Abstract: A soap film type gas flowmeter has an inverted U-shaped gas flow tube adjustably mounted in a sensor assembly. The inverted attitude of the gas flow tube prevents backflow of the soap film solution down to the sensor assembly and prevents diffusion of a heavier gas than the gas whose flow is being measured into the gas flow tube, thereby eliminating diffusion of a lighter gas through the soap film during measurement. The adjustable mounting of the gas flow tube enables optimum operation of the flowmeter for widely ranging gas flow rates. The glass flow tube is made from mandrel drawn glass to ensure high accuracy, which allows interchangeability from flowmeter to flowmeter with no change in accuracy.