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| Illustration 1 | g00786662 |
Hydraulic Fan Pump that is located on the Engine | |
The pump for the hydraulic fan is located on the front housing of the engine on the right side of the machine.
The hydraulic fan pump is a variable displacement piston pump that is driven by the drive gears of the engine.
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| Illustration 2 | g00669991 |
Piston Pump (Hydraulic Fan) (1) Housing. (2) Spring. (3) Control piston. (4) Piston. (5) Drive shaft. (6) Swashplate. (7) Retraction plate. (8) Cylinder barrel. (9) Valve plate. (10) Head. | |
The axial piston type pump is used to supply oil flow to the hydraulic fan motor. The movement of pistons (4) in the pump pulls oil from the hydraulic tank. The hydraulic oil is pressurized in the pump. The hydraulic oil is then forced to the hydraulic motor in order to rotate the fan.
When the engine is in operation and drive shaft (5) is rotating, the components that rotate are cylinder barrel (8), pistons (4), and retraction plate (7). There are nine piston assemblies in the barrel assembly. The components of the pump that remain are fastened to pump housing (1) .
When drive shaft (5) rotates,hydraulic oil from the tank is pulled into pump head (10) through the inlet passage. The oil then flows from the inlet passage through inlet passages in valve plate (9). Oil is then pulled into the openings of cylinder barrel (8). The hydraulic oil in the cylinder barrel is rotated. As the rotating group is turned the oil is pressurized by pistons (4) in cylinder barrel (8). The cylinder barrel rotates over the outlet passage in valve plate (9). The hydraulic oil is then forced out of the pump discharge port.
Each piston (4) inside cylinder barrel (8) is held against swashplate (6) by retraction plate (7). Swashplate (6) can be at any angle between the maximum angle and the neutral angle.
As shaft (5) rotates, pistons (4) follow the angle of swashplate (6). The angle of the swashplate controls the in and out movement of the pistons in cylinder barrel (8) .
The angle of swashplate (6) determines the amount of oil that is drawn into each cylinder barrel (8). As cylinder barrel (8) rotates, the swashplate angle pushes pistons (4) back into cylinder barrel (8). Pistons (4) will then push oil out of cylinder barrel (8). The oil then flows through the outlet passages of valve plate (9) .
Swashplate (6) can be at any angle between the neutral angle and the maximum angle. The neutral angle is perpendicular with drive shaft (5). When swashplate (6) is at the neutral angle, pistons (4) do not move in and out of rotating cylinder barrel (8). Therefore, no oil is drawn into the pump and no oil is pushed out of the pump. The pump has zero displacement and zero flow.
When swashplate (6) is at the maximum angle, pistons (4) move in and out of cylinder barrel (8). The in and out movement of pistons (4) allows the maximum amount of oil to be drawn in to cylinder barrel (8), and the pump will produce the maximum displacement.
The swashplate angle is controlled by control piston (3). The movement of the control piston (3) is regulated by oil pressure from the pressure and flow compensator valve.
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| Illustration 3 | g00796639 |
Pressure and Flow Compensator Valve (11) Flow compensator spool. (12) Spring. (13) Adjustment screw. (14) Pressure cutoff spool. (15) Passage for the discharge of the pump. (16) Passage to destroke piston. (17) Drain to tank. (18) Spring. (19) Adjustment screw. | |
The pressure and flow compensator valve is attached to the piston pump. The compensator valve receives a signal from the load sense port.
The pressure and flow compensator valve maintains the correct pressure and correct oil flow. The flow and pressure of the pump are maintained by either sending pump oil to control piston (3) or by draining the pump oil from control piston (3) .
The control piston (3) and spring (2) work together in order to adjust the angle of swashplate (6). The pressure and flow compensator valve prevents overloads of the pump.
To decrease the displacement of the pump, the oil that is behind control piston (3) must increase in pressure. The signal pressure and the force of spring (12) are less than the pump pressure in port passage (15). Flow compensator spool (11) is moved right. The oil that is behind control piston (3) can not flow to the case drain. Pump oil in port passage (15) now flows to port passage (16), and into control piston (3).
Pump pressure behind control piston (3) is now greater than the force of spring (2). The angle of swashplate (6) decreases. When the angle of swashplate (6) decreases, the output of the pump decreases. The pressure in port passage (15) becomes less than the combined force in the cavity and of spring (12). Flow compensator spool (11) moves left into the metering position.
If the signal pressure does not change, flow compensator spool (11) will remain in the metering position. When flow compensator spool (11) is in the metering position, the fan circuit is equalized.
To increase the displacement of the pump, the oil that is behind control piston (3) must be drained. Draining the cavity will allow the angle of swashplate (6) to increase. The signal pressure and the force of spring (12) move flow compensator spool (11) to the left which allows the oil behind control piston (3) to be drained. The force of spring (2) is now greater than the force behind control piston (3) and the angle of swashplate is increased. When the angle of the swashplate increases, the output of the pump increases.
The output increases until the outlet pressure to port (15) is high enough to move spool (11) to the right. Oil then flows through port (16) to control piston (3). The pressure of this oil overcomes the force of spring (2) and the pressure forces swashplate (6) to rotate counterclockwise. This causes a decrease in the swashplate angle, output, and pressure to port (15) .
When the pressure to port (15) is lower than the combined force of the signal pressure and spring (2), spool (11) moves to the left draining oil behind control piston (3). The oil drains to the case and the output increases. This movement of spool (11) (increasing and decreasing output) is known as metering.
Metering maintains a pump pressure that is 2100 ± 100 kPa (300 ± 15 psi) greater than signal pressure. The difference between pump outlet pressure and signal pressure is called margin pressure.
Reference: For specifications of the hydraulic fan pump, refer to the hydraulic system Specifications, "Piston Pump (Hydraulic Fan)" for the machine that is being serviced.