A Butterfly Valve is a valve which can be used for isolating or regulating flow. The closing mechanism is in the form of a disc. The operation of this valve is similar to a ball valve which has a quick shut off. They are often used because of their low cost compared to other valve designs as well as being comparatively light in weight, which in turn means less support is required during installation. The disc is housed in the centre of the pipe and passing through this disc is a rod connected to an actuator on the outside of the valve. Rotation of the actuator turns the disc either parallel or perpendicular to the flow, resulting in a pressure drop regardless of the valves position. There are various types of butterfly valves. Concentric butterfly valves use a resilient rubber seat with a metal disc. Double eccentric butterfly valves also known as high performance butterfly valves use different types of material for the valves seat and disc. Triple eccentric butterfly valves either use a laminated or solid metal disc in their design.