CYLINDER GP-HYDRAULIC 1718124 - Caterpillar

Service brake circuit
Engaging the Service Brakes
When the brake pedal is pushed, pressurized air is sent from service brake control valve (17) to relay valves (25) and (32). This air pressure opens relay valves (25) and (32). When relay valve (25) is opened, air from the tractor air reservoir (5) will flow to tractor brake actuators (24). When relay valve (32) is opened, air from the scraper air reservoirs (37) will flow to scraper brake actuators (29). The service brakes for the tractor and the scraper are now engaged.The machine can be stopped in an emergency by pulling the knob on the parking and secondary brake control valve (ON position). The flow of air pressure through parking and secondary control valve is stopped. This causes quick release and holding valves (26) and (39) to move to the RELEASED position. This removes the air pressure from the parking and secondary brake chambers of brake actuators (24) and (29). The parking and secondary brake spring force in the brake actuators causes the brake to activate.Disengaging the Parking Brakes for the Tractor by using the Service Brakes
The service brakes can be used in order to disengage the parking brakes for the tractor. When the brake pedal is pushed, pressurized air is sent from service brake control valve (17) to double check valve (22). The air pressure forces the double check valve to the right. Next, the air flows to quick release and holding valve (26). The air then flows to tractor brake actuators (24). The air pressure will compress the spring that is inside of tractor brake actuator (24). The parking brakes for the tractor are now disengaged.Disengagement of the Parking Brake for the Scraper by using the Service Brakes
The service brakes can be used in order to disengage the parking brakes for the scraper. When the brake pedal is pushed, pressurized air is sent from service brake control valve (17) to scraper relay valve (32). Scraper relay valve (32) delivers the air to double check valve (38). The air pressure forces the double check valve to the right. Next, the air flows to quick release and holding valve (39). The air then flows to scraper brake actuators (29). The air pressure will compress the spring that is inside of scraper brake actuator (29). The parking brakes for the scraper are now disengaged.Parking and Secondary Brake Circuit
The Parking brake control can be activated manually by the knob or the parking brake control can be activated automatically when air pressure in the system is too low.Automatic Operation
When there is no pressure or low pressure in the air system, air pressure sensors (2), (6), and (31) will send a signal to the tractor transmission control. The transmission control will send a signal to the parking brake control. The signal will cause the parking brake control to engage. When the parking brake control is pulled upward, the parking brake control is in the ENGAGED position. Also, the transmission control will send a signal to parking