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| Illustration 1 | g00548818 |
Parking brake control knob (1) . | |
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| Illustration 2 | g00537843 |
Parking Brake Control Valve | |
The parking brake control valve is located under the cab on the right side of the machine.
The parking brake control valve controls the flow of pressure oil for the parking brake actuator.
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| 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 front service brakes. | |
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| Illustration 4 | g00291889 |
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 front service brakes. (5) Stem for the brake control valve (parking). (6) Detent springs. (7) Detent balls. (8) Spool. (9) Retainer. (10) Spring. | |
When the parking brake control knob (1) is pushed in, the parking brake disengages. This causes spool (8) and retainer (9) to move right. This movement compresses spring (10) .
This 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 springs, 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) in order 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 stops the flow of pressure oil to the parking brake actuator. This allows 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 springs in the parking brake actuator is greater than the pressure of the oil in the cavity of the parking brake actuator. This allows the springs 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). This allows the operator to feel the internal locking mechanism of the parking brake control valve.
When the oil pressure for the parking brake actuator decreases below a preset value, the Caterpillar Monitoring System indicates a Warning Category 3 alarm.
The following warning indications will notify the operator:
- The alert indicator will flash approximately nine times per second.
- The action lamp will flash ON for one second and OFF for two seconds.
- The action alarm will sound ON for one second and OFF for two seconds.
The transmission returns to the NEUTRAL position if the transmission is in either first speed forward or first speed reverse. This will occur when the parking brake engages.
Note: The parking brake can be manually engaged and disengaged when the pressure in the system is above 10300 kPa (1495 psi). However, if the system pressure is below 10300 kPa (1495 psi), actuation force increases.
Note: If the parking brake control knob is in the ENGAGED position, the parking brake control valve will move to the ENGAGED position when the pressure difference between the pressure port and the tank port is approximately 2400 kPa (350 psi).
Note: Hydraulic tank pressure above 410 kPa (60 psi) may cause stem (5) to extend to the ENGAGED position.
Reference: For additional information on the Caterpillar Monitoring System, refer to Service Manual, SENR1394, "Caterpillar Monitoring System".