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| Illustration 1 | g00869232 |
Pump regulator (1) Swashplate (2) Outer spring (3) Inner spring (4) Swing boom pump (5) Passage (6) Piston (7) Piston (8) Passage (10) Piston (11) Piston (12) Passage (13) Passage | |
The main pump output varies from maximum output to minimum output according to the load on the machine. The angle of the swashplate determines the actual output of the main pump.
Swashplate at Maximum Angle
When the machine is not operating, the swashplate is maintained at a maximum angle by springs (2) and (3). During machine operation, the swashplate angle is varied according to the delivery pressure of the pumps and the load on the machine.
The delivery pressure from the right pump acts on piston (11) through passage (12). The delivery pressure from the left pump acts on piston (6) through passage (5) and inner passage (8) of piston (7). The force that acts on pistons (6) and (11) attempts to reduce the inclined angle of swashplate (1) against the force of springs (2) and (3). The force of springs (2) and (3) is always against the total delivery pressure from the three pumps.
When the load on the machine is light, the delivery pressure from the right pump and the left pump is low and spring (2) is not compressed by the force of pistons (6) and (11). Therefore, the swashplate maintains the maximum angle, and the pump output is maintained at the maximum flow.
Swashplate at Minimum Angle
As the load on the machine increases, pressure in passages (5) and (12) increases. The force that tries to reduce the swashplate angle also increases, and spring (2) begins to be compressed. If the pressure in passages (5) and (12) increases further, spring (3) will also begin to be compressed. When the springs are completely compressed, the swashplate will be at the minimum angle, and the pump will output the minimum flow.
The swashplate is held at a position that balances the output of the right pump, the left pump, and the swing pump. Therefore, the hydraulic horsepower is constant regardless of the load on the machine.
Constant Horsepower
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| Illustration 2 | g00833197 |
After the main pump reaches the destroke point, pump output and hydraulic horsepower are nearly constant. (1) Destroke point (2) P-Q characteristic curve | |
The curve in Illustration 2 indicates the relationship between pump flow and delivery pressure. The p-q characteristic curve is established under the following conditions: The right pump delivery pressure (P1) is added to the left pump delivery pressure (P2). Right pump delivery pressure (P1) is equal to left pump delivery pressure (P2).
The swashplate angle in the main pump is changed by the combined delivery pressure of the right pump and the left pump. As the total delivery pressure increases, output flow (Q) begins to decrease from point (1). Below point (1), pump output is nearly constant at any given point in order to maintain a constant hydraulic horsepower.