Wafer butterfly valves are the more common of the two designs of butterfly valves, the other design being lug style.
In addition to being easier to install, wafer butterfly valves are cheaper than the lug style. These two differ in a couple of senses. First, the lug butterfly valve design has threaded inserts and can be installed using nuts but no bolts whereas the wafer style requires nuts and bolts. Both are attached in conjunction with flanged butterfly valves, the centre piece bolted into where the piping meets, protected by the extended edges of flanges that serve as a tight and efficient seal.
Basically, the lug style is employed more often in environments where the pipes may need to be separated without bothering the other side, while wafer valves are effective against backflow. Because of the prevalence of the uni-directional system preference, the wafer design is more popular. The only disadvantage is that, unlike lug designs, wafer butterfly valves cannot be moved. Because of the advances in machining techniques, both styles can be built to fit perfectly, ensuring the most precise and leak free valve possible.
Wafer butterfly valves consist of a seal that fits around the wall of a pipe, a round disc, and a control lever. The wafer butterfly valves discs’ rotates ninety degrees at the turn of the lever. When the disc is parallel to the flow of water, the valve is in open position and lets all gases or liquids pass; when the handle is turned, the disc rotates around to a position parallel to the flow of water.
In this closed position, the disc fits snugly into the seal and blocks all flow through the pipe. Wafer butterfly valves can be made of a variety of materials, including stainless steel, plastic, and other metals. Although plastic is cheaper, it is not used as often because it is more prone to corrosion then the metals used, such as cast iron.
Aluminum is also occasionally incorporated to make the gasket part of the valve, since it is a lightweight and flexible metal. Wafer butterfly valves are used to control the flow in water distribution, chemical services, and ventilation applications.