CD CHAPTER. Fluid Power THE ENGINEERING DESIGN APPLICATION LEARNING OBJECTIVES

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1 CD CHAPTER Fluid Power 1 LEARNING OBJECTIVES After completing this chapter, you will: Calculate unknown values in given fluid power applications. Draw graphic diagrams of hydraulic circuits. Make graphic diagrams of hydraulic circuits based on sequence of operations functional descriptions. Prepare pictorial diagrams of hydraulic circuits. Make graphic diagrams of pneumatic circuits. Develop fluid power systems from engineering sketches, component lists, or from sketches of revised units. THE ENGINEERING DESIGN APPLICATION When a drafter begins a fluid power drafting project, she or he works from one of several starting points. The drafter may receive an engineer s sketch and a list of components for a new unit, or a sketch for an addition to an existing unit. The drafter may need to show the finished product with a Component List (or Bill of Materials) and/or include a Sequence of Operations List. In Example 1, the engineer has given the draftsperson a rough sketch and bill of materials for a hydraulic circuit. (See Figure 1.) The drafter used a CADD system to produce the final product shown in Figure 2. Figure 3 shows the actual top-mounted hydraulic power unit described in Figure 2. A top-mounted unit means that the pump and motor are mounted on top of the tank. In FIGURE 1 Example 1 engineer s sketch. Courtesy Fluid-Air Components, Inc. (Continued) 1

2 2 Fluid Power THE ENGINEERING DESIGN APPLICATION (continued) FIGURE 2 Example 1 final product. Courtesy Fluid-Air Components, Inc. a skid-mounted unit, they are mounted on the bottom of the tank. In Example 2, the drafter has received the following sequence of operations and functional description to describe what takes place in the hydraulic circuit. Figure 4 shows the resulting hydraulic graphic diagram. Note the use and function of a sequence valve (7) in this example. Sequence of Operations 1. With motor (3) running, lever on valve (6) is raised manually. Delivery of pump (4) is directed into head end of cylinder (8) for pressing phase. 2. When pressure reaches the setting of valve (7), flow is sequenced through (7) to drive motor (9). FIGURE 3 Top-mounted hydraulic power unit. Courtesy Fluid- Air Components, Inc. (Continued)

3 Fluid Power 3 THE ENGINEERING DESIGN APPLICATION (continued) 3. Manually depressing lever shifts (6) to return cylinder (8) and permit pump (9) to stop. 4. When piston of (8) returns, valve (6) is mechanically centered, unloading delivery of (4) to tank through valve (6), but maintaining sufficient pressure drop to hold work head in raised position. Functional Description Valve (5-A) provides overload protection. Valve (7) causes work to be pressed with cylinder (8) before motor (9) starts to rotate and ensures minimum pressure during operation of (9). It also controls maximum thrust of cylinder (8). Valve (5-B) limits maximum torque of motor (9). Valve (6) controls direction of motion of cylinder (8) and the running and stopping of (9). In Example 3, the same sequence of operations and functional description are used for a pneumatic circuit. The resulting pneumatic graphic diagram is shown in Figure 5. Key COMPONENT LIST Quantity Name, Model Number, and Manufacturer (1) 1 Reservoir, oil, 30 gal. cap., Co. A (2) 1 Strainer, ST104, Co. A (3) 1 Motor, Electric, 5 HP, 1800 rpm, NO-13-53, Co. JKS (4) 1 Pump, 7 1/2 GPH at 1800 rpm, FE-22-52, Co. VCS (5) 2 Valve, relief, FE-12-76, Co. EECS (6) 1 Valve, directional control, DE-04-77, Co. QJS (7) 1 Valve, sequence, DE-18-49, Co. CS (8) 1 Cylinder, differential, AU-21-43, Co. CPM (9) 1 Axial motor, fixed displacement, MO-1313, torque 15 in. lb./100 psi, displacement.96 cu. in./rev., Co. E FIGURE 4 Example 2 hydraulic graphic diagram. FIGURE 5 Example 3 pneumatic graphic diagram.

