| 摘要 |
In an hydraulic system a solenoid-operated valve mechanism is used to control delivery of pressure fluid to a part of the system, the fluid being circulated by a pump from a reservoir through the valve mechanism and back. The valve mechanism has a solenoid-operated valve biassed open, and closed when the solenoid is energized to generate pressure fluid, the valve then being operated in response to the pressure and a pressure-responsive valve-opening mechanism, such that when the pressure rises above a first threshold level the pressure acts to keep the valve closed, until the pressure reaches a second threshold level at which the valve-opening mechanism is operative to cause the valve to open provided the solenoid is de-energized. The valve-opening mechanism comprises a valve which opens at the second threshold level to allow pressure fluid into a cavity defined by a piston to cause the pressure to fall and the valve to open.
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