| 摘要 |
<p>A valve assembly comprises a valve seat having a flow passage (102), and closure means (107) which is movable by an operating member (111) into and out of engagement with the valve seat to close and open the flow passage (102). The valve seat comprises a main seat (101) element having a main flow passage (102) and an intermediate seat element (103) having an intermediate passage (104) communicating with the main flow passage (102). The operating member is movable from a closed position of the valve assembly to open the valve assembly. During a first part of the movement of the operating member (111, 112), the closure means (107) is withdrawn from the intermediate valve seat (103) and, during a second part of the movement of the operating member (111, 112), the intermediate valve seat (103) is withdrawn from the main valve seat (107).</p> |