4 4 Fluid Power INTRODUCTION For thousands of years, water has been controlled for various uses by utilizing dams, water wheels, and tanks. The practical application of this fluid in motion was the beginning of the science of hydraulics. Today, hydraulics and pneumatics are referred to as fluid power or fluidics. A fluid is defined as something that can flow and is able to move and change shape without separating when under pressure. Fluid power, therefore, includes both liquids and gases. The science of hydraulics refers to liquids and the science of pneumatics refers to gases. The fluid power technology of using the flow characteristics of a liquid or gas to perform work is used extensively in the operation and control of automobile and aircraft systems, machine tools, earth moving equipment, ships, and spacecraft. To understand the concept of fluid power systems, it is necessary to first look at the basic principles of force, pressure, work, and power. FORCE, PRESSURE, WORK, POWER Force can be described as any action that produces motion or alters the position of an object. In the U.S. Customary System, force is usually expressed in pounds, whereas in the International System it is expressed in newtons. Pressure is the force per unit area exerted on an object. It is shown mathematically as: Pressure = Force/Unit Area. When using force expressed in pounds, the common unit area is a square inch. The pressure is described as pounds per square inch, or psi. When using force expressed in newtons, the unit area is one square meter. However, in this case, instead of the pressure being described as one newton per square meter, it is called a pascal (Pa). Since this measurement is inconveniently small for most engineering work, the kilopascal (kpa), which is 1,000 newtons per square meter, is more commonly used. One psi equals kpa. Work is the measurement of force applied to an object multiplied by the distance the object is moved. Therefore, no work is done unless the object is moved or displaced. Work is described mathematically as: Work = Force Distance. In the U.S. Customary System, distance is expressed in either inches or feet. Work, therefore, is measured in in.-lb or ft-lb. For example, if a force of 800 pounds displaces an object 3 feet, the amount of work done is 2,400 ft-lb. In the International System, the distance is expressed in meters. If a force of 300 newtons displaces an object 40 meters, the amount of work done is 12,000 newtonmeters, or joules (J). The joule is the amount of work done when one newton is displaced a distance of one meter. A kilojoule (kj), which is 1,000 joules, is more commonly used than a joule. Therefore, 12,000 joules would be shown as 12 kj. A joule equals.7377 ft-lb. Power is described as the work accomplished per unit of time. In other words, an equal amount of work can be done by a high-powered motor in a short time or by a low-powered motor in a long time. The mathematical expression is Power = Work/Time. Units of power are expressed in foot-pounds per minute, or in joules per second. The more common expressions are horsepower, which equals 33,000 ft-lb per minute, and watt, which equals one joule of work per second. For example, imagine an assembly line motor pushing an object from one conveyor belt to another belt 8 feet away with a force of 1,000 lb in 5 seconds. The work being done is 8,000 ftlb. The amount of time is 1/12th of a minute, or minute. In one minute, the amount of work done is 8,000 ft-lb + 1/12 = 96,000 ft-lb/minute. Therefore, the motor has a horsepower of 96,000/33,000 or 2.9. HYDRAULICS The science of hydraulics had its beginning in about 1650 when a French mathematician and physicist named Blaise Pascal first observed the law that became known as Pascal s principle. It states that if a pressure is exerted at one portion of fluid that is at rest in a closed container, then that pressure is transmitted equally in all directions without loss through the rest of the fluid and to the walls of the container. (See Figure 6.) What this means in a hydraulic circuit is that pressure applied to one part of the system (a piston, for example) will affect another part of the circuit (another piston) with the same pressure. The amount of force produced on the second piston depends on the area of that piston. Similarly, the amount of work done depends on the distance that the second piston was moved. Figure 7 shows an example of this principle. In this simple hydraulic circuit, the surface of piston A is 10 square inches. When a force of 50 lb is applied, the pressure exerted in the fluid, on all walls, and against the surface of piston B is 5 lb per square inch (psi). The force of piston B is, therefore, 5 psi 100 square inches, or 500 lb. If piston A moves a distance of 20 feet, the amount of work done is the force distance, or 50 lb 20 feet, FIGURE 6 Pascal s principle. FIGURE 7 Pascal s principle in a hydraulic circuit.

5 Fluid Power 5 or 1,000 ft-lb. The same work will be done at piston B. Since the force at piston B is 500 lb, the work will be 1,000 ft-lb divided by 500 lb (work divided by force equals distance), and the piston will move 2 feet. Another way to conceptualize this is to imagine the fluid at piston A being displaced to piston B. In other words, since the surface area of piston A is 10 square inches and piston A moves 20 feet (240 inches), the total amount of fluid displaced to piston B is 2,400 cubic inches. Since piston B has a surface area of 100 square inches, the piston moves 24 inches, or 2 feet. HYDRAULIC SYSTEMS AND EQUIPMENT Hydraulic systems perform work by transmitting energy from a power source through pressurized fluid to actuators (in the previous example, the actuator was piston B). In most cases, the pressurized fluid is a water-soluble oil or water-glycol mixture, with oil being the fluid used most frequently. In all hydraulic circuits, there are five basic elements, regardless of the work performed or the complexity of the system. These five elements are: a reservoir, a driver, a pump, valves, and an actuator. Hydraulic Pump The hydraulic pump is used to pressurize the liquid in the hydraulic system. The pump brings in air at its inlet by creating a partial vacuum, thereby creating the atmospheric pressure that forces the hydraulic liquid through the rest of the system. Pumps such as this, in which the liquid is displaced mechanically, are called positive displacement pumps. Most pumps used in hydraulic systems are of this type. These pumps are divided into two types: reciprocating and rotary. A reciprocating pump pressurizes the liquid by using a back and forth, straightline motion such as that produced by a piston, plunger, or diaphragm. A rotary pump uses a circular motion such as that produced by gears, vanes, or cams. (See Figure 9.) Remember that a hydraulic pump only pressurizes the liquid, thereby producing the flow. It does not pump pressure. A piston pump is shown in Figure 10. Reservoir The reservoir, similar to the drawing in Figure 8, is the holding tank for the hydraulic fluid. It can also help in separating air and contaminants from the fluid, as well as dissipating some of the heat that is produced within the system. Driver The driver may be an electric motor or an internal combustion engine which drives the pump. (a) RECIPROCATING PISTON PUMP (b) GEAR PUMP (c) VANE PUMP FIGURE 8 Hydraulic reservoir. FIGURE 9 Positive displacement pumps.

