The principle of measurement is that as thc,liquid flows through the meter it moves a measuring element which seals off the measuring chamber into a series of measuring compartments each holding a definite volume. As the measuring element moves, these compartments are successively filled and emptied. Thus for each complete of the measuring element a fixed quantity of liquid is permitted to pass from the inlet to the outlet of the meter.
The seal between measuring element and the measuring chamber is provided by a film of measured liquid. The number of cycle of the measuring element is indicated by means of a pointer moving over the dial, a digital totalizer or some other form of register, driven from the measuring element through an adjustable gearing.