| 摘要 |
The preferred embodiment of the invention disclosed herein includes a main check valve movable between a fully closed and fully open position in response to the flow requirements from a pressure source to a demand system and including an intermediate position wherein the flow to the demand system corresponds to a predetermined minimum flow from the pressure source. Also included is a bypass valve for controlling the flow from the pressure source to a recirculation system. In the fully closed position of the main check valve, the bypass valve is in a fully open position whereby a predetermined minimum flow from the pressure source is maintained; in the intermediate position of the main check valve, the bypass valve is closed and remains closed between the intermediate position of the main check valve and its fully open position. Operation of the bypass valve is responsive to movement of the main check valve and is controlled by fluid from the inlet side of the main check valve which acts on opposite faces of a piston associated with the bypass valve. The pressure on one face of the piston is controlled by a pilot valve of the throttling type which valve is responsive to the position of the main check valve such that pressure on the one face of the piston is vented when the main check valve is closing and is increased when the main check valve is opening.
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