ELECTRONICS GP-ENGINE 4197848 - Caterpillar

The upper pump supplies oil to right body (46) through inlet port (37). The oil then flows through center bypass passage (24) and parallel feeder passage (9). The lower pump supplies oil to left body (45) through inlet port (36). The oil then flows through center bypass passage (16) and parallel feeder passage (34) .When all the control levers are in the NEUTRAL position, upper pump oil flows through center bypass passage (24), negative flow control orifice (29) and return port (8) back to the hydraulic tank. Lower pump oil from inlet port (36) flows through center bypass passage (16), negative flow control orifice (21) and return port (8) back to the hydraulic tank. Oil in parallel feeder passages (9) and (34) remains blocked by each control valve stem.Activation of any control lever provides two paths for upper pump oil. One path flows through center bypass passage (24) to right travel control valve (13). The other path flows through parallel feeder passage (9), attachment control valve (14), bucket control valve (15) and boom I control valve (18). Activation of any control lever also provides two paths for lower pump oil. One path flows through center bypass passage (16) to left travel control valve (11) and control valve (25) for stick I. The other path flows through parallel feeder passage (34) to swing control valve (26) .Individual Valve Operation
Illustration 6 g00472174
Bucket control valve (neutral position) (10) Load check valve (15) Control valve (bucket) (16) Center bypass passage (17) Line relief valve (bucket cylinder rod) (28) Line relief valve (bucket cylinder head end) (34) Parallel feeder passage (47) Pilot port (48) Port (49) Return passage (50) Passage (51) Pilot port (52) Spring (53) StemThe bucket control valve is used as a typical example for describing the operation of individual control valves.When the pilot control valve levers are in the NEUTRAL position, pilot oil does not flow to port (47) and port (51) from the pilot control valve. Stem (53) is centered in the NEUTRAL position by the force of spring (52). The upper pump oil flows through center bypass passage (16) to the hydraulic tank.
Illustration 7 g00472175
Bucket control valve (10) Load check valve (16) Center bypass passage (34) Parallel feeder passage (47) Pilot port (48) Port (49) Return passage (50) Passage (54) Passage (55) PortWhen the bucket control valve is moved to the CLOSE position, pilot oil is supplied to pilot port (47). Stem (53) moves to the left. Center bypass passage (16) is closed and passage (54) becomes opened. Port (48) is now connected to return passage (49) .Oil that is in parallel feeder passage (34) flows through load check valve (10), passage (50) and passage (54). The oil then flows to port (55). The bucket cylinder rod extends. When the bucket cylinder rod extends, the displaced oil in the rod end flows to port (48) .Oil flows through port (48) to return passage (49) and back to the hydraulic tank.Negative Flow Control Signal
Illustration 8 g00472968
Hydraulic schematic (negative flow control) (16) Center