TM10-3930-660-20 18-6. MAIN CONTROL VALVE ASSEMBLY - ADJUST/REPLACE (Cont’d) C. d. e. f. g. h. Operate boom extend function until boom is fully extended. Continue to hold boom control lever in extend position so hydraulic oil passes over relief valve. Read relief valve pressure on pressure gauge. To increase relief pressure, turn adjusting screw clockwise (in). To decrease pressure, turn adjusting screw counterclockwise (out). When desired relief pressure is obtained, release boom extend lever. Hold adjusting screw in position and tighten jam nut (6). Install acorn nut (5). 4. ADJUST MAIN RELIEF VALVE BETWEEN 2,750 AND 2,850 psi a. b. c. d. Operate boom extend, retract, hoist or lower function until hydraulic oil is passing over relief valve. Continue to hold hydraulic lever in that position so oil passes over relief valve during relief valve adjustment. Turn main relief valve adjusting screw counterclockwise (out) until pressure on gauge reads between 2,750 and 2,850 psi. Release hydraulic function lever. Hold adjusting screw in position and tighten jam nut (4). Install acorn nut (3). 5. STOP ENGINE, TM10-3930-660-10. WARNING Hydraulic oil in the system can be under pressures over 3000 psi with the engine OFF. ALWAYS relieve pressure in hydraulic lines before attempting to remove any component in the hydraulic system. With engine OFF, starter switch in RUN position, and MLRS attachment on the ground, move control levers through all operating positions several times to relieve line pressure. Relieve pressure in hydraulic oil tank by loosening filler cap very slowly. Failure to follow these precautions could result i n 6. serious personal injury. REMOVE PRESSURE GAUGE. Unscrew pressure gauge from main relief valve plug assembly port (2). 18-23