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| Illustration 1 | g06015406 |
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Hydraulic schematic (negative flow control) (1) Center bypass passage (2) Center bypass passage (3) Passage (4) Passage (5) Orifice (6) Relief valve (negative flow control) (7) Negative flow control line (8) Orifice (9) Negative flow control line (10) Relief valve (negative flow control) (11) Return passage (12) Drive pump (13) Idler pump (22) Return line (23) Port | |
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| Illustration 2 | g01436671 |
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Main control valves (rear view) (7) Negative flow control line (9) Negative flow control line | |
When cylinders or motors are not in operation, negative flow control pressure flows from center bypass passage (1) and center bypass passage (2). When fine control of the pilot control valves is needed, negative flow control oil flows from center bypass passage (1) and center bypass passage (2).
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| Illustration 3 | g01436673 |
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Relief valve (negative flow control) (stick II control valve) (3) Passage (4) Passage (8) Orifice (10) Relief valve (negative flow control) (11) Return passage (14) Plug (15) Spring (16) Body (17) Valve (23) Port | |
Oil flow from drive pump (12) goes to center bypass passage (2). The oil then goes through passage (3) and orifice (8) to return passage (22). Orifice (8) restricts the oil flow. The pressure in passage (3) increases. A negative flow control pressure now goes through passage (4) and negative flow control line (9) to the pump regulator. The negative flow control of the regulator causes the pump to destroke.
Relief valve (10) consists of body (16), plug (14), valve (17) and spring (15).
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 (10) allows part of the oil to flow by valve (17) and through return passage (11).
When all controls are in NEUTRAL position, all of the drive pump oil goes through center bypass passage (2). The oil then goes through orifice (8) and return passage (22). The oil then goes back to the hydraulic tank.
Maximum negative flow control pressure in passage (3) now goes to the drive pump. The pump cylinder rotates to the minimum angle. At the minimum angle, the drive pump destrokes. The minimum amount of oil flow is provided.
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| Illustration 4 | g01436702 |
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Control valve (2) Center bypass passage (18) Parallel feeder passage (19) Port (20) Stem (21) Passage | |
When partial implement operation is started, pilot pressure shifts stem (20) slightly to the left. Pilot pressure partially opens passage (21). Pilot pressure partially closes center bypass passage (2). Part of the drive pump oil from center bypass passage (2) goes to orifice (8). The remainder of the oil goes through parallel feeder passages (18) and passage (21) to port (19). The oil flow in center bypass passage (2) now decreases. The resistance to oil flow through orifice (8) decreases and the negative flow control pressure in passage (3) 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, stem (20) moves to the left. Center bypass passage (2) closes. There is no oil flow through passage (3). When there is no oil flow through passage (3), 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 allows fine operation of implements for precision work.
Negative flow control operates in the same manner for idler pump (13).