Rotameters are an unusual type of flow meter. Note that flow meters are devices that measure the flow rate of a gas or liquid, this generally being the linear, nonlinear, volumetric or mass flow rate. Rotameters, on the other hand, determine flow rate using a rotating float inside a closed tube. A float is a shaped weight that is usually made from either a ceramic or anodized aluminum. Because it is partially composed of a slightly narrowing, or tapered, tube, the rotameter falls into the category of flow meters called variable area flow meters.
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History of Rotameters
The first of their kind that included a rotating float was invented in 1908 in Aachen, Germany, by an inventor named Karl Kueppers. Rotameters themselves were first branded by a British company called GEC Elliott Automation, Rotameter Co. Rotameters are frequently utilized as cost-effective flow monitoring devices for both gases and liquids, most commonly as part of flow systems that have lower flow rates.
Design of Rotameters
The work of a rotameter begins when the float is placed inside this tube. Flowing fluids enter from the bottom and pass through the tube regularly; according to the rate at which this fluid is flowing, the float moves up or down. The float, which must have a higher density than the fluid, is able to move vertically because of the forces of gravity and the drag forces of the fluid flow. The fluid inside the tube pushes it upward until the force of gravity on the float is equalized with the force of fluid on the float. Once said forces have reached equilibrium, the float can stop moving.
Once stationary, it will sit at a specific vertical position that coincides with the rate of fluid flow. To assist in the interpretation of the flow rate, manufacturers of rotameters place graduation marks along the side of the vertical tube. To visually determine flow rate, operators simply find and read the graduation mark that most closely aligns with the resting place of the float. Specifically, readings are usually taken from the top of the widest part of the float. Usually, floats are shaped either as ellipsoids or spheres, and they may be partially colored or diagonally grooved.
While many meter operators choose to simply read flow rate results this way, some operators use rotameters that are equipped with monitoring systems to which the results can be transferred and read digitally. For optimal interior visibility, most rotameters are made from glass tubes, but they can also be made from metal. In addition, rotameters can be produced using a multiple tube design that makes it possible for them to measure multiple liquid streams at once.
Installation of Rotameters
Rotameters are very simple to install, use and read. Since they do not have to be paired with straight pipe runs, they can be installed virtually anywhere in a fluid flow system. They are highly accurate and, as they are available in a wide range of constructions and configurations, they are very flexible. Made from clear glass, they are inexpensive to make, but still maintain high resistances to chemical action and thermal shock. In addition, rotameters do not require any external fuel or power. Instead, they use only the properties of the fluid it is measuring and gravity to determine flow.
This is an excellent feature for manufacturers looking to reduce their energy usage. Of course, it should be mentioned that, from time to time, a rotameter may require the assistance of a pressure transducer to electronically read the position of a float. This would generally only be in the case if the liquid inside a rotameter obscures the reading. For any simple flow metering application, interested parties can rely on single tube rotameters. Or, for more complex applications that involve more than one flowing stream, multiple tube rotameters give just as strong a performance. Exceptionally simple and exceptionally accurate, rotameters are one of the best volumetric flow meters on the market today.
Things to Consider When Choosing a Rotameter
Anyone researching the purchase of a rotameter should make sure to investigate certain application factors and meter features. For example, potential customers should note what type of fluid they will be monitoring and pay attention to the fact that rotameters are best for use with non-corrosive materials. Potential customers should also determine the number of flowing streams for which they require monitoring and whether their application calls for a meter valve. After gathering the answers to all these questions, interested parties should take their specifications to a flow meter manufacturer, who will determine and build the best rotameter for them.