What is a Rotameter and How Does it Work?

In industries that deal with fluid substances, various tools and devices are used to monitor, regulate, and measure the flow of liquids and gases. These are essential processes that ensure desired or effective products are produced. Devices that are commonly used are called flow meters which come in numerous types. These devices offer accuracy when it comes to monitoring and measuring the flow of fluids. Most of them are used to monitor and regulate the pressure and temperature of fluids. We have discussed many of these flow meters in our previous posts. Today, we are going to look at a particular flow meter called the rotameter. We will first define it, and then we will move to how it works, and finally, we will tell you what you need to consider before buying a rotameter for your system.

A rotameter is a fluid flow measuring tube device that is made from either glass, plastic, or metal which is usually stainless steel. It is used to measure liquid flow in many variables compared to other flow meters. In other words, its flow measurement range is wide. It is mainly used in fluids that have low-pressure drops. A rotameter has a component inside it called the float, which response linearly to the flow rate of the fluid to the flow of the fluid in the tube. This flowmeter is also easy to set up.

How a Rotameter Works 

A rotameter has a tapered tube, making it ideal for measuring variable-area flows. This is what makes it one of the most used flow meters in different industries. In the tapered tube, there is a component called a float that rises when fluid flows into the tube. Exerted pressure makes the float go up the tube. This means that if the pressure is high, the float will move further up the tube. This is triggered by the volumetric flow of the liquid. The float is raised differently depending on the fluid going through the tapered tube. In gases, the float height doesn’t require buoyancy. To raise the float, only the flow velocity is needed. When measuring the flow rate in liquids, both buoyancy and velocity of the liquid are required.

When setting up a rotameter, it needs to stay in a vertical position. This is to allow the float to move upwards when fluids go in through the tube from the bottom. When the fluid is not flowing in through the tube, the float will stay at the bottom of the tube. The height that the float stains is proportional to the tube wall and the flow rate. Across the tube, the size of the annular opening is increased as differential pressure decreases when the float goes up.

An equilibrium is reached as the force is exerted upwards and the float reaches a fixed position. What results from this is the levitation of the float from the flow of the fluid inside the tube. When equilibrium is reached, it allows the user to read the fluid viscosity and density.

Rotameters come in different types and sizes and what determines the size uses the application. The right size and whether the rotameter is calibrated properly determines how the user reads the data. The user can read data directly off the scale if everything is set properly. Designs from the previous rotameters had free floats that were rotated by the fluid pressure or gas changes. This is where the name rotameter was derived. Today, we have rotameters that allow the user to use the valve to adjust the flow rate manually.

When using fluids other than water or gas, the user will have to convert readings into standard formats. But in water and air, which are commonly used, the rotameter will have calibration data and direct reading scales. The unit used to determine the flow rate in water is GPM, while in air or gas, the unit used is in standard cubic feet per minute (scfm).

The manufacturer is the one who is supposed to provide nomographs, slide rules, or the software used in getting the size of the rotameter. The user will also get calibration tables for standard flow values.

What to consider when looking for a Rotameter

1. Conditions set for operation – The user needs to understand the conditions that the rotameter will operate in. These conditions include the temperature and the flow pressure of the liquid or gas. The user also needs to know the max and min flow rate required in an application.
2. The pipe used in the system – Before opting to buy a rotameter, the user also needs to know the size of the pipe used in the system. This will help to establish the size of the rotameter.
3. The kind of rotameter– The user also needs to consider the type of rotameter suitable for that particular installation or application. The reason being that several rotameters are available in the market such as meters that provide direct readings and those that need lookup tables.
4.  Accuracy needed – It is also good to know exactly the accuracy required in an application before choosing a rotameter.

Conclusion 

These are the elements and the factors you need to know about a rotameter. The user should always check the buoyancy of the fluid when dealing with liquids while in gas substances, buoyancy is not necessary. If you are going to use a mass-flow rotameter, it works best with fluids with low viscosity.