TM10-3930-660-20 18-6. MAIN CONTROL VALVE ASSEMBLY - ADJUST/REPLACE (Cont’d) 3. 4. a. b. c. d. Remove acorn nut (3) covering slotted head adjusting screw. While holding adjusting screw, loosen and back off jam nut (4) which secures adjusting screw. To increase relief pressure, turn adjusting screw clockwise (in). To decrease pressure, turn adjusting  screw  counterclockwise (out) . When desired relief pressure is obtained, hold adjusting screw in position and tighten jam nut (4). Install acorn nut (3). STOP ENGINE, TM10-3930-660-10. REMOVE PRESSURE GAUGE. 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 in 5. 6. serious personal injury. Unscrew pressure gauge from main relief valve plug assembly port (2). INSTALL MAIN RELIEF VALVE PLUG ASSEMBLY  . Screw main relief valve plug assembly (1) into port (2) and tighten. Replace transmission cover, para.  16-6. ADJUSTMENT  -  BOOM EXTEND RELIEF VALVE 1. CONNECT PRESSURE GAUGE TO VALVE PORT. The main relief valve pressure must be adjusted above normal operating pressure to permit the boom extend relief valve pressure to be adjusted. Main relief valve pressure is then returned to normal operating pressure at the end of this procedure. 18-21