| 摘要 |
<p>Apparatus for controlling the working stoke of the hydraulic props of a mine roof support unit is disclosed. The control apparatus comprises a control valve whose input side is connected to a hydraulic pressure line, and whose output side is connected to a working chamber of each of the props via a respective supply line. A sequence valve is provided in the supply line leading to one of the props. The sequence valve is such as to open the associated supply line when subjected to a predetermined hydraulic pressure, this predetermined hydraulic pressure being at least approximately equal to the hydraulic pressure necessary to overcome the resistance to the working stroke of another of the props. The sequence valve has a tubular valve body, a valve closure element mounted within the valve body, and a valve seat positioned within the valve body. A spring is provided for biassing the valve closure element towards the valve seat. A control piston carries the valve seat, the control piston having a piston face which, when subjected to hydraulic pressure in the biassing direction of the spring, is effective to displace the control piston so as to move the valve seat away from the valve closure element, thereby opening the sequence valve.</p> |
