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| Illustration 1 | g00832146 |
Bank Valve (1) End section (tank) (2) Section for boom raise/lower (3) Pilot port (4) Work port (5) Section for boom extend/retract (6) Port for pilot supply and pressure reducing valve (7) Load sense port for steering (8) Section for auxiliary services (9) Section for left stabilizer (10) Section for right stabilizer (11) Solenoid housing (12) Relief valve for auxiliary services (13) Supply port for frame leveling control valve (14) Load sense port to pump port (15) Implement relief valve (16) Relief valve for auxiliary services (17) Tank return port from the frame leveling control valve (18) Load sense port for the frame leveling control valve (19) Section for the system for the fork tilt (20) Supply port for the steering metering unit (21) Inlet section (22) Pump inlet (23) Main outlet to tank (24) End section (implement relief valve) | |
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| Illustration 2 | g00760218 |
Location of the bank valve | |
The bank valve is located on the right side of the machine in the engine enclosure.
Implement sections (2), (5), and (19) are operated by pilot oil pressure. Implement sections (8), (9), and (10) are operated by solenoids.
The pump delivery line is connected to port (22) of inlet section (21) which is equipped with a flow control valve. The flow control valve provides a priority flow to the steering system from port (20) .
When the flow requirements of the steering system have been met, supply oil flows through a gallery which passes through each of the implement sections to end section (1) .
A load sensing system connects the implement sections and the inlet section to the pressure and flow compensator valve on the pump. The pressure and flow compensator valve matches the pump output to the maximum implement pressure or steering pressure that is required in the system.
A pressure reducing valve is located in inlet section (21). The pressure reducing valve supplies the pilot control system for the implement sections, the service brake boost pressure and the front axle differential lock control.
The maximum working pressure of the implement section is controlled by the implement relief valve (15). The implement relief valve is operated by the load sensing pressure.
Port (23) is the main tank return port from the bank valve.
Relief valves (12) and (16) are operated by load pressure at the auxiliary work ports on implement section (8). The relief valves are set at a lower pressure than the implement relief valve in the end section. Refer to Systems Operation, "Auxiliary System" for further information on the operation of the relief valves.
Implement sections (2) and (5) are equipped with directional spools that are closed at the work ports when the spool is in the NEUTRAL position. Oil can not return to the hydraulic tank and the work ports are not connected together.
Note: Early implement sections (2) and (5) were equipped with directional spools that were open at the work ports when the spools were in the NEUTRAL position.
Implement sections (8), (9), (10) and (19) are equipped with directional spools that are open at the work ports when the spools are in the NEUTRAL position. Oil can return to the hydraulic tank and the work ports are also connected together.
All of the implement sections contain a pressure compensating check valve. The pressure compensating check valves allow the oil flow to be proportionally divided between each of the operating circuits when the flow demands of the system exceed the total flow that is available from the pump. The check valves also maintain constant cylinder speed which is proportional to the position of the joystick control. The cylinder speed is independent of engine speed.
Load Sensing
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| Illustration 3 | g00832659 |
Bank Valve (Load Sensing System) (1) Signal passage (2) Work port passage (3) Resolver valve (4) Passage for steering port (5) Port to frame leveling control valve (6) Relief valve passage (7) Port to pump regulator valve (8) Cartridge for implement relief valve (9) Section for right stabilizer (10) Section for left stabilizer (11) Section for auxiliary services (12) Section for the system for the fork tilt (13) Inlet section (14) Section for boom extend/retract (15) Section for boom raise/lower (16) Pressure compensating check valve (17) Communications passage | |
The pump output is adjusted by the load sensing system to the highest implement demand. Operation of the pump is described in Service Manual, SENR1237.
Sections (9), (10), (11), (12), (13), (14), and (15) contain the following components: signal passage (1), work port passage (2) and resolver valve (3). The components are called out only in boom raise section (15) of Illustration 3. The steering section is contained in inlet section (13) .
The highest working pressure in the system is transmitted to the pump regulator valve section by way of resolver valves (3) and communication passage (17) .
For example, if the boom raise section is in operation, pressure is transmitted through work port passage (2) to the left side of resolver valve (3). If no other section is in operation, or if sections are operating at a lower pressure, the resolver is held to the right and the work port pressure is transmitted through signal passage (1) and the communication passage (17) to the pump regulator valve.
If the work port pressure was higher in any of the other implement sections, or in the section for steering (inlet) (13), pressure would be transmitted through the work port passages, signal passages, and resolver valves of the sections to the right of the boom raise section. Resolver valves (3) would be offset to the left and the higher working pressure would be transmitted through passage (1) and passage (17) to the pump regulator valve.
Maximum working pressure of the implement sections is controlled by relief valve (8) which is operated by load sensing pressure which is transmitted through passage (17) .
Pilot Oil Pressure Operated Implement Sections
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| Illustration 4 | g00851435 |
Implement Section in Neutral Position (1) Pilot chamber (2) Spool (3) Return passage (4) Main pressure gallery (5) Feeder passage (6) Metering slots (7) Pilot chamber (8) Spring (9) Pilot port (10) Work port (11) Bridge passage (12) Work port (13) Spring (14) Pressure compensating check valve (15) Passage (16) Passage (17) Resolver valve (18) Passage (PP) Pump pressure (R) Return oil | |
Illustration 4 shows spool (2) in the NEUTRAL position. The spool is centered by springs (8) and (13) .
View (A-A) shows an implement section with a spool that is open at the work ports when the spool is in the NEUTRAL position. The work ports are connected together and oil is returned to the hydraulic tank. This type of spool is installed in the following implement sections: coupler tilt, auxiliary services and stabilizers.
