Rotameter

All You Need To Know About Rotameters

Accurate flow rate monitoring is vital for any liquid or gaseous fluid measurement and control system. Properly controlling flow in all situations leads to operating efficiencies, auxiliary equipment failures, safety, and the longevity of the system. 

Rotameters are one of the most trustable measurement instruments for liquid or gaseous flow applications. It is a very simple, very effective measuring device used in laboratories, industries, and processing units in almost every country today. 

What is a Rotameter?

A rotameter is a variable area flow meter tube designed to measure the flow rate of liquid or gas in close tubes. A representative measurement rotameter consists of a tapered tube in a vertically oriented fashion with a float in the tube that rises or falls depending on the flow rate of the fluid travelling through it. As the fluid flow rate increases, the upward force on the float increases until equilibrium is reached. Equilibrium is reached when the upward force from the fluid is equal to the downward force of gravity.

Another reason for the popularity of rotameters in applications is their ease of use, automatic accuracy, no external power, and direct reading of flow.

Working Principle of a Rotameter

Rotameters utilize the variable area principle. The fluid enters from below and the float starts moving upwards again thanks to the tapered tube. As the float rises in the tube, the tapered tube area increases. As the area increases, the velocity of the fluid decreases which reduces the drag force slowing the float motion until the force equals the products gravitational force. At that point the float remains stationary and the float's height indicates a pre-created calibration value of flow rate.

Current forces acting on the float are:

• Buoyancy
• Drag Force
• Weight

The only equilibrium position of the float is determined from the relative sizes of these forces. The flow rate is then determined by reading a scale on the tube or an indicator that aligns with the float.

Types of Rotameter Available in The Market 

• Metal Tube Rotameter: Usually come equipped with magnetic sensors and transmitters, used in high-pressure applications and in high-temperature applications. Also utilized in chemical and petroleum industries. 
• Glass Tube Rotameter: The most common and economical rotameter, offers direct visual reading. Used in laboratories, and for water, air, and low-corrosive fluids.  
• Plastic Tube Rotameter: Lightweight and resistant to corrosion. Used in water treatment plants and low-pressure applications.
• Bypass Rotameter: Used large pipeline systems to measure the flow from a side stream or bypass flow.
• Purge Rotameter: A miniature rotameter that has a rotatable float (and/or low flow rates) and is usually composed of automatic flow inside analytical instruments and gas chromatography.

Rotameter Applications

Like other types of flow meters, rotameters can be used in a variety of industries and applications including, but limited to:

• Chemical & Petrochemical Plants: Used to measure corrosive/chemical gas and liquids (at pressures or heat).
• Gas Distribution: A variety of gases are used in industry, different rotameters could be used to measure oxygen, nitrogen, hydrogen, etc.
• Water & Wastewater Treatment: Used to monitor the flow rate of treated & untreated water and solids/sludge, as well as flow rate of any treatment chemicals. 
• Pharmaceutical Industry: For dosing of active ingredients or solvents (and/or other liquids). 
• HVAC Systems: For air or duct measurement in a cooling and heating processes. 
• Laboratory and Research: Used in bench-scale experiments for visual monitoring.
• Food and Beverage: For hygienic flows of liquids such as water, juices or milk. 

Advantages of Rotameters

• Real-Time Signals: Measure flow rate changes instantly.
• Simple Usage: No moving parts and does not require an external power source.
• Reduced Maintenance: Fewer points of wear and easy to clean.
• Cost-Effective: Economically priced for either low or high volume systems.
• Compatible with Automation: Can be incorporated into alarm or transmitter systems for remote readings.
• Versatile: Can be used with both liquids and gases.

What to Consider When Choosing a Rotameter

Selecting the right rotameter requires consideration of several key factors:

• Type of Fluid: Gas or liquid? Corrosive or not corrosive? Clean or laden with particulates?
• Flow Rate Range: It is important to ensure the rotameter is calibrated for the flow rate you expect.
• Pressure and Temperature: Make sure the materials of the tube and float can withstand the conditions of your system.
• Accuracy Level: If you want precise dosing or operate a sensitive flow process, be sure to select a more accurate model.
• Material Compatibility: Be sure to select materials (e.g. stainless steel, PTFE or PVC) appropriate for resisting corrosive conditions.