Inverting limiting relay valve with interlock

Claim 1

For use in a fluid pressure braking system of the dual circuit type in which one circuit includes a spring applied fluid pressure released actuator, and a manually operable valve for controlling the application of fluid pressure to said circuits, the invention which comprises a first valve means movable to a first position to supply fluid pressuRe from a source to said actuator to move the latter to a brake released position and movable to a second position to release fluid pressure from said actuator, to graduate spring brake application thereof in accordance with fluid pressure supplied to said other circuit, and means controlled by fluid pressure from the source for positively preventing fluid pressure release operation of said valve means so long as the fluid pressure from the source is above a predetermined value, said means including a first pressure responsive member for moving said valve means, resilient means for actuating said member to move the valve means to said first position, said member having a motive area, a second valve means movable to a first position for normally connecting said motive area with the atmosphere, and movable to a second position to connect said motive area with the other circuit, and a second pressure responsive member axially aligned with said second valve means and movable in response to fluid pressure from said source to allow the second valve means to occupy its first position, the second pressure responsive member being spring-actuated to positively move the second valve member to its second position.