Gas flow meter is a mechanical device for automatically measuring quantities of gas. Some of the more popular than others depending on application and requirements. The most important types are:

Diaphragm flow meters — Diaphragm flow meters are gas meters in which the passage of gas through two or more chambers moves diaphragms which are geared to a volume-indicating dial. Sizes up to 20,000 cubic feet per hour and 1,000 Ibf/in2 working pressure are available.

Coriolis mass flow meters — Coriolis mass flow meters are type of meters in which the gas flow is measured in terms of mass by utilizing the velocity and density of the gas stream to calculate the mass of a gas flowing in unit time.

Orifice flow meters — Orifice flow meters are used for measuring the flow of fluid through a pipe or duct by measurement of the pressure differential across a plate having a precision machined hole in its center. Ratings up to very high throughput and pressure are available.

Rotary displacement flow meters — The positive-pressure blower principle in reverse is used in these meters in which gas pressure turns twin matching impellers and the quantity of gas passing through is proportional to the number of revolutions. These meters are made in the range of 3,000 to 1,000,000 cubic feet per hour and for pressures up to 1,200 Ibf/in2.

Turbine flow meters — Turbine flow meters are type of meters in which there is a turbine wheel or rotor made to rotate by the flowing gas. The rate or speed at which the turbine wheel revolves is a measure of the velocity of the gas.

Venturi flow meters — Venturi flow meters are meters in which the flow is determined by measuring the pressure drop caused by the flow through a Venturi throat. The flow rate is proportional to the square root of the pressure drop across the throat.

Ultrasonic flow meters — Ultrasonic flow meters are non-intrusive devices that use acoustic vibrations to measure the speed of gas movement by measuring the speed at which sound travels in the gaseous medium within the pipe. Ultrasonic sound is transmitted into a pipe with flowing liquids which predicts the speed of sound in a gas with a known pressure, temperature, and composition.

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