Q1. a) What does pressure refer to in relation to hydrostatics?
b) What is it dependent on?
Q2. Figure below contains a depiction of an embossing press in which a single-acting cylinder is used for ejecting the processed parts. With the help of circuit diagrams, describe how this cylinder can be activated using 2/2 and 3/2 valves. Compare the two diagrams with regard to extension and retraction of the piston rod and draw your conclusions. Also, calculate the advancing pressure (p) for a piston rod whose diameter d = 60 mm and with a load weight F = 5 kN. Ignore the resistances for this calculation.
Q3. 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 800 kPa, 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?
Q4. a) What is the function of a directional control valve?
b) What are the three main types of pressure control valves?
Q5. 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. Calculate the flow rate that the pump would deliver.
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 m2/s. Is the flow in the pipe laminar or turbulent?
Q6. a) What happens during transitional flow?
b) What are the parameters required to determine Reynold's number?
Q7. a) A double rod hydraulic cylinder with 50 mm diameter piston and a 100 mm diameter cylinder are shown in the figure, and 7000 kPapressure is applied. A concrete wall stops the rod which prevents the piston from moving. Determine the force exerted on the wall by the piston.
b) 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.
Q8. a) Explain Bernoulli's Principle with regard to an aerofoil.
b) 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.
Q9. 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?
Q10. What causes side loading in cylinders? How can it be minimized?
Q11. a) What is the basis for piston rod design? Explain the significance of area ratio.
b) List 4 of the likely causes for slow or erratic motion of an actuator in a hydraulic equipment.
Q12. a) Give a graphic representation of the 6 different types of pressure control valves.
b) 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.
Q13. 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 3200 kPa is acting on diameter of 10 mm seating area?
Q14. Name 6 of the factors on which the designation of a directional control valve is normally based on.
Q15. a) Identify the actuation methods from the illustrated graphic.
b) What are the key considerations in choosing the valve actuation method?
Q16. a) What is valve overlap?
b) Why is some amount of valve overlap desirable?
c) Define the term zero overlap.
Q17. a) Explain briefly the different valve configurations shown.
b) Name three typical applications in which Tandem centre spool configuration is used.
c) What is the chief disadvantage associated with this configuration?
Q18. Explain in brief the working of pressure control valves.
Q19. a) List three of the primary causes for pressure surge in hydraulic systems.
b) What is pressure override?
c) Describe its effects on hydraulic components.
Q20. a) What is the main drawback with regard to the use of AC coils in proportional valves?
b) Distinguish between force-controlled and stroke-controlled proportional solenoids.
Q21. a) What are proportional valves and where are they used?
b) Name the different types of proportional valves.
c) For which type of applications are Pilot-operated proportional pressure relief valves normally used?
d) Describe in brief, the principle of working of a proportional flow control valve.
Q22. Explain the advantages associated with servo control using an example.
Q23. Describe the sequence of operations for the mechanical hydraulic servo system shown.
Q24. a) Name the common types of elements (4 fixed and 4 sensitive) used with pressure transducers.
b) List some of the applications in which linear displacement transducers are used.
c) What generates noise in amplifiers?
Q25. Consider the hydraulic lift system in the figure below, with 10 mm rod and 50 mm cylinder, used to lift a 500 kg load.
a) A handpump is being used with a stroke of 7 cm3 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?