TM 10-6640-238-13 2-11 f. Air System Controls and Indicators.  Figure 2-7 and Table 2-7 list the controls and indicators for the air system. Table 2-7.  Air System Controls and Indicators Index Number Control or Indicator Function 1 Air Compressor ON/OFF Controller Energizes motor start/stop circuit at pressure switch. 2 Pressure Switch Starts and stops compressor automatically at required pressures. Compressor starts at 60 psi, and stops at 120 psi. 3 Safety Valve Provides safety relief if air pressure in tank goes above 150 psi. 4 Tank Drain Valve Provides tank moisture drain. 5 Air System Isolation Valve Provides isolation of air system. 6 Air Pressure Gauge Indicates air pressure in tank. 7 Air Service Valves Provides service access to air system.  Two stopcock valves are located on roadside wall, one on curbside wall, and one in fume hood. 8 Air Regulators Provides adjustment for regulated air pressure.  Two air regulators are located inside the mechanical room (behind boiler) and one on the curbside wall. 9 Air Filter Provides filtered air to gum bath piping and has red pop up piston to indicate filter element replacement.  The air filter is located inside the mechanical room (behind boiler). 10 Globe Valves Provides regulated air pressure to RVP Test System components.