Float flowmeter (Rotameter)

A float flowmeter (often called a rotameter) is a simple and reliable device used to measure the flow rate of a liquid or gas in a pipe.

Operating principle

• The device consists of a tube, generally conical and transparent, inside which a float moves.

• The fluid flows from bottom to top:

  • The upward force of the fluid tends to lift the float.

  • The weight of the float and friction forces pull it downward.

• The balance point reached corresponds to a stable position of the float in the tube.

• This position is directly related to the instantaneous flow rate, and can be read on a graduated scale on the tube.

Characteristics

• Type of reading: direct and visual.

• Compatible fluids: clear liquids, gases, compressed air.

• Measurement range: suited for low to medium flow rates.

Advantages

• Simple, robust, and economical design.

• No electrical power required.

• Direct and immediate reading.

• Low pressure loss.

Limitations

• Less accurate than electronic flowmeters.

• Not suitable for opaque, viscous, or particle-laden fluids.

• Must be installed in a vertical position with upward flow.