NET, LEFT UNDER SIDE 0857469 - Caterpillar

Illustration 5 shows the negative flow control operation at the main control valve when the boom I and boom II control valves are in the BOOM UP position.The joystick for the boom has been moved fully to the BOOM UP position. Pilot oil has fully shifted the boom I control valve and the boom II control valve. The oil delivery from drive pump (16) flows into the front half of the main control valve. The oil delivery flows through center bypass passage (12) to the boom I control valve. The Oil delivery from idler pump (19) flows into the rear half of the main control valve. The oil delivery flows through center bypass passage (15) to the boom II control valve. Since the spool in the boom I control valve is fully shifted, center bypass passage (12) is blocked. The spool in the boom II control valve is shifted to the left. Center bypass passage (15) is blocked. All of the oil delivery from the drive pump and the idler pump flows to the head end of the boom cylinders. No oil flows to negative flow control orifices (4) and (5) . No negative flow control pressure is created in center bypass passage (12) and center bypass passage (15) . Since no negative flow control pressure is sent to the drive pump regulator or the idler pump regulator, the pump regulators move the swashplates of the pumps toward the maximum angle position. The output flow of the drive pump and idler pump is increased since no negative flow control pressure is created in center bypass passage (12) and center bypass passage (15) .During machine operation, the machine ECM sends a signal to the proportional solenoid valve for negative flow control (17) . Negative flow control pressure in the center bypass passage is blocked when the control valve spools shift. The machine ECM parameters control the flow and pressure of the pumps. The machine ECM regulates the negative flow control pressure that will be supplied to the pump regulator. The negative flow control pressure forces the swashplate in the pump to the correct angle to limit the flow and pressure from the pumps.Fine Control Operation
Illustration 6 g02008338
Boom I and Boom II control valves (fine control) (12) Center bypass passage (13) Parallel feeder passage (14) Parallel feeder passage (15) Center bypass passage (22) Port (23) Spool (24) Passage (25) Spool (P) Pilot pressureWhen the joystick for the boom is in the NEUTRAL position, spool (23) and spool (25) are in the NEUTRAL position. The oil delivery from the drive pump flows through center bypass passage (12) to negative flow control orifice (4) . The oil delivery from the idler pump flows through center bypass passage (15) to negative flow control orifice (5) . When the joystick for the boom is partially moved from the NEUTRAL position in order to perform a fine control operation, pilot pressure (P) enters the control valves at the pilot ports. Pilot pressure shifts spool (23) and