What is a butterfly valve?
As far as valves go, butterfly valves are a fairly new design. They are simple, easy to install, and easy to use.
A butterfly valve uses a disc that turns 90° to allow materials to flow through. This is different from other valves that move the disc out of the way entirely or use a hollow globe to redirect or open and close flow. The disc of a butterfly valve allows it to be used for throttling flow as well as closing it entirely. This style of valve is especially useful (depending on the specific type of butterfly valve) for water, gasses, fire protection, viscous materials, and high-pressure/ high temperature water. They are thinner than other styles of valve which makes them preferable in situations where space is an issue. Many butterfly valves use an actuator to assist opening, throttling, and closing flow, but you may encounter lever-operated butterfly valves as well.
One unique aspect of the disc is that it is hollow through the middle. This is so that the stem can be inserted into it. Sometimes the stem is rectangular or hexed so that it can be fitted inside the disc. Other butterfly valves have a round stem that is secured in place by bolts that go through the disc and stem. These are not appropriate for systems with corrosive materials because it can lead to corrosion of the bolt, and consequently, the stem.
Butterfly valve bodies are often round, but they can be more elliptical as well. You might come across oblong or elliptical butterfly valves when dealing with a vent system. Otherwise, a round or circular body is more common.
The two body styles for butterfly valves are lugged and wafered. The important difference between the two when it comes to marine application is the guide holes, also called lead holes. These holes are located around the edge of the valve. The area that protrudes out around the holes are commonly called the legs or the ears of the valve.
Lugged butterfly valves are normally threaded, and provide more stable support for mating with connections, but are not necessarily used to secure the flange. Wafered butterfly valves are not threaded and, in some cases, may not even have lead holes. The benefit of this is that when the holes are not in the way, the valve can be more easily positioned before being seated, allowing for better use of space in tight situations.
Be aware of what your intended purpose for a butterfly valve is before determining which style to use. The seat of a disc valve changes its type entirely! The original design of the butterfly valve used a metal-on-metal seal. This is fine in situations where a little bit of seepage is acceptable. In traditional butterfly valves, there are normally o-rings attached to the inlet and outlet of the valve for a tighter seal with the connection.
There are also high performance butterfly valves, which have been developed to create a tighter seat and less seepage. When ordering this style of valve, you will also need a gasket to place with your connection, because this part is not always included. Sometimes, high performance butterfly valves are used for fire safety purposes. They can function as a shut-off when a fire occurs and prevent fire from passing through a ventilation system. For this purpose, makes sure that you are considering that your gasket could melt and allow flow to seep through. The gasket needs to match the function just like the valve does.