5. BUCKET IN OPERATION 5. BUCKET IN OPERATION ARM CYLINDER BUCKET CYLINDER BOOM CYLINDER SWING MOTOR ps1 ps2 T3 T1 T2 T4 TRAVEL MOTOR A1 A2 FRONT PUMP REAR PUMP PILOT PUMP HYDRAULIC TANK 480A3HC14 When the RH control lever is pulled left, the bucket spool in the main control valve is moved to the roll in position by the pilot oil pressure (pb8) from the remote control valve. The oil from the A2 pump flows into the main control valve and then goes to the large chamber of bucket cylinder. The oil form the A1 pump flows into the large chamber of bucket cylinder through confluence oil passage in the main control valve by bypass cut pilot pressure (pa11).
At the same time, the oil from the small chamber of bucket cylinder returns to the hydraulic oil tank through the bucket spool in the main control valve. When this happens, the bucket rolls in. The excessive pressure in the bucket cylinder head side is prevented by relief valve. The cavitation which will happen to the head side of the bucket cylinder is also prevented by the make-up valve in the main control valve. 3-18 3-18 R A5 pb5 ARM 1 pa5 B4 A4 pb4 pa4 A3 B3 pb3 B2 pa3 A2 elief valve OPTION Mak e up valve BOOM 2 pb2 SWING DR3 pa2 B1 pc6 TRAVEL(LH A1 pb1 pa1 TRAVEL(RH) TRAVEL STRAIGHT pr1 P1 PSPT PP PA PH PS SWING TRAVEL( RH) TRAVEL(LH TRAVEL STRAIGHT A6 pb6 pa6 ) P3 P2