Innovations In Variable Area Flow Meters (Rotameters)

Interview conducted by G.P. ThomasSep 23 2013

Jim Dillon, the global product manager for variable area products at Brooks Instrument, speaks to AZoM about recent developments in rotometers and the new MT3809 from Brooks Instruments.

Brooks has recently released the new MT3809 rotameter – could you briefly explain the how a rotameter works and which industries would benefit from it?

Variable Area Flow Meters, commonly called rotameters, are a cost-effective solution for flow measurement of liquids, gases or steam. The VA meter has excellent measurement repeatability, which provides process stability and consistency.

External power is not required for operation; therefore, they deliver a fail-safe flow rate under any circumstance.

VA flow meters can be made from a variety of wetted materials for process fluid compatibility, high-pressure and high temperature conditions, and hazardous locations.

The basic principles of how a rotameter works are outlined below:

• The customer’s flow raises a float in a tapered tube increasing the area for passage of the fluid.
• The float will reach a stable position when the force exerted by the flowing fluid + the buoyancy equals the gravitational force.
• A change in flow rate upsets this force balance and the float will move up or down until it again reaches a position where the forces are in balance.
• Variable area meters can be installed directly after pipe fittings or valves without adverse effects on the meter accuracy.
• The meters are also inherently self-cleaning since the flow of gas or liquid between the tube wall and the float provides a scouring action which discourages the build-up of foreign matter.

More details are shown in the following diagram.

Image credit: Brooks Instrument.

The primary industries served by variable area meters (rotameters) are chemical, petro-chemical, oil and gas production. But you can find VA in pharmaceutical, food and beverage, water and wastewater and metals and mining.

In your view, how is this new model unique in its field?

VA meters in general are unique because they can be used to meter liquids, gases or steam. But the model 3809G can be used in applications where process fluid temperatures range from -198°C to 420°C / -325°F to 780°F. It can also work in environments with pressures as high as 6000 PSIG /420 bar.

Furthermore, the 3809G is available with special request to operate with process temperatures up to 20,000 PSIG / 1400 bar. This is the broadest temperature range of any VA meter on the market. This broad temperature range applies to mechanical indicator or meters with electronics such as alarms or transmitters.

Also, the explosion proof housing can be installed in any hazardous area. This saves customers the hassle inherent in buying different meters for different hazardous, classified areas.

How accurate is the MT3809 under harsh conditions?

The customer provides application details. Each meter is calibrated for the customer’s process conditions either using the customer’s fluid or simulating the customer’s fluid.

In this way, the meter is custom fit for the customer’s application. The key is accurate process fluid information, which assures an accurate and great performing meter.

How has Brooks ensured that the MT3809 is both durable and safe?

Our design procedures require testing of the products to the rated specifications. MT3809 has been tested for temperature, accuracy and general performance.

The meter was also vibration tested to confirm that it is capable of handling pipe vibrations. Competitive meters were also tested and found to be unable to pass the vibration tests done on model 3809G.

The new MT3809 Variable Area Flow Meter (Rotameter) from Brooks Instruments. Image Credit: Brooks Instrument

Could you explain the theory behind the use of magnetic coupling for flow rate indication?

The float and the indicator each contain a magnet. A bond is formed between the two magnets. As the float moves due to flow rate changes the pointer tracks with the float movement.

The customer reads the flow rate based on the pointer aligning with the markings on the scale. The magnetic bond was tested for durability and the magnetic bond is strong enough for the fastest flow surge.

Are there any corrosion resistant materials options available for the metering of aggressive fluids?

Yes, model 3809G can be manufactured with Hastelloy C-276, Inconel 625 or Titanium Grade II.

These materials were chosen because they are resistant to very corrosive chemicals. Selecting the right material for your process fluid assures a long meter life.

What have been the major advancements in rotameters in the last few years, and how can they be improved for the future?

Rotameters have gotten smaller in size with a standard lay length. They are capable of a broader process temperature range and digital communications are being introduced.

A very big change has been requests for more certifications, such as positive material identification and agency approvals based on the country where the meters are being installed.

Another improvement that would be good for everyone is general acceptance of IECEX approvals on the alarms and transmitters. Almost every country has agency approvals. This restricts suppliers of equipment plus adds expense to the meters because gaining these country based approvals can be very costly.

If the world accepted IECEX as the standard all of suppliers, engineers and users would be talking the same “language” at least for approvals.

About Jim Dillon

Jim is the global product manager for variable area products (rotameters) at Brooks Instrument.

A long-time employee of Brooks Instrument, Jim Dillon has a BA in Mathematics from Temple University, as well as an MBA from DeSales University.

He is very familiar with variable area meter products as a result of holding numerous positions in engineering.