Basic Hydraulic Operation
The operation of a typical hydraulic system is illustrated in Figure Basic Hydraulic Operation below. 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 Basic Hydraulic Operation below, one method of pressure control involves returning hydraulic oil to the oil reservoir. The pressure control box shown on Figure below is usually a relief valve that provides a means of returning oil to the reservoir upon overpressurization.
The high pressure oil flows through a control valve (directional control). The control valve changes the direction of oil flow, depending upon the desired direction of the load. In Figure 8 the load can be moved to the left or to the right by changing the side of the piston to which the oil pressure is applied. The oil that enters the cylinder applies pressure over the area of the piston, developing a force on the piston rod. The force on the piston rod enables the movement of a load or device. The oil from the other side of the piston returns to a reservoir or tank.
