concentric or double offset butterfly valve. 3

For seawater local chemical conditions of the seawater and amount/type of impurities and service-type (how often to operate) and type and size of operator, selection of materials of valve and sealing, and details and solidity of construction of both types (including stem solidity) will weigh a lot.

That is: a good, suitable choice of a centric (concentric) valve might be a good choice for the application.

On a general basis a double eccentric (double offset) valve is a better construction with generally longer lifetime, and much less fear of disc sticking to a deformed seat sealing over time, or unable to close for the same reason.

BUT: all depending on factors mentioned above for both types. Seawater is tricky. Try to get references for longterm use with access to free discussions with customers for both types before you make your choice. Special weight on materials for valves, surface protection and sealing material and construction.

Search this forum for earlier discussions on differences and advantages for both types on a general basis.(Have been up in several threads)

For comparison between two actual constructions of each type you have to go in very deep details both for the valves and the application. Do not forget downtime and cost of repair as an evaluation factor. This could be high for an unsuitable construction.

Triple offset if positive isolation is required.

Hi Shajahan,

Triple offset Butterfly Valves are the best solution for Sea water application , we call it as high performance butterfly valves metal seated, , a very few manufacturers worldwide who make large diameters of these types 2 in Korea up to DN 4000mm (4 meters dia)

Seat from nickel alum. bronze (alloy), stem from monel etc..., body carbon steel WCB or St.St.

We have install 20 pieces from DN4000 in middle east.

Kandeloo

Just a quick note: "triple offset" is NOT the same as "high performance".

Probably every User of this Forum already knows that, but I believe it is worth writing a line to avoid confusion in any possible Newcomer ;-)

Thanks,
'NGL
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Considering the large diameters of the valves, and hence probably a limited number of producers and competitors, the most important qualification factor would probably bee that the producer can show to long-term operation references for the proposed valve, as mentioned in my first post.

At a guess your pressure requirements are low (?????). Even then the pressure for reference valves should at least be the same, and reference valves diameter not too far off.

Even with low pressures one fear would be small seat lekages over time, increasing with grit (and abrasion) as well as possible cavitation if wrong use (strong throtteling) of the valves.

This is one of several reasons that use (and functional requirements) of the valves must be described/studied in detail.

Soft sealings and/or centric construction is not off as an alternative if long-term references can be given. For this diameter, however, you will probably find competitive, more advanced constructions than centric with or without soft seat sealing.

Soft or metallic sealings is an issue in itself.

PU (polyurethane) soft sealings have been used with success for water turbine (hydroelectric plant) inlet valves , with 'sweet' water and larger amounts of abrasive particles, but I am not saying that this is the best for your case.

Even at low pressure for such large valves: do not underestimate solidity of stem and strength of stem fastening to disc. Necessary torque could increase drastically oveer time!

To qualify suppliers at a high level producer should be asked to present (mechanical) strength calculations for the valve construction, and necessary operational forces at normal water speed and for 'emergency/worst case' operation.

Thank you to all for interesting comments and stars!