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| Illustration 1 | g00544134 |
Hydraulic schematic (1) Stick drift reduction valve (2) Line relief valve (stick cylinder rod end) (3) Main control valve (4) Pressure switch (implement and swing) (5) Pressure switch (travel) (6) Boom drift reduction valve (7) Line relief valve (boom cylinder head end) (8) Return port (9) Parallel feeder passage (10) Load check valve (11) Control valve (left travel) (12) Control valve (straight travel) (13) Control valve (right travel) (14) Control valve (attachment) (15) Control valve (bucket) (16) Center bypass passage (17) Line relief valve (bucket cylinder rod) (18) Control valve (boom I) (19) Control valve (stick II) (20) Relief valve (negative flow control) (21) Orifice (negative flow control) (22) Control valve (boom II) (23) Line relief valve (stick cylinder head end) (24) Center bypass passage (25) Control valve (stick I) (26) Control valve (swing) (27) Load check valve (28) Line relief valve (bucket cylinder head end) (29) Orifice (negative flow control) (30) Relief valve (negative flow control) (31) Main relief valve (32) Line relief valve (boom cylinder rod end) (33) Logic valve (34) Parallel feeder passage (35) Pressure switch (boom raise) (36) Inlet port (rear pump) (37) Inlet port (front pump) (38) Inlet port (pilot pump) (39) Negative flow control line (40) Negative flow control line (41) Front pump (42) Rear pump (43) Pilot pump (44) Hydraulic tank | |
Introduction
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| Illustration 2 | g00472171 |
Main control valve (front view) (4) Pressure switches (Implement and Swing) (5) Pressure switch (travel) (11) Control valve (left travel) (12) Control valve (straight travel) (13) Control valve (right travel) (14) Control valve (attachment) (15) Control valve (bucket) (18) Control valve (boom I) (19) Control valve (stick II) (22) Control valve (boom II) (23) Line relief valve (stick cylinder head end) (25) Control valve (stick I) (26) Control valve (swing) (28) Line relief valve (bucket cylinder head end) (31) Main relief valve (35) Pressure switch (boom raise) (45) Left body (46) Right body | |
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| Illustration 3 | g00472172 |
Main control valve (bottom view) (6) Boom drift reduction valve (7) Line relief valve (boom cylinder head end) | |
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| Illustration 4 | g00472173 |
Main control valve (bottom view) (1) Stick drift reduction valve (2) Line relief valve (stick cylinder rod end) | |
The main control valve includes left body (45) and right body (46). The main control valve is coupled together with bolts in order to make one assembly.
The lower pump supplies oil to left body (45) through inlet port (36). The following control valves are in parallel in left body (45) .
- Control valve (straight travel) (12) .
- Control valve (left travel) (11) .
- Control valve (swing) (26) .
- Control valve (stick I) (25) .
- Control valve (boom II) (22) .
The upper pump supplies oil to right body (46) through inlet port (37). The following control valves are in parallel in right body (46) .
- Control valve (right travel) (13) .
- Control valve (attachment) (14) .
- Control valve (bucket) (15) .
- Control valve (boom I) (18) .
- Control valve (stick II) (19) .
The upper pump oil flow and lower pump oil flow is controlled by the main control valve. The oil flow is supplied to cylinders and/or motors that are selected for operation. Return oil from cylinders and/or motors enters the main control valve. The oil then flows out of return port (8) and back to hydraulic tank (44) .
Components in Left Body (45)
- The line relief valve (stick cylinder head end) (23) will limit the circuit pressure of the stick.
- Orifice (29) and relief valve (30) regulate the negative flow control.
- Stick drift reduction valve (1) prevents stick cylinder drift when the main control valve is in the NEUTRAL position. Line relief valve (2) is located on stick drift reduction valve (1). Line relief valve (2) is for the rod end of the stick cylinder.
- Main relief valve (31) limits the main hydraulic system pressure.
- Load check valve (10) prevents cylinder drift.
- Pressure switch (35) ensures a proper speed for the boom raise.
The description of some components that are installed on the main control valve or in the main control valve will be listed separately. Refer to the appropriate sections that are in this module for further information on the components.
Components in Right Body (46)
- Line relief valve (bucket cylinder rod end) (17), line relief valve (bucket cylinder head end) (28) and line relief valve (boom cylinder rod end) (32) limit the circuit pressure in the respective circuits.
- Relief valve (20) and negative flow control orifice (21) destroke the upper pump when the control levers are in the NEUTRAL position or when the control levers are moved partially.
- When the control levers are in the NEUTRAL position, boom drift reduction valve (6) prevents boom cylinder drift. Line relief valve (7) is located on boom drift reduction valve (6). Line relief valve (7) is for the head end of the boom cylinders.
- Pressure switch (4) generates electrical signals for the Automatic Engine Speed Control. Travel pressure switch (5) generates electrical signals for the Automatic Engine Speed Control.
- Load check valve (27) prevents cylinder drift.
