A butterfly valve (also called a throttle valve) has a rotating disk in the body, which closes the flow passage in the valve. The disc is rotated by a shaft located on the centreline of the disc. One end of the shaft seats in a bearing in the body and the other end passes through the body out to a knob or other actuator. The sealing of the disc in a closed position is either soft (rubber, plastic) or hard: metal-metal.

Butterfly valves are mostly used with flanged connections:

• flanged – the valve has flanges,
• wafer – the valve is installed directly between the sealing faces of the pipeline flanges,
• wafer and lug – the valve has threaded eyes for mounting to each flange separately.

Butterfly valves can be of the simplest concentric construction – with the shaft on the centreline of the disc, double-eccentric (double-offset) with the shaft axis shifted back and aside in relation to the centreline of the disc, and triple-eccentric (triple-offset) with an additional shift of the sealing surface axis.

The body of the butterfly valve is usually made of cast iron or stainless steel, the disc of cast iron or stainless steel, the seal of EPDM, NBR, Viton, silicone or PTFE. Working pressures from a few to several tens of bar. Nominal diameters up to DN 400 and larger. There are many butterfly valve versions driven by a pneumatic actuator.

The butterfly valves are used in all kinds of industrial applications, for fluids, chemicals, gases, dust, food substances. Suitable versions can be used in potentially explosive atmospheres, ATEX zones.