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| Illustration 1 | g01514626 |
Schematic of the hydraulic fan motor (1) Inlet port from the hydraulic fan pump (2) Hydraulic fan motor (3) Outlet port to the hydraulic oil cooler (4) Check valve (5) Case drain line to the hydraulic oil tank | |
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| Illustration 2 | g00910588 |
Typical diagram of a gear motor | |
High pressure oil from the hydraulic fan pump flows into inlet port (1). The pressurized oil causes the motor shaft to rotate. The oil exits fan motor (2) through outlet port (3) .
Gear motors operate because of a pressure differential. The differential is between the inlet and the outlet of the motor. The pressure differential acts across the gear teeth. This creates a force that rotates the gear.
There are two paths around the gear. One path is around the outside of the gears. The other path is through the intersection of the gears. The pressure works against the area of one tooth. A gear motor has two tooth forces working in one direction and one tooth force working in the opposite direction. The result of the force causes the output shaft to rotate.
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| Illustration 3 | g00912909 |
View of the area of one tooth | |
The resistance of the fan blade causes an increase of pressure at the motor inlet. This causes a higher pressure differential across the motor and across each tooth. The arrow in Illustration 3 shows the area of a tooth. The oil pressure times the area of one tooth determines the one tooth force that is developed. The tooth force that is multiplied by distance A will equal the torque that is developed. Dimension A shows the distance from the center of the shaft to the tooth.
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| Illustration 4 | g01514640 |
Rear view of a gear motor | |
Check valve (4) allows the reverse flow of oil through hydraulic fan motor (2).
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| Illustration 5 | g01514642 |
Typical view of a makeup valve (1) Fan motor inlet (3) Fan motor outlet (4) Check valve | |
Note: Illustration 5 shows the makeup valve during normal operation of the motor.
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| Illustration 6 | g01514643 |
Typical View of a Makeup Valve (1) Fan motor inlet. (3) Fan motor outlet. (4) Check valve. | |
Note: Illustration 6 shows the movement of check valve (4) as the fan motor is going into shutdown.
The gear motor is equipped with a makeup valve. The makeup valve will allow oil that is exiting the hydraulic motor to return to the motor inlet during the reduction of flow from the pump or a complete shutdown. If the pressure at outlet line (3) is higher than the pressure in inlet line (1), oil will open check valve (4). The oil will flow through check valve (4) and back to inlet (1). The makeup valve eliminates cavitation of the fan motor (2) during reduced oil flow. The return oil from hydraulic fan motor (2) is used as makeup oil in order to prevent a vacuum condition in hydraulic fan motor (2). This condition happens when the fan slows and/or the fan stops. When the hydraulic fan pump slows down, the supply of oil to fan motor (2) is reduced. Fan motor (2) will continue to rotate because the resistance of the air that is being pushed through the radiator is not strong enough to stop the fan blade from turning fan motor (2). Continued rotation of fan motor (2) creates a vacuum in the makeup valve. The vacuum causes a lower pressure in fan motor inlet (1). The combined force of lower pressure in fan motor inlet (1) and the force of spring is below than the force of the pressure of the return oil in fan motor outlet (3). Check valve (4) will open.
ReferenceFor additional information about the specifications for the hydraulic fan motor, refer to the Service Manual module Specifications, "Gear Motor (Hydraulic Fan)" for the machine that is being tested.
ReferenceFor additional information about testing and adjusting the fan motor, refer to the Service Manual module Testing and Adjusting, "Hydraulic Fan Speed - Test and Adjust" for the machine that is being tested.