The signal duplication valve is located in the center manifold of the main control valve.
The signal duplication valve uses main pump pressure to replicate the true load signal. The replicated load signal is called the duplicate load signal. The purpose of the signal duplication valve is to eliminate pressure spikes in the load sensing circuit. The duplicate load sensing circuit is used for the main pump regulators during implement movement. Duplicate load signal pressure is also ported to the flow compensator valves and the pressure differential relief valves. The additional pressure increases the amount of pressure that is required to open the flow compensator valves and the differential relief valves. During combined implement operations, implements requiring lower flow rates will be regulated by the flow compensators to optimize the pump flow.
ReferenceFor more information about the flow compensator valves, refer to Systems Operation, "Load Check Valve and Flow Compensator Valve". For more information about the differential pressure relief valves, refer to Systems Operation, "Relief Valve (Differential Pressure)".
The main pump regulators use load signal pressure as in input to control the output of the main pumps. Two load signal pressures are present in the main control valve: true load signal and duplicate load signal.
A load signal selector solenoid valve is implemented to provide either the true load signal or the duplicate load signal to the pump regulators. True load signal pressure is used for travel-only conditions. Duplicate load signal pressure is used for implement-only conditions.
Note: During a combination of a travel function and an implement condition, the true load signal pressure is used.
When the machine is inactive, the load signal selector solenoid directs the true load signal pressure to the pump regulators.
ReferenceFor more information about the load signal selector solenoid valve, refer to Systems Operation, "Load Signal Selector Solenoid Valve".
Note: When no implement or travel condition exists, true load signal pressure is equal to the return hydraulic system pressure. Signal duplication valve will maintain the duplicate load signal pressure.
 | |
| Illustration 1 | g02143253 |
Signal duplication valve during implement movement or travel (1) Chamber (2) Center manifold (3) Passage (oil flow to the hydraulic tank) (4) Passage (oil flow to the hydraulic tank) (5) Passage (true load signal pressure) (6) Passage (duplicate load signal pressure) (7) Passage (duplicate load signal pressure) (8) Passage (pump delivery pressure) (9) Passage (pump delivery pressure) (10) Passage (center chamber) (11) Signal duplication valve spool (PD) Pump delivery pressure (PL) True load signal pressure | |
The true load signal pressure in passage (5) pushes the left end of spool (11). Spool (11) moves to the right. When spool (11) moves to the right, pump delivery pressure (PD) in passage (9) flows through passage (8) to chamber (10). Oil flow to passage (3) is blocked. Pump delivery pressure enters the signal duplication valve and passes through the orifices from the center chamber (10) into passage (7) in spool (11). Pump delivery pressure pressurizes the passage (7) of the signal duplication valve spool and chamber (1) of the signal duplication valve. The pressure on the right end of spool (11) is duplicate load signal pressure.
As duplicate load signal pressure in chamber (1) rises, spool (11) shifts to the left. When spool (11) moves to the left, the passage for pump delivery pressure (8) partially closes and the drain passage (4) partially opens. Duplicate load sensing signal pressure on the right end of spool (11) is reduced. True load signal in passage (5) shifts spool (11) to the right. The true load signal pressure in passage (5) and the load sensing signal pressure in passage (6) will balance spool (11). The left side of spool (11) has a greater surface area than the right side of spool (11). The difference in the surface area of the spool allows a lower true load signal pressure to balance the higher duplicate load signal pressure.