Hydraulic Gear Pump for the Charge and Steering System
Location and Function
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| Illustration 1 | g00928284 |
(1) Gear pump (charge and steering) | |
Gear pump (1) is located on the right side of the engine. The gear pump is a fixed displacement pump that is mounted to the accessory drive on the engine.
The gear pump supplies oil to the following components:
- Steering system
- Fan motor
- Propel system
- Leveling blade system (if equipped)
Components of the Gear Pump
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| Illustration 2 | g00928698 |
(1) Pump (2) Relief valve (3) Priority valve (4) Load sense line from metering pump (5) Excess line to fan motor (6) Priority line to metering pump | |
The gear pump (charge pump) includes the following components:
(1) Pump
(2) Relief valve
(3) Priority valve
Priority valve (3) is a proportional valve. This valve acts as a pressure compensated flow divider. The priority valve divides the flow between the metering pump (steering circuit) and the fan motor (charge circuit). The priority valve will deliver adequate flow to the metering pump (steering circuit) before the flow is allowed to go to the fan motor (charge circuit). The return flow from the metering pump (steering circuit) returns into the charge circuit.
The pressure in the steering system is regulated by relief valve (2). See Specifications, Systems Operation/Testing and Adjusting, "Relief Valve (Steering) - Test and Adjust" for the correct pressure setting. Consequently, this is the maximum pressure that will be produced in the steering circuit.
Operation and Oil Flow
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| Illustration 3 | g00934703 |
Hydraulic Schematic for a Right Turn (1) Gear pump (steering and charge) (2) Relief valve (3) Priority valve (4) Excess line to the fan motor (5) Load sense line from the metering pump (6) Priority line to the metering pump (7) Valve envelope (8) Pilot input (9) Pilot input (10) Valve envelope (11) Valve envelope (AA) System pressure (AB) Sump (AC) Activated components (AD) Load sense (AE) First pressure reduction (load sense) | |
The steering pump contains gear pump (1), relief valve (3), and priority valve (3). Gear pump (1) provides pressure oil to the following components: fan motor, metering pump, propel pumps and blade control valve (if equipped).
The gear pump is always turning when the engine is running. As a result, the gear pump is always delivering pressure oil to priority valve (3) when the engine is running. In a no turn condition, the pressure at pilot input (8) will increase. As a result, valve envelope (11) will become active and will send full oil flow to the fan motor.
Priority valve (3) is a pilot operated proportional valve. Consequently, when you turn the steering wheel demand for oil will be split between the fan motor and the metering pump. This is a result of an increase of the oil pressure at pilot input (9) when the pressure increases in the load sense line (5). With less demand from the metering pump, pilot pressure at pilot input (9) will decrease and pressure at pilot input (8) will increase. Extreme steering input at the steering wheel will result in a higher demand for oil at the metering pump. As a result, less oil will be going to the fan motor.
The hydraulic schematic in Illustration 3 shows a right hand turn. Valve envelope (7) is active. This will divide oil between the fan motor and the metering pump.
The flow to the fan motor will be reduced when the steering input is extreme. Valve envelope (10) will be activated if the steering input continues to be extreme. As a result, fan speed will be reduced.
Reference: See Specifications, Systems Operation/Testing and Adjusting, "Steering, Fan and Leveling Blade System" for more information.
If the pressure in the steering system increases to the pressure setting for relief valve (2), the valve will open. This will cause the excess pressure to escape to the suction side of gear pump (1) .