Gas Metering Device

Device for Measuring Gas

Gas metering is the measurement and recording of the amount of gas passing through the pipeline. The device for measuring gas is called a gas meter or gas flow meter, which is used to accumulate the volume or mass of gas passing through the pipeline. Some flow meters only measure the amount of gas passing through per unit time, and the accumulated amount must be displayed after a conversion mechanism. Since gas metering is easily affected by temperature and pressure, a temperature and pressure compensation device can be attached to the metering device.

Development of Flow Meter

The earliest gas metering device was a gas storage tank with a volume scale and the ability to rise and fall. In 1816, Englishman S. Clegg invented the first wet gas meter, which changed the method of charging by gas usage time or nominal gas consumption of the burner. Then, a dry gas meter with a built-in diaphragm was successfully designed, laying the foundation for modern diaphragm gas meters. Later, there were Pitot tube flowmeters, impeller flowmeters, Venturi flowmeters, heat capacity flowmeters, orifice flowmeters and Roots meters.

Metering principle According to the metering principle, gas metering devices can be divided into direct metering and indirect metering. There are several metering chambers inside the direct metering gas meter, and the amount of gas passing through is directly measured and accumulated according to the volume of the metering chamber. There are two types of direct metering gas meters: dry type and wet type. Diaphragm meters and Roots meters are dry types and are commonly used in small and medium flow measurement. Indirect metering gas meters do not have metering chambers. They use a certain physical property of the gas flow to convert it into flow, and then introduce the time factor to obtain the cumulative value. For example, orifice flowmeters that use air flow pressure difference, turbine flowmeters that use air flow velocity, and vortex flowmeters that use air flow obstruction to form vortices, etc., are mostly used for large flow measurement. According to the gas pressure in the pipeline, the gas metering device can withstand low pressure, medium pressure or high pressure respectively.

The widely used diaphragm gas meter (see figure) is equipped with a flexible film that can expand and contract with the entry and exit of gas. A metering chamber is formed on both sides of each film. A slide valve is placed above the metering chamber to alternately connect the metering chamber with the inlet and outlet of the gas meter. When gas enters a metering chamber, the film expands, compresses its adjacent metering chamber, and discharges the gas. This repeated alternating action is transmitted to the recording device through the mechanical structure, and the amount of gas passing through is accumulated.