5. BUCKET IN OPERATION ARM CYLINDER BUCKET CYLINDER BOOM CYLINDER SWING MOTOR ps1 T3 T4 ps2 T1 T2 pa10 B9 A9 TRAVEL MOTOR Relief valve ARM2 pb9 pa5 pc1 (34,2) A8 B8 pa9 pb8 (34,1) P2 BUCKET DR2 pa11 pa8 TURNING JOINT pc2 A7 B7 pc2 pc7 BOOM1 pb3 pb7 pa3 pa7 B6 pc6 TRAVEL-RH pb6 pa6 A6 STRAIGHT TRAVEL P3 P2 A1 A2 FRONT PUMP REAR PUMP PILOT PUMP HYDRAULIC TANK 900L3HC14 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 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 boom 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.
3-16 1 1 1 pa PO B A B B1 A A1 DR pc A3 B3 pb ARM1 5 4 4 OPTION 7 7 3 B2 pa3 BOOM2 A2 pb2 SWING DR3 pa2 pc6 B1 A1 pp ab 11 TRAVEL-LH pr1 P1 PSPT PP PA P SH PS 3 BOOM2 2 SWING 3 2 6 11 TRAVEL-LH