circuit relief valves are normally located in the directional control valve housing but control the maximum oil pressure between the directional control valve and the working actuator. 48 HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1

48 C-1 DESCRIBE HYDRAULICS LEARNING TASK 2 Circuit relief valves are normally direct acting. The control valve housings may also have anti-cavitation (make-up) valves and lift (load) check valves. A low-pressure area on one side of a cylinder may result if an attachment is lowered faster (via gravity) than the pump is able to deliver oil. A vacuum will form, causing the oil to boil, forming air in the system, resulting in pump damage. Anti-cavitation (make-up) valves are installed to prevent this. The lift/tilt (load) check valves are located at each spool valve in the housing. The lift check valve prevents reverse oil flow when the spool valve is first pulled and the pump pressure is low. If reverse flow occurs, the attachment will lower a short distance before the oil catches up and forces the attachment to lift. This is an undesirable condition that could cause damage. TILT CONTROL VALVE DUMP Head end Load check valve Rod end Line relief makeup valve Line relief valve Tilt back pilot hydraulic actuator Pilot oil chamber Tilt spool Tank port Supply passage Passage to next valve Internal passage Tank port Pilot oil chamber Dump pilot hydraulic actuator Figure 13. Anti-Cavitation, Circuit Relief Valves, and Lift (Load) Check Valve Unloading Valves Unloading valves are normally closed and used when the hydraulic system has a closed centred spool (no flow past the spool). The pump is fixed displacement. If traditional relief valves are used, the flow will return to reservoir and the system pressure will be very high. This causes extreme heat and the pump will fail. Unloading valves are designed to allow the oil to return to the reservoir at a low pressure to keep the oil from overheating. The unloading valve also acts as a system relief to protect the system from high pressures. HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1 49

49 LEARNING TASK 2 C-1 DESCRIBE HYDRAULICS The unloading valve must have a one-way check and an accumulator. The oil flows past the one-way check valve and on to the system directional control valves. The directional control valve is closed so the pressure builds and charges the accumulator. At system pressure, the pilot poppet unseats and the unloader piston lifts to dump the pump oil to the reservoir. The one-way check valve seats and the accumulator slowly discharges, keeping the poppet valve off its seat and the unloader piston continues to dump the pump oil at a low pressure. As the pressure drops in the accumulator, the pilot valve closes and this causes the unloader piston to close and the one-way check unseats to recharge the accumulator and feed the system. Figure 14. Unloading Valve Pressure-reducing Valves Pressure-reducing valves are normally open and then close to regulate downstream pressure. Equipment pilot operated hydraulic controls require a low oil pressure for the pilot controls. A pressure-reducing valve may be used to feed the pilot controls. By doing this, one pump can feed two different circuits that require different operating pressures. Pressure-reducing valves can be either direct acting or pilot operated. The adjusting screw in Figure 15 is set to the desired downstream pressure. The downstream oil flows through the control pressure passage, the orifice in the spool, and fills the spool cavity. The pilot poppet feels the oil pressure and bleeds off oil in the spool cavity allowing the spool to move over and restrict the oil getting downstream. The oil flowing downstream will match the downstream leakage regulating the downstream pressure. 50 HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1

50 C-1 DESCRIBE HYDRAULICS LEARNING TASK 2 Pilot Adjusting valve Drain screw Drain Inlet Spring Inlet Spool Orifice Reduced pressure outlet Reduced pressure outlet A System pressure is below valve setting Control pressure B Regulating secondary system pressure Figure 15. Pilot Operated Pressure-reducing Valve Pressure Sequence Valves Sequence valves are normally closed and feed a secondary circuit at a specific primary circuit pressure. This will establish an order to a number of circuits as the operator works the hydraulics. The spool valve in Figure 16 will lift when the pressure rises high enough and the oil will feed the upper outlet port. This could be used in a tree sheer application where the first sequence port feeds the clamp cylinders and the second sequence port feeds the saw. Inlet To primary circuit First sequence valve closed To secondary circuit Second sequence valve closed Figure 16. Sequence Valve HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1 51

51 LEARNING TASK 2 C-1 DESCRIBE HYDRAULICS Counter Balance Valves (Load Lock Valves) Counter balance valves are normally closed and are used to hold the pressure in a hydraulic cylinder for safety support. Mounted directly to the cylinder on the rod end in this case. The cylinder cannot drift down if a hydraulic line ruptures. This system is used on some crane outriggers. Notice in Figure 17A the oil cannot leave the cylinder until the pressure in the return gets high enough to move the piston and spool valve. This would be a power down circuit. A B Figure 17. Counter Balance Valve Brake Valves Brake valves are normally closed and used on cranes to control hydraulic winches. Brake valves are a safety feature that prevents the cable from spooling out under load until the operator powers the circuit down. Notice the hydraulic lock-up when braking the hydraulic motor will be turned by the load on the cable, creating a hydraulic lock-up. When raising, the oil uses the one-way check valve to bypass the spool. 52 HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1

52 C-1 DESCRIBE HYDRAULICS LEARNING TASK 2 A B Figure 18. Brake Valve Directional Control Valves Directional control valves control the direction in which oil flows in a hydraulic system (Figure 19 and Figure 20). Directional valves will have a number of ports that are labeled as: pump port reservoir port working ports The valve housing pump port and working ports can be either normally closed or open depending on the design of the system. HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1 53

53 LEARNING TASK 2 C-1 DESCRIBE HYDRAULICS 2 Control valve 3 Valve body 5 To hydraulic functions From the pump 4 To reservoir 5 To hydraulic functions 7 8 Pump flow Return flow 6 Valve spool 9 Trapped oil Figure 19. Open Centre Directional Control Valve Pump flow Return flow Trapped oil Figure 20. Closed Centre Directional Control Valve 54 HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1

54 C-1 DESCRIBE HYDRAULICS LEARNING TASK 2 The main types of directional control valves are: spool valves rotary valves poppet valves Spool Valves Spool valves are made from round stock steel. The spool valve is cut to form lands, lubrication/balancing grooves, and throttling slots. The valve housing is made of cast to form the passages and machined to accommodate the spool valve. The spool lands must act as the seal from one oil gallery to another. The balancing grooves fill with oil to suspend the valve in the housing. The throttling slots are cut on the edge of the lands to allow the operator gradual engagement of the circuit (Figure 22) Figure 21. Spool Valves HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1 55

55 LEARNING TASK 2 C-1 DESCRIBE HYDRAULICS Figure 22. Throttling Rotary Valves Rotary valves work great as steering valves. The spool rotates in the housing to direct oil to the desired circuit. The spool valve has lubrication grooves and throttling slots (Figure 22). The spool is hollow to direct the oil through the centre as the spool is rotated (Figure 23). Figure 23. Rotary Valve 56 HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1

56 C-1 DESCRIBE HYDRAULICS LEARNING TASK 2 Poppet Valves Poppet valves function like a one-way check valve but the operator controls oil in the spring cavity. With oil in the spring cavity, the valve is hydraulically locked in the closed position. The operator will pull the control lever, which bleeds oil from the spring cavity, and the poppet moves off its seat allowing oil to feed the desired circuit. This system is used with pilot oil controls. Figure 24. Poppet Valves HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1 57

57 LEARNING TASK 2 C-1 DESCRIBE HYDRAULICS Volume/Flow Control Valves Volume control valves regulate the amount of oil flow to a part of a hydraulic system. This is done either by throttling the oil or by diverting the oil to the reservoir. Flow control valves control the speed of a circuit. Closed Partly open Wide open Figure 25. Restricting Flow Control Types of flow/volume control valves are: non-compensated valves compensated valves flow divider valves Non-compensated Flow Control Valves Non-compensated flow control valves may be fixed (Figure 26) or adjustable (Figure 27). Fixed flow control valves function as an orifice. Orifices may be in lines, spool valves, housings, or other control valves. All orifices experience an oil pressure drop across the orifice as the oil passes through. The orifice downstream oil pressure will be lower than the upstream oil pressure. Each orifice can handle a certain volume of oil with no noticeable difference in pressure upstream to downstream. As the flow across the orifice increases, pressure rises upstream (back pressure) and pressure drops downstream. Engineers design control valves that function based on the pressures created from the orifice effect. 58 HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1

58 C-1 DESCRIBE HYDRAULICS LEARNING TASK 2 Pressure drop Oriface Figure 26. Fixed Orifice Adjustable orifices can change the pressure drop depending on the position of the needle valve. This allows the operator to select the amount of pressure drop and the speed of the working circuit. Closed Partly open Wide open Figure 27. Adjustable Orifice Compensated Flow Control Valves Some actuators require a constant speed no matter what s happening in the system. Three conditions cause the actuator to change in speed: The pump changes speeds, which causes the oil flow to change. The oil changes temperature, the oil viscosity changes, which causes the oil flow to change. The working pressure changes, which causes the oil flow to the working circuit to change. The compensated flow control valve can adjust to these conditions maintaining actuator speed. HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1 59

59 LEARNING TASK 2 C-1 DESCRIBE HYDRAULICS The compensated flow control valve in Figure 28 can do basic adjustment for the conditions above. When the pump changes speeds, the flow through the fixed orifice will change causing the pressure drop across the orifice to change. This will cause the control piston to move either opening or restricting the control orifice which controls the oil to the actuator. When the oil viscosity changes, the pressure across the fixed orifice will change causing the control piston to move either opening or restricting the control orifice which controls the oil to the actuator. When the actuator pressure changes, the pressure in the control piston cavity changes causing the control piston to move either opening or restricting the oil to the actuator. Control orifice Fixed orifice Control orifice fully open Outlet Orifice Inlet Control orifice fully closed (compensating) Figure 28. Compensated Flow Control 60 HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1

