| 摘要 |
An in line pressure sensitive back flow prevention valve assembly adaptable for high volume flow applications comprising an elongated housing having a fluid inlet and outlet at opposite ends thereof, an axial control rod reciprocally mounted therein, a valve motor piston carried by one end of the rod in sliding engagement with the housing inwardly spaced from the fluid inlet and an elongated double poppet valve slidably mounted within the housing on the control rod and defining with a second slidably mounted piston, an upstream check valve and, with a slidably mounted sleeve, a downstream check valve. Biasing spring urge the motor piston toward the fluid inlet and the check valves to the closed position. The valve elements are sized to utilize the fluid forces acting thereon to open the valve assembly in response to slight decreases in downstream pressure and to cooperate with the biasing springs to close the valve assembly in response to significant increases in downstream pressure. A zone of substantially reduced pressure is provided within the housing about the double poppet valve between the check valves when the valve assembly is in the closed position to prevent back flow through the valve. A channel in the housing communicates with the reduced pressure zone for venting the zone to atmosphere in response to decreases in line pressure to maintain a reduced pressure within the zone when the valve assembly is in the closed position.
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