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| Illustration 1 | g01067589 |
(1) Solenoid valve (2) Solenoid valve (3) Solenoid valve (4) Relief valve (5) Port (6) Signal duplication valves (7) Relief valve (8) Inlet (9) Solenoid valve (10) Control circuit for the work tools (11) Relief valve (12) Lift circuit (13) Relief valve (14) Tilt circuit (15) Relief valve (16) Auxiliary hydraulic circuit (17) Port (18) Relief valve | |
As you look toward the engine, the work tool control valves for the 248B and the 268B machines are located under the cab on the left side of the machines. The work tool control valves are single castings.
The work tool control valves are closed center, proportional, pressure compensated valves. The highest pressure in the system is sensed across all circuits. This pressure is also sensed at the pump. This pressure causes the pump to upstroke. Also, this pressure causes the pump to destroke.
The hydraulic system divides the oil flow between the active circuits. The oil that is directed to a circuit is controlled by a compensator valve that is in the load sensing circuit. The valves are pressure compensated. When the pump can supply the flow demand, the circuits will not slow down. When the pump cannot supply the flow demand, the flow is divided proportionally between the activated circuits. The circuits that are active will move at a slower rate of speed because of the reduced flow of oil in each circuit.
The oil enters the valves at inlet (8). Then, the oil flows to the spools for the following circuits.
- Control circuit for the work tools (10)
- Lift circuit (12)
- tilt circuit (14)
- Auxiliary hydraulic circuit (16)
Port (5) for the load signal circuit is on top of the valves between pressure port (7) and the relief valve for the load signal circuit (4). Oil flows through port (5) to the pump control valve that is on the piston pump in order to control the flow from the piston pump.
When you energize the C+/C− control circuit the high flow solenoid is energized. The electro-hydraulic hydraulic relief valve (4) energizes simultaneously with the high flow solenoid. This enables a higher signal pressure to be sent to the work tool. The pump regulator and the pump will then supply the necessary flow in order to satisfy the work tool.
The control circuit for the work tools contains solenoid (3) and solenoid (9). The auxiliary hydraulic circuit contains solenoid (1) and solenoid (2). The solenoids are controlled by the auxiliary hydraulic ECM. The solenoids control the flow of pilot oil to the spools.
When you press one of the two buttons on the pilot operated hydraulic control for the work tool a signal is sent to the auxiliary hydraulic ECM. The auxiliary hydraulic ECM sends a signal to either solenoid (3) or solenoid (9). The solenoid is activated and the spool moves to the proper position.
The position of the spool in the auxiliary hydraulic circuit controls the amount of oil that flows to the work tool. The position of the spool is variable. The position of the thumb wheel or pressing one of the buttons on the pilot operated hydraulic control for the work tool controls the position of the spool. A signal from the thumb wheel or the buttons is sensed by the auxiliary hydraulic ECM. The auxiliary hydraulic ECM sends a signal to either solenoid (1) or solenoid (2) in order to position the spool for the auxiliary hydraulic circuit.
The lift circuit contains relief valve (11) that is in the line to the head end of the cylinders. The tilt circuit contains relief valve (13) in the line to the head end of the cylinders and relief valve (18) in the line to the rod end of the cylinders. The auxiliary circuit contains relief valve (15) in the line that connects to the "B" port.
Port (17) is for the accumulator for the pilot operated hydraulic control for the work tools.
HOLD Position
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| Illustration 2 | g01070493 |
In the HOLD position, oil from the pump flows through the inlet to the pump passage (1). Springs (2) center all of the spools. This blocks the flow of the oil.
Some of the oil flows from the pump passage through orifice (3) to the auxiliary pump passage (4). The oil is trapped in the auxiliary pump passage. The compensator valves (5) in all of the spools are seated. The signal duplication valves (6) in all of the spools are in a HOLD position. The relief valve for the load signal circuit (7) drains the oil from the load sensing circuit to the tank.
Control Circuit for the Work Tool
Control Circuit "C+"
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| Illustration 3 | g01070753 |
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| Illustration 4 | g01070671 |
When you press the button (1) on the right side of the pilot operated hydraulic control for the work tools, a signal is sent to the "C+" relay for the auxiliary circuit. The "C+" relay for the auxiliary circuits energizes solenoid (2). Solenoid (2) controls the flow of oil to couplings (3) for the control circuit for the work tool "C+". Solenoid (2) moves upward. Pilot oil flows from line (4) through the solenoid to the left side of the spool. When the oil pressure overcomes the force of spring (5), the spool shifts to the right. Pump supply oil from line (6) flows through the internal passages in the spool to the feeder passage.
