 | |
| Illustration 1 | g00955961 |
(1) 657E Scraper (2) Tractor (3) Operator's compartment (4) Scraper brake actuator (5) Retarder hydraulic control valve (6) Transmission pressure switch (7) Solenoid valve (air horn) (8) Pressure protection valve (9) Air control valve (service brake) (10) Scraper relay valve (11) Quick release and holding valve (12) Air tank (Scraper) (13) Retarder air control valve (14) Transmission pressure switch (15) Check valve (air tank) (16) Scraper hydraulic control valve (17) Solenoid valve (Differential lock) (18) Brake actuator (tractor) (two) (19) Solenoid valve (apron) (20) Parking and secondary brake control valve (21) Air pressure gauge (22) Quick release and holding valve (23) Pressure switch (Parking brake light) (24) Double check valve (25) Orifice (26) Quick release valve (Differential lock) (27) Relay valve (tractor) (28) Differential lock control (29) Retarder air control regulator (30) Air horn (31) Retarder hydraulic control valve (tractor) (32) Air compressor (33) Air compressor governor (34) Air dryer (attachment) (35) Check valve (air tank) (36) Air tank (tractor) (two) (37) Pressure switch (brake air) (38) One-way check valve (39) Air relief valve (air tank) (40) 651E Scraper | |
All of the brakes in the brake system are shoe type brakes. There is a brake at each wheel of the tractor and at each wheel of the scraper. These brakes are activated by air pressure in brake actuators (4) and (18). The brake actuators provide three types of brakes:
- Service
- Secondary
- Parking
Air compressor (32) sends air to air tanks (36) and air tank (12). The flow of air is divided into three separate circuits:
- Service brake
- Parking and secondary brake
- Accessory air circuits
Service Brake Circuit
When the brake pedal is pushed, pressurized air is sent from service brake control valve (9) through orifice (25) to relay valves (10) and (27). This air pressure opens relay valves (10) and (27). When relay valve (27) is opened, air from the tractor air reservoir (36) will flow to tractor brake actuators (18). When relay valve (10) is opened, air from tank (12) will flow to scraper brake actuators (4). The service brakes for the tractor and the scraper are now engaged.
The scraper brakes activate before the tractor brakes because of orifice (25) in the line to relay valve (27) .
When the service brakes are applied, air pressure from parking and secondary brake control valve (20) flows through the following components: double check valve (24), quick release and holding valves (11) and (22) and parking and secondary brake chambers of brake actuators (4) and (18). This releases the parking and secondary brakes. When the brake pedal is pushed before the parking and secondary brakes are released, double check valve (24) allows air pressure to go to quick release and holding valves (11) and (22) and to the parking and secondary brake chambers of brake actuators (4) and (18). This releases the parking and secondary brake in order to prevent the application of the parking and secondary brake in addition to the service brake. Releasing the parking and secondary brake prevents damage to the brake slack adjusters and the brake camshafts.
Parking and Secondary Brake Circuit
Parking and secondary brake control valve (20) can be activated in two ways. First, the valve may be activated manually by pulling up on the knob in the cab. The valve may also be activated automatically when air pressure in the system is too low.
When there is no pressure in the air system, the knob on the parking and secondary brake control valve is pulled up in the ON position. There is no air pressure in the parking and secondary brake chambers of brake actuators (18) and (4). The parking and secondary brake spring force in the brake actuators keeps the brakes activated.
After the engine is started and the air pressure is above 380 ± 35 kPa (55 ± 5 psi), the knob on the control valve must be pushed in and held for a moment in the OFF position. Air pressure now flows from parking and secondary brake control valve (20) to the following components: double check valve (24), quick release and holding valves (11) and (22) and parking and secondary brake chambers of brake actuators (4) and (18). The air pressure overcomes the spring force of the parking and secondary brake actuators. The parking and secondary brakes are released.
The machine can be stopped in an emergency by pulling the knob on the parking and secondary brake control valve (20) (ON position). The flow of air pressure through parking and secondary brake control valve (20) is stopped. This causes quick release and holding valves (11) and (22) to move to the RELEASED position. This removes the air pressure from the parking and secondary brake chambers of brake actuators (4) and (18). The force of the parking and secondary brake spring in the brake actuators causes the brakes to activate.
Accessory Circuits
Air pressure for the accessory air circuits goes from brake control valve (9) to pressure protection valve (8) and the air supply to retarder air control valve (13). The pressure protection valve opens at approximately 517 + 68 kPa (75 + 10 psi). This blocks the air pressure to the junction block. The remainder of the air pressure is saved for the brakes and for the retarder.
The flow of air is from the junction block to the following components: solenoid valve (17), air pressure gauge (21), solenoid valve (7) and solenoid valve (19) .
Air horn (30) is controlled by solenoid valve (7). When the air horn switch is pushed, solenoid valve (7) opens. This permits air pressure to go to air horn (30) .
Note: For more information on the air system and hydraulics for the retarder, see Systems Operation/Testing and Adjusting, "Retarder".