Abstract: A fluid control system providing a backup system for activating a pair of brakes on a vehicle includes a pair of double check valves with cross bleed located near the brakes. Each double check valve is connected at one end to a brake control valve which is in turn connected to a main pump and reservoir. The second ends of the double check valves are commonly connected to a secondary brake control valve which is connected to an accumulator which is fluid pressurized from the main pump. The center connections between the two ends of each of the double check valves are connected to one of the pair of brakes. The double check valves respond to pressure differentials to connect the main pump or the accumulator, whichever is supplying the greater pressure, to the brakes.

Abstract: A piston-type accumulator in a hydraulic circuit is provided with an interior sleeve proximate the gas valve for limiting piston movement and providing a minimum predetermined accumulator gas volume. By monitoring the pressure of the gas charge in the minimum predetermined gas volume, it may be determined whether the accumulator retains sufficient energy for proper operation in the hydraulic circuit or requires recharging.