Why called butterfly for butterfly valve?

Because this valve has a centric line through it, and control by a stem going through the disc and drive it open just like a wing of butterfly, that is why it is called 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.
Butterfly valves and controls：
The butterfly valve is not only simple in structure, small in size, light in weight, low in material consumption, small in installation size, small in driving torque, simple and fast in operation, but also has good flow regulation and closing and sealing characteristics at the same time. It has been developed in the past ten years. One of the fastest valve varieties. The use of butterfly valves is very extensive. The variety and quantity of its use continue to expand, and it is developing towards high temperature, high pressure, large diameter, high sealing performance, long life, excellent adjustment characteristics, and one valve with multiple functions.