Q1.
a) 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.
b) Compare the two diagrams with regard to extension and retraction of the piston rod and draw your conclusions.
c) 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.
Q2.
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. (2 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. (4 marks)
Q3.
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?
How much power is required to lift the load at this speed?
Q4.
a) Give a graphic representation of the 6 different types of pressure control valves. (4 marks)
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. (8 marks)
Q5.
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.
What will the spring force be if a pressure of 3200 kPa is acting on diameter of 10 mm seating area?
Q6.
a) What is valve overlap? (2 marks)
b) Why is some amount of valve overlap desirable? (1 mark)
c.Define the term zero overlap. (2 marks)
Q7.
a) Explain briefly the different valve configurations shown. (3 marks)
1) 2) 3)
b) Name three typical applications in which Tandem centre spool configuration is used. (1.5 marks)
What is the chief disadvantage associated with this configuration? (1.5 marks)
Q8.
Explain in brief the working of pressure control valves.
Q9.
Explain the advantages associated with servo control using an example.
Q10.
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?
What is the work and power required from the electric motor?
