Hydraulic components - Directional control valve

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Directional control valves are third on our list of main hydraulic valve classification. These valves allow fluid flow into more than one path when the fluid is also coming from multiple paths, or even one source. They have a spool inside that regulates which path is permitted to receive or give flow. The position of the spool is the determining factor on which paths will be active. They can be electronically controlled or manually controlled.

Directional control valves have three functions:

To isolate a certain branch of a circuit Bypass valves or return-line filters Deny flow in one direction Protect hydraulic components against surges in pressures

These functions typically operate in combinations.  Most directional control valves are of a spool-type design. A spool is used to control fluid flow and to connect internal passages and port. The spool has lands and undercuts, housed within precision-machined casing. As the spool shifts, the lands and undercuts open and close flow paths. Spool-type valves are widely used because they can be shifted to two, three, or more positions for routing fluid between different combinations of inlet and outlet ports. Ports refer to the number of lines into and out of the valve. They are sometimes referred to as “ways”. For example, 4-way, 3 position valves.

The actuator is a mechanism used to move the position of the spool in a directional control valve. The four basic methods of actuation include:

Manually-operated: The spool is shifted manually by moving a handle, pushing a button, or stepping on a foot pedal. Mechanically-operated: The spool is shifted by mechanical linkages such as a cam and rollers. Solenoid-operated: When an electric coil or solenoid is energized, it creates a magnetic force that pulls the armature into the coil. This causes the armature to push the spool of the valve. It should be noted that solenoids alone are not strong enough to move a directional control valve spool when fluid flow is greater than 25 gpm and cannot generate large forces unless supplied with large amounts of electrical power. However, they are used extensively. Pilot-operated: Pilot pressure is initiated when the fluid pressure in a fluid power system shifts the spool into its desired position. By applying a pilot signal (for either hydraulic or pneumatic systems) against a piston at either end of the valve spool, pilot pressure is introduced which pushes the piston to shift the spool.

Manual operated Mechanical operated Solenoid operated Pilot operated