6. BUCKET OUT OPERATION ARM CYLINDER BUCKET CYLINDER BOOM CYLINDER SWING MOTOR ps1 T3 T4 ps2 T1 T2 pa10 B9 TRAVEL MOTOR Relief valve pb9 A9 (34,2) ARM2 A8 B8 pa5 pc1 pa9 (34,1) P2 BUCKET pa11 pb8 pa8 TURNING JOINT DR2 pc2 A7 B7 pc2 BOOM1 pb3 pb7 pa3 pa7 pc7 pc6 TRAVEL-RH pb6 A6 B6 pa6 STRAIGHT TRAVEL P2 P3 A1 A2 FRONT PUMP REAR PUMP PILOT PUMP HYDRAULIC TANK 900L3HC15 When the RH control lever is pushed right, the bucket spool in the main control valve is moved to the roll out 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 small chamber of bucket cylinder.
The oil from the A1 pump flows into the large chamber of bucket cylinder though confluence oil passage in the main conrtol valve by bypass cut pilot pressure (pa11). At the same time, the oil from the large 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 out. The excessive pressure in the bucket cylinder rod side is prevented by relief valve. The cavitation which will happen to the rod side of the bucket cylinder is also prevented by the make- up valve in the main control valve.
3-17 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