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A fluid valve operative based on a pressure differential through the utilization of different size pressure receiving piston faces. A first fluid, through pressure on an enlarged piston face, maintains a valve spool so shifted as to allow for a through passage of a second fluid. Upon a blocking of t

A fluid valve operative based on a pressure differential through the utilization of different size pressure receiving piston faces. A first fluid, through pressure on an enlarged piston face, maintains a valve spool so shifted as to allow for a through passage of a second fluid. Upon a blocking of the first fluid, the second fluid, acting on a relatively smaller valve surface, actuates the valve and blocks through passage of the second fluid. The shifting of the valve presents yet a smaller pressure receiving face to the first fluid which, in conjunction with an exhaust port, provides a fail safe lock out requiring manual resetting of the relay.

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A valve comprising a valve body, an elongated bore within said body, a first fluid inlet port, an outlet port, a bleed port, second fluid inlet port, valve member slidable within said bore, means for positioning said valve member in a first position whereby communication is permitted between said fi

A valve comprising a valve body, an elongated bore within said body, a first fluid inlet port, an outlet port, a bleed port, second fluid inlet port, valve member slidable within said bore, means for positioning said valve member in a first position whereby communication is permitted between said first inlet port and said outlet port but communication is precluded between said bleed port and said outlet port, means for positioning said valve mEmber in a second position whereby communication is permitted between said bleed port and said outlet port but is precluded between said first inlet port and said outlet port, and means for preventing pressure exerted against said valve member through said second inlet port from moving said valve member from said second position to said first position, wherein said preventing means includes first and second enlarged portions of said bore intermediate said second fluid inlet port and said first fluid inlet port, one of said enlarged portions sealingly accommodating said valve member and the other of said enlarged portions being of such greater diameter than said valve member as to not sealingly accommodate said valve member.