| 摘要 |
<p>A self-contained, pilot-operated valve is provided with a plug for controlling the flow of a fluid through an orifice between inlet and outlet openings. A spring located about a stem projecting from the plug urges the plug into sealing engagement with the orifice. By means of a bellows surrounding the spring and having one end connected to the stem, an interior space is created, which space is in communication with the inlet opening through a restricted conduit. The interior space is also in communication with the outlet opening via a pilot valve. Operation of the pilot valve controls the pressure in the interior bellows space and hence the degree to which the bellows is compressed. This compression affects the plug stem and hence the position of the plug with respect to the valve seat. In order to prevent an overpressure on the bellows when the valve is open, a valve operator closes off the communication between the interior space of the bellows and the outlet opening, thereby allowing the pressure on the inside of the bellows to build up to prevent a collapse of the bellows.</p> |
