Directional control valve

Directional control valves are one of the most fundamental parts in hydraulic machinery as well as pneumatic machinery. They allow fluid flow into different paths from one or more sources. They usually consist of a spool inside a cylinder which is mechanically or electrically controlled. The movement of the spool restricts or permits the flow, thus it controls the fluid flow.

The spool (sliding type) consists of lands and grooves.The lands block oil flow through the valve body. The grooves allow oil or gas to flow around the spool and through the valve body. There are two fundamental positions of directional control valve namely normal position where valve returns on removal of actuating force and other is working position which is position of a valve when actuating force is applied. There is another class of valves with 3 or more position that can be spring centered with 2 working position and a normal position.

Directional control valves can be classified according to-

Example: A 5/2 directional control valve would have five ports and two spool positions.

Ports are the one which helps the liquid to flow through them. Mainly there are 4 ports P-pump, t-tank or oil sump, A&B- flow of liquid to inlet and outlet of tank

Including the normal and working positions which a valve spool can take there are types like two position, three position and proportional valve ...

Manual, spring, electrical, pneumatic, and hydraulic.

Manually operated valves work with simple levers or paddles where the operator applies force to operate the valve. Spring force is sometimes used to recover the position of valve. Some manual valves utilize either a lever or an external pneumatic or hydraulic signal to return the spool.

Mechanically operated valves apply forces by using cams, wheels, rollers, etc., hence these valves are subjected to wear.

A hydraulically operated DCV works at much higher pressures than its pneumatic equivalent. They must therefore be far more robust in nature so are precision machined from higher quality and strength materials.

They are widely used in the hydraulics industry. These valves make use of electromechanical solenoids for sliding of the spool. Because simple application of electrical power provides control, these valves are used extensively. However, electrical solenoids cannot generate large forces unless supplied with large amounts of electrical power. Heat generation poses a threat to extended use of these valves when energized over time. Many have a limited duty cycle. This makes their direct acting use commonly limited to low actuating forces.

Often a low power solenoid valve is used to operate a small hydraulic valve (called the pilot) that starts a flow of fluid that drives a larger hydraulic valve that requires more force.

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Wikipedia