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| Illustration 1 | g03721065 |
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Compensator valves (1) Line to signal limiter valve (2) Load sensing signal (3) Line to next compensator (4) Load sensing port (5) Cross-drilled passage (6) Supply oil (7) Passage to cylinder (8) Feeder passage (9) Control spool (10) Line to pump controls | |
The view at the left is a flow compensator valve in NEUTRAL. Duplicated signal pressure (2) from the circuit with the highest work port pressure keeps the compensator valve closed. Feeder passage (8) is open to the tank through control spool (9).
Signal pressure (2) from the circuit with the highest work port pressure regulates the flow through all activated control valves.
When a single hydraulic circuit is activated from the NEUTRAL position to the HIGH PRESSURE position and from a pump STANDBY condition, control spool (9) is shifted. Pump supply oil enters feeder passage (8) below the flow compensator. Pressure increases and the compensator valve moves up. When the valve moves up, the center passage in the compensator opens cross-drilled passage (5) to load sensing port (4).
Supply oil (6) enters load sensing signal line (2) and flows to the pump controls. Supply oil (6) also flows to the spring chamber above the compensator valve.
The signal oil flows to the load sensing spool in the main pump control group. The pump control reacts to the change in flow demand and the pump upstrokes in order to increase flow. The increased flow increases the pressure in feeder passage (8) below the compensator valve.
When supply pressure (6) in feeder passage (8) increases to more than the circuit pressure, the load check valve opens. Also, pump flow goes past the load check valve and to the circuit.
The spring on the top of the compensator valve works with signal oil (2) in order to balance the forces that are working below the compensator. When the forces are in balance, the supply oil is metered through cross-drilled passage (5) in order to provide signal oil. When the compensator is balanced, signal oil pressure (2) is equal to the oil pressure in feeder passage (8) minus the spring force.
For the circuit with the highest pressure, the compensator spring controls the maximum pressure differential between feeder passage (8) and passage (7) to the cylinder. The signal pressure and the circuit pressure will be equal. The compensator valve duplicates the actual pressure of the work port by using supply oil from feeder passage (8).
When more than one circuit is activated, the highest circuit pressure is directed through internal passages to the spring chamber at the top of all compensator valves.
When the same circuit pressure is working on all of the compensators, the differential pressure across all of the control spools (9) is equal, shown in Illustration 1 for the compensator on the right and in the middle. The pressure differential across all of the control spools (9) is equal, even if the pump cannot satisfy the flow demand for all activated circuits.
For example, if the margin pressure is
When the pump cannot provide the flow that is required for all circuits, the compensator valves move downward in order to increase the pump flow. The pressure differential will be less than the pressure differential that is shown in the example. The pressure differential will be equal for all control spools.
The center compensator shows the result of activating an additional circuit with a lower circuit pressure than the first activated valve.
Load sensing signal (2) from the compensator on the right is directed to the top of the flow compensator valve in the middle with the low circuit pressure. When the control valve is moved, pressure oil in feeder passage (8) moves the compensator valve upward. The compensator valve does not move up enough to open the load sensing signal line to feeder passage (8) due to the higher forces working above the compensator spool.
The compensator valve will respond to changes in the circuit pressure by opening and closing the passage between feeder passage (8) and the passage to the cylinder in order to maintain a constant flow rate for a given displacement of a control spool.