Flow Meters and Indicators

A flow meter, or rotameter, is an instrument used to measure linear, nonlinear, mass or volumetric flow rate of a liquid or a gas. It is the most widely used variable-area flow meter because of its low cost, simplicity, low pressure drop, relatively wide range-ability, and linear output. They are also simple to install and maintain.

In operation, the rotameter is positioned vertically in the fluid system with the smallest diameter end of the tapered flow tube at the bottom. This is the fluid inlet. The float, typically spherical, is located inside the flow tube. When fluid is introduced into the tube, the float is lifted from its initial position at the inlet, allowing the fluid to pass between it and the tube wall. As the float rises, more and more fluid flows by the float because the tapered tube's diameter is increasing. Ultimately, a point is reached where the flow area is large enough to allow the entire volume of the fluid to flow past the float. This flow area is called the annular passage. The float is now stationary at that level within the tube, as its weight is being supported by the fluid forces which caused it to rise. This position corresponds to a point on the tube's measurement scale and provides an indication of the fluid's flow rate.

Standard Sizes

1/4" - 8" diameter

Sizes and materials are brand specific. Click on a manufacturer below for available products. Please contact Aetna Plastics for pricing information.


Blue-White Industries, Ltd.
  • Size Range: 1/4" - 2"
  • Materials: Polysulfone and Acrylic
  • Products: F-300, F-400, F-410N, F-420N, F-430N, F-550 Acrylic Flowmeters
Georg Fischer
  • Size Range: 3/8" - 2 1/2"
  • Materials: Polyamide and Polysulfone
  • Products: Type SK Variable Area Flow Meter
  • Size Range: 1/2" - 8"
  • Materials: Acrylic and Pyrex®
  • Products: Sight Glasses and Level Indicators
  • Size Range: 1/2" - 6"
  • Materials: PVC
  • Products: RFA Series, RFP Series