| 摘要 |
A blowout preventer comprises apparatus for allowing the pressure above and below its rams to equalize before the rams are opened. At least one of the rams has a bypass passageway therethrough disposed so as to allow communication between well zones above and below the rams, respectively. The bypass passageway also has a straight-sided tubular sealing section intermediate its ends. A sealing piston carrying a circumferential seal sized to engage the sealing section of the bypass passageway is reciprocable in that passageway to move the circumferential seal into and out of engagement with the sealing section and thereby respectively prevent or permit fluid flow through the bypass passageway. Where the actuator shaft for the ram is connected to the ram by a lost motion type connection, the sealing piston may be carried on the shaft. The sealing piston or other valve member may be carried on a carrier loosely mounted on an inner end of the shaft for lateral play, thereby allowing for "self-centering" of the valve element with respect to the surface against which it must seal. |
