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What to consider in selecting the right isolation valve
By Mark Gimson , director of marketing and international sales, Cla-Val
There are many isolation valves available for a municipal water system and selecting the right one impacts the efficiency, reliability, and maintenance of the water supply network. An isolation valve is typically either in the fully open position or the fully closed position. Gate valves and butterfly valves are most commonly used for this use, and check valves are also a good consideration. Occasionally, an eccentric plug valve is selected, but they are primarily used for raw or wastewater applications, as the shape allows them to always close or open even if there is small matter passing through the pipeline. Ball valves are an inexpensive consideration for small pipes, but tend to not last as long. A water system manager or operator has many things to consider when selecting an isolation valve for their system. Here are some questions that can help determine the right isolation valve for the right situation. WHAT IS IN THE FLUID? One of the most important considerations is the fluid that is going through the valve. Is it raw water that may have debris or treated water that may have chemicals? Does the water system treat with free chlorine, ozone, or chloramines for disinfection? Nitrile rubber (Buna-N) and ethylene propylene diene monomer (EPDM) elastomers are the most widely used in the industry, and some believe that EPDM holds up better with chloramine use. What is the temperature and pressure, as the valve must be able to withstand the system’s operating conditions? WHAT IS THE PIPE DIAMETER? The size of the line that the isolation valve will be in is another important consideration to maintain pressure integrity and prevent
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leaks. Gate valves are most often used on lines up to 12in in diameter and are available with flanged connections and mechanical joint connections, along with several different connection combinations. Gate valves are full port multi-turn resilient wedge valves that have either a handwheel operator or — on buried service — a gear operator and a 2in operating nut. Gate valves are often used as isolation valves on the inlet of a flow meter as they are full port valves with no obstruction in the line and do not count against the meter’s upstream and downstream requirements for accuracy. Another advantage of a gate valve is that in most cases by exercising the valve, a complete shutoff is ensured. The common alternative to a gate valve is the butterfly valve. These valves are most often used in 3in through 144in pipe-diameter
water systems. Like gate valves, they are available in both flanged and mechanical joint connections. Robb White, general manager for ESI Water — a provider of water and wastewater process and control solutions — said, “One advantage of a butterfly valve over the gate valve is that the lay length is shorter. The larger the pipe size, the greater that difference is. The benefit of a shorter lay length is that the valve can reduce the footprint of the piping design.” Butterfly valves are quarter-turn lever operated and available through 8in pipe diameter with gear and handwheel or gear and 2in operating nut, 8in and larger. Butterfly valves are generally less expensive than gate valves. “A disadvantage of a butterfly valve is that it has the shaft and disc in the pipe flow that means there is a permanent obstruction to flow, which is why they are used on clean water systems only,” he added.
40 Water & Wastewater Asia | September-October 2024
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