Fluid actuated piston valve

Claim 1

A piston valve comprising a housing having a longitudinallyextending bore therein, a plurality of ports in the peripheral wall of said housing and communicating with said bore, a piston slidable longitudinally in the bore in the housing between two operative positions in each of which at least some of said ports are interconnected in different pairs through passages in said piston, means for applying a different source of actuating fluid pressure to respective ends of said piston, whereby the application of one of the sources of actuating fluid pressure to the end of said piston appropriate to the movement required will effect movement of the piston from one operative position to the other, wherein the improvement comprises one of said means for applying actuating fluid pressure for effecting the movement in one direction derives its fluid pressure from a source externally of the valve, and the other of said means for applying the actuating fluid pressure for effecting movement in the other direction comprises duct means communicating with one port to which a fluid pressure is applied from a source externally of the valve, said one port being one of one of said pairs of ports, through one of said passages in said piston when the latter has been moved in said one direction and an end portion of the housing adjacent the relevant end face of the piston, a restriction in said duct means, and a closable control orifice positioned externally of said valve and leading from said duct means between the restriction therein and said end portion of the housing, the conTrol orifice being openable to atmosphere 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.