3.
ARM ROLL IN OPERATION TRAVEL MOTOR-LH TRAVEL MOTOR-RH L/H R E D R E D R/H SWING MOTOR R E D PP DR PP PP A(FW) B(BW) DR2 DR1 DR1 DR2 A(FW) B(BW) ARM CYL EXTENSION CYL DOZER CYL STOP VALVE B(CW) A(CCW) T D B C A G H F E T P TURNING JOINT SOLENOID SELECTOR 3WAY VALVE BUCKET CYL BOOM CYL C2 C3 C1 C4 P2 P1 B/SWING CYL Pa8 Pa10 Pb8' DR2 Pa8 Pa6 Pa7 Pa4 Pa5 AC Pa3 Pa1 Pa2 DOZER MAIN CONTROL VALVE Pb10 T2 Pb6 Pb7 Pb4 Pb8 Dr1 BU Pp1 T1 Pb3 Pb1 Pb2 TRAVEL DOZER Pb5 R/H L/H 2 4 3 1 DOWN 1 2 UP Pb6 Pa6 Pb7 Pa7 Pb1 Pa1 A B C D 7 B/SWING 2WAY OPT BOOM SWING BUCKET ARM E SAFETY 2-SPEED ACC A1 A2 K1 K2 LH 1 2 RH LH 1 2 RH LH 1 2 3 2 RH IN OUT UP DOWN OUT IN 4 4 1 3 P1 P2 P3 P4 P2 P1 K3 T Pa3 Pb2 Pb3 Pa2 Pb4 Pa4 Pb5 Pb10 Pa10 Pb8 E SOLENOID VALVE K4 TR Pa5 Pa8 HYD TANK S1 MAIN PUMP 189AK3HC12 When the left control lever is pulled back, the arm spool in the main control valve are moved the to roll in position by the pilot oil pressure from the remote control valve.
The oil from the P2 and P3 pump flows into the main control valve and then goes to the large chamber of arm cylinder. At the same time, the oil from small chamber of arm cylinder returns to the hydraulic oil tank through the arm spool in the main control valve. When this happens, the arm rolls in. The cavitation and excessive pressure in the bottom of the arm cylinder is also prevented by the make-up valve and the relief valve in the main control valve. 3-13 10 A10 BUCKET A9 B8 BOOM B7 A7 TRAVEL(LH) P1 P2 A6 B6 A5 B5 A4 B4 TRAVEL(RH) ARM PTO P3 B3 A3 B2 ARM SWING CROWD A2 B1 A1 BS MRV-P1 MRV-P2 Relief Make up valve valve MRV-P3