VALVE GP-MAIN CONTROL 1186809 - Caterpillar

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(30) Pilot and braking pump
(31) Steering pump The pilot system has a two section gear type pump. The two pump sections are: pilot and braking pump (30) and steering pump (31). The pumps use the hydraulic tank as a common reservoir. Pilot and braking pump (30) supplies oil for the parking brake, service brake, and the pilot oil for the steering and implement systems. Steering pump (31) supplies oil for the operation of the steering system to turn the machine.Reference: For more information on the steering system, refer to Systems Operation, Testing and Adjusting, Steering System.Reference: For more information on the braking system, refer to Systems Operation, Testing and Adjusting, Braking System.
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(25) Brake accumulator charging valve
(38) Check valve Oil for the parking brake, service brake and pilot systems is drawn from hydraulic tank (34) to pilot and braking pump (30). The oil then flows through check valve (38) to brake accumulator charging valve (25).Brake accumulator charging valve (25) has two functions. Brake accumulator charging valve (25) maintains the pressure in the brake accumulator at a constant range while the engine is running. Also brake accumulator charging valve (25) divides pump flow between the brake accumulator system and the pilot system.
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(35) Pilot relief valve
(37) Pilot oil filter Oil flows from brake accumulator charging valve (25), through pilot oil filter (37) to pilot relief valve (35). Pilot relief valve (35) maintains the pilot system at a constant pressure, pilot relief valve (35) relieves excessive pilot system pressure through a line to the hydraulic tank (34).
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(27) Check valve
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(21) Selector and pressure control valve The pilot oil flows through check valve (27) to selector and pressure control valve (21).While the brake and pilot pump is supplying oil to the pilot oil system, selector and pressure control valve (21) will block the flow of alternate oil into the pilot oil system.If the brake and pilot pump fails, or oil is not available, then selector and pressure control valve (21) will allow alternate oil to flow into the pilot oil system from the steering system and the main hydraulic system. When the engine is off, selector and pressure control valve (21) provides pilot oil to pilot control valve (24) via implement and steering solenoid valve (12) to lower the bucket. High pressure oil from the head end of lift cylinders (6) enters the pilot system through selector and pressure control valve (21). The selector and pressure control valve (21) reduces the oil pressure and lets lower pressure oil flow to pilot control valve (24) via implement and steering solenoid valve (12). When pilot control valve (24) is moved to the LOWER position, pilot oil flows to the lift spool in main control valve (1). The lift spool moves to the LOWER position allowing the bucket to be lowered.
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(12) Implement and steering solenoid valve Oil from check valve (27) also flows to implement and steering solenoid valve (12).When the implement and steering solenoid valve (12) is energized, pilot oil