Miscellaneous Mechanical Components
In a hydraulic system, the oil pressure at the inlet to the cylinder is 1500 psi, and
the area of the piston over which the oil pressure acts is two square inches.
Calculate the force exerted on the piston.
Since F = P x A, the force of the oil on the piston is calculated as follows.
F = 1500 lbf/in.2 x 2 in.2
= 3000 lbf
A hydraulic valve requires a force of 1848 lbf to be opened. The piston area is 3 square
inches. How much pressure does the hydraulic fluid have to exert for the valve to move?
Since F = P x A, then
P 616 lbf/in.2
The operation of a typical hydraulic system is illustrated in Figure 8. Oil from a tank or
reservoir flows through a pipe into a pump. Often a filter is provided on the pump suction to
remove impurities from the oil. The pump, usually a gear-type, positive displacement pump, can
be driven by an electric motor, air motor, gas or steam turbine, or an internal combustion engine.
The pump increases the pressure of the oil. The actual pressure developed depends upon the
design of the system.
Most hydraulic systems have some method of preventing overpressure. As seen in Figure 8, one
method of pressure control involves returning hydraulic oil to the oil reservoir. The pressure
control box shown on Figure 8 is usually a relief valve that provides a means of returning oil to
the reservoir upon overpressurization.