Hydraulic Schematic of the Main Control Valve
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| Illustration 1 | g00810520 |
Hydraulic schematic (1) Return port (2) Line relief valve (stick cylinder head end) (3) Line relief valve (stick cylinder rod end) (4) Parallel feeder passage (5) Load check valve (6) Swing control valve (7) Left travel control valve (8) Straight travel control valve (9) Main relief valve (10) Main control valve (11) Pressure switch (implement and swing) (12) Pressure switch (travel) (13) Right travel control valve (14) Load check valve (15) Attachment control valve (16) Grapple control valve (17) Line relief valve (head end of grapple cylinder) (18) Line relief valve (grapple cylinder rod end) (19) Center bypass passage (20) Boom raise pressure switch (21) Boom I control valve (22) Line relief valve (boom cylinder rod end) (23) Line relief valve (boom cylinder head end) (24) Stick II control valve (25) Relief valve (negative flow control) (26) Negative flow control orifice (27) Negative flow control line (28) Boom II control valve (29) Negative flow control orifice (30) Relief valve (negative flow control) (31) Stick I control valve (32) Logic valve (33) Inlet port (lower pump) (34) Inlet port (upper pump) (35) Inlet port (pilot pump) (36) Hydraulic tank (37) Lower pump (38) Upper pump (39) Negative flow control line (40) Pilot pump | |
Introduction
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| Illustration 2 | g00813888 |
Main control valve (front view) (3) Line relief valve (stick cylinder rod end) (6) Swing control valve (7) Left travel control valve (8) Straight travel control valve (9) Main relief valve (11) Pressure switches (implement and swing) (12) Travel pressure switch (13) Right travel control valve (15) Attachment control valve (16) Grapple control valve (17) Line relief valve (head end of grapple cylinder) (20) Boom raise pressure switch (21) Boom I control valve (23) Line relief valve (boom cylinder head end) (24) Stick II control valve (28) Boom II control valve (31) Stick I control valve (41) Right body (42) Left body | |
Main control valve (10) is located in the hydraulic system between the pumps and actuators (cylinders and motors). The main control valve includes right body (41) and left body (42). The right body and the left body are made up of control valves. Each control valve operates individually. The two parts of the main control valve are coupled with bolts in order to make one assembly. The following control valves are in parallel in right body (41) .
- Right travel control valve (13) .
- Attachment control valve (15) .
- Grapple control valve (16) .
- Boom I control valve (21) .
- Stick II control valve (24) .
The following control valves are in parallel in left body (42) :
- Boom II control valve (28) .
- Stick I control valve (31) .
- Swing control valve (6) .
- Left travel control valve (7) .
- Straight travel control valve (8) .
The upper pump oil flows into the main control valve through inlet port (34). The lower pump oil flows into the main control valve through inlet port (33). The upper pump oil flow and the lower pump oil flow are controlled by the main control valve. The oil flow is supplied to the cylinders and/or motors that are selected for operation. Return oil from the cylinders and/or motors enters the main control valve. The oil then flows out of return port (1) and back to hydraulic tank (36) through the return line.
The main control valve controls the negative flow control signal. The main control valve also prevents cylinder drift with the load check valves. In addition, the main control valve limits the circuit pressure through a system of relief valves. When the main control valve is in the NEUTRAL position, no pump oil flows to the cylinders and the motors.
Right Body
- Line relief valves (22) and (23) are installed in order to limit the pressure in the boom circuit. Line relief valves (17) and (18) limit the pressure in the grapple circuit.
- When the control levers are in the NEUTRAL position or when the control levers are moved partially, relief valve (25) and negative flow control orifice (26) destroke the main pump.
- Pressure switch (11) generates a signal for the Automatic Engine Speed Control. Pressure switch (12) also generates a signal for the Automatic Engine Speed Control.
- Load check valve (14) prevents oil loss from a high pressure circuit to a lower pressure circuit.
- Pressure switch (20) ensures that the boom is raised at the optimum speed.
Left Body
- Line relief valves (2) and (3) limit the pressure in the stick circuit.
- Relief valve (30) is for the negative flow control. Orifice (29) is for the negative flow control.
- Main relief valve (9) limits the pressure in the main hydraulic system.
- Load check valve (5) prevents oil loss from a high pressure circuit to a lower pressure circuit.
Descriptions of some components that are installed on the main control valve or in the main control valve are provided separately. Refer to the appropriate sections in this module for further information on the components.
- For more information on straight travel control valve (8), refer to Systems Operation, "Control Valve (Straight Travel)".
- For more information on logic valve (32), refer to Systems Operation, "Combined Function Hydraulic Operation".
