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| Illustration 1 | g00847805 |
Location of the Hydraulic Fan Pump | |
The hydraulic fan pump is mounted to the front engine housing on the right hand side of the machine.
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| Illustration 2 | g00721683 |
Operation of the pump and pressure and flow compensator valve (1) Adjustment for the pressure compensator spool (2) Cutoff spring (3) Adjustment for the flow compensator spool (4) Margin spring (5) Pressure and flow compensator valve (6) Passage to the thermostatic valve (7) Flow compensator spool (8) Pressure compensator spool (9) Actuator piston (10) Hydraulic fan pump (11) Bias spring (12) Pump outlet (13) Drive shaft (14) Pump inlet (15) Cylinder barrel assembly (16) Swashplate (17) Internal passage (LL) Sump oil | |
Hydraulic fan pump (10) has the following characteristics: variable displacement, load sensing, compensation for pressure and compensation for flow. This piston type pump has variable flow and pressure. The flow and pressure are dependent on the system demands that are sensed by pressure and flow compensator valve (5) .
When the engine is off, there is no signal (6) to pressure and flow compensator valve (5). Margin spring (4) pushes flow compensator spool (7) completely to the right. Any pressure that is behind actuator piston (9) is vented to the case drain across flow compensator spool (7) .
When there is no pressure behind actuator piston (9), bias spring (7) is able to hold swashplate (9) at the maximum angle.
When the engine is started, drive shaft (13) starts to rotate. Oil flows into the piston bore from pump inlet (14). Oil is forced out of pump outlet (12) and into the system as cylinder barrel assembly (15) rotates.
Upstroking
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| Illustration 3 | g00721094 |
Operation of the pump and pressure and flow compensator valve (4) Margin spring (5) Pressure and flow compensator valve (6) Passage to the thermostatic valve (7) Flow compensator spool (9) Actuator spool (12) Pump outlet (16) Swashplate (17) Internal passage (AA) Supply oil (DD) Signal oil (EE) Suction oil (LL) Sump oil | |
When the hydraulic fan circuit requires flow, the pressure from pump outlet (12) is reduced.
Passage (6) connects to the thermostatic valve. The thermostatic valve restricts the flow from the signal line to the tank. Supply oil (AA) flows through internal passage (17) to the left of the spool.
Margin spring (4) and signal oil (DD) apply a combined force to the left of spool (7). Supply oil (AA) also applies a force to the right of the spool. The force on the left is greater than the force on the right.
The spool moves to the right which blocks the flow of oil to actuator piston (9). Oil that is in the chamber for the actuator piston (9) is vented to the case drain across flow compensator spool (7). This allows bias spring (11) to move swashplate (16) to a greater angle.
The pump now produces more flow. This condition is known as "upstroking".
Reference: For additional information on the thermostatic valve, refer to Testing and Adjusting, "Hydraulic Fan System".
The following conditions can result in upstroking the pump:
- When the fan circuit is initially activated, the load sensing signal increases the output flow of the pump.
- The hydraulic fan pump will upstroke when the thermal relief valve closes due to the increase in temperature of the engine coolant.
- If the demand on the hydraulic fan system remains constant or the demand increases, the implement hydraulic pump will upstroke when the engine speed decreases.
Constant Flow
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| Illustration 4 | g00721673 |
Operation of the pump and pressure and flow compensator valve (3) Adjustment for the flow compensator spool (4) Margin spring (5) Pressure and flow compensator valve (6) Passage to the thermostatic valve (7) Flow compensator spool (9) Actuator piston (10) Hydraulic pump (11) Bias spring (12) Pump outlet (13) Adjustment for the flow compensator spool (16) Swashplate (17) Internal passage (AA) Supply oil (BB) Reduced supply oil (DD) Signal oil (EE) Suction oil (LL) Sump oil | |
When a constant flow of oil is demanded by the fan drive circuit, the supply oil pressure from pump outlet (12) will increase on the right side of flow compensator spool (7). The pressure on left side of flow compensator spool (7) is the sum of the following pressures: load sensing signal (6) and margin spring (4). Flow compensator spool (7) will meter the force on both ends of the spool. Once the forces become equal on each end of the spool the system will stabilize.
Swashplate (16) is held at a relative constant angle in order to maintain the required flow.
The difference between the pressure of load sensing signal (6) and the supply oil pressure is called margin pressure. Margin pressure is the value of margin spring (4) .
Margin pressure is 2000 ± 100 kPa (290 ± 15 psi). Margin pressure is adjusted by turning adjustment screw (3) on flow compensator spool (7) .
Destroking
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| Illustration 5 | g00721335 |
Operation of the pump and pressure and flow compensator valve (4) Margin spring (5) Pressure and flow compensator valve (6) Passage to the thermostatic valve (7) Flow compensator spool (9) Actuator piston (10) Hydraulic pump (11) Bias spring (12) Pump outlet (16) Swashplate (17) Internal passage (AA) Supply oil (BB) Reduced supply oil (DD) Signal oil (EE) Suction oil (LL) Sump oil | |
When less flow is required, hydraulic fan pump (10) destrokes. Hydraulic fan pump (10) destrokes when the force at the right of flow compensator spool (7) becomes greater than the force at the left.
Flow compensator spool (7) moves to the left which allows more oil flow to actuator piston (9). Pressure on actuator piston (9) is now increased.
The increased pressure overcomes the force of bias spring (11) which moves swashplate (16) to a reduced angle. When the pressure from pump outlet (12) matches the force at the left of flow compensator spool (7), the spool returns to a metering position. Implement hydraulic pump (10) will return to a constant flow.
The following conditions result in destroking the implement hydraulic pump:
- If the engine speed increases, the hydraulic fan pump destrokes.
- If the engine coolant temperature decreases enough, the thermostatic valve will open.
- If there is a slight reduction in the operating pressure, or there is a reduction in the built-in system leakage.
When implement hydraulic pump (10) destrokes, supply oil pressure from pump outlet (12) decreases on the right side of flow compensator spool (7). The pressure on the left side of flow compensator spool (7) is the sum of the following pressures: load sensing signal (6) and margin spring (4). Flow compensator spool (7) will meter the force on both ends of the spool. Once the forces become equal on each end of the spool the system will stabilize.