| 摘要 |
There are disclosed three embodiments of a gate valve having a fail safe actuator which is especially useful in a subsea environment at considerably depth below water surface. The gate is urged to open position by control pressure and is moved to closed position, upon loss of a controlled condition, by means of a spring acting between the actuator and the stem. In one embodiment, when the body pressure is low, a floating ring sealably shiftable within an annular space between the stem and actuator is urged by body pressure into a position to engage a stop on the stem, and thus provide a force urging it in a direction to close the gate, when body pressure is below ambient, and by ambient pressure to a position to engage a stop on the actuator when body pressure is above ambient. In a second embodiment of the invention, the valve includes a balance stem which is spring-pressed to engage the end of the gate opposite its operating stem, when body pressure is low relative to ambient, but moves out of engagement with gate and into a limited position in engagement with the actuator, when body pressure is high relative to ambient. In the third embodiment of the invention, the valve includes both the floating ring and the spring-pressed balance stem of the first and second embodiments.
|
