Thomas B Golden
Nursing in Dallas, TX

4934652, Jun 19, 1990

Dec 11, 1989

7/449707

Thomas A. Golden - Dallas TX

Otis Engineering Corporation - Carrollton TX

F16K 31122

251 636

An actuator for opening and closing the gate of a surface safety valve includes a primary piston and an auxiliary piston. The primary drive piston is directly connected to the valve stem, while the auxiliary piston is slideably connected thereto. Extension movement of the auxiliary piston is stopped by a divider plate after initial breakaway forces are overcome. The thrusting force developed by the auxiliary piston during a valve opening operation is transmitted to the valve stem and the primary piston by a shuttle sleeve. The shuttle sleeve is radially spaced about the valve stem, thereby defining a bridge annulus which maintains fluid communication between the primary pressure chamber and the auxiliary pressure chamber at all times. The thrusting force produced by the auxiliary piston is combined with the thrusting force produced by the primary piston to break the static gate seal and overcome the gate drag during a first stage of operation. After breakaway has been accomplished, the auxiliary piston is mechanically decoupled from the valve stem, whereby the valve stem is driven only by the primary piston at a substantially reduced thrusting force level during a second stage of operation, thereby avoiding gate damage which might otherwise occur if the valve stem velocity was not restrained.