A butterfly valve (also called a throttle valve) has a swivelling disk in the valve body which closes the flow passage in the valve. The disc is rotated by the rod attached along the diameter of the disc. One end of the rod seats in a bearing in the body and the other end goes through the body out to the knob or other drive. The sealing of a disc in a closed position is either soft (rubber, plastic) or hard – metal-metal.

The butterfly valves are generally used with one of the flange connections:

• flanged type butterfly valves – the valve has two flanges,
• wafer type butterfly valves – the valve is mounted directly between the sealing faces of pipeline flanges,
• lug type butterfly valves – the valve has threaded lugs to enable mounting each of the flanges separately.

The butterfly valves can be of the basic, simplestconcentric construction – a rod placed along the diameter of the disc, double-eccentric, double-offset with the rod axis offset backwards and aside from the disc diameter line triple-eccentric, triple-offsetwith additional offset of sealing surface axis.

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

The butterfly valves are used in all industrial applications, for fluids, chemicals, gases, dust, foodstuffs. The appropriate versions can be used in potentially explosive atmospheres, ATEX zones.