A rotameter measures the flow rates of liquids or gases using a vertical tube with a float that rises and falls according to the flow rate. The float strikes a balance between the upward push of the liquid or gas stream and the downward pull of gravity. Different shapes of floats are available, and the reading is taken from the center or top of the float. Rotameters can be used in many different applications and do not require an external power source. They can also be used as a bleed-type flowmeter to deliver a constant rate of lubricants to bearings.
A rotameter measures the flow rates of liquids or gases in industrial use. The basic design of a rotameter includes a vertical tube of gradually increasing diameter made of glass or other transparent material, within which a float will rise and fall according to the flow rate of the liquid or gas. The float rises when the flow is high, as it is forced to seek more diameter between itself and the outside of the pipe to accommodate the force of the flow. When the flow is lower, gravity allows the float to find an equilibrium which can be compared to the internal linear scale for a reading. As the float rises and falls, it rotates on its axis, giving rise to the name of the rotameter.
Floats come in different shapes: circular, triangular or elliptical. The reading from the internal linear scale is taken from the center of the float form or the top of the float, as directed in the device manual. Sometimes, a float is colored so that an observer can easily determine whether it is stuck or spinning freely. Although it’s called a float, it doesn’t actually float on liquid. Instead, it’s designed to take advantage of a scientific principle known as the principle of variable area, which allows the float to strike a balance between the upward push of the liquid or gas stream and the downward pull of gravity.
As the flow rate changes, the float moves up or down in response and then settles into a new equilibrium of flow velocity versus gravity. The linear scale inside shows a range of 0% to 100% on most rotameters. Conversion charts for different types of liquids or gases can be used to determine the correct reading for the particular liquid or gas under test. Some rotameters, however, are designed to provide digital readouts of flow rate and temperatures. Others use a needle valve, to give not only a flow reading, but also a flow reading at different pressures.
The basic design of a rotameter, whether made of glass, plastic or metal, does not require an external power source but operates according to the fundamental laws of physics. As long as a rotameter is held rigidly vertical it will give good readings and can be used in many different applications. They can be used in both liquid and gas pipelines and can be fitted with high and low limit alarm systems. Research departments in different types of processing industries are also using these devices. A rotameter can also be used as a bleed-type flowmeter to deliver a constant rate of lubricants to bearings to reduce production downtime.
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