Hydraulic valve is an automation component operated by pressure oil, which controls and regulates the flow direction, pressure, and flow rate of fluid to meet the requirements of starting, stopping, moving direction, force, torque, speed or rotation speed, action sequence, and overcoming load of the executing component, so that the system works in coordination according to the requirements. Hydraulic valves are controlled by the pressure oil of the distribution valve and are usually used in combination with electromagnetic distribution valves. They can be used for remote control of the on/off of oil, gas, and water pipeline systems in hydropower stations. The component used in hydraulic transmission to control fluid pressure, flow rate, and direction. The one that controls pressure is called a pressure control valve, the one that controls flow is called a flow control valve, and the one that controls on/off and flow direction is called a directional control valve.

The installation of hydraulic valves should comply with the manufacturer's specifications. Self designed valves should be tested according to relevant standards, such as performance tests and pressure tests, before installation. Attention should be paid to the orientation of the inlet and outlet ports, as valves with symmetrical inlet and outlet ports are prone to reverse installation and may cause accidents. Some valve components often have double holes with the same function for easy installation, and the unused one needs to be blocked after installation. When installing pressure valves with similar appearances, special attention should be paid to distinguishing them to avoid incorrect installation.

To avoid air infiltration, the connection should be well sealed. When installing plate valves, it is necessary to check the quantity, specifications, compression capacity, etc. of each oil port seal. The installation screws (usually 4 or 6) should be symmetrically and uniformly tightened step by step. Tightening them one by one can cause deformation of the valve body and inconsistent compression of the sealing ring, leading to oil leakage and even damage to the sealing components. Valves installed with flanges should not be screwed too tightly, as sometimes over tightening can result in poor sealing. When tightening is necessary, if the original seal or material cannot meet the sealing requirements, the seal form and material should be replaced. Electromagnetic directional valves are generally suitable for horizontal installation, and when installed vertically, the electromagnet is generally facing upwards (for two position valves). This factor should be considered when designing the installation plate. This principle is also applicable to other types of directional valves.

The component used in hydraulic transmission to control fluid pressure, flow rate, and direction. The one that controls pressure is called a pressure control valve, the one that controls flow is called a flow control valve, and the one that controls on/off and flow direction is called a directional control valve. Pressure control valves are divided into relief valves, pressure reducing valves, and sequence valves according to their purposes. The flow control valve regulates the flow rate by adjusting the throttle area between the valve core and valve body and the local resistance it generates, thereby controlling the movement speed of the actuator. Directional control valves are divided into one-way valves and directional valves according to their purposes.

In the late 1960s, an electro-hydraulic proportional control valve was developed based on the aforementioned hydraulic control valves. Its output (pressure, flow rate) can continuously vary with the input electrical signal. According to their different functions, electro-hydraulic proportional control valves are divided into electro-hydraulic proportional pressure control valves, electro-hydraulic proportional flow control valves, and electro-hydraulic proportional directional control valves.