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| Illustration 1 | g02162002 |
Main control valve (component location) (1) Slow return check valve (2) Return line to hydraulic tank (3) Bypass check valve | |
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| Illustration 2 | g02161987 |
Slow return check valve (4) Port (return oil from the main control valve from left valve bank) (5) Line (relief valve and makeup oil for swing motors) (6) Passage (return oil to bypass tube) (7) Valve (8) Return line to hydraulic oil cooler (9) Line (return oil from the fan motor) | |
Slow return check valve (1) regulates the flow of return oil in the return system in order to maintain a back pressure in the return oil system for quick operation of the makeup valves in the implement circuits.
Return oil from the swing relief valves flows from line (5) to slow return check valve (1). Return oil from the fan motor flows from line (9) to slow return check valve (1). Return oil from the main control valve flows into port (4) and combines with return oil from the swing relief valves and the fan motor. The increased return oil pressure in passage overcomes the force of the spring on the spool in valve (4). The spool in valve (7) moves toward the open position. This valve opening allows the return oil to flow through return line (8) to the hydraulic oil cooler. The cooled oil then flows to the return filters and the hydraulic tank.
When the temperature of the hydraulic oil is low, the viscosity of the hydraulic oil is high. The resistance to oil flow through the hydraulic oil cooler is high. This resistance results in higher than normal oil pressure in the return system at slow return check valve (1). Return oil will flow through passage (6) to the bypass tube. The bypass tube will direct oil to bypass check valve (3) to regulate the flow of return oil in the return system in order to regulate the hydraulic oil temperature.