| 摘要 |
<p>A fail-safe valve actuator includes a hydraulic piston (17) and cylinder (15) for driving the valve stem (9) and gate member (35) of a gate valve into a first flow control state responsive to sufficient pressure delivered by a fluid or gas supply line (92). Upon failure or other loss of sufficient control line pressure, a volute spring (7) drives the cylinder (15), and hence the stem (9) and gate member (35), axially outward resulting in the valve being moved into a second flow control state. Retaining rings (94, 102) are provided to retain the volute spring in a precompressed state during disassembly of the actuator for servicing.</p> |