60 C-1 DESCRIBE HYDRAULICS LEARNING TASK 2 Flow Divider Flow Control Valves Flow divider flow control valves feed oil to two circuits from a single input. The flow divider valve can be designed to divide the flow in any proportion between the two circuits. The two fixed orifices in Figure 29 feed oil to the ends of the floating piston. When the pressure drops on either end of the floating piston, the piston will move, restricting the oil to the side with lower pressure. This stabilizes the circuit, maintaining the proper ratio of oil flow to the two outlets. Changing the size of either orifice will change the ratio of oil to the two outlets. Outlet 2 Outlet 1 Inlet Figure 29. Flow Divider Valve Control of Valves There are four ways in which hydraulic valves can be controlled: manually hydraulically electrically/electronically pneumatically Directional control valves are linked to the control levers through either: mechanical linkage rods hydraulic hoses electrical wires air hoses HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1 61

61 LEARNING TASK 2 C-1 DESCRIBE HYDRAULICS Each system will give the operator a different feel for lever action. Most modern systems use computers to control the spools and the control levers communicate with these computers. This gives the operator fingertip controls. Valves may or may not be adjustable depending on their particular function and on their location in the system. The maintenance required for control valves is low, providing that the oil in the system is kept clean. Valves can be adjusted by loosening a jam nut and turning the adjusting screw with a screw driver (Figure 31). Figure 30. Hydraulic Controls Pilot Adjusting valve Drain screw Drain Inlet Spring Inlet Spool Orifice Reduced pressure outlet Reduced pressure outlet A System pressure is below valve setting Control pressure B Regulating secondary system pressure Figure 31. Adjustment on a Pressure-reducing Valve Other valves may require partial disassembly in order to make adjustments. The circuit relief valve shown in Figure 32 can have shims added or removed to alter spring tension. 62 HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1

62 C-1 DESCRIBE HYDRAULICS LEARNING TASK 2 Figure 32. Circuit Relief Valve and Housing Actuators The actuator does the work in a hydraulic system. It converts fluid power into mechanical power. Actuators attach to the working implements of the equipment (e.g., blades and buckets). Most actuators are either cylinders or hydraulic motors. Cylinders A cylinder is the component that receives the hydraulic energy and converts it into linear mechanical force that can do work. A cylinder is a type of actuator that produces force in a straight line and is very common on heavy equipment. Cylinders are classified as: single-acting double-acting A single-acting cylinder uses hydraulic force to extend a piston. A spring, or gravity acting on a load, retracts it. A forklift lift cylinder is an example of a single-acting cylinder. Oil port Piston seals Piston Vent port Rod seal Mount Rod seal Cylinder housing Removable cylinder Figure 33. Single-acting Cylinder HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1 63

63 LEARNING TASK 2 C-1 DESCRIBE HYDRAULICS In a double-acting cylinder, oil moves the piston in both directions. As oil under pressure is pumped in to extend the piston and rod, oil in the other half of the cylinder must be pushed out and returned to the reservoir. Double-acting cylinders are used where oil pressure is needed to move the cylinder rod in both directions. Loader booms use double-acting cylinders. Oil port Piston seals Piston Oil port Rod seal Mount Rod seal Cylinder housing Removable cylinder Figure 34. Double-acting Unbalanced Cylinder Telescoping cylinders are used in areas that require a long stroke but lack sufficient room to put a single- or double-acting single stroke cylinder. Truck boxes and scraper ejectors are examples that require a telescoping cylinder, as there is not enough room under the box or on the scraper with the cylinder retracted. Telescoping ejector cylinder Figure 35. Telescoping Ejector Cylinder Cylinders are made in different sizes depending on the kind of work they must perform. These differences include: diameter of the cylinder (and piston) length of the cylinder (and the stroke of the piston) If you know the stroke of the piston and the bore diameter, you can calculate how much hydraulic fluid is pumped in and out each time it operates. This can also be used to calculate cycle times of the cylinder. Unbalanced double-acting cylinders will extend slower than they retract because the rod is occupying space 64 HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1

64 C-1 DESCRIBE HYDRAULICS LEARNING TASK 2 in the cylinder. However, the cylinder will develop more power extending than retracting. Cylinders are mounted on machines to maximize speed and power for that application. Figure 36. Hydraulic Cylinder Some cylinders, such as the one in Figure 36, have a safety device which prevents the piston from bottoming out. This prevents any damage that would occur if the piston hit the bottom of the cylinder. Orifice Oil outlet closed Figure 37. Cylinder with Cushioning Device Piston seals trap hydraulic oil on either side of the piston. These seals are required to prevent the hydraulic cylinder rod from drifting down and the loss of hydraulic power. Hydraulic oil is prevented from escaping from the rod end of the cylinder with the use of packing glands. These packings need to be adjusted or replaced to prevent oil leaks and to prevent the entry of dirt and other contaminants into the hydraulic system. HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1 65

65 LEARNING TASK 2 C-1 DESCRIBE HYDRAULICS Cylinder head Seal Piston seals Figure 38. Hydraulic Cylinder Head and Seals Hydraulic Motors Hydraulic motors are the opposite of hydraulic pumps. Pumps are mechanically driven to develop fluid flow, whereas motors are fluid-driven to develop mechanical energy. Motors can be gear, vane, or piston types. Motors will have the same size inlet as outlet ports to accommodate reversing. Unlike linear cylinders, motors turn which allows for torque. The amount of torque the motor develops will depend on the internal displacement and the oil pressure feeding the motor. The speed of the motor will depend on the motor displacement and the volume of oil feeding the motor. 4. These two teeth have only tank line pressure opposing them. Inlet 2. Segments of two meshing teeth tend to oppose rotation, making the net torque available, a function of one tooth. 1. These two teeth are subject to high pressure and tend to rotate gears in the direction of the arrows. Outlet 3. Pressure between teeth in these segments push both ways and do not affect torque as oil is carried around to the outlet port. Figure 39. Gear Type Motor 66 HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1

66 C-1 DESCRIBE HYDRAULICS LEARNING TASK 2 Cover port Cam ring Body port Spring Vane Shaft seal Drain Pressure plate Rotor Pressure plate Bearing Felt wiper Shaft Figure 40. Vane Type Motor Valve plate Port connections Cylinder block sub-assembly Piston and shoe sub-assembly Shoe retainer plate Swash plate (stationary) Housing These parts rotate Shaft seal Bearing Driveshaft Figure 41. Piston Type Motor HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1 67

67 LEARNING TASK 2 C-1 DESCRIBE HYDRAULICS Connecting Lines The components in a hydraulic system must be connected with lines and couplers. Lines and couplers are less complex than the components of the system, however a clear understanding of how they are assembled and what they are designed to do will save costly down-time for equipment. Lines refer to rubber hoses and metal tubes. Couplers refer to the fittings that join the lines together. Line and Coupler Selection Engineers select lines and couplers for each application based on the loads put on them and always include a margin for safety. Factors affecting the choice of lines and couplers include: maximum oil pressure in the circuit minimum oil pressure in the circuit maximum oil temperature of the circuit minimum oil temperature of the circuit maximum oil flow in the circuit minimum oil flow in the circuit minimum bend radius equipment vibrations equipment hinge points outside ambient temperatures distance between components location of components When replacing lines or couplers, you must understand the limitations of each type. Most manufacturers recommend replacing a line or coupler based on its part number. This minimizes the possibility of installing an incorrect component. However, many companies make their own line assemblies which can lead to incorrect line installation. 68 HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1

68 C-1 DESCRIBE HYDRAULICS LEARNING TASK 2 Figure 42. Lines and Couplers Lines and couplers are covered in greater detail in Competency C-2, Learning Tasks 3 and 4. Hydraulic Fluids Hydraulic fluids are chosen for each application based on start-up, warm-up, and operating loads put on the oils. The oil must flow instantly, no matter how cold it is, when the equipment is started in order to lubricate the pump. The oil must warm up quickly lubricating, cleaning, and sealing the components. It must operate under extreme pressures and high temperatures while transferring energy to the actuators. Qualities of Hydraulic Fluids Hydraulic fluid serves a number of functions beyond its main purpose of transferring power: prevent the formation of sludge, gum, and varnish prevent rust maintain viscosity over a wide temperature range prevent corrosion separate water prevent and stabilize foaming lubricate under extreme pressures and temperatures help seal Hydraulic oil is covered in greater detail in Competency A-10, Learning Tasks 2 and 3; and in Competency C-2, Learning Task 2. HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1 69

69 SELF TEST 2 C-1 DESCRIBE HYDRAULICS SELF TEST 2 1. What component is driven by mechanical force to create hydraulic flow? a. control valve b. relief valve c. cylinder d. pump 2. How are hydraulic pumps rated? a. output force, pressure, and flow rate b. displacement, output force, and pressure c. pressure, displacement, and flow rate d. output force, displacement, and flow rate 3. What component prevents excessive pressure on the pump? a. direction control valve b. pressure reducing valve c. volume control valve d. unloading valve 4. What component controls the speed of a hydraulic actuator? a. direction control valve b. spool valve c. volume control valve d. pressure control valve 5. What type of hydraulic cylinder uses hydraulic force to move a piston both in and out? a. two-way b. double-acting c. single-acting d. single-way 6. What is the purpose for the cylinder rod piston seals? a. prevent external leaks b. prevent loss of hydraulic power c. control piston lubrication d. act as a piston cushion 70 HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1

70 C-1 DESCRIBE HYDRAULICS LEARNING TASK 3 LEARNING TASK 3 Describe Types of Hydraulic Systems There are two main types of hydraulic circuits: open-centre and closed-centre. There are variations on both of these main types. These names for basic hydraulic systems describe the position of the main control valve when it is in the neutral (or non-operating) mode. It also describes what s happening to the oil when it enters the valve housing. Open-centre means the oil passes through the valve unrestricted and returns to the hydraulic tank in the neutral position. Closed-centre means the valve has blocked the oil passage and there is no oil flowing through the valve housing in the neutral position. Each of these two systems will have special pumps to feed the system. Open-centre Systems In an open-centre system, the spool of the control valve is open when the system is in neutral, waiting to be put to work. The fixed displacement pump is in continuous operation whether the system is being used for work or not. The control valve must remain open so that the hydraulic oil may continue to circulate and return to the reservoir without creating pressure. Figure 1 shows the open-centre system in neutral. The pump feeds oil through the open centre of the valve and back to the reservoir, while the spools of the valve blocks the oil in the circuits that operate the cylinder. This valve is referred to as an open-centre valve with closed ports. This is also called a tandem-centre, because while the centre is open to allow the oil from the pump to circulate, the two lines to the actuator are blocked in the neutral or centre position to hold the load. HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1 71

