Two designs of flow-meter, and a method of calibration

A compact form of capillary-tube flow-meter is obtained by enclosing the capillary in the widened arm of a U-tube manometer. A modification of Beckett's pulsing gas meter is described, in which a stream of gas displaces liquid from an inner to an outer tube; when a certain pressure-difference is reached, the breaking of a liquid seal allows the gas in the inner tube to be discharged so that the original conditions are restored. The volume discharged per pulse from such a meter was found to be 10 per cent. greater at high speeds than at low. Calibration of meters of small capacity is effected by connecting them to a graduated tube that has a soap film across its bore. When the walls of this tube are wet, the film is mobile and stable, so that gas may be collected and measured at a pressure that is almost exactly atmospheric.