Valve Magazine - Spring 2010

As water first enters the drinking water system and into the pump station, it passes through four potentially different types of valves: ball, check, gate, butterfly—the workhorse valves of the entire system.

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provide complete 100% shutoff. The ball valve, along with the butterfly valve and plug valve, are part of the family of quarter-turn valves. Ball valves are durable and usually work to achieve perfect shutoff even after years of use. For this reason, they are an excellent choice for shut-off applications (and are often preferred to gate valves for this purpose). They offer the fine control that may be necessary in throttling applications, superior to a check valve or a gate valve.

Check valves, by design, allow flow in only one direction and are generally used in the pump control application. These valves allow water to move in only one direction—into the pump station or treatment plant to be treated and then out into the rest of the system. Reverse flow produces the effect of having the valve close. Check valves are a common and inexpensive means of pump control and can be used in both water and wastewater applications.

Gate valves are the most common type of valve found in water distribution systems and live up to their name. They are the gatekeepers of the system and are designed to be either fully open or closed. The gate, or wedge, of the valve is raised and lowered by a stem or screw, which is operated by a hand wheel or valve key. When fully open, gate valves provide almost unrestricted flow because the gates are pulled fully out of the water path.

Butterfly valves can be either modulating or open and closed, with varying levels of openness, which make them a suitable choice over gate valves for modulating applications and filtration. Each butterfly valve consists of a body in which a disk rotates on a shaft to open or close the valve. Because the disk of a butterfly valve stays in the water path when in the open position, the valve creates a higher resistance to flow than a gate valve. Butterfly valves are flow control devices and are often used in the filtration process and to prevent backflow of water into the system.