What Are Rotameters?

Rotameter (ABB)

Rotameters are a type of variable area flow meter used for measuring the volumetric flow rate of a fluid. A tapered tube, usually glass, has a float that gets pushed by the drag force of the flow being measured and is pulled down by gravity. The simple operating principle and design makes rotameters a popular choice, and they are able to measure high flow rates as well as very low flow rates.

The rotameter has a number of advantages for use in a process. No external power or fuel is required, only the corresponding flow and gravity. They are simple devices that can be produced from low-cost materials, which is a main reason for the rotameter’s widespread use across many applications. Additionally, the area of the flow passage increases when the float moves, resulting in a linear relationship. The clear glass used also allows for a low risk of thermal shock and resulting issues from measuring chemicals. Rotameters also typically do not experience large drops in pressure, are simple to install, and are repeatable for long periods of time as long as they are operating under the same process conditions.

A few limitations exist in rotameters, the first of which relates to the fact the rotameter relies on displacement to function. A rotameter made to measure a certain substance at a particular temperature is only going to be accurate when measuring the substance and process qualities originally intended. While a rotameter can be scaled to measure different densities and viscosities, a limitation exists when the fluid characteristics being measured change in complexity. Secondly, while floats are often designed to function independent of viscosity, it can be difficult to ensure their effectiveness. Additionally, measurements being evaluated via rotameters can be uncertain when the float oscillates or near the bottom of the scale being used by the rotameter.

Certain fluids may also obscure the reading on the rotameter since the reading must be read through the flowing medium. This limitation can be countered by coupling he rotameter with a transducer in certain process applications. Another option for readability involves using a magnetic float that can be accompanied by a follower outside the tube, allowing the operator to easily read the measurement.

For more information about rotameters, visit https://teco-inc.com/ABB.