What is a variable area flowmeter? A variable area flowmeter (rotameter) is a flowmeter that measures the volumetric flow rate of liquids and gases. There is no difference between a variable area flowmeter, a rotameter or a flowmeter, and these terms are interchangeable. Within a variable area flowmeter, a gas or liquid moves a float until it reaches equilibrium, the technique for measuring flow rate. The user can easily read the flow rate of gas or liquid on a scale located next to the tube or on a scale located on the tube.

Rotameter applications extend to all industries because it was and still is an economical way to measure very low and very high flow rates, especially with the GT1600 series glass tube rotameter. Brooks Instrument’s flow experts often ask users why they select flowmeters. Their top six answers below explain why a rotameter continues to be successful.

1. No external power supply required – Rotameters are mechanical devices that do not require power to provide gas or liquid flow measurement. Because they do not require power, users install rotameters in hazardous and remote areas where it is expensive to supply power. The MT3809 series flowmeter is one such example.
2. You can see the process – Users can easily read the flow measurement and examine their process. For example, does the process look dirty or cloudy? If so, the filters may need to be changed. Also, is the process the right color, and are there bubbles in the liquid? One solution is the Sho-Rate™ Series rotameter.
3. Rotameters are cost-effective – Both the price and function of the rotameter contribute to labor savings. Rotameters can be installed with other flow measurement technologies and can also be used to complement them at an economical price.
4. Easy to install and maintain – Install the rotameters by connecting the process line to the inlet and outlet. Make sure the rotameter is in an upright position before putting it into operation.
5. Low pressure drop – Most small rotameters have only a few inches of water column pressure drop, which means that rotameters are often installed at many locations in the process. Small pressure drops mean smaller pumps!
6. Repeatability – Given the same process conditions, a rotameter will accurately repeat the flow measurement day after day.

These six features and advantages demonstrate that rotameters will continue to be important products for measuring the flow of gases and liquids now and in the future. An application note on wastewater treatment plants demonstrates how variable area flowmeters work in this process.