Water Company Finds Ultrasonic Metering Solution

Metering problems on a large distribution main lead water company to seek a new solution.
Water Company Finds Ultrasonic Metering Solution
An extended status display connected to the FLEXIM ultrasonic flowmeter helps the user judge the measuring situation and the current accuracy directly during the measurement.

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The Aquarion Water Company recently discovered it had a flow measurement problem with a large customer.

Aquarion, the largest investor-owned water utility in the Northeast, serves 49 cities and towns throughout Connecticut’s Fairfield, New Haven, Hartford, Litchfield, Middlesex and New London counties, drawing water from a series of reservoirs and wells. But its measurement problem was not with its home or business customers.          

“We also wholesale water to United Water over the border in New York state,” says John Schultz, senior operations specialist for Aquarion. “We send them about 4 million gallons a day and they in turn supply the drinking water for Port Chester, Rye, and Rye Brook, New York. We used to measure that volume with a turbine meter and bill them accordingly. Last year during our annual check of the meter, we found it was reading high. We want to be accurate and keep the folks at United happy, so we set out to repair or replace it. Easier said than done.”          

The manufacturer of the meter had ceased to make meters for any pipe over 10 inches in diameter. The pipe Aquarion used to supply United is 14 inches.    

“And we couldn’t find replacement parts, either,” Schultz says. “We tried other reputable manufacturers, but the story was the same — all had ceased to make meters for larger-diameter pipe. So it was clear that we would have to find another solution.”          

Schultz eliminated most metering options because they intruded into the water flow and/or because they didn’t accurately measure low flow.          

“A key consideration for intrusive meters like venturis is that we have very little headloss available,” Schultz says. “It’s only about 45 psi at the transfer site. I don’t want any headloss at all. I also wanted to be sure we could measure lower flows accurately. Venturis and other technologies weren’t considered because they were very costly to install, they require a lot of maintenance and they are not as precise at low flows as we wanted. So we were looking at nonintrusive meters and that narrowed the field to full-bore mag and ultrasonic meters.”

Mag meter problems

There were three problems with the full-bore mag meter. First, most manufacturers don’t recommend their meters for pipes over 12 inches in diameter because the meters for larger pipes require a crane and a crew of installers, and that means added expense. Second, it does not read flow rates below 0.3 feet per second. The ultrasonic Schultz was looking at could read flow rates as low as 0.03 feet per second. But the third problem sealed the deal for ultrasonic.          

“There was no standard from the American Water Works Association [AWWA] for full-bore mag meters and there was one for ultrasonic,” Schultz says. “We definitely wanted to go with AWWA standards.          

“The ultrasonic I decided to go with was from FLEXIM AMERICAS. I have a good deal of experience with ultrasonic flowmeters. Most aren’t robust enough for my applications. I put these things in pits and they have to be able to stand up to their environment.”

The FLEXIM meter adheres to AWWA 750-10, notes Lin Abraham, the FLEXIM field service engineer who performed the installation for Aquarion. “We also meet the American Society of Mechanical Engineers standard ASME MFC 5M that governs the use of ultrasonic flowmeters in closed conduits and provides a National Institute of Standards and Technology traceable certificate of the calibration of the meter’s transducers. We’re the only ultrasonic flowmeter manufacturer who can say that.”

How ultrasonic metering works

“One of the major benefits of ultrasonic flowmeters is that, unlike traditional meters, they contain no moving parts and do not need frequent calibration and maintenance,” explains John Van Nostrand, FLEXIM AMERICA’s southern regional manager. “Measurements are made using the transit time difference method. It exploits the fact that the transmission speed of an ultrasonic signal depends on the flow velocity of the carrier medium. An ultrasonic signal moves slower against the flow direction of the medium and faster when it is in the flow direction.          

“For the measurement, two ultrasonic pulses are sent through the medium, one in the flow direction and the second against it. The meter’s transducers work alternately as transmitter and receiver. The transit time of the signal sent in the flow direction is shorter than that of the signal sent against the flow. The meter measures the transit time difference and calculates the average flow velocity. Since the ultrasound signals propagate in solids, the meter can be mounted directly onto the exterior of the pipe noninvasively. And the transducer paste problem was solved by FLEXIM engineers who developed solid mounting pads that don’t need replacing and conform to the shape of the pipe.          

“The amount of straight run that is usually required to obtain best accuracy is 10 to 5 upstream/downstream diameters,” Van Nostrand says. “So a 10-inch pipe needs 150 inches or 12.5 feet of straight pipe. We find that we can squeeze this down to 5 diameters upstream and still maintain the meter accuracy with multi-beam meters.”          

Aquarion installed an ADM 7407 Dual Beam volume flowmeter. It simply clamps onto the exterior of the pipe. The meter was installed with the K Transducer, which is often used in water and wastewater utility applications. The K Transducer is low frequency and delivers a strong signal through ductile iron. The FLEXIM meter can measure low-velocity flow rates as low as 0.03 feet per second, which is 10 times lower than the electromagnetic flowmeter.          

“It is nonintrusive and does not require cleaning or maintenance,” Schultz says. “It does not come into contact with the water, so it has no wear and tear. Unlike other ultrasonic flowmeters, FLEXIM uses a patented permanent coupling pad, so there is no need to take the sensors off the pipe to reapply ultrasonic couplant. With the old turbine meters no longer available, the industry is looking for alternatives. I believe I have found one that is much better than what we were used to."

About the author

Jack Sine is a freelance writer specializing in environmental issues and the chemical, power and HVACR industries.


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