Oil Pressure, Dual, Set for 4-Engine Aircraft, Type B-9A USSR Air Vacuum Regulating

Air Vacuum Regulating

the aircraft is at its maximum allowable airspeed or maximum allowable mach speed

According to the Maintenance Interchangeability gude dated Feb 1945

When rotated to the desired letter by the Sender

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Oil Pressure, Dual, Set for 4-Engine Aircraft, Type B-9A USSR Air Vacuum RegulatingHere is a set of WWII era Type B 9A Dual Oil Pressure Indicators, as used in four engine of the US Army Air Force such as bombers B 17, B 24, and B 29 and transport C 54. These are Bendix Autosyn indicators, which used pressure sensors at the engines which electrically transmitted the signal to these electrical indicators. Both are labeled "AF US ARMY" on their faces. The indicator marked for engines 3 & 4 has a 1944 manufacturing serial number