| 摘要 |
In an hydraulic system an unloader valve is disposed in a supply line between a pump and an hydraulic accumulator. The unloader valve is operative to prevent the accumulator from being overcharged and to allow the pump to re-charge the accumulator should the pressure stored therein fall below a desired minimum value. The unloader valve incorporates a control valve comprising a spool and a pressure responsive slave which is operated by fluid pressure under the control of the control valve. The spool is movable between a first position in which the accumulator is isolated from the slave so that pump pressure is supplied to the accumulator and acts through a membrane on a trapped volume of gas under pressure, and a second position in which fluid pressure from the accumulator acts on the slave to unload the pump. The membrane of the accumulator acts directly on the spool to control movement of the spool between the two positions. In an alternative embodiment, the membrane acts indirectly on the spool through an operating rod and an operating member.
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