SEAL KIT 1379403 - Caterpillar

During combined operations of BOOM RAISE and STICK IN, the pilot oil pressure from pilot control valve for the boom (4) activates pressure reducing valve for boom priority (9). Pressure reducing valve for boom priority (9) causes oil flow priority to the head end of boom cylinders (1) during this combined hydraulic operation.When the joystick is moved to the STICK IN position, a portion of the pilot oil from pilot control valve for the stick (41) flows through pressure reducing valve for the boom priority (9) to stick II control valve (42). As the joystick for the boom is moved farther from the NEUTRAL position during a BOOM RAISE operation, pilot oil pressure from pilot control valve for the boom (4) increases. This gradual increase in pilot oil pressure causes the spool in pressure reducing valve for the boom priority (9) to shift.A portion of the pilot oil that flows to stick II control valve (42) from pilot control valve for the stick (41) is routed to the hydraulic tank. The pilot oil pressure that acts on stick II control valve (42) decreases. Stick II control valve (42) shifts toward the NEUTRAL position. The amount of oil flow from the main pumps to the stick hydraulic circuit decreases. The decrease in oil causes a greater portion of the oil flow from the main pumps to flow to the head end of boom cylinders (1).Since, the pilot oil pressure from pilot control valve for the boom (4) 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. Boom priority automatically activates when the joystick reaches a certain position during a BOOM RAISE operation.Reference: For more information concerning boom priority, refer to Systems Operation, "Pilot Hydraulic System".Boom Lower
Illustration 5 g06161188
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) Pilot control valve (boom and bucket)
(10) Parallel feeder passage
(14) Boom drift reduction valve
(15) Passage
(16) Boom I control valve
(17) Spring
(18) Check valve
(19) Boom regeneration proportional reducing valve
(20) Boom II control valve
(24) Valve
(25) Load check valve
(26) Passage
(27) Return passage
(32) Drive pump
(33) Pilot pump
(34) Idler pump
(43) Pilot line
(44) Negative flow control line
(45) Boom regeneration valve
(46) Passage
(47) Valve
(48) Drain line
(49) Center bypass passage
(50) Port
(51) Port
(52) Orifice
(53) Orifice
(54) Pilot lineDuring a BOOM LOWER operation, the oil delivery from only drive pump (32) is supplied to boom cylinders (2) through boom I control valve (16). Boom I control valve (16) operates alone. Boom II control valve (20) is not operational in the BOOM LOWER operation.The BOOM LOWER operation contains a regeneration circuit. During a BOOM LOWER function, orifice (52) in boom I control valve (16) and boom regeneration valve (45) are operational in the boom hydraulic circuit. The return oil flow from the head end of boom cylinders (2) flows through boom regeneration valve (45). Oil then flows through boom regeneration valve