4. ARM OUT OPERATION ARM CYLINDER BUCKET CYLINDER BOOM CYLINDER P5 P4 Pi2 Rs MU Pi1 Pn1 Pn2 TRAVEL MOTOR SWING MOTOR PBa P02 P04 PAb1 PDb2 A2 PUMP A1 PUMP PILOT PUMP HYDRAULIC TANK 330S3HC12 When the left 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.
3-17 BC1 N RV2 Cck DR9 Co P05 Do PCo PDo OPTION Ca Holding valve Da BC2 NRV1 Cco CoR AkR LCk1 LCk2 DoR OPTION LCo Relief valve CaR DaR BUCKET BbkR DR7 CRa PaL ARM1 Make up valve LCa LCa2 ARM2 PAa2 DR6 Csp Db2 BOOM2 Ccb SWING P/R LCar LCbk BbR ARM REGEN P02 Abk PBrc PAbk DR4 Cs Ds PCs PDs DR5 SWING P03 DR3 Ctl Dtl PCtl PDtl SH Patt ( TR RIG AVH ET L) PS DR1 P01 PtrPS TS Cs Ds PCs PDs DR5 SWING LCs AbR LCb CRb BOOM1 P03 DR3 Ctl Dtl PCtl PDtl Patt (RIGHT) TRAVEL DR1 BtR AtR (RIGHT) TRAVEL (LEFT) TRAVEL MRV