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| Illustration 1 | g02164126 |
Main control valve in the NEUTRAL position (1) Drain line (2) Passage (load sensing signal pressure) (3) Passage (pump flow) (4) Shuttle valve (5) Signal duplication valve (6) Orifice (7) Passage (pump flow) (8) Passage (pump flow) (9) Solenoid valve (neutral bypass) (10) Neutral flow control valve (11) Differential relief valve (12) Signal relief valve (low pressure) (13) Passage (pump flow) (14) Signal relief valve (high pressure) (15) Passage for true load signal pressure (16) Solenoid valve (high/low relief) for travel and stick (17) Passage (load signal pressure from the stick circuit) (18) Passage (load signal pressure from the left travel circuit) (19) Passage (load signal pressure from the right travel circuit) (20) Differential relief valve (21) Line relief valve (stick cylinder rod end) (22) Passage (return oil flow) (23) Line (return oil) (24) Hydraulic tank (25) Front pump (26) Rear pump (27) Passage for duplicate load signal pressure (28) Load signal selector valve (29) Load signal reduction valve | |
The following explanation of the limiting of circuit pressure is given for the stick circuit or the travel circuit. The limiting of circuit pressure in the boom circuit and the bucket circuit is performed in the same way.
The circuit pressure is limited while the main control valve is in the NEUTRAL position.
When the main control valve is in the NEUTRAL position, the machine is at a no-load condition. The machine ECM energizes solenoid valve (9) (neutral bypass). Pilot oil flows through solenoid valve (9) and to neutral flow control valve (10). The pilot oil shifts neutral flow control valve (10). Pump output pressure in passage (3), passage (7), and passage (8) flows to neutral flow control valve (10). The pump output pressure flows through neutral flow control valve (10) to the return system and hydraulic tank (24). At this time, the standby pressure of the pumps is maintained at approximately 1960 kPa (285 psi) by the load sensing regulators at the pumps. This pressure is the margin pressure setting of the load signal adjustment on the pump regulators.
Note: Margin pressure is the difference between pump system pressure and the load (working pressure) of the hydraulic system.
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| Illustration 2 | g02168694 |
Main control valve with travel control valves and stick control valve shifted (1) Drain line (2) Passage (load sensing signal pressure) (3) Passage (pump flow) (4) Shuttle valve (5) Signal duplication valve (6) Orifice (7) Passage (pump flow) (8) Passage (pump flow) (9) Solenoid valve (neutral bypass) (10) Neutral flow control valve (11) Differential relief valve (12) Signal relief valve (low pressure) (13) Passage (pump flow) (14) Signal relief valve (high pressure) (15) Passage for true load signal pressure (16) Solenoid valve (high/low relief) for travel and stick (17) Passage (load signal pressure from the stick circuit) (18) Passage (load signal pressure from the left travel circuit) (19) Passage (load signal pressure from the right travel circuit) (20) Differential relief valve (21) Line relief valve (stick cylinder rod end) (22) Passage (return oil flow) (23) Line (return oil) (24) Hydraulic tank (25) Front pump (26) Rear pump (27) Passage for duplicate load signal pressure (28) Load signal selector valve (29) Load signal reduction valve | |
The maximum circuit pressure is limited when the machine is at a load condition.
When the stick control spool is shifted or the travel control spool is shifted, signal relief valve (14) (HPC ON) or signal relief valve (12) (HPC OFF) limits the maximum load sensing signal pressure that is generated by the load sensing system. During a slow operation of the stick, and during a slow operation of the travel motors, the maximum pump discharge pressure will be maintained at 3000 kPa (435 psi) above the load sensing signal pressure by differential relief valves (11) and (20) .
When the joystick for the stick or the travel levers/pedals are operated, electrical signals are sent to the machine ECM. The machine ECM de-energizes solenoid valve (9) (neutral bypass). Neutral flow control valve (10) closes. The pump output pressure is blocked from flowing to the return system by neutral flow control valve (10). Movement of the stick cylinder or the travel motors will not occur until the pump discharge pressure increases high enough to open the load check valves in the stick circuit or the counterbalance valves on the travel motors.
The true load signal pressure increases rapidly in passages (17), (18), and (19). The pump delivery pressure increases rapidly in passage (7). The true load signal pressure flows to signal duplication valve (5). The signal duplication valve shifts to the right. The pump delivery pressure in passage (7) flows through signal duplication valve (5). Pump delivery pressure is restricted by orifice (6). The restricted pump delivery pressure begins to shift signal duplication valve (5) to the left. Signal duplication valve (5) restricts the flow of pump delivery pressure to be used for the duplicate load signal pressure. The duplicate load signal pressure becomes equal to the true load signal pressure. The duplicate load signal oil flows through orifice (6) in order to reduce any spikes in the signal network.
