4. ARM OUT OPERATION ARM CYLINDER BUCKET CYLINDER BOOM CYLINDER SWING MOTOR TRAVEL MOTOR pa5 pc1 pa9 (34,2) P2 pa11 pb8 (34,1) A7 pa8 TURNING JOINT B7 pc2 pb3 pb7 pa3 pa7 pc7 pc6 A6 B6 PT PS P1 P2 PH PA PP PS SH A1 A2 FRONT PUMP REAR PUMP PILOT PUMP HYDRAULIC TANK 900L3HC13 When the LH control lever is pushed forward, the arm spools in the main control valve are moved to the roll out position by the pilot oil pressure from the remote control valve. The oil from the A1 and A2 pump flows into the main control valve and then goes to the small chamber of arm cylinder.
At the same time, the oil from the large chamber of arm cylinder returns to the hydraulic oil tank through the arm spools in the main control valve. When this happens, the arm rolls out. The excessive pressure in the arm cylinder rod side is prevented by relief valve. When the arm is roll out and the control lever is returned to neutral position, the circuit for the holding pressure at the rod side of the arm cylinder is closed by the arm holding valve. The cavitation which will happen to the rod side of the arm cylinder is also prevented by the make-up valve in the main control valve.
3-15 Arm holding valve ps1 pa11 DR1 pc1 B5 A5 pb9 pb5 1 1 1 Relief valve pa PO B A B B1 A A1 DR pc A3 B3 pb ARM1 5 4 4 OPTION 7 7 3 pb9 ARM2 B8 A8 BUCKET DR2 pc2 p 3 BOOM2 2 SWING 3 2 6 11 TRAVEL-LH