71 LEARNING TASK 3 C-1 DESCRIBE HYDRAULICS Oil from pump returns to the reservoir Load Reservoir Relief valve Pump in continuous operation In neutral, pump oil flows through the valve Control valve Oil locks piston in place Figure 1. Open-centre Valve Figure 2 shows the open-centre system in operation. The control valve has been shifted so that the flow of oil coming from the pump can no longer simply return to the reservoir. It is now directed to the bottom of the cylinder where it extends the piston and rod. At the same time, the control valve has opened a path for the non-pressurized oil in the top half of the cylinder to flow back to the reservoir as the movement of the piston displaces it. When the operator pulls the lever, the pressure after the pump must rise high enough to overcome the resistance to lift. This may take a second or two to react and move the cylinder. The open-centre type of system is very common it s the least efficient but also the cheapest. This oil returns to reservoir Load Relief valve Valve shifts to direct oil to cylinder Control valve Pressure from pump raises piston and load Figure 2. Open-centre Valve in Operation 72 HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1

72 C-1 DESCRIBE HYDRAULICS LEARNING TASK 3 Closed-centre Systems In a closed-centre system, the main control valve is closed when the system is in neutral. The reason for this is that the variable displacement pump, unlike the continuous operation fixed displacement pump in an open-centre system, is de-stroked when the system is not required to perform any work. It continues to run, but is effectively in neutral and does not pump any oil. The valve shown in Figure 3, which illustrates a closed-centre system in neutral, closes off or deadends the oil line from the pump at a specified pressure. The valve also blocks off the return line to the reservoir so that the cylinder piston is maintained in its present position, just as it was in the open-centre system in neutral. Oil locks piston in place Pump destroked Figure 3. Closed-centre Spool Valve in Neutral Position Figure 4 shows a closed-centre system in operation. The control valve has been shifted to open the line from the pump to the bottom of the cylinder. The pressure in the line from the pump drops and the pump is triggered to start operation again. The valve also opens the line from the top half of the cylinder to the reservoir so that the low-pressure oil displaced by the moving piston can return to the reservoir. This system is much more efficient than the opencentre as the pump is always under pressure and when the operator pulls the lever to lift a load, the oil is already at a working pressure at the spool valve. This minimizes the lag time for the oil pressure to build high enough to lift the load. This system can operate at 90 95% efficiency. HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1 73

73 LEARNING TASK 3 C-1 DESCRIBE HYDRAULICS Oil returns to reservoir Load Pump starts pumping oil Oil locks piston in place Figure 4. Closed-centre Valve in Operation Vented System Vented systems require a tank-mounted breather. Vented Tanks/Reservoirs Vented hydraulic reservoirs allow the air in the top of the reservoir to flow in and out of the reservoir through a top vent. The vent must have a filter to clean the air. All hydraulic reservoirs must have an air space at the top of the reservoir to allow for oil expansion and contraction. As the oil heats up, the oil will expand and this forces air from the top of the reservoir. As the oil cools, it will contract the vent allows air to enter the reservoir to prevent a vacuum. The level of oil in a reservoir will change as cylinders extend and retract. Venting allows air to enter and exit the reservoir in response to this. This happens thousands of times each day as the operator works the machine. 74 HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1

74 C-1 DESCRIBE HYDRAULICS LEARNING TASK 3 Fill cap Breather/vent Return line Gauge Intake filter To pump Sump end Strainer Baffle Drain plug Figure 5. Vented Reservoir Pressurized System In some cases, the oil may not flow fast enough and the pump may starve for oil. This is called cavitation and causes damage to the oil pump. Insufficient flow may result from cold oil, sudden rpm changes, or having a pump mounted above the reservoir oil level. In order to address this, a pressurized hydraulic reservoir may be used. There are a number of ways to pressurize the air in the top portion of the hydraulic reservoir: sealed and pressurized reservoir sealed and pressurized regulated cap hydraulic reservoir air regulator Sealed and Pressurized Reservoir In a sealed and pressurized reservoir, there are no air breathers or regulators in the reservoir. When you close the filler cap, air is trapped in the reservoir. The operator starts the engine causing the oil to heat and expand. As the oil expands, the trapped air is pressurized. This helps to force oil to the pump and minimizes cavitation. HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1 75

75 LEARNING TASK 3 C-1 DESCRIBE HYDRAULICS Fill cap Return line Gauge Intake filter To pump Sump end Strainer Baffle Drain plug Figure 6. Pressurized Reservoir Sealed and Pressurized Regulated Cap With a sealed and pressurized regulated cap, there are no breathers on the hydraulic reservoir. The cap is made as a pressure regulator, similar to a radiator cap. When you close the cap, air is trapped in the hydraulic reservoir. The operator starts the engine causing the oil to heat and expand. As the oil expands, the trapped air is pressurized. This helps to force the oil to the pump and minimizes cavitation. If the reservoir pressure exceeds the cap pressure setting, the cap regulator will control the maximum pressure. When the operator shuts off the engine, the oil will cool causing the pressure to drop. The pressure regulator cap will prevent a vacuum from forming in the hydraulic reservoir. Vent to atmosphere Atmospheric valve Pressure relief valve Figure 7. Pressure Regulated Cap 76 HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1

76 C-1 DESCRIBE HYDRAULICS LEARNING TASK 3 Hydraulic Reservoir Air Regulator With a hydraulic reservoir air regulator, the equipment has an air system that feeds air to the reservoir-mounted air regulator. This reduces the air system pressure to approximately 69 KPa (10 psi). This ensures that the hydraulic pump will always have oil on the suction side, preventing cavitation. Reservoir air supply and regulator Figure 8. Reservoir and Air Regulator HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1 77

77 SELF TEST 3 C-1 DESCRIBE HYDRAULICS SELF TEST 3 1. What is the purpose for a pressurized reservoir? a. air must be prevented from entering the oil b. pressure helps cool the oil c. to prevent the pump inlet line not adequately filling with oil d. very high system pressures are encountered 2. Where are open-centre hydraulic systems most often used? a. where high system efficiency is not a requirement b. where high system pressures are required c. where accurate motion control is a priority d. where cost of the components are not a concern 3. What is the identifying characteristic of a closed-centre hydraulic system? a. they are equipped with a fixed displacement pump b. they are equipped with a pressure compensated pump c. they are equipped with an accumulator d. they are equipped with a directional valve that blocks pump flow 4. What is the purpose for the vented hydraulic system? a. increase hydraulic reservoir head pressure b. allow movement of filtered air into and out of the tank c. prevent hydraulic reservoir head pressure d. present reservoir over pressure 78 HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1

78 C-1 DESCRIBE HYDRAULICS LEARNING TASK 4 LEARNING TASK 4 Interpret Basic Hydraulic Diagrams Symbolic diagrams, cut-a-ways, and diagrams are popular ways to represent hydraulic components and systems. You ll use these diagrams to help troubleshoot and repair hydraulics. Types of Diagrams The main types of diagrams are: schematics pictorials and cut-a-ways Figure 1 and Figure 2 show the differences between a schematic and a pictorial. The schematic shows how each component links to each component in the system. The pictorial shows the shape and exact relationship in space to each component. You ll use both types of diagrams when trouble-shooting and repairing. HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1 79

79 LEARNING TASK 4 C-1 DESCRIBE HYDRAULICS Implement lockout valve Pressure reducing valve Pilot valve Manual lower valve Shuttle valve Lift cylinder Tilt cylinder Line relief valve Line relief valve Makeup valve Makeup valve Lower Tilt left Lift spool Tilt spool Tilt right Raise Line relief valve Tip/ Tilt cylinder Tip forward Tip back Line relief valve Main relief valve Tip spool Figure 1. Schematic 80 HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1

80 C-1 DESCRIBE HYDRAULICS LEARNING TASK 4 Figure 2. Pictorial Schematics Schematics are made up of a group of symbols connected with lines. Schematic and schematic symbols do not show the exact shape of a component, but rather a two-dimensional drawing that represents that component. These symbols are a visual shorthand. Symbols rely on squares, rectangles, diamonds, circles, and lines to represent the components. Basic Symbols Basic rules when interpreting symbols: Symbols and diagrams do not show internal workings, or pressures and temperatures. Each symbol is drawn in the neutral or normal position before it s activated. A normally open valve will be drawn open and a normally closed valve will be drawn closed. Some manufacturers will draw a second schematic showing a circuit in the working position. Symbols can be rotated or shown in an unusual position and still be correct as long as the lines are connected properly to the symbol. Symbols can be drawn in any size. Lines may be drawn in any width. HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1 81

81 LEARNING TASK 4 C-1 DESCRIBE HYDRAULICS There is no indication as to the size of lines on a schematic. Although colour is not required, some manufacturers use it for clarity. Specifications are used by some manufacturers, but are not required. Symbol Shapes Circles with marks inside represent pumps or motors. The circle represents rotation. Figure 3. Circle Symbol Figure 4. Valve Symbol Squares with marks inside represent valves. Squares are also called envelopes. Two envelopes in the symbol represent two positions for the valve. Three envelopes in the symbol represent three positions and so on. Figure 5. Two and Three Position Valve Diamonds with marks inside represent oil treatment, such as filters, coolers, and heaters. Figure 6. Oil Treatment Symbol 82 HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1

