Positive displacement and turbine meters, being volumetric measuring devices, cannot differentiate between liquid, air and vapor. Although the air content, in most instances, is small when compared with the product, it will contribute to measurable error. Large amounts of free air or vapor entrapped in a piping system, not only compromises meter accuracy but can lead to overspeeding of the measuring unit, creating excessive wear or possible unit failure. To insure accurate liquid measurement, it is necessary to remove all vapor and free all entrained air from the system prior to entry into the measuring unit.
