| 摘要 |
In-line control valve constructions are described which include a piston-type valve assembly and a plurality of control chambers (C1, C2, C3, C4) controlled via one or more control ports (CP1, CP2) to provide a normally-open valve which may be closed by controlling the fluid pressure applied to the control port (CP1, CP2), or a normally-closed valve which may be opened by controlling the fluid pressure applied to the control port (CP1, CP2). Also described are valves which have a balanced construction and which therefore include relatively small actuators for opening and closing the valve.
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