Solenoid valve (16) is used to select either signal relief (12) or signal relief (14) for limiting the duplicate load signal pressure. The duplicate load signal pressure flows through solenoid valve (16) to signal relief valve (12) during a travel or travel with implement operation. The machine ECM energizes solenoid valve (16) for implement-only operations. When solenoid valve (16) is energized, the duplicate load signal pressure flows through solenoid valve (16) to signal relief valve (14). Signal relief valve (14) limits the duplicate load signal pressure during implement-only operations. The duplicate load signal pressure is regulated by signal relief valve (12) or (14). The oil that passes through the signal relief valves flows through passage (1) to hydraulic tank (24) .
The duplicate load signal oil from orifice (6) flows into passage (2). From passage (2), the duplicate load signal pressure goes to the flow compensator valves above the stick control spool and travel control spools. The duplicate load signal pressure also flows to differential relief valve (20) .
The load signal pressure (duplicate load signal or true load signal) flows to the pump regulators on the front pump and the rear pump. The load signal pressure acts on the load sensing control spools in the pump regulators. The load signal pressure will cause the front pump and the rear pump to move to an upstroke condition or a destroke condition. For implement-only operations, duplicate load signal pressure is supplied to the pump regulators for pump output control. For travel or travel with implement operations, true load signal pressure is supplied to the pump regulators for pump output control. Load signal selector solenoid valve (28) is used to determine when true load signal pressure and duplicate load signal pressure is used for pump output control.
- When only the stick circuit is used, the machine ECM energizes solenoid valve (16) and solenoid valve (28). True load signal pressure is blocked at load signal selector solenoid (28). The duplicate load signal pressure is directed to signal relief valve (14). Signal relief valve (14) limits the duplicate load sensing signal pressure that is generated by the load sensing system. The duplicate load signal pressure flows to the flow compensator valves. The flow compensator valves then determine the oil flow priority to the hydraulic circuits. The duplicate load signal pressure also flows to differential relief valves (11) and (20) limiting the pump output pressure. The duplicate load signal pressure flows through solenoid valve (28) and load signal reduction valve (29) to the pump regulators.
- When only the travel circuit is used, the machine ECM does not energize solenoid valve (16) or solenoid valve (28). Duplicate load signal pressure is blocked at load signal selector solenoid (28). The duplicate load signal pressure is directed to signal relief valve (12). Signal relief valve (12) limits the duplicate load sensing signal pressure that is generated by the load sensing system. The duplicate load signal pressure flows to the flow compensator valves. The flow compensator valves then determine the oil flow priority to the hydraulic circuits. The highest true load signal pressure from the travel circuit flows to signal duplication valve (5). The input of the highest true load signal at signal duplication valve (5) will cause the duplicate load signal pressure to match the true load signal pressure. The duplicate load signal pressure flows to differential relief valves (11) and (20) limiting the pump output pressure. The true load signal pressure flows through solenoid valve (28) and load signal reduction valve (29) to the pump regulators.
- When the stick circuit and the travel circuit are used at the same time, the machine ECM does not energize solenoid valve (16) or solenoid valve (28). Duplicate load signal pressure is blocked at load signal selector solenoid (28). The duplicate load signal pressure is directed to signal relief valve (12). Signal relief valve (12) limits the duplicate load sensing signal pressure that is generated by the load sensing system. The duplicate load signal pressure flows to the flow compensator valves. The flow compensator valves then determine the oil flow priority to the hydraulic circuits. The highest true load signal pressure from the stick circuit or the travel circuit flows to signal duplication valve (5). The input of the highest true load signal at signal duplication valve (5) will cause the duplicate load signal pressure to match the true load signal pressure. The duplicate load signal pressure flows to differential relief valves (11) and (20) limiting the pump output pressure. The true load signal pressure flows through solenoid valve (28) and load signal reduction valve (29) to the pump regulators.
ReferenceFor more information concerning the operation of the signal relief valves, refer to Systems Operation, "Relief Valve (Signal)".
ReferenceFor more information concerning the pressure settings for the signal relief valves, refer to Testing and Adjusting, "Specifications".
Pulses (spikes) in circuit pressure are reduced by the differential relief valves when the pumps destroke rapidly.
During normal machine operation, when the pump discharge pressure rises to 3000 kPa (435 psi) or more above the duplicate load signal pressure, the differential relief valves open. The pump delivery flow is sent back to the hydraulic tank. Oil from front pump (25) and rear pump (26) flows through passage (3) and passage (8) to differential relief valves (11) and (20) which enables the oil to return to hydraulic tank (24) .
ReferenceFor more information concerning the differential relief valves, refer to Systems Operation, "Relief Valve (Differential Pressure)".
The circuit pressure is limited by the line relief valves.
ReferenceFor more information concerning the operation of the line relief valves, refer to Systems Operation, "Relief Valve (Line)".
ReferenceFor more information concerning the line relief valve pressure settings, refer to Testing and Adjusting, "Specifications".