Hydropneumatic valve actuator

Claim 1

A valve actuator comprising an outer cylindrical casing having a closure member at each end thereof, one of said closure members having an axial bore therethrough, an inner cylindrical casing positioned in said outer casing coaxial therewith and transversely spaced therefrom to define an elongated annular chamber with said outer casing, a piston slidably mounted in said inner casing, said piston having a piston rod extending axially therefrom through said axial bore in said one closure member, means providing communication between said annular chamber and the portion of said inner casing between the other closure member and said piston means for charging said annular chamber and the portion of said inner casing between the other closure member and said piston with gas under pressure, means to supply the portion of said inner casing between said one closure member and the piston with liquid under a pressure higher than said gas under pressure, said piston having a pair of spaced annular sealing members in its outer periphery defining seals with respect to the inner wall surface of said inner casing at least one of said pair of sealing members preventing gas leakage into the portion to be charged with liquid and means to detect liquid leakage past at least one of said pair of said sealing members, said leakage detecting means including passageway means for communicating the outer periphery of the piston between said pair of sealing members with the ambient, said passageway means including normally closed relief valve means for venting liquid in said passageway means by opening at a pressure lower than liquid pressure in said inner casing between said one closure member and the piston, said relief valve remaining closed at pressures between said gas pressure and said liquid pressure such as to prevent venting to ambient of gas leakage past another of said sealing members into said passageway means.