RETAINER 4V9575 - Caterpillar

Service Brakes
The main components of the service braking system are:* Service Brake Valve (11)* Accumulators (7) and (26)* Brake Groups (1), (8) and (9)The oil supply is from the main hydraulic system. Oil from hoist and service brake hydraulic pump (25) flows to service brake valve (11) through line (10). Pump oil can flow through the service brake valve to lines (6) and (27), which are connected to accumulators (7) and (26). When the pressure in these lines reaches 17500 kPa (2540 psi) the system is fully charged.During the charging process, system pressure is connected to load sense line (20), which is connected to the pump control section through shuttle (resolver) valve (19). This causes the pump swashplate angle to increase and increases the supply of oil to the system. When the system is fully charged, the load sense line is connected to tank and pump output falls (unless there is a demand from the hoist hydraulic system).The operation of the hydraulic pump is described in the Hydraulic System Service Manual Module, form SENR8228.When the system is fully charged, oil at 17500 kPa (2540 psi) is present in the lines between the service brake valve and the accumulators. Accumulators (26) are for the tractor brakes and accumulators (7) are for the trailer brakes.When the service brake pedal is pressed, the valve connects line (27) to line (21) and line (6) to line (28). Oil flows through line (21) to apply the tractor brakes and through line (28) to apply the trailer brakes.When the service brake pedal is released, lines (21) and (28) are connected to return line (22) and the brakes are released. Lines (6) and (27) are blocked but the pressure in these lines will be lower than it was before the brake application was made.Succesive brake applications will further reduce system pressure. When the pressure falls to 15500 kPa (2250 psi) the service brake valve connects this pressure to the load sense line and the pump comes back on load to re-charge the system.Pressure switch (13) is a normally open switch which closes when pressure is connected to the brake group lines (21) and (28).Pressure switch (12) is a normally closed switch which opens if brake system pressure falls below 11500 kPa (1670 psi). This switch operates the low brake pressure indicator.Parking Brake
The main components of the parking brake system are:* Solenoid Valve (4)* Accumulator (2)The system is supplied with oil at transmission pump pressure from transmission oil filter (3).When the parking brake control is in the ENGAGED position, the solenoid valve is de-energized. Transmission oil is blocked at the valve spool and oil in the parking brake (17) is connected to tank (the output transfer gear case) through lines (16) and (15). The parking brake is then engaged by spring force.When the parking brake control is in the DISENGAGED position, the solenoid valve is energized. Transmission oil flows through the valve to the parking brake. This oil pressure disengages the brake.When the engine is not