As the oil flows into the feeder passage, oil pressure increases. This increase in oil pressure causes the compensator valve (7) to move to the left. The oil flows through the compensator valve to the spool. The oil flows through the spool to line (8). Then, the oil flows to coupling (3) .
Some of the oil that flows through the compensator valve (7) flows through a passage in the compensator valve into the spring chamber that is beside the compensator valve. The flow of oil into the spring chamber causes the oil pressure in the chamber to increase. The oil pressure in the spring chamber will equal the oil pressure that is flowing to the work tool.
The oil pressure in the spring chamber is sensed on the right side of the signal duplication valve (9). If this circuit is the only circuit that is active, or this circuit has a work port pressure that is higher than the other circuits that are active, the signal duplication valve will move to the left. This allows oil from the auxiliary pump passage (10) to flow into the load sensing passage (11) until the oil pressure in the load sensing passage is equal to the oil pressure that flows to the work tool. When the pressures are equal, the signal duplication valve shifts right to a metering position.
Oil returns from the work tool to couplings (12) for circuit "C-". The oil flows through the spool to return passage (13). Then, the oil flows to the tank.
Control Circuit "C-"
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| Illustration 5 | g01070773 |
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| Illustration 6 | g01070776 |
When you press the bottom button (14) on the right side of the pilot operated hydraulic control for the work tools, a signal is sent to the "C-" relay for the auxiliary circuit. The "C-" relay for the auxiliary circuits energizes solenoid (15). Solenoid (15) controls the flow of oil to coupling (12) for control circuit for the work tool "C-". Solenoid (15) moves upward. Pilot oil from line (4) flows through the solenoid to the right side of the spool. When the oil pressure overcomes the force of spring (16), the spool shifts to the left. Pump supply oil from line (6) flows through the internal passages in the spool to the feeder passage.
As the oil flows into the feeder passage, oil pressure increases. This increase in oil pressure causes the compensator valve (7) to move to the left. The oil flows through the compensator valve to the spool. The oil flows through the spool to line (17). Then, the oil flows to coupling (12) .
Some of the oil that flows through the compensator valve (7) flows through a passage in the compensator valve into the spring chamber that is beside the compensator valve. The flow of oil into the spring chamber causes the oil pressure in the chamber to increase. The oil pressure in the spring chamber will equal the oil pressure that is flowing to the work tool.
The oil pressure in the spring chamber is sensed on the right side of the signal duplication valve (9). If this circuit is the only circuit that is active, or this circuit has a work port pressure that is higher than the other circuits that are active, the signal duplication valve will move to the left. This allows oil from the auxiliary pump passage (10) to flow into the load sensing passage (11) until the oil pressure in the load sensing passage is equal to the oil pressure that flows to the work tool. When the pressures are equal, the signal duplication valve shifts right to a metering position.
Oil returns from the work tool to couplings (3) for circuit "C+". The oil flows through the spool to return passage (13). Then, the oil flows to the tank.
RAISE and LOWER Circuit
RAISE Position
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| Illustration 7 | g01070950 |
When the operator moves the pilot valve (work tool) to the RAISE position, pilot oil flows from line (1) to the spool. When the pilot oil overcomes the force of spring (2), the spool moves to the right. Pump supply oil flows from line (3) to the spool. The oil flows through the spool to the feeder passage.
As the oil flows into the feeder passage, oil pressure increases. This increase in oil pressure causes the compensator valve (4) to move to the left. The oil flows through the compensator valve to the spool. The oil flows through the spool to line (5). Then, the oil flows to the head end of the lift cylinders (6) .
Some of the oil that flows through the compensator valve (4) flows through a passage in the compensator valve into the spring chamber that is beside the compensator valve. The flow of oil into the spring chamber causes the oil pressure in the chamber to increase. The oil pressure in the spring chamber will equal the oil pressure that is flowing to the lift cylinders.
The oil pressure in the spring chamber is sensed on the right side of the signal duplication valve (7). If this circuit is the only circuit that is active, or this circuit has a work port pressure that is higher than the other circuits that are active, the signal duplication valve will move to the left. This allows oil from the auxiliary pump passage (8) to flow into the signal duplication valve (9) until the oil pressure in the signal duplication valve is equal to the oil pressure that flows to the work tool. When the pressures are equal, the valve shifts right to a metering position.
