| 摘要 |
In a safety valve having an axially shiftable actuating sleeve operable to move a valve head from a closed to an open position, the actuating movement of the actuating sleeve is normally produced by a small diameter piston mounted on an axially extending spindle secured to the valve housing and cooperating with a primary cylinder which is abuttingly secured to the actuating sleeve. A secondary spindle and cooperating cylinder are provided which are supplied with fluid pressure by an entirely separate line extending to the well surface. The second cylinder has only abutting contact with the actuating sleeve and may be utilized to effect the movement of the actuating sleeve in the event of the failure of the primary cylinder. In a modification, a fixed cylinder housing defines a pair of secondary cylinder bores in which secondary rod pistons are slidably mounted to effect the movement of the actuating sleeve. In both modifications, collet latches prevent return movement of the secondary cylinder or secondary rod pistons, thus locking the valve head in an open position. |