82 C-1 DESCRIBE HYDRAULICS LEARNING TASK 4 Rectangles with marks inside are used for cylinder-type actuators. A B C D Figure 7. Cylinders Figure 8. Hydraulic Lines or or Figure 9. Oil Direction Hydraulic lines and enclosure are indicated by one of the four listed below: Figure 8A shows a main feed line. These lines run from the pump to the actuators. Figure 8B shows a drain line. Drain lines return unused bleed-off oil to the tank. Figure 8C shows a pilot line. Pilot lines are used as signal lines in circuits. Figure 8D shows an enclosure line. Enclosure lines are used to indicate components that are within another component. Figure 9 shows direction of oil flow. Figure 10 shows variability, which is used on valves, pumps, and motors. Figure 10. Variability HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1 83

83 LEARNING TASK 4 C-1 DESCRIBE HYDRAULICS There are two acceptable methods to indicate whether lines are connected or passing each other. In Method A, lines crossing perpendicular to each other indicate no connection. Lines with a dot at the point of intersection indicate connection. In Method B, non-connecting lines are shown with a raised partial loop at the point of intersection. Connecting lines are shown as crossing perpendicular with each other. Method A Non-connecting Method B Non-connecting Method A Connecting Method B Connecting Figure 11. Method A Connections Figure 12. Method B Connections 84 HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1

84 C-1 DESCRIBE HYDRAULICS LEARNING TASK 4 Component Symbols Major hydraulic components are more complex than the basic symbols. Once you understand the basics, you can figure out the different combinations in schematics. Hydraulic Tanks Hydraulic tanks show an open or closed rectangle to indicate an atmospheric vented tank or a pressurized tank. Vented tank Pressurized tank Figure 13. Vented and Pressurized Tanks Schematics can be very complex if they show only a single hydraulic tank symbol. In order to simplify the schematic, they will often show multiple tank symbols even when there is only one physical tank in the system. Hydraulic Pumps Pump symbols will show the following information: unidirectional bidirectional fixed displacement variable displacement pressure compensated drain line driven and direction of rotation HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1 85

85 LEARNING TASK 4 C-1 DESCRIBE HYDRAULICS Figure 14 shows a unidirectional fixed displacement pump driven by an electric motor clockwise. M Figure 14. Unidirectional Pump Figure 15 shows a bidirectional fixed displacement pump driven by an engine counter-clockwise. Figure 15. Bidirectional Pump Figure 16 shows unidirectional pressure compensated variable displacement pump with an oil drain to reservoir. The diagonal arrow through the pump indicates variable displacement. Figure 16. Variable Displacement Pump The box on the left with an upright arrow indicates that the pump is sensing the outlet oil pressure to control the stroke. The drain line from the bottom of the pump indicates that the pump will be piston type with a drain for internal leakage. 86 HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1

86 C-1 DESCRIBE HYDRAULICS LEARNING TASK 4 Directional Control Valves International Standards Organization (ISO) are used and recognized by all technicians. Because of this, certain rules must apply to all directional control valves: Valves can be in only one position at a time. All the line connections from the valve must come from one envelope. All the line connections must come from the envelope that shows the valve in the neutral position. All valve control actuators (foot lever, hand valve, solenoid, or pilot) should be shown pushing all envelopes laterally. Arrows inside envelopes show the direction of oil flow when that envelope is moved to the centre position. The spool valve in Figure 17 is a closed-centre spool valve, as the oil cannot flow through the valve until it is activated. The spring pushes the spool up, blocking the flow. The symbol at the right has the lower envelope next to the spring indicating the closed centre. The valve in Figure 17 is a 2-way, 2-position, closed-centre, manually activated, spring centre valve. 2-way means that there are two line connections to the valve. 2-position means that the valve has two distinct positions to direct the oil. Figure 17. Directional Control HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1 87

87 LEARNING TASK 4 C-1 DESCRIBE HYDRAULICS The spool valve in Figure 18 is an open-centre valve as the oil passes through the valve until it is activated, which blocks the oil to pump but opens the downstream line to the tank. The spring pushes the spool valve up, opening the pump to actuator passage. The symbol on the right has the lower envelope next to the spring indicating the open centre is activated in neutral position. Figure 18 is a 3-way, 2-position, open-centre, manually activated, spring centre valve. 3-way indicates the number of line connections. Figure 18. Directional Control 88 HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1

88 C-1 DESCRIBE HYDRAULICS LEARNING TASK 4 The directional control valve in Figure 19 is a 4-way, closed-centre, 3-position valve, and manually activated valve. The cut-a-way pictorial helps to visualize the oil flow in the schematic symbol. The centre envelope must show the line connections. The centre envelope is a 4-way valve as it has four line connections. The ports are labeled as P for pump, T for tank, A for actuator port, and B for actuator port. The envelope on the left shows the directional arrows crossed reflecting the direction of oil through the valve if the left envelope was moved to the centre position. The envelope on the right shows the directional arrows straight through reflecting the direction on the oil through the valve if the right envelope was moved to the centre position. There are three different envelopes indicating three positions for the valve. Figure Way, 3-Position Valve HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1 89

89 LEARNING TASK 4 C-1 DESCRIBE HYDRAULICS Refer to Figure 20 and identify the number of positions for the lift/lower directional control valve. Figure 20. Caterpillar Loader Hydraulic Schematic Pressure Control Valves Pressure control valves show a single envelope with indicators on the envelope as to the type of pressure control. Pressure control valves will have a directional arrow in the middle indicating normally open or normally closed. Pressure controls will have a pilot line reflecting upstream or downstream pressure sensing. Pressure controls may have a reservoir symbol on the spring cavity. Pressure controls may have a diagonal arrow through the spring indicating adjustable. 90 HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1

90 C-1 DESCRIBE HYDRAULICS LEARNING TASK 4 Figure 21. Pressure Reducing Figure 22. Pressure Relief, Sequence, or Priority Flow Control Valves Flow control valves do not use envelopes in the symbol. The symbol may show: fixed orifice variable orifice pressure compensating temperature compensating one-way check valve Figure 23. Fixed Orifice Figure 24. Variable Orifice Figure 25 is an adjustable pressure compensated and temperature compensated flow control valve. Figure 25. Flow Control Valve HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1 91

91 LEARNING TASK 4 C-1 DESCRIBE HYDRAULICS Actuators Motor symbols are circles, just like pump symbols. However, the internal arrows face inward to indicate that it s receiving oil. Figure 26. Reversible Motor Cylinder symbols are rectangles with lines indicating whether they are singleacting or double-acting (Figure 27 and Figure 28). Figure 27. Single-acting Cylinder Figure 28. Double-acting Cylinder 92 HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1

92 C-1 DESCRIBE HYDRAULICS LEARNING TASK 4 Pictorials and Cut-a-ways Pictorials help greatly when trouble-shooting. They help identify: equipment configurations location of major components location of lines and fittings location of pressure testing points location of flow testing points how oil flows through components how components move when activated Figure 29. Control Valve Housing TILT CONTROL VALVE DUMP Head end Load check valve Rod end Line relief makeup valve Line relief valve Tilt back pilot hydraulic actuator Pilot oil chamber Tilt spool Tank port Supply passage Passage to next valve Internal passage Tank port Pilot oil chamber Dump pilot hydraulic actuator Figure 30. Tilt Control Valve HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1 93

93 LEARNING TASK 4 C-1 DESCRIBE HYDRAULICS Standards Schematics follow the standard as set out in International Standards Organization (ISO ) Fluid Power Systems and Components. Manufacturers use this standard as a base and may enhance it with the use of colour and adjustments. Pictorials and cut-a-ways follow no defined standard although manufacturers try to make them as clear and informative as possible. 94 HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1

94 C-1 DESCRIBE HYDRAULICS SELF TEST 4 SELF TEST 4 Study Figure Y and answer questions 1, 2, and 3. 5 ADVANCE psi M 10 g/m 5 g/m 1200 psi Figure Y. 1. What is the maximum volume delivered by the pump assemblies to the control valve (4) in the position shown in Figure Y? a. 5 gpm b. 8 gpm c. 10 gpm d. 15 gpm 2. What valve is labelled 3? a. pressure control valve b. unloading control valve c. directional control valve d. check valve HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1 95

95 SELF TEST 4 C-1 DESCRIBE HYDRAULICS 3. How many positions does valve 3 have? a. 1 b. 2 c. 3 d HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1

96 COMPETENCY C-2 SERVICE HYDRAULIC COMPONENTS C-2 SERVICE HYDRAULICS HEAVY MECHANICAL TRADES: LINE C HYDRAULICS

97 Goals When you have completed the Learning Tasks in this Competency, you will be able to: describe selected hydraulic components select hydraulic fluids for hydraulic applications select and assemble hydraulic hoses and fittings demonstrate safe work procedures for hydraulic systems service perform scheduled maintenance on hydraulic systems HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1 99

98 100 HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1

99 C-2 SERVICE HYDRAULICS LEARNING TASK 1 LEARNING TASK 1 Describe Hydraulic Components Seals Hydraulic seals are identified by their shape and design. Since hydraulic seals must withstand extreme conditions, it s important that they meet system demands. Hydraulic seals are designed and selected based on: expected operating pressures expected heat of operation expected wear characteristics oil compatibility dimensions of the seal bore and shaft type of material the seal works against whether the application is static or dynamic the amount of motion between the seal and metal surface Do not select and use a seal based solely on its size. Choose a seal based on the manufacturer s recommendation. Seals and Applications O-ring The o-ring is the most popular seal used in hydraulic systems. O-rings are designed for use in o-ring grooves in which the o-ring is compressed approximately 10 20%. In dynamic applications, the o-ring groove may be wider than the o-ring itself to allow it to roll back and forth. This lubricates the o-ring, minimizing wear. Some o-rings require a back-up ring to help support against the oil pressure. Most back-up rings are made from synthetic plastic or rubber. The o-ring must always face the pressured oil with the back-up ring as a support. The back-up ring in Figure 1 prevents the o-ring from squeezing into the gap between the plunger and the cylinder wall. HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1 101

