The body contains the internal parts of the butterfly valve. Depending on the purpose and the media flowing through it, the body can be made of different materials such as brass, stainless steel or PVC. For example, metals are often used when there are high pressure and temperature. On the other hand, for corrosive media, Alloy 20 is often employed because it provides resistance to strong acids such as sulfuric acid.
The disc allows or prohibits the media to pass through the valve. The many variations to the disk provide different degrees of flow control or sealing force.
Together with the disc, the seat forms the anti-leak seal for the butterfly valve. Stopping of the media flow happens when seat surrounding the inner diameter of the body seals the disk. While elastomeric seal such as Teflon is more common, seal materials also include clamp rings, O-ring or a rubber ring.
The stem connects the disc to the actuator, sometimes called the wheel or the handle, depending on the design and orientation. The stem transmits the motion of the handle to the disc. Without it, the actuator cannot manually open or close the disc.
Also called the handle, the actuator controls the opening and closing of the valve from the outside of the valve body. There are three actuator styles designed for safety when a failure occurs:
This means that when the actuator fails, the valve remains open.
This means the actuator remains closed when there is actuator failure.
This means that the actuator can be manually manipulated when failure happens.