Hydraulic actuator for control of valves

Claim 1

A hydraulic actuator assembly for controlling a valve, comprising, a housing defining a cylindrical bore forming a piston chamber and an end cap section forming an end chamber, transversely extending wall means having a central opening and being between said piston and end chambers, said housing forming a sleeve portion spaced from said wall means and having a central opening of lesser diameter than said wall means, piston means having a head portion slidably disposed in said piston chamber and a body portion of lesser diameter extending through said sleeve portion central opening, an actuator spindle connected to said piston means body portion, a cylindrically shaped piston extension of smaller diameter than said piston attached to said piston and extending into said end chamber, said piston extension being in sliding and sealing engagement with said wall means central opening, said housing having inlet and outlet passage means for said piston chamber to operate said piston, said housing having inlet air passage means for providing a piston return pressure gas in said end chamber, said piston head having a cylindrically shaped protruding portion which forms annular chamber means in surrounding relation to said piston extension when said protruding portion is in abutting engagement with said wall means, said housing having emergency passage means in fluid communication with said annular chamber when said protruding portion abuts said wall means to effect an emergency moving of said piston in a valve closing direction when a pressure medium is admitted into said emergency passage means.