100 LEARNING TASK 1 C-2 SERVICE HYDRAULICS Static No pressure Plunger Rod Cylinder Closed End Dynamic Pressure O-ring Back-up ring Pressure Figure 1. O-ring and Back-up Ring 102 HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1

101 C-2 SERVICE HYDRAULICS LEARNING TASK 1 O-rings may be used on: hydraulic lines (static) hydraulic cylinder pistons (dynamic) hydraulic cylinder heads (dynamic and static) pump housings (static) motor housings (static) Figure 2. Static Type O-ring Seals and Packing HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1 103

102 LEARNING TASK 1 C-2 SERVICE HYDRAULICS U and V Packings U and V packings are multiple-piece seals used to trap high-pressure oil against a rotating or sliding shaft. They are used in dynamic applications and are made from synthetics, natural rubber, and plastics. They re shaped like a cup and the open side must face the high-pressure oil. U and V packings are used on: pump and motor shafts hydraulic cylinder head (cap) to rod hydraulic piston Figure 3. V Packing Spring-loaded Lip Seals Spring-loaded lip seals are used in dynamic applications. The seals can be single or double lip depending on the application. The primary lip must face towards the oil. The seal has a steel backing that supports the seal in the housing. Spring-loaded lip seals are used on: Pump and motor shafts. (Pump and motor shaft seals face towards the pressure oil. This prevents the oil from leaking past the shaft.) Hydraulic cylinder head (cap) to rod wiper. (Hydraulic cylinder wiper/ scraper seals face away from the oil. These seals are designed to clean the cylinder rod as it retracts into the cylinders. This prevents dirt and air from entering the cylinder.) 104 HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1

103 C-2 SERVICE HYDRAULICS LEARNING TASK 1 Oil side Rubber up Lip seal Metal stiffener Garter spring Figure 4. Spring-loaded Lip Seal Figure 5. Spring-loaded Pump Shaft Seal Cup and Flange Packing Cup and flange packing are dynamic application and look like the spring-loaded lip seal but are made of synthetic rubber/plastics. These seals are only used on hydraulic cylinder pistons and head to rod seals. Figure 6 shows one type of synthetic rubber and plastic type seal used in cylinders. Figure 7 identifies the inner/outer and wiper seals located in the rod guide (cylinder head). Figure 6. Synthetic-type Cup Seal HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1 105

104 LEARNING TASK 1 C-2 SERVICE HYDRAULICS Figure 7. Cylinder Seals Cylinder Head (Cap) Seals Cylinder head (cap) seals are a special high-pressure dynamic seal. Oil must be trapped in the cylinder at high pressures as the rod extends and retracts. Cap seals are a three-piece seal: teflon seal that rides on the moving rod rubber expander ring to force the teflon seal against the rod back-up ring to support the expander ring and teflon seal Cylinder rod Figure 8. Three-piece Cap Seal Metallic Seals Metallic seals are a dynamic type seal used in high-temperature applications. 106 HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1

105 C-2 SERVICE HYDRAULICS LEARNING TASK 1 Metallic seals are found on some excavator hydraulic cylinder piston seals. Metallic seals resemble engine piston rings. The ends of the seals overlap to minimize leakage. Figure 9. Metallic Piston Rings Hoses and Lines Hoses and lines connect major components. They act as the conduit for highpressure, fast-flowing fluid in each hydraulic circuit. Hoses and lines must carry fluid with minimal influence on the flow. Sizing, location, and bends can have a large effect on the ability of the fluid to flow from one component to another. Hoses are primarily rubber-based, with nylon or steel plies added for strength. Hoses are very flexible and can be routed around objects. Detailed information on hydraulic hoses is covered in Learning Task 3. Line is a general term used to describe both hoses and tubing. It s common to use both tubing and hoses in one run (length) as they offer many advantages. Figure 10. Hydraulic Hoses HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1 107

106 LEARNING TASK 1 C-2 SERVICE HYDRAULICS Fittings Hydraulic fittings are the couplers for each hose. Each type of hydraulic hose will have special fittings that will connect hose-to-hose or hose-to-tubing. You must be able to identify and use many different types of hydraulic hose and tubing fittings. Each type of hydraulic fitting has its own clamping and sealing style. Figure 11. Hydraulic Fittings Filters and Strainers Filters and strainers are used in a hydraulic system to trap and retain contaminants that enter the fluid. Since heavy equipment often operates in dusty conditions, there is a strong likelihood of contaminants entering the system. Additionally, metal fragments produced inside the system from normal wear and tear will also contaminate the system. The function of hydraulic oil is to lubricate parts as well as transmit power. The presence of contaminants will wear and score metal components in the system. Filters and strainers are used to remove as many contaminants as possible. Filters and strainers perform the same function. Strainers are coarser than filters and are used to remove large particles. Filters are much finer and are used to remove much smaller particles. This requires special filter ratings and specific locations (relative to the oil flow) for the filters. 108 HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1

107 C-2 SERVICE HYDRAULICS LEARNING TASK 1 Filter and Strainer Ratings To distinguish between filters and strainers, and between different sizes, strainers are rated according to a mesh or a sieve number and filters are rated according to micron size. Strainers are most commonly made of wire screen, which is why they re rated with a mesh or sieve number. The higher the mesh number, the finer the screen rating. Filters use two rating methods: micron rating beta rating Micron Rating Filters can be made from wire screen or from a number of other materials such as specially treated paper. They are commonly rated by micron size. A micron (abbreviated µ) is a very small measurement equal to one millionth of a metre ( in.). Some filters are constructed so they can filter out particles that are as small as 2µ. With the close tolerances of hydraulic components, filters have to keep out small particles or the efficiency and operating life of the equipment will quickly decrease. Filters are usually given a nominal micron rating as opposed to an absolute rating. For example, a filter might have a nominal rating of 15µ. This means that it will capture most of the contaminants that are 15µ or larger. The filter s absolute rating will be higher (e.g., 30µ) and this indicates that the filter will catch everything 30µ or larger in size. Relative Sizes Since a micron is so small, it s difficult to appreciate just how fine a filter is. The following list is meant to demonstrate just how small a micron is: visual lower limit (40 microns) white blood cells (25 microns) red blood cells (8 microns) bacteria (cocci) (2 microns) Some hydraulic systems have filters that are rated at 2 microns. This could filter out white and red blood cells! Although you cannot see contaminants that are 30 microns in size, they are large enough to damage pumps, motors, and valves. Because of this, you must be very careful when servicing, repairing, or troubleshooting any hydraulic system. HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1 109

108 LEARNING TASK 1 C-2 SERVICE HYDRAULICS Beta Rating Beta rating is the measured ability of a filter to capture particles of a certain size. The tests are done in accordance with procedures established by the International Standards Organization (ISO). The ISO test is conducted at different micron levels (5 microns, 10 microns, 20 microns, 30 microns) and compares the number of particles of that size in the fluid before and after passing through the filter. e.g., Testing is done at the 20 micron level. There are 100 particles in the fluid before passing through the filter. If there are 100 particles (at least 20 microns in size) after passing through the filter, the beta rating will be 100/100 = 1. If there are 50 particles (at least 20 microns in size) after passing through the filter, the beta rating will be 100/50 = 2. If there are 10 particles (at least 20 microns in size) after passing through the filter, the beta rating will be 100/10 = 10. If there are 2 particles (at least 20 microns in size) after passing through the filter, the beta rating will be 100/2 = 50. Most filters will have a beta rating of 50 or higher, at the 5- to 10-micron level, in hydraulic systems. Filter Types Hydraulic filters are either surface or depth filters. The function of each type is to allow oil to pass through while retaining contaminating particles. Surface filters are designed with numerous folds or pleats to increase the surface area that can trap and retain particles. Depth filters may contain more than one kind of filter substance. For example, a paper element on the outside, and cotton or cellulose on the inside. By directing the oil throughout the body of the filter, rather than just through its surface, they can filter more effectively. 110 HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1

109 C-2 SERVICE HYDRAULICS LEARNING TASK 1 Figure 12. Surface Filter Paper Pleats Figure 13. Supported Pleats Figure 14. Depth Screen Element The amount of material a filter can trap varies with the filter design, but all filters have to be changed regularly or they begin to restrict the flow of oil and prevent the hydraulic system from working effectively. The two most common types are cartridge filters and spin-on filters (Figure 15 and Figure 16). Cartridge filters have a replaceable element that fits into a covered housing. A spin-on filter has both the filter element and housing in a self-contained unit. Figure 15. Cartridge Element Figure 16. Spin-on Element HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1 111

110 LEARNING TASK 1 C-2 SERVICE HYDRAULICS Hydraulic Filtering Systems The most common filtering system is the full-flow system which filters all the oil each time it goes through a cycle. The number of filters required to do this effectively will depend on the particular machine and the extent of its hydraulic systems. It s common to have a coarse screen ahead of the pump, and another finer filter on the return line to the reservoir. The coarse filter, usually a strainer, is less likely to restrict flow to the pump and interfere with the system s operation, while the finer grade filter will catch contaminants before they get to the reservoir. There may also be a high-pressure filter between the pump and control valve. It s common to have more than one type of filtering system on equipment/trucks: suction filter protects the pump from contaminants high-pressure filter protects the valves from contaminants return filter protects the pump from contaminants Figure 17. Filter Locations Filter Bypass and Indicators Hydraulic filters may have bypass valves and indicators. The bypass valve is either a disc or a plunger under spring pressure. As the filter restricts, the oil pressure before the filter rises. This pressure pushes against the disc or plunger and forces it off its seat. This allows some of the oil to bypass the filter and move through the hydraulic system. 112 HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1

