Brake control system with metering pump relief

In a brake control system (10) for actuation of a spring applied pressure released brake (11) between engaged and disengaged conditions for respectively stopping and allowing rotation of a rotatable member (12), the system including a pump (16), a control valve (19) having an inlet port (18) connected to the pump and an outlet port (22) connected to an actuating chamber (14) of the brake, said control valve being movable between a first position at which the inlet port (18) is blocked from the outlet port (22) and a plurality of operative positions at which communication between the inlet (18) and outlet (22) ports is controllably modulated, a metering pump (23) having an inlet port (24) and an outlet port (26) with said inlet port (24) being connected to the actuating chamber (14) of the brake, said metering pump being drivingly connected to the rotatable member (12), a conduit connecting the outlet port (26) of the metering pump with the inlet port (18) of the control valve (19), and means (29) for normally maintaining the pressure in the conduit (28) at a predetermined operating level, the improvement comprising:

• means (36) for relieving the pressure in the outlet port (26) of the metering pump (23) at a pressure level lower than said predetermined operating level when fluid flow therethrough is below a predetermined flow rate so that the working pressure differential across the metering pump is reduced.