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| Illustration 1 | g00602519 |
Schematic of Air Systems and Brakes (1) Air pressure gauge (2) Control valve (service brake) (3) Flow check valve (4) Air relief valve (5) Valve (brake) (6) Valve (brake) (7) Reserve tank (8) Wet tank (9) Parking and secondary brake control valve (10) Parking brake control valve (11) Dry tank (12) Parking brake (13) Air/hydraulic cylinder (tractor) (14) Double check valve (15) Air/hydraulic cylinder (scraper) (16) Quick release and holding valve (17) Double check valve (18) Air compressor governor (19) Air compressor | |
Service Brake Circuit
When the brake pedal is pushed, pressurized air is sent from control valve (2) to double check valves (14) and (17). The air then flows from the double check valves to the air/hydraulic cylinders.
Control Valve (Service Brake)
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| Illustration 2 | g01043145 |
(20) Delivery ports (21) Supply ports (22) Exhaust port | |
The service brake control valve is located underneath the operator compartment. The valve is directly connected to the service brake pedal.
The service brake control valve is actuated by the service brake pedal. When the service brake pedal is depressed the service brake control valve opens. The valve delivers air to the relay valves. The main supply for the valve comes from the air tanks on the tractor. There are two air tanks on the scraper that supply air to the valve in the event of a loss of air pressure. Exhaust port (22) will evacuate air when the brakes are released. This will allow the machine to move. The service brake control valve is the main control valve for the brake system.
Valve (Brake)
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| Illustration 3 | g01043146 |
(23) Piston (24) Spring (25) Control port (26) Delivery port (27) Exhaust passage (28) Valve (29) Supply port | |
During normal machine operation, air pressure flows to control port (25). The air pressure pushes up on piston (23). This forces spring (24) into compression. Valve (28) comes in contact with the valve body so that air flow is blocked from supply port (29) to delivery port (26). Delivery port (26) is now open to exhaust passage (27). When air is flowing from delivery port (26) to exhaust passage (27), the service brakes remain deactivated.
When there is a loss of air pressure in the brake system, the air pressure in control port (25) is released through this valve. Spring (24) pushes down on piston (23). This pushes valve (28) away from the valve body. Air pressure from the reserve air tanks now flows from supply port (29) and out delivery port (26). This delivers air pressure to the service brakes. The service brakes are now activated.
Double Check Valve
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| Illustration 4 | g01043150 |
Double Check Valve (30) Inlet passage (31) Outlet passage to housing assembly on the wheel brake (32) Shuttle (33) Inlet passage | |
A double check valve is connected to the scraper relay valve. When the brake pedal is depressed and the knob of the parking brake control valve is depressed, there is no air pressure at inlet passage (33). Air pressure from the brake control valve causes shuttle (32) to move to the right. Air pressure flows from outlet passage (31) to the housing assemblies in the wheel brakes of the scraper. This will activate the service brakes on the scraper.
When the brake pedal is released and the parking brake control valve is pulled to the OUT position, there is no air pressure at inlet passage (30). Air pressure through inlet passage (33) causes shuttle (32) to move to the left. The air pressure flows from outlet passage (31) to the housing assemblies in the wheel brakes of the scraper. This will activate the brakes on the scraper.
Secondary Brake Circuit
When there is air pressure in all of the air tanks, the service brakes can be used as secondary brakes. Parking and secondary brake control valve (9) can be activated manually by the knob or parking and secondary brake control valve (9) can be activated automatically when air pressure in the system is too low.
Air flows from air tanks (11) to parking and secondary brake control valve (9). The air holds the parking and secondary brake control valve in the OPEN position. The air then flows from the parking and secondary brake control valve to valves (brake) (5) and (6). The air then flows to double check valves (14) and (17). The air now flows to the air/hydraulic cylinders.
Parking Brake Circuit
Parking brake control valve (10) is activated in two different ways. Parking brake control valve (10) can be activated manually by the knob or the valve can be activated automatically when air pressure in the system is too low.
When there is no air pressure in the system, the knob on the valve is pushed out. There is no air pressure in the parking brake actuator. The spring force in the parking brake actuator keeps the brake activated.
After the engine is started and air pressure is at the correct pressure for operation, the knob on the parking brake control valve must be pushed in and held for a moment in the OFF position. Air pressure now flows from parking brake control valve (10) to the parking brake actuator in parking brake (12). The air pressure puts the spring of the brake actuator in compression. The parking brake is released.