6 6 Fluid Power FIGURE 10 Piston pump. Courtesy Parker Hannifin Corporation. FIGURE 11 Hydraulic valves. Courtesy Parker Hannifin Corporation. Valves Valves are devices that control the pressure, direction, and flow of liquids in the hydraulic system. They accomplish this by opening, closing, or partially obstructing passageways throughout the system. A variety of hydraulic valves is shown in Figure 11. The discussion of valves in the following section is divided into three categories: pressure control valves, directional control valves, and flow control valves. Pressure Control Valves Pressure control valves are used to maintain a particular pressure within the system. The relief valve is the most common of this type. It remains closed until a predetermined pressure is reached, at which time it opens automatically, allowing the fluid to pass through the valve to return to the reservoir. Figures 12 and 13 show how this is accomplished. The type of valve illustrated is a spool valve, so named because of the movable portion inside the casting. In Figure 12, the valve is in the closed position. The spring, which forces the spool to the far left, has a particular pressure setting. When the inlet pressure of the hydraulic fluid exceeds the spring setting, as in Figure 13, the spool is forced against the spring, thereby allowing the fluid to pass through the outlet holes to the reservoir or tank. Both the inlet and outlet holes are called ports. These valves provide protection to other parts of the system from the damage that can be caused by pressure that is too high. A sequence valve operates on basically the same principle as that of the relief valve. The difference is that instead of the fluid being returned to the reservoir, it is routed to another part of the system to perform more work. This is necessary in systems that must provide work in the proper sequence. Pressure-reducing valves, unlike relief valves and sequence valves, are normally open. One of their functions in hydraulic systems is to allow a secondary circuit to operate at a lower pressure than the primary circuit. See Figure 14 for an example of a pressure control valve. FIGURE 12 Closed relief valve. IN OUT OUT FIGURE 13 Open relief valve. FIGURE 14 Pressure control valve. Courtesy Parker Hannifin Corporation.

7 Fluid Power 7 Directional Control Valves Directional control valves are used to control the direction that the fluid flows in the system. The simplest of directional control valves is the check valve. (See Figure 15.) This ball check valve allows the fluid to flow in only one direction. As long as the inlet pressure is greater than the pressure of the internal spring, the fluid flows through the valve and to the rest of the system. If the flow begins to reverse or if the pressure drops below the pressure of the spring, the spring pressure seats the ball and the flow stops. FIGURE 15 Check valve. Multiple-way valves provide for the opening or closing of different flow paths. They usually contain a spool. These valves are classified by both the number of ports they contain and the number of spool positions. For example, two different two-way (referring to two ports), two-position valves are illustrated in Figure 16. Valve A in position 1 is normally closed, or in its unactuated position. When the push button is pressed and the valve is actuated (position 2), the spool slides to the left and the fluid is allowed to flow through the valve from port P (pressure) to port T (tank). With valve B, the unactuated position is open (position 1). When the push button is pressed and the valve is actuated, it then becomes closed as in position 2. Figure 17 shows a three-way, two-position valve. In position A, the fluid flows from port P through the valve and out port A. Port T is blocked. In position B, port P is blocked and the fluid flows from port A to port T. Two types of directional control valves are shown in Figure 18. P P T T (1) NORMALLY CLOSED, OR UNACTUATED P VALVE A (2) ACTUATED P T T (1) NORMALLY OPEN, OR UNACTUATED VALVE B FIGURE 16 Two-way, two-position directional control valves. (2) ACTUATED A A T P T P POSITION A FIGURE 17 Three-way, two-position valve. POSITION B

8 8 Fluid Power FIGURE 18 Directional control valves. Courtesy Parker Hannifin Corporation. FIGURE 21 Flow control valves. Courtesy Parker Hannifin Corporation. Flow Control Valves Flow control valves control the rate of flow through the hydraulic system. One type of flow control valve, the throttle valve, is illustrated in Figure 19. Figure 20 shows a flow control valve with a fixed output. In this type of valve, the rate of flow is not affected by variations in the inlet pressure. Two types of flow control valves are shown in Figure 21. Actuators An actuator in a hydraulic system is the device that converts the fluid power to mechanical energy for the purpose of performing work. Actuators are either linear or rotary. Linear actuators are most often a cylinder or ram. The singleacting cylinder is the simplest of this type. (See Figure 22.) In a FIGURE 22 Single-acting cylinder. Courtesy International Standards Organization (ISO). single-acting cylinder, the fluid force is applied to only one surface of the piston, which is the head end of the cylinder. The piston is retracted by an external force, such as a spring or the force of gravity. In a double-acting cylinder, such as the one illustrated in Figure 23, the fluid force can be applied to either surface of the piston. This allows the movement of the piston to be controlled hydraulically in two directions. This double-acting cylinder with a single piston rod is a differential type because there is a difference in the piston surface area between the right and left. Since the area at the left is larger, the force applied to that surface is greater, and the work stroke is slower and more powerful than the opposite work stroke. The nondifferential type of double-acting cylinder shown in Figure 24 has a double-ended piston rod that extends FIGURE 19 Throttle valve. CONTROL ORIFICE INLET OUTLET FIXED ORIFICE FIGURE 20 Flow control valve. FIGURE 23 Double-acting cylinder. Courtesy International Standards Organization (ISO).

