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| Illustration 1 | g00602403 |
Schematic of Air Systems and Brakes (1) Air pressure gauge (2) Air control valve (service brake) (3) Flow check valve (4) Air relief valve (5) Valve (brake) (6) Pressure protection valve (7) Air block (8) Seat suspension (9) Valve (brake) (10) Wet tank (11) Dry tank (12) Reserve tank (13) Control valve (differential lock) (14) Parking and secondary brake control valve (15) Control valve (parking brake) (16) Air horn (17) Solenoid valve (air horn) (18) Parking brake (19) Air/hydraulic cylinder (tractor) (20) Double check valve (21) Air/hydraulic cylinder (scraper) (22) Quick release and holding valve (23) Double check valve (24) Air compressor governor (25) Air compressor | |
All of the brakes in the brake system are shoe type brakes. There is a brake at each wheel of the tractor and the scraper. These brakes are activated by air pressure in air/hydraulic cylinders (19) and (21) .
The system for the tractor-scraper is divided into two sections, air flow and oil flow.
The oil flow comes from the hydraulic brake system. The hydraulic brake system is actuated by air. The tractor has an air/hydraulic cylinder, brake lines and caliper assemblies. The scraper has an air/hydraulic cylinder, brake lines and caliper assemblies. Each air/hydraulic cylinder has a fluid reservoir. Maintenance of the fluid level is done separately.
Air extends the rod in the air chamber as the brake pedal is pushed. The air chamber pushes the cylinder piston. Piston movement sends oil through the lines into the caliper assemblies. Oil pushes on the back of the pistons at each caliper. The pistons push the pads (friction) against the brake discs.
When the brake pedal is released, the air pressure against the air/hydraulic cylinder is relieved. The piston is retracted and hydraulic oil pressure is released off the pistons for the caliper. The residual pressure valves (check valves) keep a 30 ± 10 kPa (4.5 ± 1.5 psi) back pressure on the pads in order to keep the pads against the discs. The pistons and pads are not returned by springs. The pistons and pads release the grip on the disc. The pads do not move away from the discs. No adjustment is needed when the pads begin to wear. The pads have little contact with the discs. The pads keep the discs clean.
The air flow comes from three air tanks (10) , (11) , and (12) . The air tanks are filled by air compressor (25) . Air compressor (25) sends air to air tanks (10) . The flow of air is divided into four separate circuits:
- Service brake
- Secondary brake
- Parking brake
- Accessory air circuit
Service Brake Circuit
When the brake pedal is pushed, pressurized air is sent from control valve (2) to double check valves (20) and (23) . The air then flows from the double check valves to the air/hydraulic cylinders.
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 (14) can be activated manually by the knob or parking and secondary brake control valve (14) 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 (14) . 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 (9) . The air then flows to double check valves (20) and (23) . The air now flows to the air/hydraulic cylinders.
Parking Brake Circuit
Parking brake control valve (15) is activated in two different ways. Parking brake control valve (15) 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 (15) to the parking brake actuator in parking brake (18) . The air pressure puts the spring of the brake actuator in compression. The parking brake is released.
Accessory Air Circuit
Air pressure for the accessory air circuit flows from control valve (2) to pressure protection valve (6) and air block (7) . When pressure protection valve (6) opens, air pressure is sent to the remainder of the accessory circuit.
The accessory circuit supplies air to the following components:
- Seat suspension (8)
- Differential lock control valve (13)
- Air horn (16)