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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 | g02161955 |
Bypass check valve (4) Valve (5) Return line to hydraulic tank (6) Line (return oil from the swing control valve) (7) Passage (return oil to bypass tube) (8) Port (return oil from the main control valve from right valve bank and neutral bypass valve) | |
When the temperature of the hydraulic oil is low, the viscosity of the hydraulic oil is high. This results in higher than normal oil pressure in the return system. Bypass check valve (1) regulates the flow of return oil in the return system in order to regulate the hydraulic oil temperature and return oil pressure.
Return oil from the swing control valve flows from line (6) to the bottom port of bypass check valve (1) to passage (7). Return oil from the main control valve flows into port (8) and combines with return oil from the swing control valve in passage (7). 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 will cause the return oil pressure in passage (7) to be greater than the oil pressure at normal operating temperature. The increased return oil pressure in passage (7) overcomes the force of the spring on the spool in valve (4). The spool in valve (4) moves toward the open position. This valve opening allows a portion of the return oil to flow through return line (5) and neutral flow control valve (3) to the hydraulic tank. This results in increased return oil flow to the hydraulic tank and decreased return oil flow to the hydraulic oil cooler. Since the amount of return oil flow to the hydraulic oil cooler is decreased, the temperature of the return hydraulic oil now raises to the normal operating range at a faster rate. The pressure of the oil in the return system is reduced.
As the temperature of the return oil increases, the return oil pressure in passage (7) decreases. The decrease in return oil pressure in passage (7) allows the force of the spring to move the spool in valve (4) toward the closed position. As the opening in valve (4) decreases, return oil flow to the hydraulic tank decreases and return oil flow to the hydraulic oil cooler increases. As a result, the hydraulic oil temperature is maintained at a moderate level.