9 Fluid Power 9 FLUID POWER DIAGRAMS Types of Diagrams FIGURE 24 Double-acting, nondifferential cylinder. Courtesy International Standards Organization (ISO). through both ends of the cylinder. The surface areas of both sides of the piston are equal, so the forces in both directions are also equal. Several types of cylinders are shown in Figure 25. Rotary actuators can be of the gear, vane, or piston type (refer to Figure 9). Filters and strainers are also a necessary part of the hydraulic system to ensure long life of the components. They keep the hydraulic fluid clean by removing foreign particles. See Figure 26 for a wide variety of filters. Four types of diagrams are used when representing fluid power systems. They are: graphic, pictorial, cutaway, and combination diagrams. Each type emphasizes a different aspect of the system. A graphic diagram emphasizes the function of the circuit and of each component. The components consist of simple geometric shapes that are linked together with interconnecting lines. (See Figure 27.) This type of diagram is most frequently used for designing and troubleshooting fluid power circuits. A pictorial diagram, as in Figure 28, is used to show the piping between components. The drawings of the components themselves are pictorial and do not attempt to show the function or method of operation. FIGURE 25 Cylinders. Courtesy Parker Hannifin Corporation. FIGURE 27 Graphic diagram. FIGURE 26 Filters. Courtesy Parker Hannifin Corporation. FIGURE 28 Pictorial diagram.

10 10 Fluid Power The purpose of a cutaway diagram is to show the principal internal working parts and the function of each component. Sometimes several cutaway drawings are used to show the different flow paths that are possible depending upon the position of the various moving parts. (See Figure 29.) A combination diagram uses graphic, pictorial, and cutaway symbols with interconnecting lines. (See Figure 30.) This type of diagram provides a way to emphasize function, piping, or flow paths for each component as needed. FIGURE 29 Cutaway diagram. FIGURE 30 Combination diagram. Symbols ANSI The national standard related to this discussion is Fluid Power Diagrams, ANSI/(NFPA)T3.28.9R1. Symbols are arranged in the diagram to facilitate the use of direct and straight interconnecting lines. Where components have definite mechanical, functional, or otherwise important relationships to one another, their symbols are so placed in the diagram. Single lines are used in graphic diagrams. Double lines are used in cutaway diagrams. Pictorial and combination diagrams can use single or double lines or both. Graphic diagrams and symbols are best suited to international use and standardization because of their simplicity. The remainder of this section shows graphic symbols that were approved by the International Organization for Standardization (ISO). Figure 31 shows several graphic symbols commonly used. Control valves, except for nonreturn valves, are usually shown in single or multiple squares known as envelopes, with ports shown on the active envelope. (See Figure 32.) ISO Single envelopes indicate pressure or flow control valves in which there are an infinite number of positions possible. This allows the system to operate at a constant predetermined pressure or flow. Pressure control valve symbols are shown in Figure 33. The symbol for the pressure relief valve is the one that would be used for the valve shown in Figures 12 and 13. The sequence valve differs from the pressure relief valve only in that the fluid flows to other parts of the circuit to perform more work instead of returning to the reservoir. Flow control valve symbols are shown in Figure 34. The throttle valve symbol would be used for the valve in Figure 19, with the arrow indicating that the valve is adjustable. The symbol for a flow control valve with variable output would be used for the valve in Figure 20. Directional control valves are shown in multiple envelopes with each envelope indicating a distinct operating position. Several possible flow paths for these and other valves are shown in Figure 35. Figure 36 shows examples of valves with the ports open, and Figure 37 shows examples of valves with ports closed or blocked. Figure 38 shows the symbols used for various methods of actuating (or controlling) valves. Figure 39 shows how these graphic symbols correlate with unactuated and actuated directional control valves. In position 1, this unactuated two-way, two-position valve is normally closed. In the graphic symbol shown above it, the active ports are blocked. In position 2, the valve is actuated and flow through the valve occurs. Its graphic symbol shows the active ports on the envelope with the flow path. ANSI Note that when possible, the envelope nearest the control symbol (in this case, a push-button control) represents the condition that occurs when the valve is actuated.

11 Fluid Power 11 WORKING LINE PILOT LINE (FOR CONTROL) DRAIN LINE (a) FLOW LINES JOINING LINES CROSSING LINES FIXED CAPACITY HYDRAULIC PUMP WITH ONE DIRECTION OF FLOW FIXED CAPACITY HYDRAULIC PUMP WITH TWO DIRECTIONS OF FLOW ONE DIRECTION TWO DIRECTIONS (b) FLOW VARIABLE CAPACITY HYDRAULIC PUMP WITH ONE DIRECTION OF FLOW (f) PUMPS RESERVOIR OPEN TO ATMOSPHERE RESERVOIR WITH INLET PIPE AND DRAIN LINE ABOVE FLUID LEVEL RESERVOIR WITH INLET PIPE AND DRAIN LINE BELOW FLUID LEVEL RETURNED BY UNSPECIFIED FORCE SINGLE-ACTING CYLINDERS PRESSURIZED RESERVOIR (c) RESERVOIRS RETURNED BY SPRING M M ELECTRIC MOTOR HEAT ENGINE DOUBLE-ACTING DIFFERENTIAL CYLINDERS (d) ENERGY SOURCES CHECK VALVE (SEE FIGURE 15) SHUT-OFF VALVE DOUBLE-ACTING NONDIFFERENTIAL CYLINDERS FILTER OR STRAINER (g) CYLINDERS ACCUMULATOR (e) MISCELLANEOUS FIGURE 31 Graphic symbols. A three-way, two-position directional control valve is shown in Figure 40 along with its graphic symbol. Since the valve is controlled by an unspecified pressure in both directions, it is not possible to tell from the graphic symbol which position is actuated. In position 1, the flow from the pressure port P exits port A. In position 2, port P is blocked, and the flow from port A goes to the reservoir through port T. This valve could be used in a hydraulic circuit with a singleacting cylinder as shown in Figure 41. When the valve is in position 1, the pressurized flow from the pump flows through the valve, through the adjustable flow control valve, into the cylinder, forcing the piston up. When the valve is in position 2, the fluid pressure from port P is blocked and is diverted back to the reservoir through the pressure relief valve. Gravity from the piston forces the fluid in the cylinder back through the check valves and through port A to the reservoir. ANSI Note that the graphic symbol for reservoir can be used in one graphic diagram as often as necessary.

