| 摘要 |
<p>An unloader valve in which the valve body has an inlet opening between an outlet opening and a by-pass opening and in which the flow of fluid is controlled by two valves, both of which open and close in relation to a single unitary plunger. The plunger is hollow from adjacent the inlet opening to the outlet opening so that fluid flows from the inlet opening through the hollow plunger to a check valve and the outlet opening. The plunger is presettably biased to close a by-pass valve between the inlet and by-pass openings, thus regulating the pressure at the outlet opening. The valve also contains an override piston, one surface of which is exposed to the outlet opening. When the output is shut off, the resulting outlet pressure drives this piston against the end of the plunger, and fully opens the by-pass valve to permit the fluid to flow from the inlet to the by-pass opening, thus not only protecting against excessive pressure build-up but also lowering the inlet pressure to a low unloading level. A seal around the plunger moves only incrementally while outlet pressure is regulated and moves under a very low pressure differential. The seal around the piston moves only when the piston is driving the plunger to fully open the by-pass valve or returning with the plunger when the by-pass valve closes, so that its wear is transitional. When the by-pass valve is fully open, neither seal moves. As a result, wear on the seals around the plunger and piston alternates and is minimized, resulting in a compact longlife valve.</p> |
