What Is a Spool Valve?

by Kevin Caron

A spool valve is part of a hydraulic system that directs the flow of hydraulic fluid. The valve is made up of spools that rotate or slide to block and open channels in a hydraulic system.


Spool valves direct the flow of fluid to and from other valves within a hydraulic system. A typical four-way spool valve has openings leading to and from another valve, as well as from the fluid pump and to the fluid reservoir.

Rotary Spool Valves

A rotary spool valve consists of a fixed tubular sleeve, within which is a rotating, x-shaped piece called the "core." This valve functions much like a revolving door, with each bend of the core functioning as a portal for hydraulic fluid to leave and enter the valve.

Sliding Spool Valves

Sliding spool valves are slightly more complex than rotary spool valves. In sliding spool valves, the spool is grooved and slides in and out of position within the sleeve, alternately blocking and opening the fluid intake and outtake portals.

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