A butterfly valve is a type of valve that can be used to control or isolate flow. A disc is used as the closing mechanism. The operation is comparable to a ball valve, allowing for quick shutoff. Butterfly valves are commonly used because they are less expensive than other valve types and are smaller in weight, requiring less support. A rod passes through the disc and connects to an actuator on the valve's outside. The disc is turned parallel or perpendicular to the flow depending on how the actuator is rotated. The disc, unlike a ball valve, is always present within the flow, causing a pressure drop.