PIN 4152354 - Caterpillar

During combined operations of BOOM RAISE and STICK IN, the pilot oil pressure from the pilot control valve for the boom (22) activates the pressure reducing valve for boom priority (26). The pressure reducing valve for boom priority (26) causes oil flow priority to the head end of the boom cylinders (1) during this combined hydraulic operation.When the joystick for the stick is moved to the STICK IN position, a portion of the pilot oil from the pilot control valve for the stick (41) flows through the pressure reducing valve for the boom priority (26) to the stick II control valve (40). As the joystick for the boom is moved farther from the NEUTRAL position during a BOOM RAISE operation, pilot oil pressure from the pilot control valve for the boom (22) increases. This gradual increase in pilot oil pressure causes the spool in the pressure reducing valve for the boom priority (26) to gradually shift.A portion of the pilot oil that flows to stick II control valve (40) from the pilot control valve for the stick (41) is routed to the hydraulic tank. The pilot oil pressure that acts on stick II control valve (40) decreases. Stick II control valve (40) shifts toward the NEUTRAL position. The amount of oil flow from the main pumps to the stick hydraulic circuit decreases. This causes a greater portion of the oil flow from the main pumps to flow to the head end of the boom cylinders (1) .Since the pilot oil pressure from the pilot control valve for the boom (22) directly corresponds to the amount of movement or position of the joystick a gradual change to boom priority occurs. Thus, boom priority is controlled by the position of the joystick for the boom and boom priority automatically activates when the joystick reaches a certain position during a BOOM RAISE operation.The above information describes the condition of BOOM RAISE and STICK IN. During any combined function of BOOM RAISE and STICK IN, BOOM RAISE and STICK OUT, or BOOM RAISE and BUCKET CLOSE, the pressure reducing valve for boom priority allows priority flow to the head end of the boom cylinders by reducing pilot pressure to the stick I, stick II, or bucket control valves.ReferenceFor more information concerning boom priority, refer to Systems Operation, "Pilot Hydraulic System".Boom Lower
Illustration 6 g01338777
Hydraulic schematic for BOOM LOWER (1) Boom cylinders (2) Line (oil flow to boom cylinder rod end) (3) Line (oil flow from boom cylinder head end) (4) Valve (5) Boom drift reduction valve (14) Load check valve (16) Boom II control valve (17) Parallel feeder passage (18) Return passage (19) Boom I control valve (22) Pilot control valve (boom and bucket) (27) Idler pump (28) Drive pump (29) Pilot pump (33) Spring (40) Orifice (41) Boom regeneration valve (42) Port (43) Orifice (44) Negative flow control line (45) Center bypass passage (46) Port (48) Valve (49) Passage (50) Drain line (52) Pilot line (53) Pilot lineDuring a BOOM LOWER operation, the