3.2 CONSTRUCTION OF THE SHOVEL OPERATION Main Hydraulic Oil Reservoir Legend for illust. Z 21467a (1) Breather filter (5) Leakage oil filter (2) Back-pressure valve, temperature controlled (6) Main shut-off slider (3) Drain coupling, main oil reservoir (7) Collector pipe for return oil (4) Return oil filters (8) Drain coupling on collector pipe 46