Introduction
The right pump and the left pump receive signal oil pressure from the center bypass passages of the main control valve. This signal oil pressure that is created in the center bypass passages of the main control valve is called negative flow control pressure. Negative flow control pressure flows to the regulators at the right pump and the left pump in order to control the output flow of the pumps. Negative flow control pressure is created during the following machine operating conditions.
- All of the joysticks and travel levers/pedals are in the NEUTRAL position.
- Any of the joysticks and/or travel levers/pedals are partially moved from the NEUTRAL position in order to perform a fine control operation.
- A boom lower operation is performed alone.
- An open/close operation for the grapple is performed.
 | |
| Illustration 1 | g00690034 |
Main control valve (top view) (12) Negative flow control line to left pump (13) Negative flow control line to right pump | |
The right body of the control valve receives supply oil from the right pump. Negative flow control pressure from the right body of the main control valve flows through negative flow control line (13) to the right pump. The left body of the control valve receives supply oil from the left pump. Negative flow control pressure from the left body of the main control valve flows through negative flow control line (12) to the left pump. The negative flow control operation of the right pump and the left pump is identical.
 | |
| Illustration 2 | g00885182 |
Negative flow control operation (control valves in the NEUTRAL position) (1) Center bypass passage (2) Return line (3) Center bypass passage (4) Passage (5) Relief valve (negative flow control) (6) Relief valve (negative flow control) (7) Negative flow control orifice (8) Port (9) Negative flow control orifice (10) Passage (11) Return passage (12) Negative flow control line (13) Negative flow control line (14) Left pump (15) Right pump (16) Pilot pump (17) Pilot line (18) Proportional reducing valve (negative flow control) | |
 | |
| Illustration 3 | g00747365 |
Control valve (NEUTRAL position) (3) Center bypass passage | |
Illustration 2 shows the negative flow control operation at the main control valve when all of the control valves are in the NEUTRAL position. When all of the joysticks and the travel levers/pedals are in the NEUTRAL position, the spools of the individual control valves are in the NEUTRAL position. Oil flow to the cylinders and motors is blocked. Center bypass passages (1) and (3) are open.
All of the oil delivery from right pump (15) flows through center bypass passage (3), passage (4) and negative flow control orifice (9) to return line (2). Negative flow control orifice (9) restricts the oil flow. The pressure in passage (4) increases. Increased negative flow control pressure now flows through passage (10) and negative flow control line (13) to the pump regulator. The negative flow control operation of the right pump regulator causes the swashplate of the right pump to move to the minimum angle position. The output flow of the right pump is decreased due to the increased negative flow control pressure that is created in center bypass passage (3) .
Since center bypass passage (1) is also open, the negative flow control operation of the left pump regulator is identical to the negative flow control operation of the right pump regulator.
Reference: For more information concerning the negative flow control operation of the main pump regulators, refer to Systems Operation, "Pump Control (Main Hydraulic)".
 | |
| Illustration 4 | g00940210 |
Negative flow control operation (right travel control valve in the REVERSE position) (1) Center bypass passage (2) Return line (3) Center bypass passage (4) Passage (5) relief valve (negative flow control) (6) relief valve (negative flow control) (7) Negative flow control orifice (8) Port (9) Negative flow control orifice (10) Passage (11) Return passage (12) Negative flow control line (13) Negative flow control line (14) Left pump (15) Right pump (16) Pilot pump (17) Pilot line (18) Proportional reducing valve (negative flow control) | |
 | |
| Illustration 5 | g00940376 |
Right travel control valve (REVERSE position) (3) Center bypass passage | |
Illustration 4 shows the negative flow control operation at the main control valve when only the right travel control valve is in the REVERSE position.
All of the control valves in the left body of the main control valve are in the NEUTRAL position. Center bypass passage (1) is open. All of the oil delivery from the left pump flows through center bypass passage (1) to negative flow control orifice (7). Since all of the oil delivery from left pump (14) is restricted by negative flow control orifice (7), negative flow control pressure (PN) in center bypass passage (1) is at maximum pressure. The negative flow control pressure flows through negative flow control line (12) to the left pump regulator. The negative flow control operation of the left pump regulator causes the swashplate of the left pump to move to the minimum angle position. The output flow of the left pump is decreased due to the increased negative flow control pressure that is created in center bypass passage (1) .
The lever for right travel has been moved fully to the REVERSE position. Pilot oil has fully shifted the right travel control valve. The oil delivery from right pump (15) flows into the right body of the main control valve. The oil delivery flows through center bypass passage (3) to the right travel control valve. Since the spool in the right travel control valve is fully shifted, center bypass passage (3) is blocked. All of the oil delivery from the right pump flows to the right travel motor. No oil flows to negative flow control orifice (9) and no negative flow control pressure is created in center bypass passage (3). Since no negative flow control pressure is sent to the right pump regulator, the right pump regulator moves the swashplate of the right pump toward the maximum angle position. The output flow of the right pump is increased since no negative flow control pressure is created in center bypass passage (3).
 | |
| Illustration 6 | g00940022 |
Negative flow control operation (grapple control valve in the GRAPPLE OPEN position) (1) Center bypass passage (2) Return line (3) Center bypass passage (4) Passage (5) Relief valve (negative flow control) (6) Relief valve (negative flow control) (7) Negative flow control orifice (8) Port (9) Negative flow control orifice (10) Passage (11) Return passage (12) Negative flow control line (13) Negative flow control line (14) Left pump (15) Right pump (16) Pilot pump (17) Pilot line (18) Proportional reducing valve (negative flow control) (25) Pilot oil manifold | |
 | |
| Illustration 7 | g00808213 |
Grapple control valve (GRAPPLE OPEN position) (3) Center bypass passage | |
Illustration 6 shows the negative flow control operation at the main control valve when only the grapple control valve is in the GRAPPLE OPEN position.
