DOOR AS 1291276 - Caterpillar

Main Control Valve Operation in Neutral Position
Illustration 5 g00472515
Main control valve (neutral position) (8) Return port (9) Parallel feeder passage (11) Control valve (left travel) (12) Control valve (straight travel) (13) Control valve (right travel) (14) Control valve (attachment) (15) Control valve (bucket) (16) Center bypass passage (18) Control valve (boom I) (19) Control valve (stick II) (21) Orifice (negative flow control) (22) Control valve (boom II) (24) Center bypass passage (25) Control valve (stick I) (26) Control valve (swing) (29) Orifice (negative flow control) (34) Parallel feeder passage (36) Inlet port (rear pump) (37) Inlet port (front pump) (45) Left body (46) Right bodyWhen all the control levers are in the NEUTRAL position, front pump oil flows through center bypass passage (24), negative flow control orifice (29) and return port (8) back to the hydraulic tank. Rear 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.Negative Flow Control Signal
Illustration 6 g00544585
Hydraulic schematic (negative flow control) (16) Center bypass passage (20) Relief valve (negative flow control) (21) Orifice (negative flow control) (24) Center bypass passage (29) Orifice (negative flow control) (30) Relief valve (negative flow control) (39) Negative flow control line (40) Negative flow control line (41) Upper pump (42) Lower pump (56) Return Passage (57) Passage (58) Passage (60) Port (61) Return passage
Illustration 7 g00472967
Main control valve (rear view) (39) Negative flow control line (40) Negative flow control lineOil from upper pump (41) enters the main control valve. A portion of the oil then flows through orifice (21) to return passage (56). Orifice (21) restricts the oil flow. The pressure in passage (57) increases. The negative flow control now flows through passage (58) and negative flow control line (39) to the pump regulator. The negative flow control of the regulator causes the pump to destroke.When all controls are in NEUTRAL position, all of the upper pump oil flows through center bypass passage (16). The oil then flows through orifice (21) and return passage (56). The oil then flows back to the hydraulic tank.Maximum negative flow control pressure in passage (57) now flows to the upper pump. The pump cylinder rotates to the minimum angle. At the minimum angle, the upper pump destrokes. The minimum amount of oil flow is provided.Negative flow control operates in the same manner for the lower pump (42) .Individual Valve Operation
Neutral Position
Illustration 8 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 all pilot control valve levers are in the NEUTRAL position, pilot oil