| 摘要 |
A valve assembly includes a valve body with an upstream inlet, a downstream outlet, and first and second valve elements located between them and engageable with and disengageable from first and second valve seats, respectively. The first valve seat has a diameter which is less than that of the second valve seat. An actuator is operable to engage and disengage the valve elements with the valve seats to close and open the valve assembly. The assembly is configured to provide a first flow path from the inlet to the outlet when the first valve element is disengaged from the first valve seat and to provide a second flow path from the inlet to the outlet when the second valve element is disengaged from the second valve seat. Upon operation of the actuator to open the valve, initially the first valve element disengages from the first valve seat to permit fluid flow through the first flow path in order to equalise upstream and downstream pressure on the second valve element. Further operation of the actuator disengages the second valve element from the second valve seat to permit fluid flow through the second flow path. |
