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| Illustration 1 | g01383923 |
General Hydraulic System (1) Flow compensator spool (2) Pressure compensator spool (3) Bleed orifice (option) (4) Line to return filter in the hydraulic tank (5) Line to port "B"of cooler manifold (6) Generator motor (7) Relief valve (8) Flow control valve (9) Generator control solenoid (10) Generator pump (11) Bias piston cavity (12) Line from hydraulic tank port "2" (13) Line to port "L1" on the auxiliary pump (14) Displacement piston cavity (15) Line to tee on the left propel pump (16) Generator manifold | |
When the engine is not operating, the bias piston spring forces the swashplate in the generator pump to a maximum angle. When the engine is started, the pump begins to produce flow. Supply oil is sent to the pressure compensator spool and to the flow compensator spool. These spools are inside the pump. Also, supply oil is sent out of port "B" of the pump and supply oil is sent to port "P" of the generator manifold.
When the generator is not operating, the generator control solenoid is de-energized. In this situation, supply oil is blocked at the spool of the generator control solenoid. As pressure increases in the system, supply pressure forces the flow compensator spool to shift against the combined force of the margin spring and signal pressure. This shift sends some of the oil into the displacement piston cavity. This causes the pump to destroke. As the swashplate angle decreases, the displacement piston uncovers a passage for oil to flow from the displacement piston cavity and into the pump case.
At this point, supply pressure decreases, and the combined force from the margin spring and signal pressure causes the flow compensator spool to shift. This shift closes the passage for the supply oil to the displacement piston cavity. As a result, the swashplate angle increases. Eventually, the load sensing spool reaches equilibrium, and the pump operates at low pressure standby. At low pressure standby, the pump produces the flow needed in order to makeup for any system leakage. System pressure at low pressure standby is equal to signal pressure plus margin pressure.
Note: Low pressure standby is not independently adjustable. Low pressure standby may vary from one machine to another machine. Also, low pressure standby may vary in the same pump as system leakage or pump leakage increases.
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| Illustration 2 | g01383934 |
General Hydraulic System (1) Flow compensator spool (2) Pressure compensator spool (3) Bleed orifice (option) (4) Line to return filter in the hydraulic tank (5) Line to port "B"of cooler manifold (6) Generator motor (7) Relief valve (8) Flow control valve (9) Generator control solenoid (10) Generator pump (11) Bias piston cavity (12) Line from hydraulic tank port "2" (13) Line to port "L1" on the auxiliary pump (14) Displacement piston cavity (15) Line to tee on the left propel pump (16) Generator manifold | |
When the generator control switch is in the ON position, the generator control solenoid is energized. Pump supply oil flows through the flow control valve and across the generator control spool. The flow control valve can be adjusted in order to control the frequency of the generator.
Downstream from the generator control spool, supply oil is sent out of port "A" to the pump controls. Also, supply oil is sent out of port "A" of the generator valve and supply oil is sent to the generator motor. As the pump supply oil attempts to overcome the restriction of the generator motor, the pressure in the load sensing line increases. This increased signal pressure is transmitted to the flow compensator spool that is in the pump. This causes the spool to shift. The shift closes the passage for the supply oil to go to the displacement piston cavity, and the swashplate angle increases.
The generator motor begins to turn. Generator operation produces power in the high voltage circuits. Eventually, the system reaches equilibrium. At this point, the pump flow is held at a level which is adequate to fulfill the system load and the system flow requirements.
If the signal pressure reaches the setting of the pressure compensator spring, the pressure compensator pilot valve opens. The compensator pressure is set at 25000 ± 690 kPa (3625 ± 100 psi). When this valve opens, the load sensing pressure is limited. This action causes the pump to destroke until equilibrium is again established.
If the pressure reaches 28960 kPa (4200 psi) during operation, the relief valve opens. This relief valve is a fast acting valve. The valve quickly relieves pressure in the system. The valve prevents the generator from surging.