View (B-B) shows an implement section with a spool that is closed at the work ports when the spool is in the NEUTRAL position. The work ports are not connected together and oil can not return to the hydraulic tank. This type of spool is installed in the following implement sections: boom extend/retract and boom raise/lower.
Note: The early implement sections for the boom extend/retract and the boom raise/lower were equipped with spools with open centers.
Pilot chambers (1) and (7) are connected to the hydraulic tank through the joystick control.
If an upstream implement section is in operation, the load sensing signal from the implement section would pass through passage (16).
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| Illustration 5 | g00851436 |
The implement section is shown in initial pressurization when the steering wheel is stationary and no other implements have been selected. (1) Pilot chamber (2) Spool (3) Return passage (4) Main pressure gallery (5) Feeder passage (6) Metering slots (7) Pilot chamber (8) Spring (9) Pilot port (10) Work port (11) Bridge passage (12) Work port (13) Spring (14) Pressure compensating check valve (15) Passage (16) Passage (17) Resolver valve (18) Passage (PP) Pump pressure (R) Return oil (P) Pilot pressure (LP) Load pressure | |
Pilot pressure in pilot port (9) moves spool (2) to the left and the main pressure gallery (4) is connected to feeder passage (5). Bridge passage (11) is isolated from work port (12) and the passage is connected to work port (10). work port (12) is connected to return passage (3) .
A passage, which extends through all the implement sections, transmits work port pressure to the spring side of pressure compensating check valve (14) .
If other implement sections are in the operating position, the pump output is controlled by the highest work port pressure which is transmitted to the pressure and flow compensator valve on the pump through the load sensing system.
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| Illustration 6 | g00851437 |
The implement section is shown when a work tool is moving. The steering wheel is stationary and no other implements have been selected. (1) Pilot chamber (2) Spool (3) Return passage (4) Main pressure gallery (5) Feeder passage (6) Metering slots (7) Pilot chamber (8) Spring (9) Pilot port (10) Work port (11) Bridge passage (12) Work port (13) Spring (14) Pressure compensating check valve (15) Passage (16) Passage (17) Resolver valve (18) Passage (PP) Pump pressure (R) Return oil (P) Pilot pressure (LP) Load pressure | |
Further movement of spool (2) connects main pressure gallery (4) to feeder passage (5). The pressure and flow compensator valve on the pump maintains pump pressure 2780 ± 100 kPa (400 ± 15 psi) above the highest work port pressure. Pressure in main pressure gallery (4) is therefore 2780 ± 100 kPa (400 ± 15 psi) higher than pressure in feeder passage (5). There is a fixed differential pressure of 2780 ± 100 kPa (400 ± 15 psi) across metering slots (6) which connect the pressure gallery to the feeder passage.
Oil flows from main pressure gallery (4) through feeder passage (5) and passage (15). Pressure compensating check valve (14) moves up forming an orifice between passage (15) and bridge passage (11). Oil flows through this orifice and the bridge passage to port (10), which is connected to one of the ports of the implement cylinder that is being operated. The pressure compensating check valve moves up and down in response to changes in engine speed or load in order to control the size of the orifice that connects passage (15) to bridge passage (11) .
If the work port pressure increases, pressure compensating check valve (14) starts to move down in order to reduce the size of the orifice between passage (15) and bridge passage (11). The load sensing system responds and the pressure increase is transmitted to the pressure and flow compensator valve on the pump and to the spring side of the pressure compensating check valve.
If the flow demand changes, to maintain the differential across the metering slots, the load sensing signal increases the pump output and the pressure in feeder passage (5) increases. Pressure compensating check valve (14) now moves up. This allows flow to the work port. Until another change in the flow or in the load occurs, the pressure compensating check valve will not move and the pressure compensating check valve will remain in this balanced position.
Increased work port pressure is sensed on the spring side of the pressure compensating check valve in all other implement sections. This maintains the same pressure differential across the metering slots of any other directional spool which is in an operating position.
Since the pressure differential between main pressure gallery (4) and feeder passage (5) is constant, the flow rate is directly proportional to the area of the metering slots which connects the two. The flow rate is determined by the amount of the offset of the spool. If a second service is engaged, the engine speed can be changed in order to suit the operating requirement. However, the same speed will remain for the first service provided that the joystick control has remained in the same position.
The same pressure differential is maintained across the metering slots in all spools which have been moved to an operating position. The bank valve therefore operates as a flow divider when more than one service is being operated.
Implement Sections Operated by Solenoids
Auxiliary Services
The solenoids for the auxiliary system and the stabilizer system are controlled by switches. The implement sections are similar in construction and similar in operation to the implement sections for the boom raise/lower, the boom extend/retract, and the fork tilt except for the method that controls the pilot oil flow which operates the spool.
The auxiliary system and the stabilizer system are not proportionally controlled. When the controls for the auxiliary system and the controls for the stabilizer system are operated, the spools are offset fully. When the controls are in the HOLD position, the spools are in the NEUTRAL position.
End Section (Implement Relief Valve)
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| Illustration 7 | g00849845 |
(1) Cover (2) Adjusting screw (3) Spring (4) Tank passage (5) Valve poppet (6) Load sensing passage | |
The end section contains the implement pressure relief valve. The pressure relief valve controls the load sensing pressure. The relief valve is set between 22730 kPa (3297 psi) and 22950 kPa (3330 psi).
The load sensing system is connected to load sensing passage (6) from the section for the right stabilizer.
The pressure in the load sensing system acts against the valve poppet (5). The valve poppet is held against the seat by the force of spring (3). If the pressure reaches the setting of the relief valve, the poppet will raise from the seat. The oil flows through tank passage (4) to the main return gallery.