The role of a butterfly valve is to regulate the flow in which the disc takes the form of the disk. This process is similar to the process of the ball valve. The disc is positioned in the center of the pipe, and has a rod passing through, which is connected to an actuator on the outside of the valve. Rotating the actuator turns the disc either parallel of perpendicular to the flow. The disc is always present within the flow, which means a pressure drop is then induced in the flow, no matter what the valve position is. This is the major difference from the ball valve.