Parking Brake Engaged
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| Illustration 1 | g01156327 |
Service brakes disengaged. The parking brake engaged and the brake system charged. (1) Main Control Valve (1f) Relief Valve (1k) Diverter Valve (1l) Relief Valve (1o) Diverter Valve (1s) Shuttle Valve (1t) Check Valve (1u) Orifice (1v) Screen (1cc) Shuttle Valve (1gg) Shuttle Valve (9) Piston Pump (10) Service Brakes for the Trailer (Right Side) (11) Service Brakes for the Trailer (Left Side) (13) Service Brakes for the Front Axle (14) Brake Control Valve (15) Accumulator (Parking Brake) (16) Accumulator (Service Brakes for the Trailer) (17) Accumulator (Service Brakes for the Front Axle) (18) Parking Brake (20) Filter (Return Oil) (21) Pressure Switch (Transmission Signal) (22) Pressure Switch (Stop Light) (23) Manifold (24) Pressure Switch (Parking Brake) (25) Pressure Switch (Brake System Pressure) | |
When the parking brake control is in the ENGAGED position and the system is uncharged, oil from piston pump (9) enters main control valve (1) through the P1 port. Oil flows through the main control valve through screen (1v), orifice (1u), and check valve (1t) to diverter valve (1k). Oil also flows through check valve (1bb) to accumulator (15) and solenoid valve (1aa) .
Solenoid valve (1aa) is de-energized and the solenoid valve blocks oil flow to parking brake (18). The solenoid valve also directs oil from the parking brake to the tank and the parking brake is engaged by spring force.
Diverter valve (1k) allows oil to flow into the load sensing line and the resulting load sensing pressure is transmitted through shuttle valves (1cc) and (1gg) to the piston pump. This increases the output of the piston pump and oil flows though the main control valve into accumulator (15) until the accumulator is fully charged. Load sensing pressure also acts on diverter valve (1o) and the diverter valve blocks oil flow into the hoist system.
When the accumulator is charged, the increased system pressure moves diverter valve (1k) which blocks the oil flow into the load sensing system. This reduces the output of the piston pump and the pressure is maintained in the accumulator by check valve (1bb). The diverter valve directs oil in the load sensing system to the tank and any excess pressure is relieved by relief valve (1l) .
When the parking brake is engaged, pressure switch (24) detects low pressure in the parking brake system. The pressure switch sends a signal to the ECM and the parking brake indicator in the cab is illuminated.
Parking Brake Disengaged
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| Illustration 2 | g01109222 |
Service brakes disengaged. The parking brake disengaged and the brake system charged. (1) Main Control Valve (1f) Relief Valve (1k) Diverter Valve (1l) Relief Valve (1o) Diverter Valve (1s) Shuttle Valve (1t) Check Valve (1u) Orifice (1v) Screen (1cc) Shuttle Valve (1gg) Shuttle Valve (9) Piston Pump (10) Service Brakes for the Trailer (Right Side) (11) Service Brakes for the Trailer (Left Side) (13) Service Brakes for the Front Axle (14) Brake Control Valve (15) Accumulator (Parking Brake) (16) Accumulator (Service Brakes for the Trailer) (17) Accumulator (Service Brakes for the Front Axle) (18) Parking Brake (20) Filter (Return Oil) (21) Pressure Switch (Transmission Signal) (22) Pressure Switch (Stop Light) (23) Manifold (24) Pressure Switch (Parking Brake) (25) Pressure Switch (Brake System Pressure) | |
When the parking brake control is moved to the DISENGAGED position, solenoid valve (1aa) is energized. Oil is forced through the solenoid valve and screen (1dd) by the stored energy within accumulator (15). Oil flows from the PB port of main control valve (1) to parking brake (18). The resulting force overcomes the force of the internal spring within the parking brake and the parking brake is disengaged.
The fully charged parking brake accumulator (4) can disengage parking brake (3) three times before the stored energy in the parking brake accumulator is exhausted.
If there is a failure of the oil supply from piston pump (10), check valve (1bb) in main control valve (1) seats. The check valve maintains the pressure in the line to parking brake accumulator (4) .
Oil pressure in the line to the parking brake moves the contacts of pressure switch (2). This turns off the indicator in the cab.
Component Locations
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| Illustration 3 | g01107694 |
Parking brake (18) is located in the drive line in front of the center axle. | |
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| Illustration 4 | g01107695 |
Accumulator (15) is located beneath a panel and between the hydraulic tank and the battery box on the left side of the machine. | |
For the locations of the remaining components in the parking brake system, refer to Systems Operation, "Service Brake System".