Fluid pressure actuator valve

Abstract

A gas pressure actuator for effecting the reciprocation of the stem of a valve subject to high-pressure loading comprises a tubular housing secured to the valve bonnet and defining a main cylinder chamber connected in axially series relationship with an auxiliary piston chamber which, in turn, communicates with a secondary fluid pressure chamber containing a compressible spring. A rod-like actuator is slidably and sealably mounted within the actuator housing and carries a main piston which cooperates with the main cylinder chamber in sliding and sealable relationship. The auxiliary piston chamber slidably and sealably mounts an auxiliary piston which is movable independently of the main piston. The actuating movement of the main piston produced by the introduction of gas pressure into the main cylinder produces an axial movement of the actuating rod and a compression of the spring. The spring-containing secondary chamber defined by the actuator housing is filled with a virtually non-compressible fluid. The auxiliary piston can shift in response to temperature-induced expansions of the protective fluid, thus providing automatic volume compensation for such temperature variation. Additionally, the secondary chamber containing the protective fluid may be connected to an auxiliary source of pressure, such as a manual or foot-actuated pump, and sufficient pressure generated in the secondary chamber to actuate the main piston by the auxiliary piston in the event of failure of the primary source of pressured gas. Fluid dampening of the actuator is also provided.