As the cylinders extend, oil from the rod end of the lift cylinders flows through line (10) to the spool. The oil flows through the spool to return passage (11). Then, the oil flows to the tank.
LOWER Position
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| Illustration 8 | g01070976 |
When the operator moves the pilot valve (work tool) to the LOWER position, pilot oil flows from line (12) to the spool. When the pilot oil overcomes the force of spring (13), the spool moves to the left. Pump supply oil flows from line (3) to the spool. The oil flows through the spool to the feeder passage.
As the oil flows into the feeder passage, oil pressure increases. This increase in oil pressure causes the compensator valve (4) to move to the left. The oil flows through the compensator valve to the spool. The oil flows through the spool to line (10). Then, the oil flows to the rod end of the lift cylinders (6) .
Some of the oil that flows through the compensator valve (4) flows through a passage in the compensator valve into the spring chamber that is beside the compensator valve. The flow of oil into the spring chamber causes the oil pressure in the chamber to increase. The oil pressure in the spring chamber will equal the oil pressure that is flowing to the lift cylinders.
The oil pressure in the spring chamber is sensed on the right side of the signal duplication valve (7). If this circuit is the only circuit that is active, or this circuit has a work port pressure that is higher than the other circuits that are active, the signal duplication valve will move to the left. This allows oil from the auxiliary pump passage (8) to flow into the load sensing passage (9) until the oil pressure in the load sensing passage is equal to the oil pressure that flows to the work tool. When the pressures are equal, the signal duplication valve shifts right to a metering position.
As the cylinders extend, oil from the head end of the lift cylinders flows through line (5) to the spool. The oil flows through the spool to return passage (11). Then, the oil flows to the tank.
TILT DOWN and TILT UP Circuit
TILT DOWN Position
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| Illustration 9 | g01070993 |
When the operator moves the pilot valve (work tool) to the TILT DOWN position, pilot oil flows from line (1) to the spool. When the pilot oil overcomes the force of spring (2), the spool moves to the right. Pump supply oil flows from line (3) to the spool. The oil flows through the spool to the feeder passage.
As the oil flows into the feeder passage, oil pressure increases. This increase in oil pressure causes the compensator valve (4) to move to the left. The oil flows through the compensator valve to the spool. The oil flows through the spool to line (5). Then, the oil flows to the head end of the tilt cylinders (6) .
Some of the oil that flows through the compensator valve (4) flows through a passage in the compensator valve into the spring chamber that is beside the compensator valve. The flow of oil into the spring chamber causes the oil pressure in the chamber to increase. The oil pressure in the spring chamber will equal the oil pressure that is flowing to the tilt cylinders.
The oil pressure in the spring chamber is sensed on the right side of the signal duplication valve (7). If this circuit is the only circuit that is active, or this circuit has a work port pressure that is higher than the other circuits that are active, the signal duplication valve will move to the left. This allows oil from the auxiliary pump passage (8) to flow into the load sensing passage (9) until the oil pressure in the load sensing passage is equal to the oil pressure that flows to the work tool. When the pressures are equal, the signal duplication valve shifts right to a metering position.
As the cylinders extend, oil from the rod end of the tilt cylinders flows through line (10) to the spool. The oil flows through the spool to return passage (11). Then, the oil flows to the tank.
TILT UP Position
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| Illustration 10 | g01071052 |
When the operator moves the pilot valve (work tool) to the TILT UP position, pilot oil flows from line (12) to the spool. When the pilot oil overcomes the force of spring (13), the spool moves to the left. Pump supply oil flows from line (3) to the spool. The oil flows through the spool to the feeder passage.
As the oil flows into the feeder passage, oil pressure increases. This increase in oil pressure causes the compensator valve (4) to move to the left. The oil flows through the compensator valve to the spool. The oil flows through the spool to line (10). Then, the oil flows to the rod end of the tilt cylinders (6) .
Some of the oil that flows through the compensator valve (4) flows through a passage in the compensator valve into the spring chamber that is beside the compensator valve. The flow of oil into the spring chamber causes the oil pressure in the chamber to increase. The oil pressure in the spring chamber will equal the oil pressure that is flowing to the lift cylinders.
