TM10-3930-660-20 18-9. RELIEF VALVE, FRAME TILT/BRAKES - TEST/REPLACE (Cont’d) d. When desired relief pressure is obtained, hold adjusting screw in position and tighten jam nut (10). Install acorn nut (9). 5. STOP ENGINE. 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 serious personal injury. WARNING At operating temperatures, hydraulic oil is hot and under pressure. Hot oil can cause  injuries. Allow hydraulic oil to cool before disconnecting any hydraulic lines. 6. REMOVE PRESSURE GAUGE, TM10-3930-660-10. Remove pressure gauge from test tee. 7. REMOVE TEST TEE. a. Remove test tee from relief valve. b. Remove inlet hydraulic hose from test tee. 8. CONNECT INLET HYDRAULIC HOSE TO RELIEF  VALVE. Screw inlet hydraulic hose (7) onto relief valve. Tighten securely. 9. PURGE AIR FROM SYSTEM. a. Start engine, TM10-3930-660-10. b. Operate frame tilt function and tilt vehicle from side to side five times. c. Stop engine and relieve hydraulic pressure by operating frame tilt controls,  TM10-3930-660-10. NOTE Any time the hydraulic oil has been drained and changed or maintenance  has been done on the hydraulic system, it is possible that the hydraulic pumps have air in the pump cavities. This air must be purged from the cavity before the pump will operate. If necessary, refer to  paragraph  18-3. 18-41