| 摘要 |
<p>A butterfly-type step subassembly includes a substantially planar valve disc member having a peripheral groove formed in opposite surfaces thereof. Projecting inwardly from the internal walls of the subassembly housing are two non-coplanar, generally semicircular valve seat members having passageway(s) in them communicating outside the housing with a source of purified gas(es). The passageways terminate interiorly in apertures in respective recesses in the seat members positioned to be brought into communication with said grooves when said valve disc member is in substantial contact with said seat members. Means are provided to supply said purified gas(es) to said passageways in response to the movement of said planar disc member to the nominally closed position so that said gas(es) flow into the contact region between the disc and seat members under sufficient pressure to prevent said effluent from flowing through said valve when nominally closed.</p> |