The oil pressure in the spring chamber is sensed on the right side of the signal duplication valve (7). If this circuit is the only circuit that is active, or this circuit has a work port pressure that is higher than the other circuits that are active, the signal duplication valve will move to the left. This allows oil from the auxiliary pump passage (8) to flow into the load sensing passage (9) until the oil pressure in the load sensing passage is equal to the oil pressure that flows to the work tool. When the pressures are equal, the signal duplication valve shifts right to a metering position.
As the cylinders retract, oil from the head end of the tilt cylinders flows through line (5) to the spool. The oil flows through the spool to return passage (11). Then, the oil flows to the tank.
Auxiliary and High Flow Auxiliary Circuits
Auxiliary Circuit
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| Illustration 11 | g01071094 |
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| Illustration 12 | g01071107 |
In order for the standard flow for the auxiliary circuit to activate, you must press the right side of switch (1). The ECM for the auxiliary hydraulic circuit activates solenoid (2) and solenoid (3) on the auxiliary spool. Solenoid (2) is labelled "A2". Solenoid (3) is labelled "A1". Solenoid (2) and solenoid (3) move upward. The load signal relief valve (4) is in position for the standard flow auxiliary circuit.
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| Illustration 13 | g01071102 |
Pilot oil is directed to the auxiliary circuit spool by thumb wheel (5). When you roll thumb wheel (5) upward, pilot oil flows from line (6) through solenoid (2) to the spool. When the oil overcomes the force of spring (7), the spool moves to the right. Pump supply oil flows from line (8) to the spool. The oil flows through the spool to the feeder passage.
As the oil flows into the feeder passage, oil pressure increases. This increase in oil pressure causes the compensator valve (9) to move to the left. The oil flows through the compensator valve to the spool. The oil flows through the spool to line (10). Then, the oil flows to couplers (11). Couplers (11) are labelled "A2". When you roll the thumb wheel upward, the flow of oil to couplers (11) increases.
Some of the oil that flows through the compensator valve (9) flows through a passage in the compensator valve into the spring chamber that is beside the compensator valve. The flow of oil into the spring chamber causes the oil pressure in the chamber to increase. The oil pressure in the spring chamber will equal the oil pressure that is flowing to the auxiliary circuit.
The oil pressure in the spring chamber is sensed on the right side of the signal duplication valve (12). If this circuit is the only circuit that is active, or this circuit has a work port pressure that is higher than the other circuits that are active, the signal duplication valve will move to the left. This allows oil from the auxiliary pump passage (13) to flow into the load sensing passage (14) until the oil pressure in the load sensing passage is equal to the oil pressure that flows to the work tool. When the pressures are equal, the signal duplication valve shifts right to a metering position.
Oil flows back through couplers (15). The oil flows through line (16) to the spool. The oil flows through the spool to line (17). Then, the oil flows to the tank.
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| Illustration 14 | g01071102 |
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| Illustration 15 | g01071198 |
Roll the thumb wheel downward in order to increase the flow of hydraulic oil to coupling (15). When you roll thumb wheel (5) downward, pilot oil flows from line (6) through solenoid (3) to the spool. When the oil overcomes the force of spring (18), the spool moves to the right. Pump supply oil flows from line (8) to the spool. The oil flows through the spool to the feeder passage.
As the oil flows into the feeder passage, oil pressure increases. This increase in oil pressure causes the compensator valve (9) to move to the left. The oil flows through the compensator valve to the spool. The oil flows through the spool to line (16). Then, the oil flows to couplers (15). Couplers (15) are labelled "A1". When you roll the thumb wheel downward, the flow of oil to couplers (15) increases.
Some of the oil that flows through the compensator valve (9) flows through a passage in the compensator valve into the spring chamber that is beside the compensator valve. The flow of oil into the spring chamber causes the oil pressure in the chamber to increase. The oil pressure in the spring chamber will equal the oil pressure that is flowing to the auxiliary circuit.
The oil pressure in the spring chamber is sensed on the right side of the signal duplication valve (12). If this circuit is the only circuit that is active, or this circuit has a work port pressure that is higher than the other circuits that are active, the signal duplication valve will move to the left. This allows oil from the auxiliary pump passage (13) to flow into the load sensing passage (14) until the oil pressure in the load sensing passage is equal to the oil pressure that flows to the work tool. When the pressures are equal, the signal duplication valve shifts right to a metering position.
