TM10-3930-660-20 18-6. MAIN CONTROL VALVE ASSEMBLY  - ADJUST/REPLACE  (Cont’d) ADJUSTMENT   - BOOM LOWER RELIEF VALVE The main relief valve pressure must be adjusted above normal operating pressure to permit the boom lower relief valve pressure to be adjusted. Main relief valve pressure is then returned to normal operating pressure at the end of this procedure. 1. CONNECT PRESSURE GAUGE TO VALVE PORT. a. b. c* d. Remove main relief valve plug assembly  (1). Connect O to 5000 psi pressure gauge to plug assembly port (2). Remove acorn nut (3) covering slotted head adjusting screw. While holding adjusting screw, loosen and back off jam nut (4) which secures adjusting screw. 3. ADJUST BOOM LOWERING RELIEF VALVE 2. ADJUST MAIN RELIEF VALVE PRESSURE TO 3,100 psi. Engine may be operated at idle or full throttle when performing pressure tests. a. b. c. d. Start engine, TM10-3930-660-10. 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 adjusting screw clockwise (in) until pressure on gauge reads 3,100 psi. Release hydraulic function lever. PRESSURE BETWEEN 1000 AND 1100 psi. a. b. c. d. e. Remove acorn nut (9) covering slotted head adjusting screw. While holding adjusting screw, loosen and back off jam nut (10) which secures adjusting screw. Operate boom lower function until boom is fully lowered. Continue to hold boom control lever in 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) . 18-27