Isolation Valves: What to Consider in Selecting the Right Valve

Many isolation valves are available for a municipal water system. 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 or fully closed position. Gate valves are most commonly used, while check valves are also a good consideration.

By Mark Gimson, Director of Marketing and International Sales – Cla-Val

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 they typically do 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 Your Fluid?

The fluid passing through the valve is one of the most important considerations. One must ask: 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? Buna-N and EPDM elastomers are the most widely used in the industry, and some believe that EPDM holds up better with chloramine use. Temperature and pressure are also important to consider, as the valve must be able to withstand the system’s operating conditions.

What is the Pipe Diameter?

The size of the isolation valve’s line is another important consideration to maintain pressure integrity and prevent leaks. Gate valves are most often used on lines up to 12” in diameter and are available with flanged conditions and mechanical joint connections, along with several connection combinations. They 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/downstream requirements for accuracy. 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 2” operating nut.

Another advantage of a gate valve is that in most cases, exercising the valve ensures a complete shutoff.

The common alternative to a gate valve is the butterfly valve. These valves are most often used in 3” through 144” 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.”

Quarter-turn, lever-operated butterfly valves that are 8” and larger are available through 8” pipe diameter with a gear and handwheel, or gear and 2” operating nut. 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, meaning there is a permanent obstruction to flow – that is why they are used on clean water systems only,” said White.

Is the Location Prone to Backflow?

The check valve or non-return valve is the last type of common waterworks isolation valve. The purpose of a check valve is to prevent reverse flow in a pipeline. Many different styles of check valves are available for a water system. The common choices range from lever & weight, lever & spring, silent check, double disc check, wafer swing check, flex check, and a tilted disc check valve. All of these check valve options have their particular benefits and the application for which they are best suited.

Lever & weight and lever & spring check valves are the most common check valves in use. These check valves can be provided with an oil cushion or air cushion closure. A potential benefit of the lever & weight or lever & spring is that it is possible to physically open the check valve by utilizing the lever on the side of the valve. This enables operators to see if there is anything trapped underneath if the flow slows.

Silent check valves are used most on the discharge of pumps and are resilient seated to minimize noise upon closure. A downside to this valve is the added head loss across the valve. “Understanding and calculating this head loss is essential for designing efficient piping systems and ensuring the chosen valve can maintain the desired flow rate and pressure within the system,” said White.

Tilted disc check valves are commonly used in high-service pumping applications where head loss is critical. Tilted disc check valves have a very low head loss and can be furnished with top and bottom, oil-filled dashpots that allow controlled closure of the valve. This is by far the most efficient valve; the friction loss is very low, and it is ideal for big pipelines.

Flex check valves or rubber flapper check valves may be the most versatile check valves and can be used in both water and wastewater applications. The Buna encapsulated flapper is the sole moving part on this easy-to-clean, hard-wearing valve. The valve can accommodate a position indicator, which allows plant crews to determine a valve’s position quickly and easily by the visual indicator, and a backflow actuator for preventing contaminants from entering the clean water system.

“Regardless of what isolation and check valves you are considering, make sure that the valve selected meets the appropriate standards for drinking water and the appropriate AWWA standards for the valves, as this will go a long way to ensuring you get the full life expectancy with a quality valve. Having been in business for over 25 years, I cannot overemphasize the importance of scheduled valve maintenance to ensure longevity of use in the system. Most valves are in the ground and are easy to forget about, so setting and sticking to a schedule is key,” concluded White.

About the Author

Mark Gimson is the Director of Marketing and International Sales at Cla-Val, with over 40 years of experience in the mechanical and industrial engineering sector. He specializes in driving growth with a passion for expanding markets.

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