Main Control Valve Operation in Neutral Position
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| Illustration 5 | g00472515 |
Main control valve (neutral position) (8) Return port (9) Parallel feeder passage (11) Control valve (left travel) (12) Control valve (straight travel) (13) Control valve (right travel) (14) Control valve (attachment) (15) Control valve (bucket) (16) Center bypass passage (18) Control valve (boom I) (19) Control valve (stick II) (21) Orifice (negative flow control) (22) Control valve (boom II) (24) Center bypass passage (25) Control valve (stick I) (26) Control valve (swing) (29) Orifice (negative flow control) (34) Parallel feeder passage (36) Inlet port (rear pump) (37) Inlet port (front pump) (45) Left body (46) Right body | |
When all the control levers are in the NEUTRAL position, front pump oil flows through center bypass passage (24), negative flow control orifice (29) and return port (8) back to the hydraulic tank. Rear pump oil from inlet port (36) flows through center bypass passage (16), negative flow control orifice (21) and return port (8) back to the hydraulic tank. Oil in parallel feeder passages (9) and (34) remains blocked by each control valve stem.
Negative Flow Control Signal
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| Illustration 6 | g00544585 |
Hydraulic schematic (negative flow control) (16) Center bypass passage (20) Relief valve (negative flow control) (21) Orifice (negative flow control) (24) Center bypass passage (29) Orifice (negative flow control) (30) Relief valve (negative flow control) (39) Negative flow control line (40) Negative flow control line (41) Upper pump (42) Lower pump (56) Return Passage (57) Passage (58) Passage (60) Port (61) Return passage | |
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| Illustration 7 | g00472967 |
Main control valve (rear view) (39) Negative flow control line (40) Negative flow control line | |
Oil from upper pump (41) enters the main control valve. A portion of the oil then flows through orifice (21) to return passage (56). Orifice (21) restricts the oil flow. The pressure in passage (57) increases. The negative flow control now flows through passage (58) and negative flow control line (39) to the pump regulator. The negative flow control of the regulator causes the pump to destroke.
When all controls are in NEUTRAL position, all of the upper pump oil flows through center bypass passage (16). The oil then flows through orifice (21) and return passage (56). The oil then flows back to the hydraulic tank.
Maximum negative flow control pressure in passage (57) now flows to the upper pump. The pump cylinder rotates to the minimum angle. At the minimum angle, the upper pump destrokes. The minimum amount of oil flow is provided.
Negative flow control operates in the same manner for the lower pump (42) .
Individual Valve Operation
Neutral Position
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| Illustration 8 | g00472174 |
Bucket control valve (NEUTRAL position) (10) Load check valve (15) Control valve (bucket) (16) Center bypass passage (17) Line relief valve (bucket cylinder rod) (28) Line relief valve (bucket cylinder head end) (34) Parallel feeder passage (47) Pilot port (48) Port (49) Return passage (50) Passage (51) Pilot port (52) Spring (53) Stem | |
The bucket control valve is used as a typical example for describing the operation of individual control valves.
When all pilot control valve levers are in the NEUTRAL position, pilot oil does not flow to port (47) and port (51) from the pilot control valve. Stem (53) is centered in the NEUTRAL position by the force of spring (52). The upper pump oil flows through center bypass passage (16) to the hydraulic tank.
Partially Shifted
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| Illustration 9 | g00472177 |
Bucket control valve (levelling operation) (16) Center bypass passage (34) Parallel feeder passage (53) Stem (54) Passage (55) Port | |
When partial implement operation is started, pilot pressure shifts stem (53) slightly to the left. Pilot pressure partially opens passage (54). Pilot pressure partially closes center bypass passage (16). Part of the upper pump oil from center bypass passage (16) flows to orifice (21). The remainder of the oil flows through parallel feeder passages (34) and passage (54) to port (55). The oil flow in center bypass passage (16) now decreases. The resistance to oil flow through orifice (21) decreases and the negative flow control pressure in passage (57) decreases. The pump cylinder rotates to a larger angle. The larger angle causes the upper pump to upstroke. The oil flow increases.
Modulation of the exact pump output is done by inching the control levers. This allows fine operation of implements for precision work.
Shifted
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| Illustration 10 | g00472175 |
Bucket control valve (10) Load check valve (16) Center bypass passage (34) Parallel feeder passage (47) Pilot port (48) Port (49) Return passage (50) Passage (54) Passage (55) Port | |
When the bucket control valve is moved to the CLOSE position, pilot oil is supplied to pilot port (47). Stem (53) moves to the left. Center bypass passage (16) closes. There is no oil flow through passage (57). When there is no oil flow through passage (57), there is no negative flow control pressure. The upper pump output is held maximum. Upper pump oil flow is controlled by the constant horsepower flow control. Port (48) is now connected to return passage (49). The bucket cylinder rod extends. When the bucket cylinder rod extends, the displaced oil in the rod end flows to port (48). Oil flows through port (48) to return passage (49) and back to the hydraulic tank.