| 摘要 |
<p>A hydraulically operated directional control valve 10, for hydraulic cylinders of hydraulic support mechanisms in underground mining, comprises a valve piston 16 and a control piston 18 screw threaded together at 17 and reciprocable in a valve seat carrier 15 and a control piston guide 19, respectively. A control pressure introduced via ST lifts the pistons against bias of spring 21 to move valve cone 20 away from seat 22 and partially open high pressure connection P to a load connection A and to return flow connection T via gaps 28 and 33. Return flow connection T is closed when the forward end 42 of the control piston engages sealing cone 43, at which time connection P is fully opened. The interval between fully opening P and closing T can be adjusted. The valve thus achieves an opening and closing characteristic with negative overlapping and so provides gentle switching processes, so that switching impacts with high pressure peaks do not arise.</p> |
