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| Illustration 1 | g01624075 |
(1) Swing motor (2) Case drain line (3) Case drain line (4) Travel motors (5) Main control valve (6) Case drain line (7) Return passage (8) Negative flow control orifice (9) Center bypass passage (10) Center bypass passage (11) Return line (12) Negative flow control orifice (13) Return line (14) Return passage (15) Return line (16) Slow return check valve (17) Hydraulic oil cooler (18) Case drain line (19) Drive pump (20) Idler pump (21) Pilot pump (22) Fan pump (23) Fan motor (24) Bypass check valve (25) Case drain filter (Fan motor, swing motors, and travel motors) (26) Hydraulic tank (27) Return filter (28) Case drain filter (Pump) (29) Case drain line (30) Suction line | |
The oil delivery from idler pump (20) and drive pump (19) enters main control valve (5). The oil then flows to return passage (7) and return line (11) in one of the following manners.
When all joysticks and/or travel levers/pedals are in the NEUTRAL position, pump low pressure standby oil from idler pump (20) flows through center bypass passage (9) and negative flow control orifice (8) to return line (13). Pump low pressure standby oil from drive pump (19) flows through center bypass passage (10) and negative flow control orifice (12) to return line (11) .
When any one of the joysticks and/or travel levers/pedals is shifted from the NEUTRAL position, center bypass passages (10) and (9) are blocked. The return oil from the cylinders and/or motors now flows through return passage (14) to return line (13) .
The return oil from return line (11) and return passage (7) flows through return line (13) and slow return check valve (16) .
When the oil temperature is very low, most of the oil is returned through bypass check valve (24) to hydraulic tank (26). The remainder of the oil flows into oil cooler (17) and return filters (27) in hydraulic tank (26) .
When the oil temperature increases, the rate of oil flow through bypass check valve (24) decreases. This causes the rate of oil flow through oil cooler (17) to increase.
ReferenceFor more information concerning the bypass check valve, refer to Systems Operation, "Bypass Valve (Return) (Bypass Check Valve)".
Case drain oil from idler pump (20), drive pump (19), pilot pump (21), and fan pump (22) flows into case drain line (29). Case drain oil from swing motors (1) flows into respective case drain lines (3) and (2). The case drain oil from the swing motors and the travel motors flows through case drain line (18) and combines with the case drain oil from fan motor (23). All of the case drain oil from the motors now flows through case drain filter (25) to hydraulic tank (26) .
Makeup oil to the swing motors is supplied through the swing control valves. If a vacuum condition occurs at the swing motors during a swing stop the makeup oil will flow from the hydraulic tank through the swing control valves to the swing motors.
For more information concerning the makeup operation of the return hydraulic system at the swing motor, refer to the following sections in this manual.
- Systems Operation, "Check Valve (Return Makeup)"
- Systems Operation, "Oil Makeup (Swing System)"
- Systems Operation, "Relief Valve (Swing)"