| 摘要 |
<p>In an hydraulic system in which an hydraulic accumulator is charged with hydraulic fluid under pressure by means of an hydraulic pump which draws hydraulic fluid from a tank, and an unloader valve disposed in a supply line between the pump and the accumulator 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, and a pressure responsive slave which is operated by fluid pressure under the control of the control valve. The control valve comprises a valve member which 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 a second position in which fluid pressure from the accumulator can act on the slave to render the slave operative to reduce the pump pressure or disable the pump, and a cut-out spring for biassing the valve member at all times towards the first position. The valve member has different effective areas of which a smaller area is subjected to a control pressure dependent upon the pressure in the accumulator and in response to which the valve member can move at a cut-out point from the first position into the second position, and a greater area is subjected to the pressure in the accumulator, at least when the control member is in the second position, to determine a cut-in point at an accumulator pressure less than the pressure in the accumulator at the cut-out point and at which the control member can move from the second position into the first position.</p> |