Oil flows back through couplers (11). The oil flows through line (10) to the spool. The oil flows through the spool to line (17). Then, the oil flows to the tank.
High Flow Auxiliary Circuit
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| Illustration 16 | g01071094 |
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| Illustration 17 | g01071107 |
In order for the high flow auxiliary circuit to activate, you must press the left side of switch (1). When you press switch (1), the ECM for the auxiliary hydraulic circuit activates solenoid (2) and solenoid (3). Solenoid (2) and solenoid (3) move upward. Solenoid (2) is labelled "A2". Solenoid (3) is labelled "A1".
The load signal relief valve (4) moves to the position for the high flow auxiliary circuit. In position for the high flow auxiliary circuit, the load sensing relief valve allows higher oil pressure in the load sensing circuit. This allows the piston pump to output more oil to the control valve (work tool).
The function of the high flow auxiliary circuit is similar to the operation of the auxiliary circuit. When you activate the high flow auxiliary circuit, the ECM allows more electric current to flow to solenoid (2) and solenoid (3). This allows the spool to shift farther allowing more oil to flow to coupling (11) and coupling (15).
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| Illustration 18 | g01071102 |
Pilot oil is directed to the auxiliary circuit spool by thumb wheel (5). When you roll thumb wheel (5) upward, pilot oil flows from line (6) through solenoid (2) to the spool. When the oil overcomes the force of spring (7), the spool moves to the right. Pump supply oil flows from line (8) to the spool. The oil flows through the spool to the feeder passage.
As the oil flows into the feeder passage, oil pressure increases. This increase in oil pressure causes the compensator valve (9) to move to the left. The oil flows through the compensator valve to the spool. The oil flows through the spool to line (10). Then, the oil flows to couplers (11). Couplers (11) are labelled "A2". When you roll the thumb wheel upward, the flow of oil to couplers (11) increases.
Some of the oil that flows through the compensator valve (9) flows through a passage in the compensator valve into the spring chamber that is beside the compensator valve. The flow of oil into the spring chamber causes the oil pressure in the chamber to increase. The oil pressure in the spring chamber will equal the oil pressure that is flowing to the auxiliary circuit.
The oil pressure in the spring chamber is sensed on the right side of the signal duplication valve (12). If this circuit is the only circuit that is active, or this circuit has a work port pressure that is higher than the other circuits that are active, the signal duplication valve will move to the left. This allows oil from the auxiliary pump passage (13) to flow into the load sensing passage (14) until the oil pressure in the load sensing passage is equal to the oil pressure that flows to the work tool. When the pressures are equal, the signal duplication valve shifts right to a metering position.
Oil flows back through couplers (15). The oil flows through line (16) to the spool. The oil flows through the spool to line (17). Then, the oil flows to the tank.
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| Illustration 19 | g01071102 |
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| Illustration 20 | g01071198 |
Roll the thumb wheel downward in order to increase the flow of hydraulic oil to coupling (15). When you roll thumb wheel (5) downward, pilot oil flows from line (6) through solenoid (3) to the spool. When the oil overcomes the force of spring (18), the spool moves to the right. Pump supply oil flows from line (8) to the spool. The oil flows through the spool to the feeder passage.
As the oil flows into the feeder passage, oil pressure increases. This increase in oil pressure causes the compensator valve (9) to move to the left. The oil flows through the compensator valve to the spool. The oil flows through the spool to line (16). Then, the oil flows to couplers (15). Couplers (15) are labelled "A1". When you roll the thumb wheel downward, the flow of oil to couplers (15) increases.
Some of the oil that flows through the compensator valve (9) flows through a passage in the compensator valve into the spring chamber that is beside the compensator valve. The flow of oil into the spring chamber causes the oil pressure in the chamber to increase. The oil pressure in the spring chamber will equal the oil pressure that is flowing to the auxiliary circuit.
The oil pressure in the spring chamber is sensed on the right side of the signal duplication valve (12). If this circuit is the only circuit that is active, or this circuit has a work port pressure that is higher than the other circuits that are active, the signal duplication valve will move to the left. This allows oil from the auxiliary pump passage (13) to flow into the load sensing passage (14) until the oil pressure in the load sensing passage is equal to the oil pressure that flows to the work tool. When the pressures are equal, the signal duplication valve shifts right to a metering position.
Oil flows back through couplers (11). The oil flows through line (10) to the spool. The oil flows through the spool to line (17). Then, the oil flows to the tank.