| 摘要 |
A piston valve of the kind in which a piston is movable longitudinally of a housing having ports for fluid to be controlled by the piston between two operative positions in each of which at least some of said ports are interconnected in different pairs through passages in the piston, by actuating fluid pressure applied to the end of the piston appropriate to the movement required, the actuating fluid pressure for effecting the movement in one direction being applied from a source externally of the valve and the actuating fluid pressure for effecting movement in the other direction being derived from one of said ports when the piston has been moved in said one direction. Said one port is connected to an end portion of the housing adjacent the relevant end face of the piston through a restricted passage and a closable control orifice leads from the passage between the restriction therein and said end portion of the housing, the control orifice being openable to prevent the actuating fluid pressure from rising sufficiently to effect movement of the piston in said other direction and closable to permit the actuating fluid pressure to reach a value sufficient to effect movement of the piston in said other direction when said movement is to be effected.
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