Fluid-pressure-operated relay valve - comprises piston movable in stepped bore in response to pressure in control chamber to which one of it faces is exposed

摘要

The valve comprises a control piston (5) which is of differential outline and which works in a stepped bore (2) in a housing (1) to control flow between an inlet (25) and an outlet (26). The control piston (5) moves in the bore (2) in response to pressure in a control chamber to which a first face (14) of the piston (5) is exposed. A second opposite face (15) carries a head (10) to engagement with the valve (19) to first cut off communication of the outlet with an exhaust connection (21) and then to open the connection between inlet and outlet. The effective area of the first face (14) of the piston is not greater than the effective area of the opposite face (15) of the piston when the head (10) engages the valve member (19).