3. ARM IN OPERATION ARM CYLINDER BUCKET CYLINDER BOOM CYLINDER TRAVEL MOTOR P5 P4 Pi2 Rs MU Pi1 Pn1 Pn2 SWING MOTOR PBa PAb1 P02 P04 PDb2 A2 PUMP A1 PUMP PILOT PUMP HYDRAULIC TANK 330S3HC11 When the left control lever is pulled back, the arm spools in the main control valve are moved to the roll in 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 arm cylinder. At the same time, the oil from small chamber of arm cylinder returns to the hydraulic oil tank through the arm 2 spool in the main control valve. When this happens, the arm rolls in.
The excessive pressure in the arm cylinder head side is prevented by relief valve. The cavitation which will happen to the head side of the arm cylinder is also prevented by the make- up valve in the main control valve.
3-16 BC1 N RV2 Cck DR9 Co P05 Do PCo PDo OPTION Ca Da BC2 NRV1 Cco CoR AkR LCk1 LCk2 Make up valve DoR OPTION LCo CaR DaR BUCKET BbkR DR7 CRa PaL ARM1 LCa Relief valve 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