rotameter for liquid flow rate
  • Must-Know The Basics of Rotameter

Featured Image Caption: Rotameter for Liquid Flow Rate

Rotameters are liquid measurement devices used to accurately measure the flow rate of different types of fluids. The other name for this flow measuring device is the variable area flow meter. When measuring flow rate using a rotameter device, the liquid substance passes through the tapered tube, and the float found inside it will rise to measure the flow rate. Thus, in the measuring process, the cross-sectional area of the tube slowly becomes greater when the fluid passes through the tapered tube.

The initial version of variable area flowmeters had slots meant to stabilize the flow meter, the slots made the floats rotate, and that is where they got the name rotameters. The current versions of rotameters have floats designed in many shapes. The floats are also made in various materials, including glass, metal, plastic, and stainless steel. Rotameters can measure both liquids and gases. When measuring the flow rate in liquids, gravity is used to determine the flow rate. Therefore, the flow meter needs to be placed in a vertical position. As the liquid starts flowing from the bottom, the float will start rising. When there is no flow, the float will stay at the bottom of the tube. Although rotameters come in various tube sizes, the most commonly used tube range is 1/8 to 2 inches. The graduating scale found on the rotameter’s side makes it easier for the user to measure the flow rate. Variable area flowmeters depend on gravity to measure the flow rate of liquids. Therefore, they need calibration based on the type of fluid being measured.

For rotameters to measure flow rate accurately, they need to be calibrated based on flow control, temperature, and pressure. Changes in temperature, density, pressure, and float weight will determine the flow rate in the flow measurement process. Like any other flow measurement device, variable area flowmeters lose accuracy after a few months of service. In that case, they need to be calibrated once every year.

The various features in variable flow meters are what make them useful in several applications. These types of flow meters have only one moving part. This means that the measure flow rate mechanically. A rotameter device has a simple design that makes it easier to install. They can easily perform their function without any power output since they run mechanically. You can install them in areas with no electricity, and you can still use them. They are versatile flow measuring devices because they come in different types, come in many different materials, and have different inlet and outlet sizes. They give a linear scale and can measure flow rate accurately even when flow pressure is low. Variable area flowmeters that are made from plastic or glass are much cheaper than the other ones.

Among the few drawbacks of rotameters is that they have to be set up vertically to measure flow rate properly. When placed vertically, they allow the fluid to flow from the bottom and move upwards. Another constraint of variable area flowmeters is that they have to be calibrated every time you want to use them with a different fluid. Viscosity hardly affects the flow meter while reading the flow rate. However, the operator must ensure that the device is calibrated according to the fluid being measured.

Rotameter Types

Rotameters come in two main types that are designed to measure different fluids based on their applications. Let’s look at these two types of rotameters:

Orifice Bypass

The orifice plates are designed to manage and control larger flow rates. Therefore, they work well with larger flow rates installed around an orifice plate in a bypass line.


Of all the variable area flowmeters used in the industry, purge meter rotameters are the most used ones. These variable flow meter types come with a constant flow DP regulator, used to purge flow rate at optimum levels.


Like any other type of flow meter used in industries, rotameters require since they measure different types of fluids. However, to make it worthwhile, trying to find a reputable flow meter company that offers after-sales services is important as they will offer you calibration once a year.

Naman Modi

By Naman Modi
who is a Professional Blogger, SEO Expert & Guest blogger at Proteus Industries Inc. He is an Award-Winning Freelancer & Web Entrepreneur helping new entrepreneur’s launches their first successful online business.

Member since April, 2019
View all the articles of Naman Modi.

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