12 12 Fluid Power THROTTLE VALVE PORTS FLOW CONTROL VALVE WITH FIXED OUTPUT FIGURE 32 Envelopes. FLOW CONTROL VALVE WITH VARIABLE OUTPUT FIGURE 34 Flow control valve symbols. ONE THROTTLING ORIFICE NORMALLY CLOSED PRESSURE RELIEF VALVE FIGURE 35 Flow paths. SEQUENCE VALVE FIGURE 36 Valves with ports open. PRESSURE REGULATOR OR REDUCING VALVE FIGURE 33 Pressure control valve symbols. FIGURE 37 Valves with ports closed or blocked. A three-way, three-position valve is shown in Figure 42 with its corresponding graphic symbol. This is an example of a directional control valve with an intermediate position in which all ports are blocked. ISO The dashed lines between the envelopes indicate that the center position is not a distinct position; it represents a transitory intermediate condition. A four-way, three-position valve can be used with a doubleacting cylinder as shown in Figure 43. In the unactuated position, the only flow that occurs is the flow from the pump through the valve to the reservoir. When the valve is actuated right, the pressurized flow from the pump goes through the directional control valve and through the adjustable flow control valve to the lower chamber of the cylinder, pushing the piston

13 Fluid Power 13 FIGURE 38 Symbols for methods for actuating valves. P P T T POSITION 1 FIGURE 39 Two-way, two-position valve. POSITION 2 up. At the same time, the fluid in the upper chamber flows through the directional control valve to the reservoir. When the valve is actuated left, the pressurized flow is directed to the upper chamber, and the fluid in the lower chamber flows through the check valves and through the directional control valve to the reservoir. If at any time the pressure in the system exceeds a certain preset amount, such as when the piston is actuated all the way to the top, then the fluid from the pump flows through the pressure control valve (relief valve) to the reservoir.

14 14 Fluid Power P A T POSITION 1 P A T POSITION 2 FIGURE 40 Three-way, two-position valve. FIGURE 41 Hydraulic circuit.

15 Fluid Power 15 FIGURE 42 Three-way, three-position valve. FIGURE 43 Four-way, three-position valve. SYMBOL RULES ANSI These symbol rules apply to both hydraulics and pneumatics. 1. Symbols show connections, flow paths, and functions of components represented. They can indicate conditions occurring during transition from one flow path arrangement to another. Symbols do not indicate construction, nor do they indicate values, such as pressure, flow rate, and other component settings. 2. Symbols do not indicate location of ports, direction of shifting of spools, or positions of controls on actual components. 3. Symbols may be rotated or reversed without altering their meaning except in cases of (a) lines to reservoir, (b) accumulator. 4. Line width does not alter meaning of symbols. 5. Basic symbols may be shown in any suitable size. Size may be varied for emphasis or clarity. Relative sizes should be maintained. 6. Letter combinations used as parts of graphic symbols are not necessarily abbreviations. 7. In multiple envelope symbols, the flow condition shown nearest an actuator symbol takes place when that control is caused or permitted to actuate. 8. Each symbol is drawn to show normal, at-rest, or neutral condition of component, unless multiple diagrams are furnished showing various phases of circuit operation. 9. An arrow through a symbol at approximately 45 indicates that the component can be adjusted or varied. 10. External ports are located where flow lines connect to basic symbols, except where the component enclosure symbol is used. 11. External ports are located at intersections of flow lines and component enclosure symbols when enclosure is used.

16 16 Fluid Power CADD APPLICATIONS APPLICATIONS FOR FLUID POWER Fluid power graphic diagrams lend themselves well to CADD applications because of their simplicity and standardization. Several companies offer a Fluid Power Symbols Library that can be made compatible with most micro-, mini-, and mainframe CADD systems. A symbols M1740 INSERT POINT INSERT POINT library usually includes a full spectrum of graphic symbols, from basic flow and pressure control valves to complex hydrostatic transmissions. Figure 44 shows a sample page from one company s symbol library. INSERT POINT V420 INSERT POINT MAN-1 V680 INSERT POINT FIGURE 44 CADD system fluid power symbols. Courtesy Price Engineering Company Inc. PNEUMATICS In review, a fluid is defined as something that can flow and is able to move and change shape without separating when under pressure. Fluid power includes both liquids and gases. Pneumatics is the science that pertains to gaseous pressure and flow. Pneumatic devices include any tool or instrument that utilizes compressed air, such as riveters, paint sprayers, atomizers, and rock drills. Using compressed-air power is economical and safe. Pneumatic devices have no spark hazard and can be used under wet conditions without electric shock hazard. Other advantages are that pneumatic systems have relatively few moving parts, and devices can be easily exchanged with one another by pipe, tubing, or flexible hose. Pascal s principle applies to pneumatics as well as hydraulics. It states that if a pressure is exerted at one portion of fluid that is at rest in a closed container, then that pressure is transmitted equally in all directions without loss through the rest of the fluid and to the walls of the container. (See Figure 6.) Another basic physical law pertaining to pneumatics is Boyle s Law, which states that the absolute pressure of a fixed mass of gas varies inversely to the volume, provided the temperature remains constant. Note that this law is in terms of absolute pressure (psia or pounds per square inch absolute), not gauge pressure (psig or pounds per square inch gauge). At sea level, the weight of the earth s atmosphere is 14.7 psi. This is the pressure that is actually being exerted on the gauge, even though the gauge reading is zero. To find absolute pressure, 14.7 psi must be added to the gauge pressure. Figure 45 demon- 20 CU. FT. (a) 30 PSIA 10 CU. FT. (b) 60 PSIA 5 CU. FT. (c) 120 PSIA FIGURE 45 Boyle s Law with gauges reading absolute pressure.

