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| Illustration 1 | g00547905 |
When the oil is cold, most of the return oil bypasses the oil cooler. When the oil temperature exceeds 55°C (131°F) the cooler bypass valve closes in order to block flow directly to the hydraulic tank.
The cooled return oil leaves the oil cooler. Then, the oil goes through the return oil filter and into the hydraulic tank.
Cooler Bypass Valve
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| Illustration 2 | g00547906 |
Engine compartment (5) Cooler bypass valve | |
Cooler bypass valve (5) is used to regulate the hydraulic oil temperature. The valve is also designed to act as a relief valve in the event of the cooler is plugged.
The cooler bypass valve includes a cartridge and a piston. The expansion element is held in the piston by a spring and a circlip. A second spring encloses the spring plate. The spring projects into the chamber.
An adjustment screw is provided on the end of the valve housing. Turning the screw changes the piston position. The cooler bypass is now closed and the oil is forced through the cooler. The proper operation of the cooler bypass valve can be checked by using the adjustment screw.
All return oil that flows through the return oil manifold forces the thermo-element against the force of the springs. Play in the thermo-element allows the hydraulic oil to bypass the cooler. Oil enters the chamber and flows around the expansion element that is located above the thermo-element. At an approximate oil temperature of 50°C (122°F), the expansion element begins to expand. The expanding element compresses the one spring while the other spring is moved closer to the housing. This reduces free play of the spring. When the oil temperature reaches approximately 55°C (131°F), the piston closes the initial play. The hydraulic oil now flows through the oil cooler.
When the maximum pressure in the oil cooler is exceeded due to a plugged core, the cooler bypass valve acts as a relief valve. In this operation, the oil forces thermo-element against the forces of the springs. The oil can now flow to the return oil filter and to the hydraulic tank.