This report supersedes report of March 30, 1922, with the same title published in Information Circular No. 369; and report of April 28, 1921, entitled "The Sylphon Fuel Pump," published in Information Circulary No. 281. The report describes the Bellows fuel pump and provides diagrams and drawings of the pump. It describes the appropriate maintenance and repair procedures for this pump and lists tests that should be performed after pump overhaul (including the benchmarks the pump should meet to be ready for re-installation).