 | |
| Illustration 1 | g00508487 |
(1) Top cover (2) Three-point hitch control valve (3) Implement control valves ("+" quick coupler port for extended cylinder and "-" quick coupler port for retracted cylinder) (4) Inlet manifold | |
The implement control valve bank consists of the following components: top cover (1), three-point hitch control valve (2), three or four implement control valves with quick couplers (3) and inlet manifold (4). The implement control valve bank is mounted on top of the rear axle housing and tilts slightly downward toward the rear of the machine.
 | |
| Illustration 2 | g00572671 |
(1) Top cover (2) Three-point hitch control valve (3) Implement control valves ("+" quick coupler port for extended cylinder and "-" quick coupler port for retracted cylinder) (4) Inlet manifold (5) Passage for the load sensing signal to the pressure and flow compensator valve (6) Inlet passage for supply oil from the implement hydraulic pump (7) Return oil passage (8) Port for low pressure return oil (AA) Supply oil (LL) Sump oil | |
Inlet manifold (4) contains inlet passage (6) for supply oil from the implement hydraulic pump. Also, inlet manifold (4) contains outlet passage (5) for the load sensing signal to the pressure and flow compensator valve.
A port for low pressure return oil (8) is available by removing the plug from the left rear of the inlet manifold. The use of a port for low pressure return oil (8) reduces the restriction in the return line from the implement.
The port for low pressure return oil is desired for the following uses: operation of hydraulic motors, hydraulic control valves that are mounted on the implement and application with case drains.
Implement control valves (3) have both O-rings and shims between the valve sections. The O-rings are used in order to seal the fluid passages. The shims are required in order to provide the proper preload on the O-rings.
The sequence of the implement control valves starts at the bottom of the implement control valve bank. The #1 implement control valve is located at the bottom of the implement control valve bank.
The #1 implement control valve and the #2 implement control valve contain load check valves in the EXTEND position. The load check valves are operated by pilot pressure. Hydraulic pressure is used in order to open the load check valves. Therefore, the engine must be running in order to release pressure from components that are attached to the #1 implement control valve or to the #2 implement control valve. The #3 implement control valve and the #4 implement control valves contain no load check valves. The #3 implement control valve and the #4 implement control valve are constructed in the same manner.
HOLD Position
 | |
| Illustration 3 | g00476426 |
Implement control valve (3) Implement control valves (5) Passage for the load sensing signal to the pressure and flow compensator valve (6) Inlet passage for supply oil from the implement hydraulic pump (7) Return oil passage (9) Passage for supply oil to other valves (10) Adjustable flow control assembly (11) Flow control spool (12) Metering sleeve for the flow control (13) Main control valve spool (14) Quick couplers (15) Load check valve (16) Detent (17) Orifice (18) Pressure limiter valve for the detent (19) Adjustment screw (20) Primary resolver (21) Secondary resolver (22) Passage for the resolved load sensing signal from the previous control valve (23) Orifice (AA) Supply oil (BB) Reduced supply oil (DD) Pilot signal oil (HH) Blocked oil (LL) Sump oil | |
Note: All implement control valves (3) have comparable components with one exception. Only the #1 implement control valve and the #2 implement control valve have the porting for load check valves (15) .
The flow priority for this machine is set up as a parallel logic hydraulic system. All of the implement control valves and the three-point hitch have an equal opportunity in order to obtain oil flow. The determining factor is the resolved pressure of each individual implement control valve. None of the implement control valves has a flow priority. If the flow demand is greater than the flow that can be supplied by the pump, the circuits with the lowest pressure will be satisfied first. The circuits with the highest pressures will be satisfied last.
When the engine is not running, the springs at the left end of flow control spool (11) keep the spool shifted to the right.
When the engine is started and the implement control valve is in the HOLD position, supply oil flows through flow control spool (11). The supply oil is then blocked by main control valve spool (13) .
Supply oil flows through a cross-drilled passage in flow control spool (11). The supply oil fills the cavity at the right end of the spool. As the pressure increases, oil forces flow control spool (11) to the left against the springs. This partially closes the holes in the metering sleeve for the flow control (12) .
The metering holes do not close completely. A pressure that is equal to the spring force value of 965 kPa (140 psi) is maintained at main control valve spool (13). This improves the response to the implement when main control valve spool (13) is shifted.
The position of flow control spool (11) routes supply oil through a common passage (9) to the balance of the implement control valve bank.
