In fluid handling sectors, measuring the flow of different liquids and gases is vital to make a product safe and effective. That is why many companies and industries utilize devices called flow meters. Flow meters help in monitoring, regulating, and measuring flow rates accurately. Flow meters also come in handy in checking and regulating the pressure and temperature of fluids. 

In this article, we are going to explore one particular tool called rotameter. This is a widely used measuring device in many industries. A rotameter is made from either glass, plastic, or stainless steel tubes. The device comes with a float placed inside the tube to measure the flow rate. The float responds to the flow rate of the fluid and the fluid in the tube linearly. What makes rotameters favorite measuring devices to many is the simplicity in setting it up and low maintenance cost. The flowmeter also has a wide measuring range and also measures flow rate with low pressure. 

The Working Principle of a Rotameter 

Rotameters come in many types, and one of them is known as variable-area rotameter. This kind of rotameter is widely used in industries and has a tapered tube. When the liquid or gas that is supposed to be measured goes through the tube, it raises the float. A great volumetric pressure goes up; it raises the float further up. When measuring the flow rate in gases, buoyancy is not needed, and you only need the flow velocity and density to get the flow rate. In liquids, velocity and buoyancy are combined to get the flow rate. 

When checking the flow rate in fluids, a rotameter is placed in a vertical position. Since the fluid will start flowing from the bottom of the tube moving upwards, the float will rise. When no fluid is flowing inside the tube, the float will remain at the tube’s bottom. As the size of the annular opening increases across the float, differential pressure decreases, and the float rises. Usually, the rotameter’s size is based on what the user is going to use its fire. Therefore, rotameters don’t only come in different types, but also different sizes. An equilibrium is reached when the float reaches a fixed position as the force is exerted upwards. When this happens, the user is then able to read the fluids density and viscosity flow rate. The levitating float brings this about as the fluid flows into the tube. 

Rotameters are also found in types that allow the user to control the flow using a valve manually. Most rotameters had free floats that rotated based on the changing gas and fluid pressure in the past. The name rotameter came about because of the free rotating floats. Rotameters used in measuring common fluids like water and air come with calibration data and direct reading scales. With other fluids, readings will have to be converted into standard formats. The unit used to measure flow rate using rotameters is in standard cubic feet per minute (scfm). In water, the unit used to measure the flow rate is in GPM. 

What to Look for Before Buying a Rotameter 

The type of rotameter – Finding the right type of rotameter is vital if you want accurate reports. Since there are many types of rotameters for different applications, the user needs to know how the rotameter will be used. 

Operating conditions – The conditions that the rotameter will be subjected to also matter when looking for a proper rotameter. What is the temperature range? What are the min and max flow rate? The pressure of the fluid is also important to note before settling for a particular rotameter. 

The pipe size – The user should also consider the size of the pipe to be used in the setup process. 


Flow meters are incredible tools when it comes to measuring the flow rate of liquids. If you are going to install a rotameter into your hydraulic system, you need to first understand the application type. This will enable you to find the right rotameter that gives accurate flow rate measurements. 

By Proteus