HYDRAULICS 1.23 Single circuit brake pressure servo valve (SAFIM) (10) NOTE: Fitted from Machines Serial No.51200472 only The brake pressure servo valve can be either single or dual depending on the model of the machine. The valve is constructed from 3 separate modules, the master cylinder, valve body and end plate. Brake pedal travel and braking pressure are set using an adjusting screw, located on the base on the brake valve. The operation of the servo valve (1) is proportional to brake pedal movement. When the brake pedal is pressed, a pivoted lever moves a master cylinder, which positions an associated sprung loaded plunger.
The plunger is in contact with the main shuttle valve in the valve body Refer to Page 1.84). The shuttle valve controls the flow of the pressure oil supply from the brake accumulator. The accumulator is supplied from the inlet (PVSP) section of the main hydraulic control valve. When the shuttle valve is moved, the oil supply from the accumulator is allowed to flow to the outlet connection in the end plate, which supplies the front and rear brakes units.
Servo Valve - Single circuit brake pedal P Pressure supply from Accumulator (11) T Return to Hydraulic Tank (1) A Supply to Brakes on Front (14) and Rear (18) Axles When the brake pedal is released, spring pressure in the master valve releases pressure on the shuttle valve and repositions the brake pedal. The shuttle valve moves under spring pressure to close the oil supply from the accumulator and divert residual oil pressure from the brake system to the hydraulic tank, releasing the brakes. Specification: Brake pressure at A 44 bar (640 psi) Dual circuit Brake pressure servo valve (SAFIM) (10) NOTE:
Fitted from Machines Serial No.51200472 only The construction and operation of the dual brake servo valve is similar to the single servo valve. The primary difference is that the front and rear brakes are operated independently of each other by separate feed and return lines from the servo valve. Servo Valve - Dual circuit brake pedal P Pressure supply from Accumulators (11) T Return to Hydraulic Tank (1) A Supply to Brakes on Front (14) and Rear (18) Axles Specification: Brake pressure at A 44 bar (640 psi)