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Corroding and obsolete valves, adoption of stricter plumbing codes, and the importance of protecting the public water supply from hazardous backflow all combined to present the city of North Las Vegas with a challenging problem.
According to Stephen Gay, cross connection control specialist for the city, more than 250 fire sprinkler systems in the North Las Vegas water system are equipped with single-swing check valves. The valves – some installed more than 20 years ago – no longer comply with the latest backflow protection standards outlined in Nevada Administrative Code 445-A.
Initial inspections have revealed other problems, Gay said. The old valves were never designed for routine testing and the city found many of the oldest single-check valves were corroded in the open position and would not work even during a backflow condition.
Gay said the challenge for the city utilities department was to find a replacement double-check detector backflow preventer assembly that satisfied a number of specific needs. The new installation would have to:
• Comply with the revised codes for protection against backflow,
• Fit within the space requirements of the existing below-grade units,
• Meet North Las Vegas's desire to get maximum performance and reliability from a new product, and
• Require minimal expense and trouble.
After a thorough review of the available products, North Las Vegas and Conbraco Industries, Inc. agreed to conduct trial applications on the Conbraco 4S Series double-check detector backflow preventer assembly. The city decided to test the DCDAs at two fire sprinkler locations. Of all the products considered, the 4S Series, with its short lay length and ease of installation, showed the most promise for the least expense. Conbraco provided the assemblies, and city crews installed them.
Stephen Gay said other conventional double-check assemblies considered by his department did not fit in the existing below-grade vaults. "The lay lengths of the single-check units are quite short. The Conbraco backflow assemblies had such a compact design, we found that they would fit below-grade with very limited modifications to the existing plumbing system," Gay said.
Moving the piping systems aboveground was considered but rejected. Cost was a concern. Gay said the additional materials required and adding a protective enclosure would boost the cost of the retrofitting substantially. The enclosure alone, he said, could add $3,000 to $5,000 to the installation. Adding enclosures would also damage the aesthetics and could hinder the sight lines for passing motorists.
In the two replacement projects, crews installed one 4-in. and one 6-in. Conbraco double-check assembly. The three-person crew completed each installation within a few hours.
"Actually, the hardest part of the job was cutting the bolts from the old single-check assembly," Gay said. "The rest was easy … putting on transitioning couplings, tightening them up, recharging the line, flushing it out, testing and certifying operation of the assembly and they were done."
He said he really appreciates how the new Conbraco assemblies are designed with ease of maintenance in mind, simplifying tests and repairs since the assembly remains in-line. "The whole check comes out right from the top … That was the first time I had seen that design," he said.
Since these backflow assemblies were installed nearly eight months ago, Gay’s department has been checking them monthly – something they could not do with the old valves. The new assemblies, he said,
"… have proven to be a very solid valve. They’ve maintained high differential pressures and haven’t needed any maintenance." In fact, North Las Vegas anticipates using the Conbraco product for future backflow retrofits.
For more information: Conbraco Industries, Inc. • Matthews, NC • Phone 704-847-9191 • www.conbraco.com