17 Fluid Power PSIG 74.7 PSIG PSIG 20 CU. FT. (a) 44.7 PSIA 10 CU. FT. (b) 89.4 PSIA 5 CU. FT. (c) PSIA FIGURE 47 Tank-mounted air compressor. Courtesy Dayton Electric Manufacturing Company. FIGURE 46 Boyle s Law with difference between gauge pressure and absolute pressure. strates Boyle s Law with gauges reading absolute pressure. As the volume is decreased by one-half, the pressure doubles. Figure 46 shows the adjustments that need to be made when the gauge reading at sea level is zero. In position a, 14.7 psi is added to the gauge pressure of 30 psi to get an absolute pressure of 44.7 psia. This figure is then doubled in position b to get 89.4 psia, and 14.7 psi is subtracted to get 74.7 psig. The same procedure applies to position c. Charles s Law also applies to pneumatics. It states that the volume of a fixed mass of gas varies directly with absolute temperature, provided the pressure remains constant. This law has many implications for pneumatic equipment, as will be seen later. Another law is that air flow occurs only when there is a difference in pressure. The flow will be from high pressure to low pressure. PNEUMATIC SYSTEMS AND EQUIPMENT There are eight elements involved in a complete pneumatic circuit: a driver, an air compressor, an air receiver, a filter, a pressure regulator, an air lubricator, valves, and pneumatic devices. A driver can be an electric motor or some other power source that drives the air compressor. An air compressor is a machine that forces air into a smaller space than it normally occupies. Two things happen with the air at this point: (1) the air pressure increases (Boyle s Law), and (2) the air temperature increases due to the increased pressure (Charles s Law). The amount of pressurized air available for useful work from the compressor is expressed in cubic feet per minute (or standard cu. ft. per min. or SCFM). This measurement of air is known as free air delivered, or FAD. The air compressor is often mounted on the top of the air receiver, as shown in Figure 47. An air receiver is the storage tank for the compressed air. Because the temperature of the compressed air has increased, FIGURE 48 Air filter. the amount of water vapor has increased also. This water needs to be removed. A drain is usually provided in the air receiver to remove any precipitation that takes place. An air filter removes water vapor and dirt. (See Figure 48.) The air enters the filter and is quickly forced into a rotary motion. The centrifugal force spins out the moisture and dirt, which then collects at the bottom and is drained by an automatic or manual valve. A pressure regulator is necessary in pneumatic systems to consistently supply the correct pressure to the pneumatic tools. (See Figure 49.) The tools usually operate with compressed air at about 90 psig, but this varies between tools. An air lubricator (pneumatic lubricator) adds measured amounts of lubricant to the air supply for the purpose of lubricating the equipment receiving the air. In an oil-fog-type lubricator, the oil in the container enters the metering chamber. Because there is a difference in pressure at that point, the oil is then sprayed into the pipeline as fog. An air lubricator should always be downstream of a pressure regulator because some oils can react with the regulator diaphragm and contaminate the air. Valves are devices that control the direction of compressed air in the pneumatic system. They are actuated manually, electrically, or by air. Pneumatic valves operate on the same basic principle as hydraulic directional control valves. For example,

18 18 Fluid Power HOUSING CONTROL SPRING PISTON POPPET FIGURE 51 Axial piston. FIGURE 49 Pressure regulator. Courtesy Parker Hannifin Corporation. FIGURE 52 Radial piston. FIGURE 50 Pneumatic valves. Courtesy Parker Hannifin Corporation. a two-way, two-position valve is similar in function to the hydraulic valve shown in Figure 16. A variety of pneumatic valves is shown in Figure 50. Pneumatic devices are the elements that use compressed air to perform work. One type of element is the cylinder, which can be either single-acting or double-acting. (See Figures 22 and 23.) Another type is referred to as an air motor. Air motors are divided into two groups based on their type of driving method (either reciprocating piston or rotor). The two main types of air motors with reciprocating pistons are the axial piston (Figure 51) and the radial piston (Figure 52). Figure 53 shows a rotary vane air FIGURE 53 Rotary vane air motor. Courtesy Dayton Electric Manufacturing Company. motor. A tool such as a grinding wheel may use a rotor type of air motor, whereas a riveting hammer can use a reciprocating piston air motor. In a hydraulic circuit, the fluid is returned to the reservoir after going through the system. In a pneumatic circuit, the compressed air is returned to the atmosphere after being used.

