Metal seated butterfly valves
In metal seated RT butterfly valves, the sealing surface between the flap and the body is made of metal, as the name suggests. As an option, the valves are available with a metal-graphite seal, in which case resistance to impurities is improved, but the temperature resistance is reduced.
As the pressure resistance and especially temperature resistance properties of metal seated butterfly valves are clearly better than those of rubber lined valves, their application range is wider.
Installation options include a model to be installed between flanges, a flanged model and a welded model.
What does ‘eccentric’ mean?
In an eccentric (offset) butterfly valve, the flap rotates eccentrically, as the name suggests (Picture 3). Through this, a higher surface pressure is achieved between the flap and the seal, as well as a quick drop of surface pressure and friction when the valve is opened. In simple words, eccentricity allows higher tightness and lower opening torque. Triple eccentricity (triple offset) enables a significantly higher surface pressure, in which case the valves comply with tightness class A of the standard EN 12266-1 by default.
- The first degree of eccentricity derives from the shaft being behind the flap.
- The second degree of eccentricity is achieved by placing the shaft to the side with respect to the flap centre line.
- The third degree of eccentricity is implemented by machining the flap or body sealing surface in an eccentric manner.
A metal seated butterfly valve is not barely an on/off type valve but, as a custom-manufactured valve, it can also be used for control applications.
Typical applications of an eccentric butterfly valve include oil and gas production and processing, petrochemical industry, chemical industry, power plants, district heating, solar thermal power plants, pulp and paper industry, steel industry, sugar industry.
Valves can be equipped with pneumatic and electric actuators.
ARI-ZETRIX®, RT and AG represent triple eccentric and Högfors double eccentric valves.
See the YouTube video of ARI Armaturen on an emergency valve.