In recent years, metal-seated eccentric butterfly valves have competed with more traditional industrial valves like the globe and ball valves for critical applications. However, even though lots of people already know how a butterfly valve works, much of the confusion lies in how such eccentric valves differ and what applications are suitable for each.
What is a Concentric Butterfly Valve?
Also known as a concentric design, this is common in general service “resilient seated” or “rubber seated” butterfly valves. The stem and disc are centered in the seat of the valve, all of which are centered in the body of the valve. The disc is in constant contact with the seat.
An advantage of this valve is the media going through the valve will not contact the body, since the seat is constructed as a sleeve or cartridge inside of the body.
Concentric butterfly valves are used in basic and specialty liquid and gas applications up to 200 PSI and up to 400 deg F. The zero offset butterfly valve can handle chemicals, coatings, food, some solids, and abrasive applications.
The Concentric butterfly valve is available in epoxy-coated cast iron and stainless steel with multiple seat materials such as Buna, EPDM, VITON, Teflon, Natural rubber, and others.
What is a Double Offset Butterfly Valve?
The double eccentric offset butterfly valve can also be called the high-performance butterfly valve or double eccentric butterfly valve. This valve is suitable for thicker media that have high pressure because its design does not allow too much contact with the disc and seat.
Features of Double Offset Butterfly Valve
The balance of this valve is in the stem placed behind the circular disc. It allows the disc to self-adjust to the center, ensuring tight sealing. Even when the valve is fully opened, the valve does not touch the soft seat, ensuring a longer service life.
What is a Triple Offset Butterfly Valve?
The triple offset butterfly valve incorporates the two offset points of the double, but it also has a third point of offsets. Relating this time to the sealing points rather than the shaft, the point of sealing on the disc and seat are both machined into an offset conical profile. This allows it to operate fully without any contact until the point of full closure as a mechanical stop. Therefore both the sealing components can be made of metal without the need for an elastomeric element.
Features of Triple Offset Butterfly Valve
As a butterfly valve, it also belongs to the quarter family. It is also lightweight and easy to operate. Installation is also a breeze since there is less pipe bracing needed. Replacement of seat rings is also easy as this valve is top-entry.
The triple offset butterfly valve has a low torque so there is no need to have larger valves. That being said, this means higher savings costs. This valve has zero leakage closure on both ends.
The introduction of soft seats increases the value of the valves. Aside from being fire-safe due to the metal seats underneath the soft ones, the valves can now self-center because of the elastomeric seat material.
