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| Illustration 1 | g06017895 |
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(1) Swing motor
(2) Travel motors (3) Case drain line (4) Case drain line (5) Makeup line (makeup oil to swing motor) (6) Main control valve (7) Return passage (8) Negative flow control orifice (9) Center bypass passage (10) Center bypass passage (11) Return line (12) Return line (13) Negative flow control orifice (14) Return line (15) Return passage (16) Slow return check valve (17) Hydraulic oil cooler (18) Case drain line (19) Drive pump (20) Fan pump (21) Idler pump (22) Bypass check valve (23) Return filter (24) Case drain filter (Pump) (25) Pilot pump (26) Fan motor (27) Case drain filter (Fan motor, swing motors, and travel motors) (28) Hydraulic tank (29) Suction line (30) Case drain line | |
The oil delivery from idler pump (21) and drive pump (19) enters main control valve (6). 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 drive pump (19) flows through center bypass passage (10) and negative flow control orifice (13) to return line (11). Pump low-pressure standby oil from idler pump (21) flows through center bypass passage (9) and negative flow control orifice (8) to return line (12).
When any one of the joysticks and/or travel levers/pedals are 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 (15) to return line (12).
The return oil from return line (11) and return line (12) flows through return line (14) and slow return check valve (16).
When the oil temperature is low , most of the oil is returned through bypass check valve (22) to hydraulic tank (28). The remainder of the oil flows into oil cooler (17) and return filter (23) to hydraulic tank (28).
When the oil temperature increases, the rate of oil flow through bypass check valve (22) decreases. This causes the rate of oil flow through oil cooler (17) to increase.
Reference: For more information concerning the bypass check valve, refer to Systems Operation, "Bypass Valve (Return) (Bypass Check Valve)".
Case drain oil from idler pump (21), drive pump (19), pilot pump (25), and fan pump (20) flows into case drain line (30). Case drain oil from swing motor (1) and travel motors (2) flows into case drain line (3) and (4). The case drain oil from the motors combines and flows through the case drain line (18). All of the case drain oil from the pumps and the motors now flows through case drain filter (27) to hydraulic tank (28).
Makeup line (5) will route return oil to the inlet port of the swing motor if a vacuum condition occurs at the swing motor during swing stop.
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)"