Description: The typical butterfly valve consists of a disc which can rotate about a shaft in a housing. The disc closes against a ring seal to close off flow. Various actuating mechanisms such as the lever, cam, etc., are used to operate the valve.

Usage: Butterfly valves are generally used in low pressure system applications where leakage is relatively unimportant. They are normally used in large diamter lines.

Advantages: Butterfly valves have a very low pressure drop and are relatively lightweight. Also, the face to face dimension is usually quite small. The diameter of the valve can be of the same order as the diameter of the connecting pipes.

Disadvantages: The leakage in a butterfly is fairly high unless special seals are used. Seals are often damaged by high velocity flow. These valves usually require high actuation forces, and are generally limited tol ow pressure systems.