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| Illustration 1 | g00843794 |
(1) Check valve (2) Makeup valve (3) Supply line (4) Return line | |
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| Illustration 2 | g00843795 |
(5) Return line from makeup valve (6) Supply line from makeup valve (7) Fan drive motor | |
Makeup valve (2) for fan drive motors (7) is located between the two fans on the radiator support beam.
Supply oil comes from the fan drive pump through supply line (3) to makeup valve (2). The supply oil goes through supply line (6) from makeup valve (2) to fan drive motors (7). Return oil from fan drive motors (7) goes through return line (5) and flows back to the makeup valve (2). The return oil flows from makeup valve (2) through return line (4) to the fan drive oil cooler. From the fan drive oil cooler, the oil flows through the fan drive oil filter to the fan drive oil tank. The return oil from fan drive motors (7) is also used as makeup oil in order to prevent a vacuum condition in the fan drive motors (7). This condition happens when the fan slows and/or the fan stops.
When the fan drive pump slows down, the supply of oil to fan drive motors (7) is reduced. Fan drive motors (7) continue to rotate because of the mass of the fan blade assembly. Continued rotation of fan drive motors (7) creates a vacuum in makeup valve (2). The vacuum causes a lower pressure in the makeup valve on the side of the oil supply. The combined force of the lower pressure on the side of the supply oil and the force of the spring in check valve (1) is less than the force of the pressure that is on the side of the return oil. This causes check valve (1) to open.
When check valve (1) is open, the return oil will flow back into makeup valve (2). The return oil enters the fan drive motors through line (5). This makeup oil circuit eliminates the possibility of cavitation in the piston motor.
The same process occurs when the machine is shut down.