All of the control valves in the left body of the main control valve are in the NEUTRAL position. Center bypass passage (1) is open. All of the oil delivery from the left pump flows through center bypass passage (1) to negative flow control orifice (7). Since all of the oil delivery from left pump (14) is restricted by negative flow control orifice (7), negative flow control pressure (PN) in center bypass passage (1) is at maximum pressure. The negative flow control pressure flows through negative flow control line (12) to the left pump regulator. The negative flow control operation of the left pump regulator causes the swashplate of the left pump to move to the minimum angle position. The output flow of the left pump is decreased due to the increased negative flow control pressure that is created in center bypass passage (1) .
The switch for the grapple has been activated for the GRAPPLE OPEN position. Pilot oil has fully shifted the grapple control valve. The oil delivery from right pump (15) flows into the right body of the main control valve. The oil delivery flows through center bypass passage (3) to the grapple control valve. Since the spool in the grapple control valve is fully shifted, center bypass passage (3) is blocked. All of the oil delivery from the right pump flows to the rod end of the grapple cylinder. No oil flows to negative flow control orifice (9) and no negative flow control pressure is created in center bypass passage (3) .
During a grapple operation, negative flow control pressure is created by pilot oil pressure and proportional reducing valve (18). When the solenoid for the grapple is activated, proportional reducing valve (18) for the negative flow control is energized. Pilot line (17) supplies pilot oil pressure to proportional reducing valve (18). The machine ECM sends a signal to proportional reducing valve (18) in order to set the negative flow control pressure. If another machine operation is performed during a grapple operation, proportional reducing valve (18) controls the negative flow control pressure of the left pump and/or right pump.
Fine Control Operation
 | |
| Illustration 8 | g00747367 |
Control valve (fine control) (3) Center bypass passage (21) Parallel feeder passage (22) Port (23) Spool (24) Passage (P) Pilot pressure | |
When the joystick for the control valve is in the NEUTRAL position, spool (23) is in the NEUTRAL position. The oil delivery from the right pump flows through center bypass passage (3) to negative flow control orifice (9). When the joystick for the control valve is partially moved from the NEUTRAL position in order to perform a fine control operation, pilot pressure (P) enters the control valve at the pilot port. Pilot pressure shifts spool (23) slightly to the left. The movement of spool (23) partially opens passage (24). Center bypass passage (3) is partially blocked.
The oil delivery from the right pump is now divided into two flow paths. A portion of the oil delivery from the right pump flows through center bypass passage (3) to negative flow control orifice (9). The remainder of the oil delivery from the right pump flows through parallel feeder passage (21) and passage (24) to port (22). The oil flow from center bypass passage (3) to negative flow control orifice (9) decreases. The flow resistance through the negative flow control orifice decreases and the negative flow control pressure (PN) in passage (4) decreases. The negative flow control pressure that is sent to the regulator at the right pump decreases. The pump regulator causes the swashplate of the right pump to move toward the maximum angle position. The output flow of the pump is increased due to the decrease in negative flow control pressure (PN) .
When the joystick for the control valve is moved to the full stroke position, spool (23) shifts fully to the left. Center bypass passage (3) is now blocked by spool (23). Since there is no oil flow through center bypass passage (24), no negative flow control pressure is created. The swashplate of the right pump is moved to the maximum angle position. The output flow of the right pump is maximum. The output flow of the right pump is now controlled by the constant horsepower flow control.
The ability to modulate the negative flow control pressure by partial movement of the joystick enables fine control of the implements.
Relief Valve (Negative Flow Control)
 | |
| Illustration 9 | g00747369 |
Relief valve (negative flow control) (2) Return line (3) Center bypass passage (4) Passage (5) Relief valve (negative flow control) (9) Negative flow control orifice (11) Return passage (17) Plug (18) Spring (19) Relief valve body (20) Valve (PN) Negative flow control pressure | |
The following description is given for the operation of the relief valve that is located in the right body of the main control valve. The operation of the relief valve for the negative flow control that is located in the left body of the main control valve is identical.
Relief valve (5) for the negative flow control consists of plug (17), spring (18), relief valve body (19) and valve (20). When any one of the joysticks and/or travel levers/pedals is at the full stroke position, the oil flow through center bypass passage (3) is blocked. No oil flows to the relief valve for the negative flow control.
When all of the joysticks and/or travel levers/pedals are suddenly returned to the NEUTRAL position, all of the output flow from the right pump flows through center bypass passage (3). The negative flow control pressure in center bypass passage (3) and passage (4) suddenly increases. When the negative flow control pressure becomes higher than the pressure setting of relief valve (5) for the negative flow control, valve (20) shifts to the left against the force of spring (18). Oil in center bypass passage (3) is now allowed to flow past valve (20) into return passage (11) to the hydraulic tank. This prevents the hydraulic shock that occurs due to sudden changes in negative flow control pressure.
After the hydraulic shock is relieved by the relief valve for the negative flow control, the force of spring (18) shifts valve (20) to the right. All of the output flow from the right pump flows through center bypass passage (3), negative flow control orifice (9) and return line (2) to the hydraulic tank.
Negative flow control pressure (PN), that is created in center bypass passage (3), reaches maximum pressure since all of the oil flow is restricted by negative flow control orifice (9). The negative flow control pressure flows to the right pump regulator. The regulator at the right pump causes the swashplate of the right pump to move to the minimum angle position. The output flow of the right pump is decreased due to the increase in negative flow control pressure (PN) .