What’s a butterfly valve?

A butterfly valve belongs to 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 rotated so as to completely block the passage. When the valve is open, the disc is rotated a quarter turn to allow unrestricted passage. The position of the disc is done from the outside of the valve.

There are different types of butterfly valves, each suitable for different pressures and uses. The resilient version, which uses the flexibility of rubber, has the lowest pressure rating. The high performance version, used in slightly higher pressure systems, has a slight offset in the position of the disc, which increases the sealing capacity of the valve and decreases its tendency to wear. The most suitable valve for high pressure systems is the tricentric butterfly valve, which uses a metal seat, and is therefore capable of withstanding a greater amount of pressure.

Butterfly valves are used in many aspects of our lives. One of the more common examples is in a car’s carburetor. In a carbureted car, the “throttle” pedal actually actuates such a valve that controls the engine’s air intake. When the driver fully depresses the accelerator pedal, the valve opens fully, as described above, to allow air to pass freely into the carburetor. The carburetor then allows enough air and gas to maintain the correct air-fuel ratio to pass through the intake valves into the combustion chambers, where it is ignited by the engine.

A butterfly valve can also be partially open. When a car is idling, the valve is only opened slightly, allowing just enough air to pass through to maintain the idle speed. When you press the accelerator pedal lightly, the valve opens a little more and so on.

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