GROUP 4 SINGLE OPERATION 1. BOOM UP OPERATION ARM CYLINDER BUCKET CYLINDER BOOM CYLINDER SWING MOTOR pb5 A5 B5 TRAVEL MOTOR pc1 (34,2) pa5 pa9 pb8 (34,1) P2 B A pa11 pa8 TURNING JOINT A7 B7 pc2 pc7 A2 B2 pb3 pb7 pa3 pa7 B6 pc6 A6 A1 B1 PT PS P1 P2 PH PA PP PS SH FRONT PUMP REAR PUMP PILOT PUMP A1 A2 HYDRAULIC TANK 900L3HC10 When the RH control lever is pulled back, the boom 1 and boom 2 spools in the main control valve are moved to the up 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 large chamber of boom cylinders.
At the same time, the oil from the small chamber of boom cylinders returns to the hydraulic oil tank through the boom 1 spool in the main control valve. When this happens, the boom goes up. The excessive pressure in the boom cylinder bottom end circuit is prevented by relief valve. When the boom is up and the control lever is returned to neutral position, the circuit for the holding pressure at the bottom end of the boom cylinder is closed by the boom holding valve. This prevents the hydraulic drift of boom cylinder. 3-12 ps1 pa11 DR1 pc1 pb9 Relief valve ARM1 pa5 PO B4 A4 B1 OPTION A1 DR7 pc7 A3 Boom holding B3 valve pb3 pb9 ARM2 B8 A8 BUCKET Boom holding valve DR2 pc2 p