Each of the implement control valves have equal access to the supply oil that is routed through passage (9) .
In the HOLD position, each flow control spool (11) shifts in order to maintain a pressure that is equal to the spring force value of flow control spool (11) at main control valve spool (13) .
Flow control spool (11) is actually a pressure reducing valve. Flow control spool (11) is controlled by the combination of the spring force value and the load sensing signal. Flow control spool (11) is used in order to control flow across an orifice.
The orifice size will vary depending on the position of flow control assembly (10) and the orifice size will vary depending on the pressure of the load sensing signal that is applied to flow control spool (11) .
RAISE Position
 | |
| Illustration 4 | g00476785 |
Implement control valve (3) Implement control valves (5) Passage for the load sensing signal to the pressure and flow compensator valve (6) Inlet passage for supply oil from the implement hydraulic pump (7) Return oil passage (9) Passage for supply oil to other valves (10) Adjustable flow control assembly (11) Flow control spool (12) Metering sleeve for the flow control (13) Main control valve spool (14) Quick couplers (15) Load check valve (16) Detent (17) Orifice (18) Pressure limiter valve for the detent (19) Adjustment screw (20) Primary resolver (21) Secondary resolver (22) Passage for the resolved load sensing signal from the previous control valve (23) Orifice (AA) Supply oil (BB) Reduced supply oil (DD) Pilot signal oil (LL) Sump oil | |
"-" Quick coupler port (14) opens to the common sump when main control valve spool (13) is shifted to the RAISE position. Also, the "-" passage for the load sensing signal opens to the common sump.
In the #1 implement control valve and the #2 implement control valve, the supply oil is initially blocked from "+" quick coupler port (14) by load check valve (15). Also, the supply oil is blocked from the passage to the common sump by main control valve spool (13) .
Working pressure at "+" quick coupler port (14) is initially blocked from the passage for supply oil by load check valve (15). The initial pressure of the supply oil at the bottom of load check valve (15) is not enough to unseat the valve.
Pressure from load sensing signal (22) enters primary resolver (20). If the "-" quick coupler port is opened to the common sump, the pressure of the load sensing signal is directed to both secondary resolver (21) and to the spring chamber of flow control spool (11). The resolved pressure of load sensing signal (5) will be sensed by the pressure and flow compensator valve. This causes the implement hydraulic pump to slightly upstroke.
Pressure from load sensing signal (5) plus the spring force value in the spring chamber move flow control spool (11) to the right. This allows a greater pressure into the passage to "+" quick coupler port (14). The higher pressure will be sensed at the implement hydraulic pump.
The pump output pressure and pressure at "+" quick coupler port (14) continue to increase until the pressure at the bottom of load check valve (15) is great enough to unseat the load check valve.
The pressure of the load sensing signal in the spring chamber would still continue to increase until load check valve (15) is unseated. Orifice (23) in the passage to the spring chamber provides a slight pressure drop.
Orifice (23) meters the rate of the pressure increase in the spring chamber. This will ultimately control the rate of the pressure increase in the passage to "+" quick coupler port (14) .
Load check valve (15) has a 10:1 ratio. In order to unseat the load check valve, the supply pressure must be at 1/10 of the value of the load pressure.
When load check valve (15) is unseated, the load pressure at "+" quick coupler port (14) is felt in the supply passage to "+" quick coupler port (14). The load pressure at "+" quick coupler port (14) is the pressure that is sensed in the signal passage to primary resolver (20) .
When the "-" quick coupler port is still open to the common sump, the pressure of the load sensing signal is directed to secondary resolver (21). Also, the pressure of the load sensing signal is directed to the spring chamber of flow control spool (11). The pressure of the load sensing signal is compared to the highest resolved pressure from the previous valves through passage (22) .
If another implement control valve is operating at a higher pressure, the load sensing signal with the highest resolved pressure is sent to the pressure and flow compensator valve.
The increase in supply oil from the implement hydraulic pump now flows into flow control spool (11). The oil flows through the small holes in the metering sleeve for flow control (12). The oil flows past main control valve spool (13) to "+" quick coupler port (14). A decrease in pressure occurs as the oil is metered through the small holes in the metering sleeve for flow control (12) .
The decrease in pressure is controlled by the following items: back pressure from the load sensing signal, spring force value of 965 kPa (140 psi) in flow control spool (11) and orifice that is created at the main control spool.