19 Fluid Power 19 PNEUMATIC DIAGRAMS Graphic symbols for pneumatic systems are identical to those for hydraulic systems with the exception of those shown in Figure 54. Pictorial and cutaway diagrams for pneumatic systems are also the same as for hydraulic systems. Figure 55 shows a simple pneumatic circuit with a nondifferential double-acting cylinder. Sometimes a conditioning unit is used in place of a filter, pressure regulator and gauge, and lubricator. A detailed symbol and simplified symbol for this unit is shown in Figure 56. Note the style of line used around the detailed symbol. This is sometimes used to represent an enclosure around several components that are combined in one unit. FIGURE 54 Pneumatic graphic symbols. FIGURE 56 Conditioning unit. FIGURE 55 Simple pneumatic circuit. PROFESSIONAL PERSPECTIVE From a professional point of view, drafting is not simply a matter of tracing symbols on paper or of shifting symbols around on a CADD screen. Drafting also involves inquisitiveness and innovation. It sometimes takes a great deal of creative thought to put together a complicated pneumatic circuit or add two extra pumps to an existing hydraulic circuit. Although you may learn many things from experienced draftspeople and qualified salespeople, your ability to think for yourself and question situations that do not make sense to you will remain your greatest asset.

20 20 Fluid Power MATH APPLICATIONS VOLUME CALCULATIONS Problem: The company wants to transfer old hydraulic fluid that fills a cylindrical tank to a recycling firm using 55 gallon drums. You have been asked to order enough drums to do the job. How many should you order? The tank is 72 inches in diameter and 11 feet long. There are 7.48 gallons to the cubic foot. Solution: Fluid power problems often involve calculating volumes. The geometry section of the CD Chapter 3, Engineering Drawing and Design Math Applications, has formulas for the volumes of some common shapes. Also, Appendix B has useful conversion factors. For this application you need to first calculate the volume of a cylinder from the formula V = πr 2 h. It is best to have all dimensions in the same units, so you use R = 3 feet (because the diameter of the tank is 6 feet) and h = 11 feet. Then substituting into the formula: V = 3.14)(3 feet) 2 (11 feet) = 311 feet 3. Next, multiply by 7.48 to obtain the volume in gallons. That gives 2,325 gallons. Finally, since each drum holds 55 gallons, divide by 55, giving 42.3 drums. So you should order 43 drums to do the job. CD CHAPTER 1 Fluid Power Test DIRECTIONS Answer the questions with short complete statements or drawings as needed. QUESTIONS 1. Why does fluidics refer to both hydraulics and pneumatics? 2. What is the difference between hydraulics and pneumatics? 3. What is the common unit of measurement of work in the U.S. Customary System? In the International System? 4. Describe the meaning of ft-lb. 5. What is a Pa and what does it describe? 6. Describe the elements in a hydraulic circuit. 7. Define a positive displacement pump and describe the two categories of this kind of pump. Do they pump pressure? 8. A relief valve is the most common pressure control valve. Describe how it works. 9. What is the difference between a relief valve and a sequence valve? 10. Compare a relief valve to a check valve. 11. What is a port in a valve? 12. Describe the purpose of a directional control valve in a fluid power system. 13. What does two-way, two-position directional control valve mean? 14. Describe the difference between a differential double-acting cylinder and a nondifferential doubleacting cylinder. 15. What is the difference between a single-acting cylinder and a double-acting cylinder? 16. What is an actuator? 17. Which type of fluid power diagram would normally be used to show the function of each component? Which would be used for troubleshooting? Which type is internationally standardized? 18. What does it mean when a valve is actuated? 19. In a graphic diagram, what is the name given to the squares used in directional control valves? 20. In a graphic diagram, how would you know which envelope of a two-way, two-position directional control valve is unactuated? 21. If a graphic symbol for a directional control valve is drawn upside down, is the meaning of the circuit changed? 22. What symbol indicates when a component can be adjusted or varied?

21 Fluid Power Can a person build a hydraulic unit from a graphic diagram only? Why or why not? 24. Describe the elements in a pneumatic circuit. 25. With an air compressor, air is compressed from 30 cubic feet to 15 cubic feet, and the pressure increases from 40 psi to 80 psi. Is this an example of Pascal s principle, Boyle s Law, or Charles s Law? 26. In a container of compressed air, the gauge reading is 20 psi. Assuming that the temperature remains constant, what will the gauge read when the air is compressed into one-half the original space? What will the gauge read when the air is compressed into one-fourth the original space? Which law describes this phenomenon? 27. Should a pressure regulator be upstream or downstream of an air lubricator? Why? 28. What is FAD? 29. Is there any difference in the basic function between a hydraulic directional control valve and a pneumatic directional control valve? 30. If only one pneumatic diagram is shown, are the valves shown in actuated or unactuated phases? 31. What is a pneumatic device? What are the two types? 32. What special considerations are necessary for pneumatics that do not apply to hydraulics? 33. What special considerations are necessary for hydraulics that do not apply to pneumatics? CD CHAPTER 1 Fluid Power Problems PROBLEM 1 What is the pressure exerted on a 10 in. 24 in. panel when a force of 1,000 pounds is applied to it? PROBLEM 2 What is the pressure exerted on a brick wall that is 4 meters high and 28 meters long when a force of 50,000 newtons is applied to it? PROBLEM 3 A 2,350 newton force is applied to an object with a surface area of 72 square meters. What is the pressure? What is the pressure in psi? PROBLEM 4 A hydraulic piston pushes an object from one conveyor belt to another conveyor belt, which is 4' 6'' away. The amount of work done is 1,800 ft-lb. How much force is being used to push the object? How many kilojoules are needed? PROBLEM 5 The hydraulic piston in the previous problem accomplishes its task in five seconds. How much horsepower is the piston performing? How many watts of power is this? PROBLEM 6 One piston in a hydraulic circuit exerts a 28 psi pressure in the hydraulic fluid. A second piston in the circuit is 12 ft. away from the first piston and is directly affected by the first piston. It has an area of 15 sq. in., which is onehalf the area of the first piston. What is the pressure exerted on the second piston? With what force does the second piston move? With what force does the first piston move? If the first piston moves 10 in., how far does the second piston move? PROBLEM 7 The gauge reading of a container of compressed air at sea level is 80 psi. The volume of that air is double. What is the psia? What is the psig? Whenever possible, draw the diagrams for the following problems using CADD and Fluid Power Symbols Library. PROBLEM 8 Make a graphic diagram of a two-way, two-position directional control valve with a solenoid actuator. PROBLEM 9 Make a graphic diagram of a directional control valve that has four ports and an intermediate position. PROBLEM 10 Make a graphic diagram of a pneumatic circuit that will lift a load with a differential single-acting cylinder. Use a conditioning unit and a two-way, two-position directional control valve. PROBLEM 11 Make a graphic diagram of a hydraulic circuit. Use a nondifferential double-acting cylinder, a check valve, a relief valve, and a three-way, two-position valve. PROBLEM 12 Make a graphic diagram of the pictorial hydraulic circuit shown in the following figure. Label each component.

