Problems For Practice

On Control Circuits

A double-acting cylinder is hooked up in the regenerative circuit of Fig.8.3. The relief valve setting is 100 bars. The piston area is 180 cm2 and the rod area is 60 cm2. If the pump flow is 0.0015 m3/s, find the cylinder speed and load-carrying capacity for the (i) extending stroke, and (ii) retracting stroke.

[Ans. (i) 0.246 m/s; 68.25 kN; (ii) 0.246 m/s; 68.25 kN]

On Accumulators

1. An accumulator has a ram of 150 mm diameter and a lift of 5 m. If the oil is supplied at 50 bar, find the necessary load on the ram, and capacity of the accumulator.

[Ans. 88.36 kN ; 441.79 kN-m]

2. What is the size of accumulator necessary to supply 2000 cm3 of oil with an allowable pressure drop from 22 MPa to 16 MPa. The precharge pressure is 13 Mpa. Take charging and discharging processes as isothermal. 

[Ans.  9025.64 cm3 or 9.02 L]

3. The car crushing system is to be designed. The crushing force requirement is such that a 0.20 m diameter hydraulic cylinder is required at a working pressure of 1.3 × 107 N/m2. Time for crushing is about 10 seconds and the stroke required to flatten the car is 2.5 m. Compare the power requirement of a circuit without accumulator and with accumulator. Accumulator details:

Time taken for charging of accumulator = 5 min; 

Initial pressure of charging (uncharged), P1 = 0.8 × 107 N/m2;

Charge pressure of accumulator, P2 = 2.4 × 107 N/m2;

Minimum pressure for crushing, P3 = 1.3 × 107 N/m2.

[Ans. (kW pump) with accumulator = 12.56 kW, and

(kW pump) without accumulator = 102.1 kW]

On Intensifiers

4. If an intensifier has an input pressure of 105 bar and the area of the input piston is 65 cm2, what would be the output pressure if the output ram has an area of 10 cm2 ? 

[Ans. 682.5 bar]

5. A hydraulic intensifier gets the low pressure liquid at a pressure of 40 bar and delivers it to a machine at a pressure of 160 bar. If the intensifier has a capacity of 0.021 m3 and stroke 1.2 m, determine the diameters of the fixed ram and the sliding cylinder to be used for this intensifier.

 [Ans. 149 mm, 298 mm]