Miscellaneous Mechanical ComponentsDOE-HDBK-1018/2-93HYDRAULICSExample 1:In a hydraulic system, the oil pressure at the inlet to the cylinder is 1500 psi, andthe area of the piston over which the oil pressure acts is two square inches.Calculate the force exerted on the piston.Solution: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 lbfExample 2:A hydraulic valve requires a force of 1848 lbf to be opened. The piston area is 3 squareinches. How much pressure does the hydraulic fluid have to exert for the valve to move?Solution:Since F = P x A, then .P FAP 1848 lbf3 in.2P 616 lbf/in.2HydraulicOperationThe operation of a typical hydraulic system is illustrated in Figure 8. Oil from a tank orreservoir flows through a pipe into a pump. Often a filter is provided on the pump suction toremove impurities from the oil. The pump, usually a gear-type, positive displacement pump, canbe 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 thedesign of the system. Most hydraulic systems have some method of preventing overpressure. As seen in Figure 8, onemethod of pressure control involves returning hydraulic oil to the oil reservoir. The pressurecontrol box shown on Figure 8 is usually a relief valve that provides a means of returning oil tothe reservoir upon overpressurization.Rev. 0ME-05Page 11
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