In the #1 implement control valve and #2 implement control valve, the oil flows past main control valve spool (13). Next, the oil flows through the open load check valve (15) and out "+" quick coupler port (14). The load check valves help prevent implement drift that may occur when an implement is raised and left in the HOLD position.
For all of the implement control valves, the pressure of the resolved load sensing signal from secondary resolver (21) flows to the left end of flow control spool (11) .
The load sensing signal pressure works with the spring force value of flow control spool (11) in order to force the spool to the right. At the same time, the pump supply pressure that is on the right end of the spool tries to push the spool to the left. These opposing forces balance flow control spool (11) in order to maintain the pressure at main control valve spool (13) .
The balancing of flow control spool (11) provide a constant flow to the implement for a given movement of the lever. Since the #3 implement control valve and the #4 implement control valve do not have the porting for load check valves, the oil flows past the main control valve spool to "+" quick coupler port (14) .
Note: Flow control spool (11) also acts as a load check valve which prevents oil from flowing back into the system when pressure at the quick coupler port is higher than supply pressure. Flow control spool (11) works as a load check valve in order to prevent implement drift when an implement hydraulic circuit is initially activated. The initial pressure of the load sensing signal is sensed at flow control spool (11). This shifts the spool completely to the right. This also prevents oil from "+" quick coupler port (14) from flowing back through the main control valve spool and into the main system. If the pump supply pressure becomes higher than the combined pressure that is required at "+" quick coupler port (14) plus the spring force value of 965 kPa (140 psi), the supply pressure shifts flow control spool (11) back to the left. This permits oil to flow past main control valve spool (13) to "+" quick coupler port (14) .
LOWER Position
 | |
| Illustration 5 | g00477111 |
Implement control valve (3) Implement control valves (5) Passage for the load sensing signal to the pressure and flow compensator valve (6) Inlet passage for supply oil from the implement hydraulic pump (7) Return oil passage (9) Passage for supply oil to other valves (10) Adjustable flow control assembly (11) Flow control spool (12) Metering sleeve for the flow control (13) Main control valve spool (14) Quick couplers (15) Load check valve (16) Detent (17) Orifice (18) Pressure limiter valve for the detent (19) Adjustment screw (20) Primary resolver (21) Secondary resolver (22) Passage for the resolved load sensing signal from the previous control valve (23) Orifice (AA) Supply oil (BB) Reduced supply oil (DD) Pilot signal oil (LL) Sump oil | |
When main control valve spool (13) is shifted to the LOWER position, pump supply passage (6) is open to both the bottom of load check valve (15) and "-" quick coupler port (14) .
When there is no load pressure in "+" quick coupler port (14), the initial pump supply pressure is able to unseat load check valve (15). This opens both "+" quick coupler port (14) and the passage for the load sensing signal to the common sump. The passage between the pump supply and the common sump is blocked by main control valve spool (13) .
The pressure at "-" quick coupler port (14) is sensed in the passage for the load sensing signal. The pressure of the load sensing signal enters primary resolver (20). The highest resolved pressure which is in "-" quick coupler port (14) is directed to secondary resolver (21) .
The pressure of the load sensing signal from "-" quick coupler port (14) is compared to the highest resolved pressure from the previous implement control valves. The highest resolved load sensing signal from "-" quick coupler port (14) causes the load sensing signal pressure to be directed through passage (5) to the pressure and flow compensator valve. This causes the pump output to increase.
Flow control spool (11) performs the same function that is described in the previous section with respect to providing flow for "-" quick coupler port (14). See "RAISE Position" for more information.
FLOAT Position
 | |
| Illustration 6 | g00477381 |
Implement control valve (3) Implement control valves (5) Passage for the load sensing signal to the pressure and flow compensator valve (6) Inlet passage for supply oil from the implement hydraulic pump (7) Return oil passage (9) Passage for supply oil to other valves (10) Adjustable flow control assembly (11) Flow control spool (12) Metering sleeve for the flow control (13) Main control valve spool (14) Quick couplers (15) Load check valve (16) Detent (17) Orifice (18) Pressure limiter valve for the detent (19) Adjustment screw (20) Primary resolver (21) Secondary resolver (22) Passage for the resolved load sensing signal from the previous control valve (23) Orifice (24) Cross-drilled passage (AA) Supply oil (BB) Reduced supply oil (DD) Pilot signal oil (LL) Sump oil | |
When the implement control lever is moved to the FLOAT position, implement valve detent (16) holds main control valve spool (13) in that position.
