The Working Principle Behind a Rotameter

Rotameter- The Working Principle Behind a RotameterA rotameter is an instrument that measures the rate of flow of fluids, gases, and steam with the help of a float inside a conical tube. There is a vast space between the tube and the float at the top. This helps to pass more water flow by it. The tube must be turned in a vertical direction because gravity works in a vertical direction too.

Working Principle of Rotameter 

The working principle of Rotameter is one of the oldest principles in flow measurement. A Rotameter is a kind of variable flow meter that is made to perform a simplistic task. In a Rotameter, a fluid or gas passes by a conical tube. This tube contains a float. It must first raise the float contained within the tube to pass through it. The buoyancy of the fluid makes the float rise When a rotameter is used to measure the flow of a fluid.

The buoyancy of a gas is negligible. That is why the velocity head of the gas makes the float move. In both cases, the greater the flow of gas or the fluid, the higher up the float in the tube moves. The float moves up and down the conical tube as the flow rate and the surface area inside the float and the conical tube wall changes. The tube is conical in shape. The annular opening increases as the float moves up. The pressure across the float decreases with the increase in differential pressure. The fluid or gas exerts an upward force to the float. This upward force is in equilibrium with the weight of the float. Hence, the float gets stabilized.

A calibration scale is either printed on the tube itself, or it is present outside with the tube. The meter can be compared to the calibration scale to measure the readings. The calibrated scale will commonly give a volumetric flow reading, for example, liters per minute (LPM).

How to read a Rotameter:

A Rotameter contains float and tube. But, a Rotameter may be equipped with an adjustment knob too. With an adjustment knob, you can control the flow rate according to your need. To read a Rotameter, consider the following instructions:

  • Firstly, you need to connect the fluid with the Rotameter.
  • Due to the pressure of the fluid or gas, the float starts to swim in the tube.
  • Now, you need to find and read the readings on the scale. Read the upper and lower levels of the scale, which gives the measurement of the rate of flow.


This was all about Rotameter and its working. The basic principle behind the working of Rotameter is simple. If you need any help regarding which kind of Rotameter Flow Meters should you choose to get the best results for your industrial need, simply visit our site at and find the best ones.

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