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The main components of a butterfly valve are as follows:

1. Body

The body of a butterfly valve is the main housing that holds other components and connects to the pipeline. Material selection depends on the application environment. Cast iron is common for its strength and cost - effectiveness. Ductile iron is preferred for better corrosion resistance and strength, often used in water - based systems like municipal water distribution. Stainless steel is chosen for more corrosive fluids or hygiene - sensitive applications such as in the food and beverage or pharmaceutical industries. Other alloys may be used for high - temperature or high - pressure scenarios.
The body's design includes features for installation, usually with flanged ends or threaded connections. Its internal geometry ensures a smooth flow path when open and proper seating of the disc when closed.

2. Disc (Closure Element)

The disc, a circular flat plate, controls fluid flow. It's made of materials like cast iron, ductile iron, or stainless steel, depending on the application, and sometimes special alloys or composites for unique fluid properties. When fully open, the disc is parallel to the flow, maximizing it. When closed, it's perpendicular to block the flow.
Surface treatments and coatings may be applied. For example, a hard - coating can prevent wear from abrasive particles, and a corrosion - resistant coating can handle corrosive fluids. Specialized disc designs like double - offset or triple - offset improve sealing and reduce leakage.

3. Shaft

The shaft enables the disc's rotation. Made of stainless steel or other corrosion - resistant materials, it provides strength and rigidity. The connection between the shaft and the disc is robust and precise, allowing for smooth rotation. The shaft's other end connects to the actuator, which provides the force to rotate the disc. The connection type depends on the actuator type, such as piston - driven for pneumatic actuators or direct/geared coupling for electric actuators.

4. Seals

Seals are crucial in a butterfly valve. There are two main types: seat seal and shaft seal.
The seat seal around the disc edge contacts the body when closed to prevent fluid leakage. Materials like elastomeric rubber are common. Different rubber compounds are chosen based on the fluid. For example, nitrile rubber for oil - based fluids and EPDM rubber for water. Other polymer - based materials or composites may also be used, and the design may have features to enhance sealing under various conditions.
The shaft seal prevents fluid leakage around the shaft. One type is the packing gland, with packing materials like braided graphite or PTFE - based materials compressed around the shaft. It can be adjusted for tightness. Another type is the mechanical seal, which has precision - engineered components like stationary and rotating faces under pressure, offering higher sealing performance but being more complex and requiring more maintenance.