PIPE AS 4N6228 - Caterpillar

Illustration 4 g03155676
Negative flow control operation (boom I and boom II control valves in the BOOM UP position)
(1) Return passage
(2) Negative flow control pressure sensor (drive pump)
(3) Passage
(4) Relief valve for negative flow control (drive pump)
(5) Passage
(6) Negative flow control orifice
(7) Negative flow control orifice
(8) Relief valve for negative flow control (idler pump)
(9) Negative flow control pressure sensor (idler pump)
(10) Port
(11) Return line
(12) Hydraulic tank
(13) Center bypass passage
(14) Parallel feeder passage
(15) Parallel feeder passage
(16) Center bypass passage
(17) Pilot pump
(18) Idler pump
(19) Proportional reducing valve (idler pump)
(20) Drive pump
(21) Proportional reducing valve (drive pump)
Illustration 5 g03163481
Boom I and Boom II control valves (BOOM UP position)
(13) Center bypass passage
(16) Center bypass passage 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 (20) flows into the front half of the main control valve. The oil delivery flows through center bypass passage (13) to the boom I control valve. The Oil delivery from idler pump (18) flows into the rear half of the main control valve. The oil delivery flows through center bypass passage (16) to the boom II control valve. Since the spool in the boom I control valve is fully shifted, center bypass passage (13) is blocked. The spool in the boom II control valve is shifted to the left. Center bypass passage (16) 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 (6) and (7). No negative flow control pressure is created in center bypass passage (13) and center bypass passage (16). No negative flow control pressure is sent to NFC pressure sensor (2) and NFC pressure sensor (9). The machine ECM sends a PWM driver to proportional reducing valves (21) and (19) in order to 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 (13) and center bypass passage (16).Fine Control Operation
Illustration 6 g03162896
Boom I and Boom II control valves (fine control)
(13) Center bypass passage
(14) Parallel feeder passage
(15) Parallel feeder passage
(16) Center bypass passage
(22) Port
(23) Spool
(24) Passage
(25) Spool
(P) Pilot pressure When 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 (13) to negative flow control orifice (6). The oil delivery from the idler pump flows through center bypass passage (16) to negative flow control orifice (7). When the joystick for the boom is partially moved from the NEUTRAL position in order to perform a fine