ROD AS 3457209 - Caterpillar

Illustration 1 g06111541
Parking Brake Control Valve
The operator platform is removed for clarity.
The parking brake control valve is located on the right side of the machine. The parking brake control valve is mounted on the top of the right side service center.The parking brake control valve controls the flow of pressure oil for the parking brake actuator.
Illustration 2 g06111554
(1) Parking brake control knob.
Illustration 3 g00291888
Parking Brake Control Valve
(2) Port for the hydraulic oil tank. (3) Port for the parking brake actuator. (4) Pressure port that is connected to the accumulator for the rear service brakes.
Illustration 4 g00910546
View A-A
(2) Port for the hydraulic oil tank. (3) Port for the parking brake actuator. (4) Pressure port that is connected to the accumulator for the rear service brakes. (5) Stem for the parking brake control valve. (6) Detent springs. (7) Detent balls. (8) Spool. (9) Retainer. (10) Spring.
Push in on the parking brake control knob (1) to disengage the parking brake. This causes spool (8) and retainer (9) to move right and compress the spring (10).This movement allows pressure oil to flow into the pressure port from the brake accumulator for the rear service brakes. The oil then flows out of the port for the parking brake actuator (3). The oil then flows into a cavity in the actuator assembly for the parking brake.When the oil pressure in the cavity for the parking brake actuator is high enough to compress the actuator spring, the parking brake disengages. The pressure of the oil keeps the parking brake in the DISENGAGED position.Pull out the parking brake control knob (1) to engage the parking brake. Pulling out on the parking brake control knob (1) causes stem (5) to move spool (8) to the left. This causes flow of pressure oil to the parking brake actuator to stop. In return allowing the oil in the cavity of the parking brake actuator to flow back to the hydraulic oil tank.With a decrease in oil pressure for the parking brake circuit. The force of the spring in the parking brake actuator is greater than the pressure of the oil in the parking brake actuator cavity. This force then allows the spring to engage the parking brake.If there is a decrease of hydraulic oil pressure in the service brake circuit during machine operation. The parking brake control valve will automatically engage the parking brake. If the machine is in either first speed forward or first speed reverse, the transmission will also shift into the NEUTRAL position.With a loss of hydraulic oil pressure, the force of spring (10) moves spool (9) to the left. This blocks any flow of oil that would normally help keep spring (10) compressed. This causes spring retainer (9) and spool (8) to move left. At the same time, stem (5) also moves to the left.Detent springs (6) and detent balls (7) move in and out of grooves that are machined into spool (8). Allowing the operator to feel the internal locking mechanism of the parking brake control valve.
Illustration 5 g03484041
Illustration