Butterfly valves use a round disc controlled by a control lever or wheel to completely shutoff a pipe. When the lever is moved a quarter turn, the disc stands upright and perpendicular to the flow of fluids, closing the valve and blocking any liquid or gas from flowing down the pipe.
High performance butterfly valves are usually made from metal like stainless steel or cast iron because they offer the most strength and durability against high pressure. They can range from less than a foot to more than a yard in diameter depending on the application. Different kinds of butterfly valves are used in different situations; triple offset butterfly valves, for example, are used for pipe lines with moderate to high pressures that require more control and tighter seals whereas AWWA butterfly valves are sanitary and are therefore used in water pipes.
High performance butterfly valves are constructed using solid pieces of high quality metal in order to exceed the standards of regular valves. These hydraulic and pneumatic valves can be used in many situations that transport water, chemicals, slurries and gases among other substances.
High performance butterfly valves are usually double offset valves that are designed to be eccentric in two places. The shaft or stem that holds the disc in the valve is mounted slightly off center compared to the center of the pipe and is also mounted behind the rubber or plastic sealing band of the seat, the actual place where the seal is created.
The double offset results in less friction between the disc and the seal, which helps the valve last longer. It also provides a tighter seal that can be successfully closed against fast moving and high pressure liquids and gases. The increased sealing ability and decreased tendency to wear down makes high performance valves second only to triple offset valves. Also, the seal can be made from materials that can withstand higher temperatures compared to standard butterfly valves.
Metal seals are sometimes used because they can accommodate temperatures up to 1200°F. High performance butterfly valves use a smooth disc surface and a one-piece shaft to prevent any leaks or weak areas. They can withstand a wide range of conditions including near vacuum pressure to working pressures of around seven hundred and twenty five psi (pounds per square inch) as well as low to high temperatures.