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| Illustration 1 | g06607374 |
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Main control valve return circuit (1) Hydraulic oil cooler (2) Line to the oil cooler inlet (3) Main control valve (4) Swing motor (5) Makeup line (makeup oil to swing motor) (6) Hydraulic tank (7) Return line to the hydraulic tank (8) Return check valve (9) Line from the oil cooler outlet | |
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| Illustration 2 | g06607400 |
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Return check valve (A) From main control valve (B) To hydraulic oil cooler (C) From hydraulic oil cooler (D) To hydraulic tank (10) Bypass check valve (11) Return check valve | |
Return check valve (8) is made up of two check valves, return check valve (11), and bypass check valve (10). Return check valve (11) is located between the main control valve and the hydraulic tank in the return circuit. The return check valve restricts the return oil flow. This restriction causes a pressure increase in the return passage in the main control valve. Makeup line (5) connects directly to this return passage.
If cavitation occurs in the swing motor, oil from the main control valve return passage flows into makeup line (5). This makeup oil is supplied to the inlet port of the swing motor to stop cavitation in the swing motor.
Note: For more information on the makeup operation, refer to System Operation , "Relief Valve (Swing)".
The return oil that flows through the return check valve is divided into two flow paths. A portion of the oil flows through port (B) to hydraulic oil cooler (1). The oil flow exiting the hydraulic oil cooler flows to port (C) and through port (D) to the return filter in the hydraulic tank. The remainder of the return oil flows through bypass check valve (10).
When the temperature of the return oil is low, the viscosity of the oil is high. The thickness of the oil results in high flow resistance within the cooler (1). Thus, the pressure of the oil in port (B) is high.
As a result of the high pressure of the return oil, bypass check valve (10) opens. Most of the return oil flows through the bypass check valve, through port (D), and to the return filter in the hydraulic tank. The remainder of the oil flows through port (B) to the hydraulic oil cooler. Since a small amount of the return oil flows to the oil cooler, the temperature of the oil increases.
As the oil temperature increases, the return oil pressure decreases. Bypass check valve (10) begins to close. A greater portion of the return oil flows to the hydraulic oil cooler. Bypass check valve (10) maintains the hydraulic oil at the optimum operating temperature.