TM 9-2320-209-20-3-2 13-25. AIR SYSTEM SAFETY VALVE REMOVAL AND REPLACEMENT. TOOLS: 3/4-inch open end wrench SUPPLIES: None PERSONNEL: One EQUIPMENT CONDITION: Truck parked, engine off, handbrake set. a. Preliminary Procedures. (1) Vent air system pressure. Refer to para 13-20. (2) If spare wheel blocks safety valve, remove spare wheel. Refer to TM 9-2320-209-10. 13-180