Main Control Valve Operation in NEUTRAL Position
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| Illustration 3 | g00306714 |
Main control valve (front view) (1) Stick II control valve (2) Boom I control valve (3) Grapple control valve (4) Attachment control valve (5) Right travel control valve (7) Left travel control valve (8) Swing control valve (9) Stick I control valve (10) Boom II control valve (12) Right body (14) Left body (18) Inlet port for upper pump oil (19) Inlet port for lower pump oil (22) Return port (23) Straight travel control valve (26) Parallel feeder passage (27) Parallel feeder passage (28) Return passage (29) Negative flow control orifice (30) Center bypass passage (31) Center bypass passage (32) Negative flow control orifice (33) Return passage | |
The upper pump supplies oil to right body (12). Oil from the upper pump goes to the right body through inlet port (18). The oil then goes through center bypass passage (30) and parallel feeder passage (26). The lower pump supplies oil to left body (14). Oil from the lower pump goes to the left body through inlet port (19). The oil then goes through center bypass passage (31) and parallel feeder passage (27) .
When all the control levers are in the NEUTRAL position, upper pump oil flows through center bypass passage (30), negative flow control orifice (29), return passage (28), and return passage (33). The oil then goes out through return port (22), and the oil returns to the hydraulic tank. Lower pump oil from inlet port (19) flows through center bypass passage (31), negative flow control orifice (32), return passage (33), and out return port (22). The oil returns to the hydraulic tank. Oil in parallel feeder passages (26) and (27) remains blocked by each control valve stem.
Activation of any control lever provides two paths for upper pump oil. One path is from center bypass passage (30) to right travel control valve (5). The other path is from parallel feeder passage (26) to attachment control valve (4), grapple control valve (3), and boom I control valve (2). Activation of any control lever also provides two paths for lower pump oil. One path is from center bypass passage (31) to left travel control valve (7) and stick I control valve (9). The other path is from parallel feeder passage (27) to swing control valve (8) .
Individual Valve Operation
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| Illustration 4 | g00812140 |
Grapple control valve (NEUTRAL position) (1) Line relief valve (grapple cylinder rod end) (2) Port (3) Parallel feeder passage (4) Load check valve (5) Passage (6) Port (7) Line relief valve (head end of grapple cylinder) (8) Pilot port (9) Return passage (10) Stem (11) Center bypass passage (12) Spring (13) Pilot port | |
The grapple 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 (8) and port (13) from the pilot control valve. Stem (10) is centered in the NEUTRAL position by the force of spring (12). The upper pump oil goes through center bypass passage (11) to the hydraulic tank.
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| Illustration 5 | g00812142 |
Grapple control valve (2) Port (3) Parallel feeder passage (4) Load check valve (5) Passage (6) Port (9) Return passage (10) Stem (11) Center bypass passage (13) Pilot port (14) Passage (15) Passage | |
When the grapple control valve is moved to the GRAPPLE CLOSE position, pilot oil is supplied to pilot port (13). Stem (10) moves to the left. Center bypass passage (11) is closed and passage (15) becomes opened. Passage (14) is now connected to return passage (9) .
Oil that is in parallel feeder passage (3) goes through load check valve (4), passage (5) and passage (15). The oil then goes to port (6). The grapple cylinder rod extends. When the grapple cylinder rod extends, the displaced oil in the rod end flows to port (2).
Oil from port (2) flows through passage (14) to return passage (9) and back to the hydraulic tank.
Negative Flow Control Signal
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| Illustration 6 | g00306718 |
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) Upper pump (13) Lower pump (22) Return line (23) Port | |
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| Illustration 7 | g00306719 |
Main control valves (rear view) (7) Negative flow control line (9) Negative flow control line | |
When cylinders or motors are not in operation, the negative flow control signal flows from center bypass passage (1) and center bypass passage (2). When fine control of the pilot control valves is needed, the negative flow control signal flows from center bypass passage (1) and center bypass passage (2).
Oil flow from upper pump (12) goes to center bypass passage (2). The oil then goes through passage (3) and orifice (8) to return line (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.
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| Illustration 8 | g00306720 |
Relief valve (negative flow control) in 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 | |
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 upper pump oil goes through center bypass passage (2). The oil then goes through orifice (8) and return line (22). The oil then goes back to the hydraulic tank.
Maximum negative flow control pressure in passage (3) now goes 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.
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| Illustration 9 | g00704973 |
Grapple control valve (2) Center bypass passage (18) Parallel feeder passage (19) Port (20) Stem (21) Passage | |
When a partial implement operation is started, pilot pressure shifts stem (20) slightly to the left. Pilot pressure partially opens passage (21), and pilot pressure partially closes center bypass passage (2). Part of the upper pump oil from center bypass passage (2) goes to orifice (8). The remainder of the oil goes through parallel feeder passage (18) and passage (21) to port (19). The oil flow in center bypass passage (2) decreases. The resistance to oil flow through orifice (8) decreases, and the negative flow control pressure in passage (3) decreases. The pump cylinder rotates to a larger angle. The larger angle causes the upper pump to upstroke, and 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 upper pump output is held at the maximum amount. Upper pump oil flow 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 the lower pump (13) .