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| Illustration 1 | g03583659 |
Hydraulic schematic (negative flow control) (1) Relief valve (negative flow control) (2) Orifice (3) Return passage (4) Passage (5) Passage (6) Center bypass passage (7) Center bypass passage (8) Relief valve (negative flow control) (9) Orifice (10) Negative flow control line (11) Negative flow control line (12) Return line (13) Negative flow control valve (14) Drive pump (15) Idler pump | |
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| Illustration 2 | g02126856 |
Main control valves (rear view) (10) Negative flow control line (11) Negative flow control line | |
When cylinders or motors are not in operation, negative flow control pressure flows from center bypass passage (6) and center bypass passage (7) . When fine control of the pilot control valves is needed, negative flow control oil flows from center bypass passage (6) and center bypass passage (7) .
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| Illustration 3 | g02126866 |
Relief valve (negative flow control) (1) Relief valve (negative flow control) (2) Orifice (3) Return passage (4) Passage (5) Passage (16) Plug (17) Spring (18) Body (19) Valve (HL) Negative flow signal pressure port (idler pump) | |
Oil flow from idler pump (15) goes to center bypass passage (6) . The oil then goes through passage (5) and orifice (2) to return passage (3) . Orifice (2) restricts the oil flow. The pressure in passage (5) increases. A negative flow control pressure now goes through passage (4) and negative flow control line (11) to the pump regulator. The negative flow control of the regulator causes the pump to destroke.
Relief valve (1) consists of body (18) , plug (16) , valve (19) and spring (17) .
When the oil flow in a center bypass passage suddenly changes, there will be a sudden rise in the negative flow control pressure. Relief valve (1) allows part of the oil to flow by valve (19) and through return passage (3) .
When all controls are in NEUTRAL position, all of the idler pump oil goes through center bypass passage (6) . The oil then goes through orifice (2) and return passage (11) . The oil then goes back to the hydraulic tank.
Maximum negative flow control pressure in passage (5) now goes to the idler pump. The pump cylinder rotates to the minimum angle. At the minimum angle, the idler pump destrokes. The minimum amount of oil flow is provided.
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| Illustration 4 | g02127293 |
Bucket control valve (7) Center bypass passage (20) Parallel feeder passage (21) Port (22) Spool (23) Passage | |
When partial implement operation is started, pilot pressure shifts spool (22) slightly to the left. Pilot pressure partially opens passage (23) . Pilot pressure partially closes center bypass passage (7) . Part of the drive pump oil from center bypass passage (7) goes to orifice (9) . The remainder of the oil goes through parallel feeder passages (20) and passage (23) to port (21) . The oil flow in center bypass passage (7) now decreases. The resistance to oil flow through orifice (9) decreases and the negative flow control pressure in passage (23) decreases. The swashplate rotates to a larger angle. The larger angle causes the drive pump to upstroke. The oil flow increases.
When the implement is moved to full operation, spool (22) moves to the left. Center bypass passage (7) closes. There is no oil flow through passage (23) . When there is no oil flow through passage (23) , there is no negative flow control pressure. The output of the drive pump is held maximum. Oil flow of the drive pump is controlled by the constant horsepower flow control.
Modulation of the exact pump output is done by inching the control levers. This action allows fine operation of implements for precision work.
Negative flow control operates in the same manner for idler pump (15) .
Negative Flow Control Valve (Flow Limit Valves)
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| Illustration 5 | g02310454 |
Negative flow control valve located in the pump compartment (13) Negative flow control valve (24) PRV for the drive pump (25) PRV for the idler pump | |
Proportional reducing valves for negative flow control (13) are used in order to control the amount of NFC signal to the pump regulators. The machine ECM receives various input signals in order to control the flow limitation from the main hydraulic pumps. When the NFC valves are energized by the machine ECM, pilot oil pressure is directed to the main hydraulic pump regulators from the pilot manifold. The pilot oil pressure causes the hydraulic pumps to destroke which reduces hydraulic oil flow.
For more information concerning the ECM logic of the negative flow control valves, refer to Systems Operation, "Electronic Control System".