| 摘要 |
A pilot operated relief valve has a main relief valve (10) and a pilot relief valve (31) connected between a control chamber (23) and drain. A restriction (16) connects the control chamber (23) to the inlet chamber (22) which is separated from the control chamber by a piston (24) integral with the main relief valve closure member (12). Thus opening of the pilot relief valve against the adjustable force of a spring (14) determines the maximum pressure in the inlet chamber (22). The control chamber (23) can also be connected to drain (70) by a pilot valve (19) which is operated by a force motor (52) against pressure in a feedback chamber (56) connected to the inlet passage (22). The energisation of the force motor (52) can be adjusted to adjust the relief pressure to a value below that at which the pilot relief valve (31) opens. Alternatively the pressure in the feedback chamber (56) can depend on the pressure at least one side of a load fed via a directional valve from the inlet passage (22). |