When the FLOAT position is selected, supply oil from flow control spool (11) is blocked. However, main control valve spool (13) has a cross-drilled passage (24) between the two center lands.
Cross-drilled passage (24) provides a path for the pressure of the supply oil which is used in order to unseat load check valve (15) .
When load check valve (15) is unseated, both "-" quick coupler port (14) and "+" quick coupler port (14) are open to the common sump.
Detent Positions
 | |
| Illustration 7 | g00477420 |
Implement Valve Detent (7) Return oil passage (13) Main control valve spool (16) Detent balls (17) Orifice (18) Pressure limiter valve for the detent (19) Adjustment screw (25) Detent positions (26) Centering spring (27) Piston (DD) Pilot signal oil (LL) Sump oil | |
Each implement control valve has the following detent positions (25) : HOLD, RAISE, LOWER and FLOAT. When the implement control lever is moved to either the RAISE position or the LOWER position, detents (25) hold both the spool and the respective implement control lever in the position that is selected. Detents (25) are located on the end of main control valve spool (13) .
A selected detent position is constant until the implement control lever is moved to a different position or until the pressure of the load sensing signal becomes greater than 17240 ± 1380 kPa (2500 ± 200 psi).
If the pressure of the load sensing signal is greater than 17240 ± 1380 kPa (2500 ± 200 psi), the pressure of the load sensing signal will move pressure limiter valve (18) to the left. When pressure limiter valve (18) moves, the pressure of the load sensing signal is felt at piston (27). Piston (27) holds the detent balls (16) in place. The pressure that is required to move piston (27) must first overcome the leak path to the common sump that is created by orifice (17). The leak path to the common sump helps prevent the premature release of detents (25) due to shock loads.
When the pressure increases, piston (27) will move to the left. This allows detent balls (16) to fall away from the RAISE position of the detent (25). Centering spring (26) then moves the main control valve spool (13) to the HOLD position. When main control valve spool (13) is moved to the "HOLD" position, pressure limiter valve (18) closes. This is due to the loss of the load sensing signal that is from the quick coupler port. Oil that is behind piston (27) flows to the common sump through orifice (17) .
Note: The kickout pressure is adjusted by turning adjustment screw (19). Adjustment screw (19) is located on the left side of the implement control valve.
Pump Signal Control Network
 | |
| Illustration 8 | g00651611 |
Pump Signal Control Network (2) Three-point hitch control valve (3) Implement control valve (4) Inlet manifold (5) Passage for the load sensing signal to the pressure and flow compensator valve (6) Inlet passage for supply oil from the implement hydraulic pump (7) Return oil passage (11) Flow control spool (13) Main control valve spool (20) Primary resolver (21) Secondary resolver (28) Check ball (AA) Supply oil (LL) Sump oil | |
Each implement control valve (3) and three-point hitch control valve (2) has a primary resolver (20) and secondary resolver (21). A resolver is a double check valve which compares two load sensing signals. The resolver will then send the highest resolved pressure to the next component in the circuit.
Primary Resolver
When main control valve spool (13) is shifted in order to direct the output flow, primary resolver (20) compares the pressures of the load sensing signals that are from the two quick coupler ports of the circuit. The highest pressure of the load sensing signals blocks the low pressure side which permits the load sensing signal to flow to secondary resolver (21) .
Secondary Resolver
Secondary resolver (21) compares the pressure of the load sensing signal of one implement control valve to the previous implement control valve.
The pump signal control network works from the top of the implement control valve bank to the bottom of the implement control valve bank. The resolved pressure from three-point hitch control valve (2) is compared against the #4 implement control valve (if equipped), or against the #3 implement control valve.
The resolved pressures are compared throughout the implement control valve bank so that the highest resolved pressure of the load sensing signals is sent from inlet manifold (4) through passage (5) to the pressure and flow compensator valve.
The highest resolved pressure of a load sensing signal will signal the implement hydraulic pump in order to adjust the displacement.
When the implement control valves are in the HOLD position, both sides of the primary resolver (20) are open to the common sump.
Note: The pump signal control network does not add the pressures of the various load sensing signals together. Instead, the highest resolved pressure of a load sensing signal plus the margin pressure will govern the pump output. The margin pressure is 1830 ± 100 kPa (265 ± 15 psi). The output of the implement hydraulic pump does not change until a different highest resolved load sensing signal is identified.
When the capacity of the pump output is exceeded, the implement control valves with the lowest pressure of the load sensing signals are satisfied first.