UNIVERSAL JOINT GP 2679150 - Caterpillar

Introduction
Illustration 1 g03383441
Location of boom joystick
One boom cylinder is used to raise or lower the boom. When the boom cylinder EXTENDS, the boom LOWERS. When the boom cylinder RETRACTS, the boom RAISES.The main hydraulic pump supplies high-pressure oil to the main control valve. Pilot oil pressure from the pressure limiting valve inside the pilot manifold creates pilot pressure that is used by the joysticks. This pressure is used to control the movement of the boom control valve. The boom control valve is located inside of the main control valve. The boom control valve controls the amount of flow into the boom cylinder and is proportional to the movement of the joysticks. The line relief valves control the pressure of the boom system.Components of the boom system include:
Boom control valve
Boom cylinder
Line relief valvesBoom Lower
Illustration 2 g03383439
Boom hydraulic schematic - boom LOWER
(1) Line (rod end of cylinder)
(2) Boom cylinder
(3) Line (pilot)
(4) Line (head end of cylinder)
(5) Main control valve
(6) Parallel feeder passage
(7) Load check valve
(8) Boom control valve
(9) Load sense control spool
(10) Load sense passage
(11) Return passage
(12) Relief valve (rod end)
(13) Passage
(14) Relief valve (head end)
(15) Passage
(16) Line (pilot)
(17) Slow return check valve
(18) Hydraulic lockout solenoid
(19) Pilot manifold
(20) Main pump
(21) Oil cooler
(22) pilot control valve (boom and bucket)
(23) Line (pilot)
(24) Pressure limiting valve
(25) Hydraulic tank
(26) Pilot oil distribution block Main pump (20) sends hydraulic oil to main control valve (5). The oil then splits into two paths. The first path the oil flows is into parallel feeder passage (6). The second path the oil flows is out of main control valve (5) and into pilot manifold (19). The high-pressure oil then flows into pressure limiting valve (24) and becomes pilot oil.When the hydraulic lockout switch is placed into the UNLOCKED position, pilot oil pressure flows from pressure limiting valve (24), through hydraulic lockout solenoid (18), and into line (23). The pilot oil then flows into pilot oil distribution block (26) and into pilot control valve (22). When pilot control valve (22) is moved to the BOOM LOWER position, the pilot oil flows into line (16). The oil then flows into main control valve (5) and shifts boom control valve (8) upwards. This action allows the main supply oil to flow into boom cylinder (2).When boom control valve (8) shifts upwards, the high pressure hydraulic oil in parallel feeder passage (6) flows through boom control valve (8). The oil then flows through passage (15) and shifts load sense control spool (9). Hydraulic oil from passage (15) now flows through load sense control spool (9) and splits into two separate paths. The first path the high-pressure oil flows is into load sense passage (10), out of main control valve (5), and into main pump (20). This action causes main pump (20) to upstroke. The second path the oil flows is into passage (13), through load check valve (7), and into boom control valve (8). The oil then flows through line (4) and into the head