| 摘要 |
A valve assembly comprises first and second valve elements 31, 33 movable by actuator 12 to engage with first and second valve seats (32, 34, Fig. 2). First valve seat 32 has a diameter less than second valve seat 34. The assembly provides a first flow path from inlet 22 to outlet 23 when the first valve element 31 is disengaged from its seat and provides a second flow path from the inlet 22 to the outlet 23 when the second valve element 33 is disengaged from its seat. Upon initial opening of the valve, first valve element 31 disengages from its seat to permit flow through the first flow path in order to equalise upstream and downstream pressure on the second valve element 33. Further opening disengages second valve element 33 from its seat to permit flow through the second flow path. |
