Paddlewheel flow meters have a paddle wheel that is perpendicular to the flow path. The rotor axis is positioned to limit contact between the paddles and the flowing media. There are many different types of paddlewheel flow meters. Examples include gas flow meters, air flow meters, liquid flow meters, and water flow meters. A gas flow meter is used to determine the flow of a moving gas in an enclosed pipe or passage. An air flow meter is used to measure airflow rate by measuring only a part of the entire flow. A liquid flow meter is used to determine the flow of quantity of a moving fluid. A water flow meter is designed to measure the flow of water. Paddlewheel flow meters carry physical, media and operating specifications, and differ in terms of output options and features.

Physical Specifcations

Pipe diameter, mounting style and end fittings are important physical specifications to consider when selecting paddlewheel flow meters. Pipe diameter is the diameter of the pipe to be monitored. Choices for mounting style include in-line, insertion, and non-invasive. In-line paddlewheel low meters are installed directly in the process line. They require a straight run of pipe for installation. By contrast, insertion-style paddlewheel flow meters require a threaded hole in the process pipe, or another means of access. Non-invasive paddlewheel flow meters do not require direct-mounting in the process flow, and can be used in closed piping systems. Some flow meters use clamps, compression fittings, or tube ends. Others use flanged, plain end, socket weld, or threaded fittings. 

Media Specifications

Media specifications for paddlewheel flow meters include media temperature range, and may define a device’s ability to accommodate liquids with suspended solids (slurries). Performance specifications for paddlewheel flow meters include velocity flow rate, gas volumetric flow rate, liquid volumetric flow rate, operating temperature and operating pressure. As a rule, a flow meter’s performance can be determined by its turndown ratio, which represents the device’s dynamic or operating range. For example, paddlewheel flow meters with a 500-SCCM flow rate and turndown ratio of 50:1 can operate effectively and resolve flow down to 10 SCCM. If these same device haves a turndown of 100:1, however, then the paddlewheel flow meters will resolve effectively to 5 SCCM.


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