For Tripple Offset Butterfly valves in sizes from 24" and above which is more preferred wafer lugged or flanged ends?
A bit depending on service and pressure class, but some points.
a) A double or triple offset (eccentric) valve, especially  in this size, will have some improved qualities compared to normal centric valves, and will be selected because of better properties for the  service, or for longer lifetime/lower necessary maintenance (often case for water service for instance).
b) A flanged valve will be easier to mount and center, and mechanically a stronger construction than wafer construction. For this size, in building length compared to wafer building length, a U-shaped flange will probably also be cheaper than screwed lugging.
c) If wafer construction is selected, at least 'stearing lugs' for hanging up and centering when mounting, should be selected. The only reason to select wafer is price.
d) If water service or comparable simple service you should also check and compare price solidity/quality of construction against complete cast body form with flanges (Type EN F4, normal short valve building length or other similar standards) and only double offset (disc and stem offset, not sealing offset).
e) Final choice to be made on quality (price over required lifetime) consideration.

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