111 C-2 SERVICE HYDRAULICS LEARNING TASK 1 When oil is cold, it doesn t pass through the filter fast enough. This creates an increase in pressure ahead of the filter and causes the bypass valve to open. As the oil warms, it thins and flows more quickly through the filter. The bypass valve will then close ensuring that all oil passes through the filter. It s important to keep the engine rpm low when the oil is cold as this minimizes the amount of oil that bypasses the filter. Filters may also have an indicator that causes a light to turn on when the filter is restricted. It s common for this indicator light to flicker when the oil is cold. This alerts the operator to maintain low engine rpm until the oil has warmed. Figure 18. Filter Bypass and Indicator HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1 113

112 SELF TEST 1 C-2 SERVICE HYDRAULICS SELF TEST 1 1. What is the purpose for an o-ring back-up ring? a. seal oil b. keep the o-ring from rolling c. help support against oil pressure d. allow the o-ring to roll 2. What is the purpose for cylinder rod wiper seals? a. hold oil in b. guide the rod c. wipe oil off the rod d. keep dirt out 3. What type of filter device would be used in the suction side of the hydraulic pump? a. 10 micron filter b. 20 micron Beta 2 filter c. 100 mesh screen d. 300 Beta 10 screen 114 HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1

113 C-2 SERVICE HYDRAULICS LEARNING TASK 2 LEARNING TASK 2 Select Hydraulic Fluids Requirements Engineers develop fluids for different hydraulic applications. Always use the appropriate service information when selecting hydraulic oils. There are many things to consider when selecting a particular fluid: starting temperature warm-up time operating temperature severity of load (light-, medium-, or heavy-duty) service period (250 hours, 500 hours, 750 hours, 1000 hours) use of hydraulic oil in an environmentally sensitive area fire-retardant hydraulic oils in fire environments Hydraulic oils must have basic requirements/properties to perform properly: Hydraulic oils must have a relatively high viscosity index. There should be very little change in viscosity as the equipment temperature changes. Hydraulic oils must have anti-oxidation properties. Hydraulic oil operates at very high temperatures which increases oxidation, resulting in acids and sludge in the oil. Hydraulic oils must prevent rust and corrosion of metal parts. Hydraulic oils must resist foaming. Foaming induces air in the hydraulic system resulting in pump failures and oil oxidation. Hydraulic oils must separate water from oil. Water causes emulsification and will result in corrosion problems, pump failures, and freeze-up in cold climates. HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1 115

114 LEARNING TASK 2 C-2 SERVICE HYDRAULICS SAE Viscosity Ratings SAE viscosity ratings were primarily developed for engine use. However, some equipment manufacturers recommend using an SAE oil when selecting a hydraulic oil. SAE viscosity oil may be either a single grade or a multi-grade oil. Always refer to the manufacturer s specification when selecting oil. SAE Single Viscosity Grade Oil SAE 5W SAE 10W SAE 15W SAE 20W SAE Multi-Viscosity Grade Oil SAE 0W-30 Semi-synthetic SAE 5W-20 ISO Viscosity Ratings The International Standards Organization has tested and developed the viscosity ratings that most hydraulic systems follow. The table below shows the ISO hydraulic oil comparisons to SAE oil viscosities. The two most common hydraulic oils used today are ISO 32 and ISO 46. Note that ISO 32 is SAE 10W oil for winter use, and ISO 46 is SAE 20 summer oil. ISO Grade Equivalent Viscosity SAE Grade Centistokes 10-6 reyns (lb s/in 2 ) 40 C 100 C 104 F 212 F 32 10W W Figure 1. ISO and SAE Ratings 116 HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1

115 C-2 SERVICE HYDRAULICS LEARNING TASK 2 Figure 2 shows an example of hydraulic oil that may be used in heavy equipment/trucks. Note that this oil has an ISO rating of AW32. Figure litre Pail of Oil Item Premium Hydraulic Oil Product Head DTE 24 Size 20 l SAE Grade 10W ISO Viscosity Grade 32 Viscosity 100 F) 165 Flash Point ( F) 395 Pour Point ( F) -10 Application For High Pressure Systems, Systems with Servo Valves, NC Control Mechanisms and all Robotics, Industrial, Marine, Mobile Service Hydraulic Equipment, Hand and Power Operated Jacks, Scissor Jacks and Hand Pumps Standards Dension HF-O, Vickers V-104C and 35VQ25 and Sundstrand Pump Tests Figure 3. Oil Specifications API Ratings The API rating system enables engine oil to be defined and selected on the basis of performance characteristics and the type of service. Because this rating was primarily designed for engine use, the API ratings may not apply to highpressure and high-temperature hydraulic systems. Hydraulic systems require more additives for the loads, pressures, and heat they re subjected to. HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1 117

116 LEARNING TASK 2 C-2 SERVICE HYDRAULICS However, some medium-pressure and temperature systems (farm tractors, loaders, etc.) may choose an API rating. Be sure to check the lubrication information for all hydraulic systems before changing or topping up oils. Manufacturer Specifications Manufacturers often define their own hydraulic specifications and have an oil supplier create the oil. The manufacturer will label the oil with their own brand name. (e.g., Caterpillar, John Deere, Komatsu, etc.) These specific hydraulic oils will always be recommended by the manufacturer of the equipment/truck as the oil was tested for this application. Synthetic/Non-synthetic (Mineral) There are two main varieties of oil: synthetic and non-synthetic (sometimes called mineral oil ). Mineral oil is based on naturally occurring petroleum, whereas synthetic oil is man-made. Synthetic oil is more expensive than mineral oil, but has a number of benefits: higher viscosity index extra additives for anti-wear, corrosion, oxidation, anti-foaming higher lubricity level for boundary layer lubrication less viscous friction causing heat higher temperature protection lower viscosity at lower temperatures Synthetic oils work very well for excavator applications since they operate at high-pressure and high temperatures. They are also great in climates that get below -20 C (-4 F). However, most equipment uses mineral oil due to its lower cost. Component/System Compatibility Companies that specialize in hydraulic components (e.g., Eaton, Vickers, Rexroth, Linde, Denison) determine lubricant specifications for their specific parts. Manufacturers of equipment and trucks work with these component makers to ensure that the lubrication specifications are correct. If you change a component to one that isn t recommended by the original manufacturer, you will need to determine the lubrication requirements of the equipment. 118 HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1

117 C-2 SERVICE HYDRAULICS SELF TEST 2 SELF TEST 2 1. What is the most important consideration when selecting hydraulic oil? a. ISO rating b. API rating c. cost of the oil d. service information 2. What is the ISO grade for SAE 20W oil? a. ISO 68 b. ISO 46 c. ISO 32 d. ISO 20 HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1 119

118 120 HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1

119 C-2 SERVICE HYDRAULICS LEARNING TASK 3 LEARNING TASK 3 Select Hydraulic Hoses and Fittings Hose Construction, Pressure Ratings, and Compatibility Each hydraulic hose is constructed from multiple layers: the inner tube, reinforcing plies, and the outer cover. The inner tube is made of synthetic rubber or thermoplastic and must be compatible with the fluid the hose carries. The plies determine the strength of the hose and there may be one or several. Each ply is made of textile, nylon, or steel and may be braided or spiraled for added strength. Low-pressure hoses will have nylon plies. Medium-pressure hoses will have one nylon and one steel ply. High-pressure hoses will have two or more steel plies. Additional plies increase the strength of the hose, but also make it stiffer. The outer cover of the hose is made of a material that will resist abrasion, corrosion, and contamination. Figure 1. Hose Construction The application of a hydraulic hose will determine its design and construction. HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1 121

120 LEARNING TASK 3 C-2 SERVICE HYDRAULICS SAE J517 Standard The Society of Automotive Engineers classifies hoses based on their construction, pressure rating, oil-compatibility, temperature rating, and dimensions. This rating standard (SAE J517) grades hoses using a 100R number which ranges from 100R1 to 100R16. SAE HOSE TYPE INNER TUBE REINFORCEMENT COVER OPERATING TEMPERATURE C ( F) 100R1-A Oil resistant synthetic rubber One wire braid Oil resistant synthetic rubber C ( F) 100R1-AT Oil resistant synthetic rubber One wire braid Oil resistant synthetic rubber non-skive -40 C 93.3 C ( F) 100R2-A Oil resistant synthetic rubber Two wire braids Oil resistant synthetic rubber C ( F) 100R2-AT Oil resistant synthetic rubber Two wire braids Oil resistant synthetic rubber non-skive C ( F) 100R2-B Oil resistant synthetic rubber Two spiral plies and one braid of wire Oil resistant synthetic rubber C ( F) 100R2-BT Oil resistant synthetic rubber Two spiral plies and one braid of wire Oil resistant synthetic rubber non-skive C ( F) 100R3 Oil resistant synthetic rubber Two textile braids Oil resistant synthetic rubber C ( F) 100R4 (Suction hose) Oil resistant synthetic rubber Textile plies or braids with spiral body wire Oil resistant synthetic rubber C ( F) 100R5 Oil resistant synthetic rubber Two textile braids separated by one wire braid Textile braid impregnated with oil resistant synthetic rubber compound C ( F) Figure 2. SAE J 517 Hose Construction Specifications 122 HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1

121 C-2 SERVICE HYDRAULICS LEARNING TASK 3 SAE HOSE TYPE I.D. INCHES MAX. O.D. INCHES MIN. BEND RADIUS IN INCHES MAX. WORKING PRESSURE PSIG MIN. BURST PRESSURE PSIG 100R1-A R1-A R1-A R1-AT R1-AT R1-AT Figure 3. SAE J517 Hose Size and Pressure Specifications ISO Standard The International Standards Organization (ISO) tests hydraulic hoses to a higher level than the SAE standard. The tests focus on pressure pulses and temperatures that are higher than normal. ISO standard hydraulic hoses are classified into four grades (A, B, C, and D) according to their resistance to impulse pressure at a specified temperature. The outside diameter (OD) of the hose refines each grade into standard (AS, BS, CS), or compact types (AC, BC, CC, DC). A, B, C, D for grade (D is the highest grade). S for Standard size. C for Compact size. Spiral-wound hoses tested to ISO standards are lighter, stronger, and last longer than traditional braided hoses. Figure 4. Spiral-wound Hose HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1 123