22 22 Fluid Power PROBLEM 13 Make a pictorial diagram of the graphic hydraulic circuit shown in the following figure. Label each component. PROBLEM 15 Make a graphic diagram of the pneumatic circuit shown. PROBLEM 14 Make a graphic diagram of a hydraulic circuit based on the following sequence of operations and functional description. Also make a component list specifying the key number, quantity, and name of component. PROBLEM 16 The hydraulic sketch in the following figure is received from the engineer. Make an appropriate graphic drawing, label the components, and make a component list. SEQUENCE OF OPERATIONS: 1. With valve (6) in the neutral position, delivery of flow from pump (4) unloads freely through valve (6) to reservoir (1). 2. With motor (3) running, valve (6) is manually actuated right, directing flow from pump (4) to extend clamp cylinder (7-A). 3. When pressure reaches setting of valve (8-A), flow is sequenced through (8-A) to extend nondifferential work cylinder (9) right. 4. When pressure reaches setting of valve (8-B), flow is sequenced through (8-B) to retract clamp cylinder (7-B). 5. Manually actuating valve (6) left, flow is directed from pump (4) to extend clamp cylinder (7-B). 6. When pressure reaches setting of valve (8-C), flow is sequenced through (8-C) to extend work cylinder (9) left. 7. When pressure reaches setting of valve (8-D), flow is sequenced through (8-D) to retract clamp cylinder (7-A). FUNCTIONAL DESCRIPTION: Valve (5) provides overload protection. Valve (6) controls direction of motion of (7-A), (7-B), and (9). Valve (8-A) causes work to be clamped by (7-A) before cylinder (9) performs work. Valve (8-B) causes nondifferential work cylinder (9) to be retracted before cylinder (7-B) is retracted. Valve (8-C) causes work to be clamped by (7-B) before cylinder (9) performs work. Valve (8-D) causes nondifferential work cylinder (9) to be retracted before cylinder (7-A) is retracted. NOTE: Item (2) is the strainer. Work cylinder (9) performs work in two directions and works in conjunction with cylinders (7-A) and (7-B). PROBLEM 17 Make a pneumatic graphic drawing using the engineer s sketch in the previous problem. Make the appropriate changes needed to depict a pneumatic circuit. Do not use a conditioning unit.

23 Fluid Power 23 MATH PROBLEMS PROBLEM 18 Find the volume, in cubic feet, of a cylindrical tank 100 inches in diameter and 18 feet in length. PROBLEM 19 Find the volume, in liters, of a hydraulic reservoir in the shape of a box measuring 20'' by 18'' by 42''. PROBLEM 20 Find the volume, in cubic centimeters, of a right circular cone having a radius of 2.54 cm and a height of 8.5 cm. PROBLEM 21 A storage tank at a paper mill is in the form of a sphere having a diameter of 15 feet. What is its volume in cubic feet? PROBLEM 22 The piston of a single-acting cylindrical linear actuator has a diameter of 3.5 cm. If the piston moves 8.5 cm, what volume of fluid, in cm 3, must have entered the actuator? PROBLEM 23 The piston of a single-acting cylindrical linear actuator has a diameter of 5 cm. If a fluid of volume cm 3 enters the actuator, how far does the piston move? PROBLEM 24 The piston of a reciprocating piston pump has a diameter of 7'' and in one stroke moves 12''. How much fluid, in cubic feet, is pumped if the pump makes 1,000 strokes? PROBLEM 25 What is the displacement, in liters, of a 225 in 3 gasoline engine? (See Appendix B, Table 4.) PROBLEM 26 The fluid in a rectangular reservoir 5' wide by 12' long is 36'' in depth. If it is transferred to a tank in the shape of a cylinder with a circular base 3' in diameter, what will be the depth of the fluid in the new tank? PROBLEM 27 Two tanks are sitting in a storage yard. One is in the shape of a cylinder with a circular base and the other is in the shape of a right circular cone. The tanks have the same height and top radius. Which tank has the greater capacity? By how much?