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What is a rotameter?


A flowmeter is a measuring instrument that determines the flow rate (amount of fluid moving through a pipe per unit of time) and the flow rate of the pipe.) of those liquids and gases that work with a constant pressure drop.

This instrument is cylindrical in shape and variable in area, and has a float inside. Its measurement is based on the capacity of the flow of a fluid to move vertically the sensitive element and thus increase its passage area, reaching a height directly proportional to the flow.

Its use is quite common and simple. It has a linear scale, a large measuring range, it is simple to install and maintain, it is manufactured in different materials according to the range of pressures and temperatures in which it is going to work.

Operating principle of the rotameter

The float inside the rotameter has a higher density than the flow to be measured. The float moves vertically in the pipe in proportion to the fluid flow and the area between the float and the pipe walls. With an increase in flow, the float height increases.

The rotameter float assumes different positions for each fluid flow to satisfy the balance between the force exerted by the fluid and the gravitational forces.

Key Applications

  • Basic flow measurement of liquids (including water) or gases.
  • Flow measurement in rotating equipment.
  • Dosing of additives for the chemical industry.
  • Process analyzers.
  • High pressure flow in oil platforms or pipeline systems.
  • Chemical injection.
  • Liquid or gas purge measurement.

Rotameter types

The rotameters are divided into a large number of types according to the material of manufacture as well as the operating mechanism, the main models being the following:

Purging It is used when the density and quantity of flow is small (in mechanical seals in pumps, differential pressure elements or bubbler measurement).
Glass Made of borosilicate. They allow to visualize the tube. Increased durability.
Bypass It is used only to measure flow rate with a linear measuring scale and a diaphragm.
Plastic Made of polycarbonate. They measure small flows. They are economical and durable.
Metallic Accurately handles a very wide range of flow rates even at high temperatures and pressures. Used for dosing expensive components in chemical industries.
Acrylic One of the most economical and accurate for measuring small diameters.
With electric transducers They use a magnetic system to be able to follow all the changes generated by the inlet flow in the tube.
With pneumatic transducers Its operation depends on the magnetic energy and pneumatic mechanism located between the two nozzles of the instrument.

How to choose the right rotameter?

Before choosing a rotameter, certain working conditions must be determined for the rotameter, among which the most important are:

  • Minimum and maximum flow rate
  • Minimum and maximum process temperature
  • Pipe size
  • Maximum process pressure
  • Accuracy required
  • Valve required
  • Presence of back pressure
  • Read directly or via a lookup table


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