| 摘要 |
An improved gate valve has a body (12) with a chamber (14) and an inlet (16) and an outlet (18) extending therethrough into said chamber, a gate (20) mounted for reciprocation in said chamber between open and closed positions, a pressure responsive actuator (30) having a housing (34), a piston (36), a connection to the gate and an actuating stem extending from the housing, and a supplemental actuator (42) having a connection to the actuator housing, an operating stem (44) connected to the actuating stem (46). The operating stem (44) has a shoulder (92) facing in the direction opposite to the direction of closing movement of the gate. Roller levers (64) are pivotally mounted to be in engagement with the exterior of the operating stem and a spring (72) urges the roller levers into tight engagement with the operating stem, the roller levers pivoting on engagement with the stem shoulder (92) to exert a closing force on the stem. In a modified form of the invention, lever-roller assemblies are provided within the actuator to increase the closing force of the piston during the last portion of its stroke by changing the spring force provided by the actuator spring. |
