Three-position, self-centering valve for control of fluid actuators and the like

Claim 1

A fluid valve assembly comprising a valve body, a first bore in said valve body, a second bore in said valve body coaxially communicating with and of smaller diameter than said first bore, a control member selectively slidable in said first and second bores between two positions, one end of said control member being slidably sealed to said first bore by outwardly extending first seal means including a piston plate, the other end of said control means being only slightly smaller in diameter than said second bore and being slidably sealed to said second bore by second seal means at least partially contained within a radially inwardly extending groove in said control member, fluid inlet means in said body communicating with said first bore, fluid outlet means in said second bore selectively to deliver fluid from said second bore to an external device for operation of the same, vent means in said second bore, and actuator means to drive the control member from the first to second position, the fluid admitted to said first bore normally exerting pressure against the piston plate to urge the control member to the first position in which the fluid outlet means and vent means are in fluid communication with one another but are isolated from the fluid inlet means by said second seal means, the fluid pressure on said piston plate being overcome when the control member is slid by the actuator means to the second position in which the fluid inlet means and outlet means are in communication with one another via the first bore and limited clearance between the control member and second bore, but are isolated from said vent means by said second seal means, the fluid pressure in the first bore because of the limited clearance being sufficient to return the control member to the first position when the actuator means is released.