| 摘要 |
<p>A "snap action" early warning bypass valve assembly (2), responsive to fluid pressure differentials and/or low pressure, functions as both an electrical switch to provide an indication of low pressure or an impending fluid bypass and as a mechanical valve to actually implement the fluid bypass. The valve assembly includes a sealing piston (24, 124) supported by a retaining surface (18, 106) having a central bore (22, 110) formed therein. The sealing piston (24, 124) contains a bypass aperture (36) and is shaped to present a differential sealing area (39) to fluid circulating within the central bore (22, 110). A spring-biased bypass disc (42, 134) covers the bypass aperture (36) to present a central sealing area (45) to fluid within the central bore (22,110). A first pressure differential acting simultaneously across the central (45) and differential (39) sealing areas forces piston (24) into contact with an electrical terminal pin (48,92,126) thus energizing an alarm circuit (48-64,90). A second, greater pressure differential acting across the central sealing area (45) alone pushes the bypass disc (42, 134) away from the bypass aperture (36) to complete the bypass operation. A low pressure sensing means (140) including a low pressure piston (142) biased to a no alarm position by spring (128) and to an alarm position by spring (150) is responsive to fluid pressure in a bypass conduit (132) below a predetermined level to energize the same alarm circuit (48-64, 90).</p> |
