Module 6 Assignment Part A TOTAL MARKS Part A = 192 TOTAL QUESTIONS Part A = 36 Question 1 [3 Marks] What does pressure refer to in relation to hydrostatics and what is it dependent on? Question 2 [14 Marks] Make a circuit diagram of a regular hydraulic plant that is used to control a double acting cylinder. Name/annotate all the components in the circuit. Question 3 [5 Marks ] a) If 1kg of mass is taken to the moon, would it still have a mass of 1 kg on the moon? b) If the absolute pressure in a hydraulic system is 8 bar, what is the gauge pressure? c) What is meant by the viscosity of a hydraulic fluid? d) For which two important hydrostatic principles is Pascal s law used? e) Why is pressure lost when there is flow along a pipe? Where does the pressure go? Question 4 [3 Marks] a) What is the function of a directional control valve? b) What are the three main types of pressure control valves? Question 5 [8 Marks] a) A 4 kw motor is driving an oil pump with an efficiency of 95% down a 10 mm diameter pipe. If the velocity of the fluid down the pipe is 1.8 m/s, what is the flow rate that the pump delivers? b) What is the pressure that the pump can deliver? c) If a 25 mm bore hydraulic cylinder is connected to the pipe, what would the forward stroke speed of the cylinder be? d) The viscosity of the oil is v = 0.00001 m 2 /s. Is the flow in the pipe laminar or turbulent? Question 6 [4 Marks] What happens during transitional flow? What are the paremeters required to determine Reynold s number?
Question 7 [3 Marks] A double rod hydraulic cylinder with 50 mm diameter piston and a 100 mm diameter cylinder are shown in the figure, and 70 bar pressure is applied. A concrete wall stops the rod so there is no movement of the piston. Determine the force exerted on the wall by the piston. Sketch on following page / 50 mm 100 mm 70 bar Question 8 [8 Marks] A hydraulic press has a ram of 25 cm diameter and a plunger of 4.0 cm diameter. Find the weight lifted by the hydraulic press when the force applied at the plunger is 400 N. Question 9 [4 Marks] Explain Bernoulli s Principle with regard to the phenomenon of draft. Question 10 [8 Marks] The diameters of a pipe are 15 cm and 20 cm at sections 1 and 2 respectively. The velocity of water flowing through the pipe is 4 m/sec at section 1. Determine the discharge through the pipe and also the velocity of flow at section 2. Question 11 [5 Marks] 40 litres /min 90 mm 30 mm 200 kg
A pump delivers 40 litres/min to a 90 mm bore/30 mm rod cylinder to lift a load of 200 kg. a) What is the pressure exerted on the piston? b) What is the speed at which the load will be lifted? c) How much power is required to lift the load at this speed? Question 12 [3 Marks] What causes side loading in cylinders? How can it be minimized? Question 13[3 Marks] What is the basis for piston rod design? Explain the significance of area ratio. Question 14 [4 Marks] What are the likely causes for Slow or erratic motion of an actuator in a hydraulic equipment? Question 15 [8 Marks] Give a graphic representation of the 6 different types of pressure control valves. Question 16 [5 Marks] In a direct acting pressure relief valve, 64 bar pressure is acting on the conical dart seating area and the dart is kept closed by a spring force of 50 kg opposing the pressure. a) Determine the bore diameter on the seat. b) What will the spring force be if a pressure of 32 bar is acting on diameter of 10 mm seating area? Question 17 [3 Marks] What are the factors on which the designation of a directional control valve is normally based on?
Question 18 [10 Marks] The circuits below are an illustration of the working of a pressure reducing valve and a high-low system employing an unloading valve. Explain the operation of the valves. Question 19 [6 Marks] Identify the actuation methods from the illustrated graphic. Question 20 [4 Marks] What are the key considerations in choosing the valve actuation method?
Question 21 [3 Marks] What is valve overlap? Why is some amount of valve overlap desirable? Question 22 [3 Marks] Define the term zero overlap Question 23 [6 Marks] Explain briefly the different valve configurations shown. a) b) c) Question 24 [5 Marks] Name a few typical applications in which Tandem centre spool configuration is used? What is the chief disadvantage associated with this configuration? Question 25[5 Marks] Explain in brief the working of pressure control valves. Question 26 [3 Marks] List out some of the primary causes for presure surge in hydraulic systems. Question 27[3 Marks] What is pressure override? Describe its effects on hydraulic components. Question 28 [4 Marks] What is the main drawback with regard to the use of AC coils in proportional valves? Question 29 [6 Marks] Distinguish between force-controlled and stroke-controlled proportional solenoids. Question 30 [5 Marks] What are proportional valves and where are they used? Name the different types of proportional valves. Question 31 [4 Marks] Pilot-operated proportional pressure relief valves are normally used for which type of application? Describe in brief, the principle of working of a proportional flow control valve. Question 32 [6 Marks] Explain the advantages associated with servo control using an example.
Question 33 [8 Marks] Describe the sequence of operations of the mechanical hydraulic servo system shown. Steering wheel Pivot point Sliding sleeve Axle Wheel Servo valve Spool Cylinder Linkage Piston rod Question 34 [5 Marks] Name some of the common types of fixed and sensitive elements used with pressure transducers. Question 35 [5 Marks] List some of the applications in which linear displacement transducers are used. Explain the reason for generation of noise in amplifiers. Question 36 [10 Marks] Consider the hydraulic lift system in the figure below, with 10 mm rod and 50 mm cylinder, used to lift a 500 kg load. 500 kg 10 mm 50 mm a) A handpump is being used with a stroke of 7 cm 3 per pump actuation. How many pump cycles would be required to lift the load 100 mm high? b) Assume you operate the hand pump at a speed of 0.3 Hz. How long would it take to lift the load 100 mm high? c) What is the work and power required from the pump operator?
d) Assume now an electric motor is being used that pump at a rate of 3 litres / min. How long would it take to lift the load 100 mm? e) What is the work and power required from the electric motor? Question 37 [5 Marks] Design a simple circuit to open and close a double acting hydraulic cylinder Question 38 [10 Marks] Show how you would control two double acting hydraulic cylinders to move in opposite directions - i.e. when cylinder A extends, B retracts and vice versa. Both cylinders should move as close to the same speed as possible Question 39 [15 Marks] When answering this question, please don t focus on showing the ladle, just show that the ram has to overcome a negative force of 4,800 newton. On your assignment, show in a table format, the properties of the various A ladle as shown in the figure below is used to pass liquid aluminum from a holding furnace into a channel leading to a die-casting machine. This movement of the ladle is enabled by a double-acting cylinder activated by a 4/2-way valve. It must be mentioned that the ladle should not be allowed to dip into the furnace when the valve is in an unactuated condition. a) Design a circuit diagram to illustrate the working of the ladle. Allow for the fact that the ladle represents a large load. b) Choose the cylinder diameter, given the following data: Maximum system pressure p = 38 bar Required lifting force F = 4800 N. The system resistances may be ignored
Question 40 [30 Marks] On a production line the metal stamping location uses two interlinked rams, Ram One (R1) extends to close the safety door then Ram Two (R2) extends to press the metal. Ram Two (R2) then retracts followed by Ram One (R1) to open the safety door. Design a circuit to do this including a safety feature to make sure both the operators hands are outside the cage. Only one ram can move at a time.