| 摘要 |
An internal safety shutoff and operating valve includes a housing defining a valve seat and a cylinder. A piston slidable in the cylinder includes a valve closure member engageable with the seat for closing the valve. A spring biases the piston toward the closed position, and an actuating assembly moves the piston against the spring to the open position. One set of main ports communicates with the valve seat between the valve seat and the cylinder, and the other set of main ports communicates with the opposite side of the valve seat. Pressure forces on the piston are balanced by a passage in the piston intercommunicating the cylinder with one set of main ports. In order to prevent leakage between the piston and the cylinder wall to the other set of ports, a seal assembly including a groove in the piston wall and a seal ring in the groove is provided. The groove includes rounded inner corners, and the seal ring is provided with inner and outer grooves interconnected by passageways. When the seal assembly is subjected to a pressure differential, the grooves and passageways equalize the pressures on both sides of the seal, and the seal is moved axially in the direction of the pressure drop against a rounded corner. The rounded corner cams the seal radially against the cylinder wall to provide position sealing with the wall of the groove and with the wall of the cylinder.
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