122 LEARNING TASK 3 C-2 SERVICE HYDRAULICS Flow Rating Hoses are rated for how efficiently fluid flows through them. Engineers monitor the pressures and temperatures across a hose. Hoses that are too small for the application will experience a pressure drop and high heat. Hoses are sized by their nominal inside diameter (ID). Figure 5. Nominal Inside Diameter Hose Applications Hydraulic hoses are used extensively in areas with much vibration and motion and are commonly used where working attachments join a machine. These attachments usually have moving parts such as: loader lift cylinders loader boom tilt cylinders crawler lift cylinders crawler blade angle and tilt cylinders grader blade lift and tilt cylinders crawler ripper cylinders skidder grapple cylinders excavator stick, bucket, and boom cylinders Fitting Types Hose fittings and couplers can be made of stainless steel, steel, brass, or aluminum. Stainless steel and steel fittings are usually used for high-pressure applications. Hose fittings can be either permanent or reusable. When fittings are crimped/wedged to the hose, the fittings are replaced whenever the hose is replaced. 124 HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1

123 C-2 SERVICE HYDRAULICS LEARNING TASK 3 Other fittings are reusable. When replacing a hose, you ll remove the hose from the machine, remove the fittings from the hose, and reinstall the fittings on a new hose. This is a quick and inexpensive method of replacing hoses. National Pipe Taper (NPT) National Pipe Taper (NPT) allows for strong connections between hoses and components as well as hoses to other hoses. Since NPT is a tapered thread, it should not be threaded into anything other than NPT. National Pipe Taper is rated for the pressures it will take: schedule 40 indicates a cast fitting suitable for low pressures schedule 80 and higher is forged and alloy steel National Pipe Taper must be schedule 80 or higher to handle high hydraulic pressures. NPT steel fittings must use pipe tape or pipe paste to ensure a proper seal in the tapered threads. NPT pipe is sized by measuring the nominal inside diameter of the female thread and adding 1 4 of an inch. Figure 6. Schedule 80 NPT Figure 7. Schedule 40 NPT HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1 125

124 LEARNING TASK 3 C-2 SERVICE HYDRAULICS Joint International Conference (JIC) JIC rates fittings for high-pressure applications. JIC fittings will use forged alloy steel and have a 37 cone or swivel on one end. These fittings work well when joining two hoses together. Nipple Swivel nut Figure 8. JIC Cone and Swivel The size of JIC fittings are determined by reading marks on the socket, nipple, or hex head swivel. Imperial-sized fittings have a dash number (e.g., -8, -12). Dividing the dash number by 16 will give you the size in inches of the appropriate hose: A - 10 fitting will require a in. ( 5 8 in.) hose. A - 12 fitting will require a in. ( 3 4 in.) hose. Metric sized fitting will show the metric equivalent (e.g., 12 mm) number stamped on the nipple and socket. O-ring Boss (ORB) O-ring boss (ORB) fittings are an excellent method to attach a line to a housing. The o-ring squeezes against the housing when the fitting is tightened. Some fittings will use a jam nut which allows the fitting to be turned to a specific orientation. The jam nut is then tightened to clamp the o-ring to the housing. ORB uses a straight (non-tapered) pipe thread. Imperial size is determined by measuring the inside diameter of the female thread and adding 1 4 inch. Metric size is determined by measuring across the male thread in millimetres. 126 HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1

125 C-2 SERVICE HYDRAULICS LEARNING TASK 3 Figure 9. O-ring Boss Fitting Figure 10. O-ring Boss and Jam Nut to JIC with Jam Nut O-ring Face (ORFS) O-ring face seal tube fittings (also known as flat face or ORFS fittings) have proven to be very effective in eliminating leakage at higher pressures. Seal-Lok fittings feature a captive o-ring groove (CORG) design for optimal sealing, and prevention of o-ring fall-out prior to final assembly. O-ring face seal tube fittings are available in steel, stainless steel, and 316 stainless steel. The Seal-Lok tube fitting consists of a nut, a fitting body, an o-ring, and a sleeve. In a Seal-Lok/flat face fitting, holding control is attained by a flat-faced flange on the end of the tube. As the nut is tightened onto the fitting body, the o-ring is compressed between the body and flat face of the tube flange. Designed to eliminate leakage in hydraulic systems and allow higher operating pressures, o-ring face seal steel tube fittings are available on hose fittings as well as tube fittings. These fittings are sold in both metric and imperial sizing. The tubing outside diameter will determine the size of the fittings. The hose inside diameter will determine the hose fittings. Figure 11. O-ring Face Connector Figure 12. ORFS Line and Connector HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1 127

126 LEARNING TASK 3 C-2 SERVICE HYDRAULICS Split Flange O-ring Face Fittings Four-bolt, two-flange clamps are mechanical connections using o-rings to seal in the pressure. The flange clamps hold down the hose to the component (pump). By removing one clamp and loosening the other, the hose can be removed and replaced. The hose can be rotated for orientation purposes by loosening the clamps. Figure 13. Assortment of Split Flange and Fittings Society of Automotive Engineers (SAE) SAE fittings are low-pressure hoses and low-, medium-, and high-pressure tubing. The hose is usually a single- or double-braided nylon, while the tubing is either plastic, copper, or steel. SAE flared fittings are at 45 angle. Steel tubing may have either single or double flares, while copper tubing will have single flares. Low-pressure Hose Fittings The low-pressure brass fitting in Figure 14 has a barbed end for the hose to slide over. Some barbs are made to hold the hose without clamps while others require a hose clamp. Figure 14. SAE Low-pressure Brass Fitting 128 HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1

127 C-2 SERVICE HYDRAULICS LEARNING TASK 3 Refer to Competency A-5, Learning Task 3 for more detail on SAE tubes and fittings. Reusable and Permanent Fittings High-pressure reusable fittings are assembled with a two-piece nipple and socket for each fitting. The socket and nipple have course threads which thread into the hose to secure the fittings. Nipple Socket Hose Size Identification Swivel Nut Socket Nipple Figure 15. Reusable Socket and Nipple Figure 16. Socket Size Identification Permanent fittings have either a one- or two-piece nipple and socket. The nipple and socket are forced into the hose and the socket is placed into a hose press to crimp the socket onto the hose and nipple. This secures the socket, nipple, and hose as a one-piece assembly. Figure 17. Reusable Hose and Fittings Figure 18. Reusable Fitting Figure 19. Permanent Fitting HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1 129

128 SELF TEST 3 C-2 SERVICE HYDRAULICS SELF TEST 3 1. What is the purpose for the SAE-J517 standard? a. provide hydraulic hose standards b. provide hydraulic oil standards c. provide hydraulic tubing standards d. provide hydraulic filter standards 2. What is the reinforcement for 100R3 hydraulic hose? a. two textile braids b. two spiral plies c. two wire braids d. oil resistant synthetic 3. What is the burst pressure of 1 2 inch 100R1-A hydraulic hose? a psi b psi c psi d psi 4. How is hydraulic hose sized? a. measuring the outside diameter b. measuring the inside diameter and add 1 4 inch c. measuring the nominal inside diameter d. measuring the outside diameter and subtract 1 4 inch 5. What is the JIC seat angle? a. 45 b c. 37 d How do split flange fittings seal? a. tapered seat b. o-rings c. tapered thread d. flared tube 130 HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1

129 C-2 SERVICE HYDRAULICS SELF TEST 3 7. What component secures the hydraulic hose to the reusable hose end? a. swivel nut b. socket c. braiding d. flare HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1 131

130 132 HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1

131 C-2 SERVICE HYDRAULICS LEARNING TASK 4 LEARNING TASK 4 Assemble Hydraulic Hose and Fittings Permanent Hose and Fittings Figure 1. Hydraulic Hose Press The tools required to assemble a permanent hose assembly are: measuring tape hacksaw or cut-off saw hose cleaner/solvent bench vise hose lubricant hose press HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1 133

132 LEARNING TASK 4 C-2 SERVICE HYDRAULICS The procedure for installing permanent fittings is as follows: 8. Measure the length of hose required, making sure to include the length of the fittings on each end. Use a fine tooth hacksaw or cut-off saw to cut the length of hose required. 9. Clean the inside of the hose to remove any cut-off material. 10. Mount the nipple in the vise, positioned so that you will be able to guide the socket/ferrule into place. 11. Apply a light lubricant on the end of the nipple and slide the hose into position. 12. Select and install the proper crimping adapters for the hose press. Crimping adapters/dies must be chosen to match the type of fitting on the hose. 13. Remove the hose assembly from the vise and place it in the hose press. (The hose is placed in the press with the socket/ferrule lined-up with the crimping adapters.) 14. Run the pump on the hose press to crimp the socket to the hose and nipple. 15. Remove the hose assembly from the vise and repeat for the opposite end. Figure 2. Permanent Hose Assembly 134 HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1

133 C-2 SERVICE HYDRAULICS LEARNING TASK 4 Reusable Hose and Fittings with Skive and No-skive Hose The tools required to assemble a reusable hose assembly are: measuring tape hacksaw or cut-off saw hose cleaner/solvent hose lubricant bench vise open end wrench The procedure for installing reusable fittings is as follows: 1. Choose whether you want a medium- or high-pressure hose (they have different types of fittings). Medium-pressure hose has only one steel ply whereas high-pressure hose has two or more steel plies. No notch Notch Medium-pressure fitting High-pressure fitting Figure 3. Medium- and High-pressure Reusable Fittings Medium-pressure hose uses a no-skive application. ( Skiving the hose involves removing the outer rubber cover to make the fitting fit.) High-pressure hose fittings (which have a notch for identification) must be skived to allow the fittings to fit onto the hose. Some newer high-pressure hose is marked as a no-skive hose and these fittings look like the medium-pressure fittings but are thicker and can handle high pressures. High-pressure no-skive hose and fittings must be matched to prevent line ruptures. 2. Measure the length of hose required, making sure to include the length of the fittings on each end. Use a fine tooth hacksaw or cut-off saw to cut the length of hose required. 3. Clean the inside of the hose to remove any cut-off material. HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1 135

