The proportional control valve is mainly used for open loop control; the output of the proportional control valve is proportional to the input signal, and the magnetic force generated by the electromagnetic coil in the proportional control valve is proportional to the current. In the traditional type of hydraulic control valve, only the hydraulic pressure setting control, for example: the pressure valve at a set pressure, the flow valve to maintain the set flow, the directional valve for the flow direction through Switch off / off. Therefore, these control valve system functions are subject to some limitations, as the technology advances, many hydraulic systems require flow and pressure can be continuous or proportional to the control valve input signal changes.Although the hydraulic servo system to meet their requirements , But also high precision, but for most industries, they do not require the system has such a high quality, and hope that under certain conditions of control performance, while low price, reliable, easy to maintain, so the ratio Control valve is developed in this context. Proportional control valve can be divided into pressure control valve, flow control and direction control valve three categories. Pressure control valve: Proportional solenoid valve to replace the pilot-operated relief valve device will become a pilot-scale proportional relief valve, the hydraulic pressure output by the input signal continuously or in proportion to control. Flow control valve: Proportional solenoid valve instead of throttle or governor valve hand device and the input signal to control the throttling valve or throttle opening, continuous or proportional control of its output flow. Therefore, the opening of the throttle can be determined by the input signal voltage. Directional Control Valve: Proportional Solenoid Instead of a directional valve, a general solenoid valve forms a direct acting proportional directional control valve. The slide shaft not only transposes it, but also translates the stroke continuously or proportionally, thus connecting the ports The oil area can also vary continuously or proportionally so the proportional directional control valve not only controls the direction of movement of the actuator but also controls its speed. The above various proportional valve hydraulic components actuated hydraulic cylinder or hydraulic motor.