Introduction
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| Illustration 1 | g03185017 |
Location of load check valves and flow compensator valves | |
Note: There are no load check valves in the travel circuit.
The function and operation of the load check valve and flow compensator valve are combined in one valve.
The load check valve is used to prevent a drop affect of implements that are suspended off the ground. The main pump pressure must be higher than the back pressure in a cylinder line in order for the load check valve to open.
The flow compensator valve is used during combined implement operations. The flow compensator valve limits oil flow to an implement that requires less pressure to function when two implements are actuated at the same time.
NEUTRAL Position
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| Illustration 2 | g03185077 |
Load check valve and flow compensator valve with main spool in NEUTRAL (1) Passage (duplicate load signal from signal duplication valve) (2) Cylinder supply port (3) Passage (true load signal from other circuits) (4) Cylinder supply port (5) Passage (true load signal to other circuits and signal duplication valve) (6) Load check valve and compensator valve (7) Orifices (8) Bridge passage (9) Feeder passage (10) Supply passages (main pumps) (11) Spool | |
While implement control spool (11) is in the NEUTRAL position, load check valve and compensator valve (6) are pushed down by spring force. Duplicate load signal is also supplied to the spring chamber of valve (6) .
Main system oil cannot flow from supply passages (10) to feeder passage (9). The oil that is in passage (3), passage (5), and bridge passage (8) is ported to the return hydraulic system. The oil that is in feeder passage (9) is trapped between spool (11) and valve (6). The oil that is in port (2) and port (4) is trapped between the implement cylinder and spool (11) .
Operation During Load Check
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| Illustration 3 | g03185237 |
Load check and flow compensator valve during load check (1) Passage (duplicate load signal from signal duplication valve) (2) Cylinder supply port (3) Passage (true load signal from other circuits) (4) Cylinder supply port (5) Passage (true load signal to other circuits and signal duplication valve) (6) Load check valve and compensator valve (7) Orifices (8) Bridge passage (9) Feeder passage (10) Supply passages (main pumps) (11) Spool | |
When the work tool is suspended from the ground, gravity creates back pressure in port (4). As an implement is operated in a minimal movement, spool (11) is shifted slightly to the left. The back pressure enters bridge passage (8). The back pressure in bridge passage (8) acts on valve (6). The back pressure flows into the spring passage between the compensator piston and the load check valve. The load check valve is held down by the combination of the spring force and the force of the back pressure.
Because spool (11) is slightly moved to the left, a minimal amount of pump oil is supplied to feeder passage (9). The pump oil in passage (9) is not able to open valve (6). Pump oil is prevented from flowing to bridge passage (8) and to port (4). The implement does not move.
Operation During Flow Compensation
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| Illustration 4 | g03186140 |
Load check and flow compensator valve during flow compensation (1) Passage (duplicate load signal from signal duplication valve) (2) Cylinder supply port (3) Passage (true load signal from other circuits) (4) Cylinder supply port (5) Passage (true load signal to other circuits and signal duplication valve) (6) Load check valve and compensator valve (7) Orifices (8) Bridge passage (9) Feeder passage (10) Supply passages (main pumps) (11) Spool | |
As spool (11) shifts, pump oil flows through the throttling slots into feeder passage (9). The compensator piston and the load check valve will move up when the pump oil pressure is higher than the back pressure from the implement. The pump oil pressure flows through orifices (7) in the load check valve to bridge passage (8). Pump oil flows from bridge passage (8) to supply port (4) and to the implement. The true load signal from bridge passage (8) is also sent to the signal duplication valve to increase the duplicate load signal pressure. The signal duplication valve duplicates the true load signal from bridge passage (8) .
The signal duplication valve sends duplicate load signal pressure to passage (1). The oil pressure in passage (1) assists in regulating the amount of pump oil needed to move implements.
During a stall condition or slow implement movements, the load sensing control spool maintains pump discharge pressure 1860 kPa (270 psi) higher than the load signal pressure. When the pump discharge pressure is higher than the load sensing signal pressure, the compensator piston will remain in the full open position.
When another implement circuit is activated and a higher duplicate load signal pressure occurs, the highest duplicate load signal flows to each compensator piston. The duplicate load signal pressure oil on top of the compensator piston pushes the compensator piston downward. This movement decreases the oil flow that flows from supply passage (9) through orifices (7) into bridge passage (8). The circuit that has less operator input will receive less pump flow in comparison to the circuit that has more operator input.
When the implement joysticks are moved back toward the neutral position, control spool (11) will shift back to the right. Pump oil pressure is blocked at supply passages (10). The true load signal pressure decreases. A reduction in the true load signal causes the duplicate load signal to be reduced as well. Reducing the duplicate load signal causes the output of the pump to be reduced as well.
All of the spools for the implement control valves operate in the same basic manner for all the implement functions.