Abstract: A seal assembly containing a plurality of nonelastomeric sealing elements for use in a valve actuator is disclosed. The valve actuator can be incorporated into a fluid transmission conduit at the surface of a producing oil or gas well. A spring member radially biases one sealing element into engagement with concentric tubular members. Additional sealing elements are radially expandable when subjected to axial compression to close any gap along the surfaces of the concentric tubular members to provide extrusion resistance, greater sealing performance, and fire resistant capability. The seals can be used under hostile conditions, such as extreme temperature and in the presence of corrosive fluids and corrosion inhibitors.

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.