TM 9-2320-209-20-3-2 Section VI. AIR BRAKE SYSTEM 13-20. AIR SYSTEM PRESSURE VENTING. TOOLS: None SUPPLIES: None PERSONNEL: One EQUIPMENT CONDITION: Truck parked, engine off, handbrake set. FRAME 1 1. The air reservoir drain cock (1) is located on different trucks in different places as shown. 2. Turn air reservoir drain cock (1) to the left 1/4 turn and let air pressure out of system. 3. When air flow stops, turn air reservoir drain cock (1) 1/4 turn to the right. END OF TASK 13-148