134 LEARNING TASK 4 C-2 SERVICE HYDRAULICS 4. If skiving is required, mount the hose in the vise and use a skiving tool to cut the rubber from the hose. Make sure to remove only as much as necessary. The notch on high-pressure hose marks how much material to remove. 5. Place the socket into the vise and turn the hose counter-clockwise onto the socket until it bottoms out. Back out the hose by turning it clockwise 1 4 turn. 6. Place a small amount of light oil on the taper of the nipple and thread it clockwise into the socket and hose until it bottoms out. Back out the nipple 1 4 turn. 7. Remove the hose assembly from the vise and repeat for the opposite end. 136 HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1

135 C-2 SERVICE HYDRAULICS LEARNING TASK 4 Figure 4. Medium- and High-pressure Fitting Installation HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1 137

136 SELF TEST 4 C-2 SERVICE HYDRAULICS SELF TEST 4 1. How is the socket installed on a reusable fitting and hose? a. socket is turned on clockwise till bottom and backed off 1 4 turn b. socket is turned on clockwise till bottom c. socket is turned on counter-clockwise till bottom and backed off 1 4 turn d. socket is turned on counter-clockwise till bottom 2. How is the nipple installed on a reusable fitting and hose? a. nipple is turned on clockwise till bottom and backed off 1 4 turn b. nipple is turned on clockwise till bottom c. nipple is turned on counter-clockwise till bottom and backed off 1 4 turn d. nipple is turned on counter-clockwise till bottom 138 HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1

137 C-2 SERVICE HYDRAULICS LEARNING TASK 5 LEARNING TASK 5 Demonstrate Safe Work Procedures Safety Blocking Equipment and Attachments When performing maintenance, repairs, or troubleshooting on equipment that requires blocking, you must follow proper safety steps to prevent personal injury or damage to equipment: Equipment and attachments must be on level ground. Use the correct service manual and bulletins for the equipment on which you are working. Equipment must be put into the service position and locked-out. The wheels must be blocked/chocked. Blocking must be sufficient for the job and follow the manufacturer s recommendations and WorkSafeBC regulations. Approved blocking must be used to support any attachments that are in a raised position (e.g., dump box or loader bucket). All equipment must have both primary and secondary blocking. Figure 1. Primary and Secondary Blocking HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1 139

138 LEARNING TASK 5 C-2 SERVICE HYDRAULICS Relieve Hydraulic Pressure Once the equipment and attachments have been blocked, you must relieve any hydraulic pressure in the lines: 1. Shut off the engine and leave the key ON. 2. Climb into the operator s seat and move the levers back and forth or place the levers into float. This allows any oil under pressure to flow back to the hydraulic tank and the attachments to settle as low as possible. (Check the manufacturer s procedures as electronically controlled hydraulics may not bleed off when the engine is shut off and the levers moved.) 3. You should repeat this procedure a number of times to make sure all the residual pressure in the hydraulic lines has been released. Reservoir Venting Once the hydraulic line residual pressures have been relieved, you must vent the hydraulic tank. Pressure in the hydraulic tank can cause injury when you disconnect a hydraulic line. Hot oil can cause third degree burns. Refer to the equipment service manual to determine safe reservoir pressure relief process. Once the pressure has been completely vented, re-tighten the cap. Actuator Neutralization Once all the residual line pressures are neutralized and the hydraulic tank pressure is relieved, the actuators are considered neutralized. However, you should always assume that there is some pressure in any line or filter that you have to replace. Always wear proper hand and eye protection before performing any service work. Temperature Hazards Hydraulic oil temperatures can reach 121 C (250 F). If the equipment is overheating, the temperatures can rise even higher. Oil at these temperatures can cause third degree burns. Always wear hand, face, and body protection when working on hot equipment. 140 HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1

139 C-2 SERVICE HYDRAULICS SELF TEST 5 SELF TEST 5 1. What is the purpose for reservoir venting? a. prevent hydraulic reservoir over pressure b. prevent hydraulic reservoir vacuum c. prevent burns from hot oil when lines are opened d. prevent oil spills when lines are opened 2. What may be the normal oil operating temperature? a. 121 C (250 F) b. 130 C (266 F) c. 140 C (284 F) d. 150 C (302 F) HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1 141

140 142 HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1

141 C-2 SERVICE HYDRAULICS LEARNING TASK 6 LEARNING TASK 6 Perform Scheduled Maintenance Hydraulic systems provide power to equipment and machines. Wear and damage will reduce the efficiency of the system or stop it completely. Hydraulic maintenance includes more than simply changing oils and filters: Equipment needs to be properly steam-cleaned to remove dirt and oil. This will allow you to better inspect the equipment. You must talk with the equipment operator to identify areas of concern. You must perform regular hydraulic operational checks to identify any problems. You must visually examine all hydraulic components and their connections. You should follow the specific maintenance manual for all equipment you service. Visual Inspection Once you ve warmed the equipment and performed an operational check on all hydraulic circuits, you can prepare to do a visual inspection. The equipment should be put into the service position: park on level ground actuator neutralization safety bar locked on articulated machines wheels chocked engine shut-off and keys removed do not start tag placed on the machine At this time you can start the visual inspection: check hydraulic levers in the cab for looseness or binding walk around the machine looking for any obvious oil leaks check the cylinders for damage and oil leaks check the cylinders hoses/piping for damage, missing support brackets, and leaks HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1 143

142 LEARNING TASK 6 C-2 SERVICE HYDRAULICS Much of your inspection for leakage will concentrate on an examination of the condition of the hydraulic lines and hoses. This includes the various connectors such as quick-couplers and the hold-down hardware, brackets, and shields. If loose, the hardware and connections should be tightened immediately. Try to determine why the connections were loose. Common errors responsible for a leak include: improper hose length which allows too little room for expansion and flexing hose in contact with moving machine parts, resulting in rubbing and chafing hose too close to source of heat, resulting in deterioration of the hose hoses twisting, subjecting them to unnatural stresses hoses installed with loops or sharp bends, also subjecting them to stress or heat improper hose size or pressure rating for the system You should replace any improperly installed hose using the correct installation principles and the correct size hose and fittings. Tighten loose connections, but only until the leak stops. Do not over-tighten, as you can cause further damage. Inspection of hoses also requires you to examine the condition of the outer cover of flexible hose. Although there may be no leak at present, any splits or cracks in the covers are likely to develop into leaks, depending on their depth. Replace hose that has significant external damage. Hydraulic lines which have become damaged may cause overheating. Lines can be pinched, dented, squashed, or bent. Replace these sections of lines. Remember that leaks not only allow oil out, but also allow air to enter which can be just as damaging. The addition of air to hydraulic oil affects the chemical structure of the oil, which can damage the metal parts it contacts. Leaks External leaks can be rated in a number of stages: Stage 1 dust collecting on the oil stain, no oil drips or oil streaks Stage 2 oil is causing streaks in the dust/dirt Stage 3 oil is dripping Stage 4 oil is flowing 144 HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1

143 C-2 SERVICE HYDRAULICS LEARNING TASK 6 Depending on the location, stage 1 and 2 oil leaks may be documented and left for a future date. Stage 3 and 4 oil leaks should be documented and repaired as soon as possible. Each shop may have a different expectation for oil leak repairs. Tightening the hose or line where the leak is located can occasionally stop external leaks. If the line needs to be loosened or removed for repair, always make sure the oil pressure has been relieved before loosening the line. Cylinders with oil leaking at the rod packing need to be repaired. Dirt and air will be brought into the hydraulic system when the rod is retracted. Always follow the maintenance manual when repairing oil leaks. Internal leakage is not directly visible. You have to become aware of the symptoms it produces in the rest of the system. For example, sluggishness in the action of components such as pumps and actuators, and creeping and drifting in cylinders. You may be able to identify internal leaks by performing a drift test on the hydraulic circuits when you perform the operational test. If the cylinders drift down when the lever is left in the hold position, the oil must be moving in the circuit, allowing the cylinders to drift. You should document this for future repairs. Hose Rubs Hose rubs occur when the hose and the material it is touching are in constant movement against each other. Hoses may rub against: other hoses other steel lines aluminum pump housings steel frames hose brackets wiring harnesses moving parts of working attachments When hoses rub against other components, the harder material will wear down the softer. If the hose is the softer material, then the hose will wear through and cause a rupture. Hose steel braids are normally harder than other steel materials. However, the hose will also wear as the steel material wears. This will eventually cause the hose to rupture. Spiral wound hose plies are very hard and usually wear down other components. This will cause damage to the other components and the hose. All hoses should be replaced if they have worn or broken plies. HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1 145

144 LEARNING TASK 6 C-2 SERVICE HYDRAULICS Hoses can be protected with straps, brackets, and sheathing. You need to look for occurrences of hose rubs and correct them as soon as possible. Sometimes the hose can be loosened and turned so that it does not contact the other component. Strap Bracket Figure 1. Hose Brackets and Straps Always remove the residual hydraulic pressure before loosening the hose. External Damage You need to check for external damage to the hydraulic system. Most damage will occur to the working attachments. check the cylinder mounting for broken pins or brackets check cylinder for dents check cylinder rods for straightness, marks, and dents in the chrome check steel lines for flattening or twisting check hose fittings for twists, dents, or distortion check all the hose brackets for damage check the hydraulic tank for damage check the boom lift and bucket leveler kick-outs for damage check the cylinder pin grease nipples for damage and pump grease into the joint 146 HEAVY MECHANICAL TRADES FOUNDATION / LEVEL 1