Control types

By Maria Hadlow06 May 2008

Directional spool valves, such as this PSL model from HAWE, designed for use with constant delivery

Directional spool valves, such as this PSL model from HAWE, designed for use with constant delivery pumps, are key to many hydraulic control systems.

There are three ways to move the spool, cartridge, or slider within a hydraulic control valve to affect the flow through it:

In full-pressure control, manually-operated levers connect directly to the spool and are subject to the full pressure of the system. Pilot-operated controls use hydraulic pressure, modified by a valve, usually lever operated, to shift the spool of the main control valve. In electro-hydraulic controls, an electrical solenoid moves the spool. The signal to the solenoid comes from relays, PLCs, or more commonly today, a microprocessor.

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