Butterfly valves are a series of quarter-turn rotary motion valves used in pipelines to shut off flow. It is often said that butterfly valves can be used to regulate flow. However, we do not recommend this as it can damage the disc and negatively affect sealing performance. They are used in a wide variety of process media and industries, especially in water supply, collection and distribution, and pumping stations, and have a wide range of use cases, especially in flow isolation. Several of their key advantages over other valve families are their simplicity and compactness, resulting in a lighter end product, lower cost, smaller installation footprint and faster actuation.

Butterfly valve parts
The following are the main butterfly valve components:

valve body
The valve body is mounted between pipe flanges - the most common end connection types are flanged, double lug and wafer.
 

The disc attached to the valve body acts as a gate to stop or throttle fluid flow; it can be thought of as equivalent to the gate in a gate valve, or the ball in a ball valve. The disc is usually drilled to receive the valve stem or shaft. There are many variations in disc design, orientation and material to improve flow, sealing and/or operating torque. For example, Hawle's 9881k dual eccentric discs are designed to reduce seal wear and "galling" and operating torque requirements.
 
Seats on the inner body
The liner is a strong elastomeric or metal leak-proof seal that holds the disc in the closed position for complete shutoff. The stainless steel weld filler and micromachined integral seat of the 9881k series ensure the seating face is resistant to corrosion and erosion. With this special type of seat design it is possible to manufacture valves according to the requirements of EN12266-A.
 
Stem
The valve shaft, also commonly called the valve stem, is the part that connects the disc to the actuator and transmits torque through itself.
 
Seals
Seals exist at multiple interfaces within the valve to ensure a tight seal during operation or to isolate the process media from the valve's internal components for a more flexible and cost-effective design.
The sealing of the seat surface is ensured by a continuous T-shaped elastic sealing ring, which is fixed on the periphery of the disc by a retaining ring, preventing the sealing ring from rolling out. In the closed position, the seal ring presses against the seat surface, providing a tight seal at the upstream and downstream ends. In the open position, the seal is completely unstressed due to the double eccentric disc design.

By eliminating process media and stem/shaft interaction, the multiple O-ring shaft seal system ensures a maintenance-free seal throughout the life of the valve. In addition, there are smaller and more common components such as bushings, bearings and fasteners that are also part of most other valve construction. Details of the actuation end parts, such as handles, levers, gearboxes and handwheels, are covered in the actuation section.