| 摘要 |
A valve apparatus has a valve body with an inlet, an outlet and a main valve seat disposed therebetween. A complementary main valve member can be moved by an actuating piston/diaphragm between open and closed positions, or located at an intermediate position therebetween. The actuating piston/diaphragm has one side exposed to an actuating chamber which receives fluid from the inlet through a metering orifice on one side, and an opposite side exposed to outlet pressure. A servo valve assembly controls flow from, and pressure within, the actuating chamber and controls movement of the main valve member. The servo valve assembly can be positioned by a relatively low force actuator in any position between extremes thereof, and acts as a master for the main valve member which follows it as a slave between open and closed positions, and any intermediate positions therebetween. The actuator is protected from high fluid forces imposed on the main valve member.
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