Basics of Rotameters

Rotameters, also referred to as variable area flow meters, have diverse industrial processing applications that range from simple to sophisticated. The devices are easy to install, require no electrical connection, and provide direct flow rate reading. They provide fail-safe flow rate readings in a wide array of industrial applications.

Rotameters: An Overview 

Developed by German inventor Karl Kueppers in 1908, Rotameters measure the volumetric flow rate of liquids and gases.

Important elements of a rotameter (variable area flow meter) include the tube and the float. Their operation is simple. The tube is fixed vertically and the fluid is fed from the bottom. It travels upward and exits from the top. The float remains at the bottom when no liquid is present and rises upward when fluid enters the tube.

The float inside the tube moves in proportion to the rate of fluid flow and the area between the tube wall and the float. When the float moves upward, the area increases while the differential pressure decreases. A stable position is reached when the upward force exerted by the fluid is equal to the weight of the float. A scale mounted on the tube records the flow rate of the liquid. Usually, the flow can be adjusted manually using a built-in valve.

Types of Rotameter 

Variable area flow meters can be categorized by the type of tube they use, which relates to their ability to withstands various pressures, temperatures, process media, and cost. Process connection size and wetted part materials vary as a function the rotameter type and construction.

Glass Tube Rotameter
(Yokogawa)

Glass Tube Rotameter - The basic glass variable area flow meter consists of borosilicate glass tube while the float is made of either glass, plastic, or stainless steel. The most common combination is a glass tube and metal float. This is suitable for a measure the flow rate of liquid of low to medium temperatures and pressures.

Applications:

• Analytical instrumentation
• Industrial processes
• Chemical production
• Pharmaceutical production
• Oil & gas extraction
• Refining processes
• Fuel cell research
• Water treatment systems

Metal Tube Rotameter
(Yokogawa)

Metal Tube Rotameter - Metal tube variable area flow meters are another type that is suitable for temperatures and pressures beyond the physical and mechanical limits of glass tube versions. They are generally manufactured of stainless steel, aluminum, or brass. The piston position is determined by the mechanical and magnetic followers that can be read from the outside of the tube. They are suitable in situations where applications conditions would damage the glass metering tubes, such as steam applications.

Applications:

• Purge liquid/ gas metering
• Liquid, oil, or gas flow measurement
• Chemical injection
• Rotating equipment flow measurement
• High-pressure flow meters on offshore oil platforms

For more information, contact Classic Controls.
https://classiccontrols.com
863.644.3642

Industrial Flow Meter Selection

Flow meter selection chart. Click on image for larger view.

Many industrial process control operations require fluid flow measurement as an essential element in the design of the process. The proper application and installation of a flow meter as part of the fluid transfer system will provide accurate flow measurement.

Industrial flow meters use different technologies to measure fluid flow rates directly or indirectly. Some of the most common technologies for fluid flow measurement are vortex flow meters, magnetic flow meters, Coriolis flow meters and rotameters.

Each separate technology has attributes that can make it more suitable for certain applications. The selection of the most appropriate flow measurement technology for an application is an initial and crucial step in the design of a functioning fluid measurement system.

Selection criteria such as fluid temperature, pressure and velocity will be included in the selection process. Further considerations include whether the fluid may be abrasive, corrosive, clean or dirty. The state of the fluid, liquid or gas, must also be taken into account.

The table above provides general guidance on which technologies to consider, based on the above mentioned factors. This will help you to focus further research on product selection.

Contact Classic Controls with any industrial flow application you may have. Their application engineers will provide guidance and advice to assure the proper flow meter is chosen.

Classic Controls
https://classiccontrols.com
863-644-3642

Level Measurement - Simple Accurate Bubbler Method

Instrument layout for level
measurement

Measuring liquid level in a tank or vessel can be accomplished in a number of ways, all of which require some arrangement of instrumentation to either infer the liquid level from the measurement of a related physical property, or directly deliver the liquid level visually using a scaled gauge arrangement. One indirect method of level measurement is often referred to as the bubbler method, so named because it employs a purging gas that continually vents from the bottom of a tube extending into a tank of liquid. Through a simple apparatus, the level of a liquid can be inferred by the amount a back pressure exerted upon the gas flowing through the tube.

Probably the greatest advantage of this method of liquid level measurement is that the liquid does not contact the sensing instrumentation. The only portion of the apparatus in contact with the liquid is a tube immersed into the tank. Basically, a purge gas flows through the immersion tube and may bubble out the immersed end of the tube, which is open to allow the contained liquid to exert a hydrostatic pressure on the purge gas. The back pressure on the gas that is exerted by the liquid contained within the tank will vary directly with the depth of the liquid. The back pressure can be correlated to a liquid level. The accuracy of the measurement is related to the proper regulation of the purge gas (explained in the application note below) and the measurement capability of the pressure transmitter. Once the depth of the liquid is derived, further calculations, employing tank shape, dimensions, and the liquid density can provide an indication of the volume and mass of the liquid. Here is an illustration of the setup, provided courtesy of Yokogawa, a recognized leader in flow and pressure measurement with a global presence. Included below, an application note from Yokogawa on applying rotameters to the setup, as well as data sheets for the instruments employed in the illustrated apparatus.

Share your level measurement challenges of all types with the application specialists at Classic Controls. Combining your process expertise with their product application knowledge will yield the best process measurement and control solutions.

Bubbler Method Liquid Level Measurement from Classic Controls, Inc.

Differential Pressure Transmitter From Yokogawa from Classic Controls, Inc.

Rotameter Variable Area Flowmeters from Classic Controls, Inc.

Selecting the Right Flow Meter Technology

Vortex Flow Meter
Courtesy Yokogawa Corp.

Magnetic Flow Meter
Courtesy Yokogawa Corp.

Many industrial process control operations require fluid flow measurement as an essential element in the process design. Accurate flow measurement can be obtained with the proper application and installation of a flow meter as part of the fluid transfer system.

Industrial flow meters employ differing technologies to directly or indirectly measure fluid flow rates. Among the many available technologies for fluid flow measurement, vortex flow meters, magnetic flow meters, Coriolis flow meters, and rotameter flow meters are among some of the most common found in industry.

Coriolis Flow Meter
Courtesy Yokogawa Corp.

Rotameter Flow Meters
Courtesy Yokogawa Corp.

Each of the separate technologies have attributes which can make them more suitable to certain applications. Selecting the most appropriate flow measurement technology for an application is one of the initial and crucial steps to designing a well functioning fluid measurement system.

Selection criteria, such as fluid temperature, pressure, and velocity will be part of the selection process. Additional considerations include whether the fluid may be abrasive, corrosive, clean or dirty. The state of the fluid, liquid or gas, must also be considered.

The table below provides quick general guidance on which technologies to consider, based upon the factors outlined above. This will help you better focus further product selection research efforts.

Flow Meter Technology Selection Table
Courtesy Yokogawa Corporation of America

Selecting the right device is not always an easy task, especially since it may be something that you do infrequently. Manufacturers often have knowledgeable local representatives that are experienced in this field and more than willing to contribute their expertise to your selection process.