Butterfly valves consist of a round disc or vane that is attached to a control lever or wheel, which when rotated as little as 90° will cause the disc to rotate and stand perpendicular to the flow of water through the pipes.
AWWA butterfly valves are made out of ductile or cast iron with stainless steel or rubber seating and all materials, coatings and lubricants must be suitable for use with drinking water. According to AWWA C504, the section that sets standards for butterfly valves that will be used in water pipes, the valves should be bubble tight and able to shutoff completely. Flanges must be used to install AWWA butterfly valves.
These valves must be carefully regulated because they come into contact with water and, while some of that water is wastewater or water that is not yet potable, the valves must be as sanitary and safe as possible. The materials help prevent rust from forming and contaminating the water. AWWA butterfly valves are used in any circumstance in which water may be ingested. AWWA valves are always readily operable because they are precisely machined to prevent sticking, a characteristic that is very attractive.
AWWA butterfly valves are standard valves; unlike high performance or triple offset butterfly valves, the disc is flat and centered. When the valve is open, the disc turns within its mounting so that it lays parallel to the direction of the pipe and the flow of water. The thickness of the disk does not pose much of an obstruction for the current. The lever control outside of the pipe may be manually or automatically operated to open and close the valve.
Torque limitations and ratings identify how much power is required to close the valve without making it over tight, so that the stem is not damaged. Most lever controlled butterfly valves are quarter turn valves. AWWA butterfly valves, however, are usually operated by a hand wheel that must be completely rotated at least once.
This allows the valve to be opened in increments to better control the water flow, thereby controlling how much water flows through the pipes and at what speed. Also, unlike ball valves that trap small volumes of liquid inside them when they close, butterfly valves completely seal out all water. There is no space in which water can become trapped and AWWA butterfly seals provide a 100% seal.