These are normally a type of valve that uses a flat plate to control the flow of water.

As well as this, Butterfly valves are used on fire apparatus and
typically are used on larger lines, such as front and rear suctions and
tank to pump lines.

A Butterfly valve is also a type of flow control device, used to make a
fluid start or stop flowing through a section of pipe. The valve is
similar in operation to a ball valve.

Some supplementary tips

Butterfly valves on water lines should be manually operated only through
a geared mechanism to prevent slamming