| 摘要 |
<p>Two check valves in series with a zone between them are mounted between the supply pipe and discharge pipe, and a relief valve vents the zone to atmosphere under predetermined pressure conditions in the pipes. A valve poppet in the upstream check valve has a pressure affected piston chamber and contains an ejector nozzle which discharges fluid when the valve is open. The discharge passes through the zone and the velocity head is directed against a valve poppet in the downstream check valve. The action of the ejector nozzle aspirates the pressure affected chamber in the upstream check valve to reduce the pressure drop when the valve is open. A valve poppet in the downstream check valve also includes a pressure affected piston area. In each check valve the flow restriction across the valve seat decreases more rapidly than the downstream flow restriction. Also, the outer surface of the valve poppet in the upstream check valve defines, with its stationamy barrel enclosure, a series of ribs and cavities which direct flow of fluid from the check valve through the ejector nozzle while minimizing flow into the aspirated chamber. A relief valve device connected to vent the zone to atmosphere has a valve stem subjected to a pressume differential between the inlet pressure to the upstream check valve and the reduced pressure in its aspirated chamber.</p> |
