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| Illustration 1 | g06070146 |
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(1) Makeup line (makeup oil to swing motor)
(2) Swing motor (3) Travel motors (4) Return passage (5) Main control valve (6) Return passage (7) Return passage (8) Bypass check valve (9) Hydraulic oil cooler (10) Slow return check valve (11) Case drain line (12) Negative flow control orifice (13) Negative flow control orifice (14) Center bypass passage (15) Return passage (16) Center bypass passage (17) Case drain line (18) Return passage (19) Case drain line (20) Return line (21) Case drain filter (22) Return filter (23) Hydraulic tank (24) Case drain line (25) Pilot pump (26) Drive pump (27) Suction line (28) Idler pump | |
The oil delivery from idler pump (28) and drive pump (26) enters main control valve (5). The oil then flows to return line (4) and return passage (7) 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 (26) flows through center bypass passage (14) and negative flow control orifice (12) to return passage (4). Pump low-pressure standby oil from idler pump (28) flows through center bypass passage (16) and negative flow control orifice (13) to return passage (7).
When any one of the joysticks and/or travel levers/pedals is shifted from the NEUTRAL position, center bypass passages (14) and/or (16) are blocked. The return oil from the cylinders and/or motors now flows through return passage (18) and/or return passage (15) to return line (20).
The return oil from return passage (4) and return passage (7) flows through slow return check valve (10) and return line (20).
When the oil temperature is low, most of the oil is returned through bypass check valve (8) to hydraulic tank (23). The remainder of the oil flows into oil cooler (9) and return filter (22) to hydraulic tank (23).
When the oil temperature increases, the rate of oil flow through bypass check valve (8) decreases. An increase in oil temperature causes the rate of oil flow through oil cooler (9) to increase.
Reference: For more information concerning the bypass check valve, refer to Systems Operation, "Bypass Valve (Return)".
Case drain oil from idler pump (28), drive pump (26), and pilot pump (25) flows into case drain line (24). Case drain oil then flows from line (24) to case drain filter (21) and into hydraulic tank (23). Case drain oil from swing motor (2) and travel motors (3) flows into respective case drain lines (11) and (17). The case drain oil then combines and flows through case drain line (19). The case drain oil from case drain line (19) then flows through case drain filter (21) and into the hydraulic tank.
Makeup line (1) will route return oil to the inlet port of swing motor (2) if a vacuum condition occurs during swing stop.
For more information concerning the makeup operation of the return hydraulic system at swing motor (2), 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)"