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| Illustration 1 | g06602656 |
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(1) Hydraulic oil cooler
(2) Return check valve (3) Bypass check valve (4) Return passage (5) Makeup line (makeup oil to swing motor) (6) Center bypass passage (7) Return passage (8) Orifice (9) Parallel feeder passage (10) Pump 2 (11) Pump 1 (12) Case drain filter (13) Return filter (14) Hydraulic tank (15) Pressure port (pump 1) (16) Pressure port (pump 2) (17) Return passage (18) Return passage (19) Parallel feeder passage (20) Center bypass passage (21) Orifice (22) Main control valve (23) Return passage (24) Right travel motor (25) Left travel motor (26) Swing motor (27) Return passage (28) Case drain line | |
Oil flow from pump 1 (11) and pump 2 (10) enters main control valve (22) at ports (15) and (16). The oil then flows to return line (4) and return passage (18) 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 pump 1 flows through center bypass passage (6) and orifice (8). The oil then flows to return passage (7), to passage (4), and return passage (27). Pump low-pressure standby oil from pump 2 flows through center bypass passage (20) and orifice (21). The oil then flows to return passage (23) and return passage (27).
When any one of the joysticks and/or travel levers/pedals is shifted from the NEUTRAL position, center bypass passages (6) and/or (20) are blocked. The return oil from the cylinders and/or motors now flows through return passage (4) and/or return passage (18) to return passage (27).
When the oil exits the main control valve at return passage (27) the oil passes through return check valve (2). From there, the oil can either flow through bypass check valve (3) back to the hydraulic tank or to hydraulic oil cooler (1) and to the tank.
When the oil temperature is low, most of the oil is returned through the bypass check valve (3) to the hydraulic tank. The remainder of the oil flows into the oil cooler (1) and return filter (13) in the hydraulic tank.
When the oil temperature increases, the rate of oil flow through bypass check valve (3) decreases. An increase in oil temperature causes the rate of oil flow through the oil cooler to increase.
Reference: For more information concerning the bypass check valve, refer to Systems Operation , "Check Valve (Return Makeup)".
Case drain oil from pump 1 and pump 2 is teed into case drain line (28) along with case drain oil from swing motor (26) and travel motors (24) and (25). The oil then flows from the line into the hydraulic tank and case drain filter (12).
Makeup line (5) will route return oil to the inlet port of swing motor (26) if a vacuum condition occurs during swing stop. This oil helps prevent motor cavitation.
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 , "Relief Valve (Swing)"