TUBE AS 2893790 - Caterpillar

Illustration 1 g00857629
Main Hydraulic Schematic (1) Tilt control lever (2) Lift control lever (3) Tilt cylinder (4) Lift cylinders (5) Shuttle valve (6) Resolver valve (7) Orifice 1.6mm (8) Main control valve (9) Accumulators (ride control) (10) Diverter valve (11) Shuttle valve (diverter valve) (12) On/off valve (diverter valve) (13) Tilt spool (14) Line relief valve (dump) (15) Line relief valve (tilt back) (16) Pilot accumulator (17) Combination valve (18) Float valve (19) Lift spool (20) Line relief valve (raise) (21) Main relief valve (22) Pilot and braking pump (23) Hydraulic tank (24) Implement pump (Tandem)The main hydraulic system is a combination of a series circuit and a parallel circuit. The hydraulic control system is typically a series circuit. However, internal passages and check valves in the tilt control valves allow some parallel oil flow. There are separate circuits for each of the implement hydraulic cylinders on the machine.The tilt control valves have two relief valves (one relief valve for each end of the cylinder). The two control valves also have load check valves in the cylinder lines. The lift control valve has a line relief valve in the cylinder head end line. The rod end line uses the main pressure relief valve for circuit protection.When the control levers are placed in the HOLD position, the position of the pilot valves blocks the flow of pilot oil. Pilot oil can not flow to the control valves, and the control levers are held in the center position (HOLD position) by springs.The implement hydraulic system has a resolver (6) in the lines of the lift circuit. Therefore, movement of the work tool is still possible when the engine is stopped. Because of the check valves, the weight of the load allows oil to flow in the lift circuit. The bucket can be lowered without the engine.Implement pump (24) provides the oil that operates the lift cylinders and the tilt cylinders. The oil flows to main control valve (8). Main control valve (8) is an open centered valve with two spools. One spool is for the lift functions and the other spool is for the tilt functions. When the valve spools are in the HOLD position, the oil flows through main control valve (9) and back to hydraulic tank (23) .Main relief valve (21) is for the flow of oil from implement pump (24). The excess oil flows back to the hydraulic tank. Oil for the case drain circuit flows through the filter screen in hydraulic tank (23) .The