With the development of hydraulic drives and hydraulic servo systems, there are a number of hydraulic systems that require continuous control of pressure, flow and direction, but do not require a high degree of control accuracy. As ordinary hydraulic components cannot meet the servo requirements, and the use of electro-hydraulic servo valves are too wasteful due to the low control accuracy required, so in recent years there has been a proportional control valve between ordinary hydraulic components (switching control) and servo valves (continuous control).

The electro-hydraulic proportional control valve (proportional valve for short) is essentially an inexpensive electro-hydraulic control valve with good resistance to pollution. Proportional valve development through two ways, one is to replace the traditional hydraulic valve with a proportional solenoid manual adjustment input mechanism, in the traditional hydraulic valve based on: the development of a variety of proportional direction, pressure and flow valve; two is some of the original electro-hydraulic servo valve manufacturers in the electro-hydraulic servo valve, based on the reduction of design and manufacturing accuracy developed.