a controller for controlling the increase in fluid brake pressure as a brake is applied irrespective of how rapidly the operator applies the brakes . the controller includes a valve between inlet and outlet ports in a valve body , the valve having opposing faces subjected respectively to pressure at the outlet and pressure in a volume chamber between the valve and a spring loaded piston and connected to the outlet through a restricted orifice . the valve seeks an equilibrium position wherein the rate of rise in pressure at the outlet is controlled and the deceleration of the vehicle is controlled even when the operator applies the brakes at an excessive rate .