A butterfly valve consists of a relatively flat circular plate with a rod through its diameter. The circular plate creates a perfect seal in the pipe in which it is installed by being flush with the pipe. The rod in the diameter of the circular plate runs out of the pipe to a turning mechanism that turns the rod and, in turn, rotates the circular valve plate. The rod, similar to the circular plate, must be flush with the walls of the hold in which it is placed, so as to eliminate the risk of leaks. It is generally unable to be seen inside the valve, because it is usually bolted between two separate plates that make up the circular plate.
