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| Illustration 1 | g00473677 |
Right Side View of the Machine | |
The arrow points to the location of the parking brake control valve.
The parking brake control valve is located on the right side of the machine under the operator's platform. The parking brake control valve controls the flow of pressure oil from the parking brake actuator and to the parking brake actuator.
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| Illustration 2 | g00473680 |
Parking Brake Control Valve (arrow) | |
The operator's cab and the platform have been removed for clarity.
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| Illustration 3 | g00473682 |
Parking Brake Control Valve (1) Pressure port that is connected to the brake accumulators. (2) Stem of parking brake control valve. (3) Spring. (4) Spool. (5) Return port to hydraulic oil tank. (6) Spool. (7) Port to parking brake actuator. (8) Retainer. (9) Spring. | |
Note: When the hydraulic tank pressure is above 410 kPa (60 psi) the stem on parking brake control valve (2) may extend outward. This will engage the parking brake.
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| Illustration 4 | g00473808 |
Instrument Panel (10) Parking brake indicator. (11) Brake oil pressure indicator. (12) Master action light. (13) Parking brake control knob. | |
When the operator pushes in parking brake control knob (13) the parking brake disengages. The spool (6), and retainer (8) move to the right in order to compress spring (9) in the parking control valve. This allows pressure oil to flow into the pressure port from accumulators (1). The oil then flows out of the port to parking brake actuator (7). The pressure oil flows to a cavity in the parking brake actuator.
The pressure of the oil will force the spring upward in the parking brake actuator. The parking brake will disengage. This oil pressure keeps the parking brake disengaged.
If the operator pulls the parking brake control knob (13) outward the parking brake engages. The stem of parking brake control valve (2) stops the flow of oil from the accumulator to the parking brake. This causes spool (6) to move left which stops the supply of oil from accumulators. The actuator oil flows back to the tank.
When the oil pressure drops in the brake system, the force of the spring in the brake actuator will become greater than the pressure of the oil which will engage the parking brake.
With a loss of hydraulic oil pressure, the force of spring (3) will move spool (4) to the right. This blocks any flow of oil that would keep spring (9) compressed. The force of spring (9) in the parking brake control valve moves retainer (8), spool (4), and the stem of parking brake control valve (2) outward.
When the hydraulic oil pressure to the parking brake actuator falls below 6890 ± 345 kPa (1000 ± 50 psi) the Caterpillar Monitoring System will indicate a Warning Category 3. This will cause parking brake indicator (10), brake oil pressure indicator (11), and master action light (12) to flash. The action alarm will also sound.
If there is an oil pressure drop in the brake system during machine operation. The parking brake control valve will automatically engage the parking brake. The transmission will return to NEUTRAL position, if the machine is in first speed FORWARD or if the machine is in first speed REVERSE. This will occur when the parking brake engages.
Note: A special drive-through mode is available by cycling the transmission direction control switch to NEUTRAL position. Return the switch to the original position before the parking brake is engaged. This mode should only be used to move the machine in case of an emergency.