Power Venturi Tube, Double Throat, AN5807-1, Type B-4A

This is a nice specimen of the Double Throat Power Venturi Tube used across US military aircraft of the US Army Air Corps/Force and US Navy before, during, and post WWII. Made by Sperry, part number 640600.

Power venturi tubes provide a source of vacuum for the operation of air-driven instruments such as directional gyros, gyro horizons, and turn and bank indicators.  The venturi is a tube shaped like a double "V" and has a small opening, called a throat, at the junction of the "Vs". It is typically installed externally on the side or beneath of the aircraft fuselage, with the small "V" pointed toward the front of the airplane. A volume of air enters the mouth of the tube, flows past the throat, continues through the broadening tube and passes out at the tail end. As the air passes the throat, it expands in the wide part of the tube, creating a partial vacuum. The vacuum draws air from the throat, which in turn sets up a vacuum in the pipe line leading from the instruments. See spec sheets in the photo gallery.

The Single Throat design, not pictured here, operates in the same manner but has smaller air volume capacity for smaller aircraft with fewer air-driven instruments.