Location of the Brake Accumulator Charging Valve
The brake accumulator charging valve is located next to the two brake accumulators on the left side of the machine.
Brake Accumulator Charging Valve
(1) Relief valve. (2) Port for the brake oil pressure switch. (3) Accumulator port for the rear brakes. (4) Outlet to the hydraulic oil tank. (5) Accumulator port for the front brakes. (6) Plug. (7) Inlet from the brake pump.
The brake accumulator charging valve contains an internal relief valve which limits the pressure in the brake circuit. A pressure switch alerts the operator when the brake oil pressure drops below the minimum operating pressure.
The brake pump supplies hydraulic oil to the brake control group. First, the oil flows to the brake accumulator charging valve. The brake accumulator charging valve maintains the pressure in the accumulators at a constant range while the engine is running.
The brake accumulator charging valve senses the lower pressure of the two accumulator pressures. A spool in the brake accumulator charging valve then moves in order to allow the hydraulic oil to flow to one accumulator or to both accumulators. The unused oil that is supplied by the brake pump is diverted back to the hydraulic oil tank.
Note: If a machine is equipped with the Traction Control System, the machine will have a 135-4391 Accumulator Charging Valve. This charging valve has the same specifications as the brake accumulator charging valve that is used on machines without the Traction Control System. However, the 135-4391 Accumulator Charging Valve will maintain a standby pressure of 4310 ± 210 kPa (625 ± 30 psi).
For machines that use a 135-4391 Accumulator Charging Valve, excess pressure oil in the supply line is not diverted back to the hydraulic oil tank. The unused pressure oil is used to supply oil to the traction control system.
Reference: For more information about the Traction Control System, refer to Specifications, Systems Operation, Testing and Adjusting, SENR6719, "938G Wheel Loader and IT38G Integrated Toolcarrier Traction Control System".