What is a gas butterfly valve?

A butterfly valve is from a family of valves called quarter turn valves. The "butterfly" is a metal disc mounted on a rod. When the valve is closed, the disc is turned so that it completely blocks off the passageway. When the valve is open, the disc is rotated a quarter turn so that it allows unrestricted passage. The position of the disc is effected from outside the valve.

gas butterfly valve is one kind of butterfly valve, the main feature is that all the functions are supported by gas just as the Electric Butterfly Valve which supported by electric.