FILM-FUSE 2389635 - Caterpillar

Illustration 1 g00802092
Parking and secondary brake valve in the ON position
(1) Passage from parking brake release pump section
(2) Relief valve
(4) Piston
(5) Air inlet passage
(6) Stem
(7) Drain passage to the front brake cooling circuit
(8) Drain passage to hydraulic tank
(9) Check valve
(10) Spring
(11) Outlet passage for the oil that releases parking brakes The parking and secondary brake valve is located on the right side of the truck frame near the hydraulic tank. The parking and secondary brake valve controls the flow of oil to the parking brakes. The parking and secondary brake control valve also provides the pilot oil for the hoist control valve.The parking brakes are applied by springs and released by hydraulic pressure. The engine must be in operation in order to have oil pressure in passage (1) from the parking brake release pump section.The parking brake reset valve, the air control valve for the parking brake, and the air control valve for the secondary brake are located in the cab. When either of these controls are in the ON position, air flow to air inlet passage (5) will be stopped. When there is no air flow to air inlet passage (5), spring (10) will keep stem (6) in place. This blocks the flow of oil from passage (1) to passage (11). When no oil flows to the parking brakes, a spring will apply the parking brakes.
Illustration 2 g00802093
Parking and secondary brake valve in the OFF position
(1) Passage from parking brake release pump section
(2) Relief valve
(4) Piston
(5) Air inlet passage
(6) Stem
(7) Drain passage to the front brake cooling circuit
(8) Drain passage to hydraulic tank
(9) Check valve
(10) Spring
(11) Outlet passage for the oil that releases parking brakes The air control valve for the parking brake and the air control valve for the secondary brake are located in the cab. When both of these controls are in the OFF position, air flow will be sent to air inlet passage (5). Air pressure forces piston (4) and stem (6) downward. When stem (6) moves downward, pressure oil from passage (1) enters passage (11). When this pressure oil flows to the brake housing, the pressure oil compresses a spring. This releases the parking brakes. Relief valve (2) limits system pressure.