If I select flanged ends for valves from valve/flange database, do I still need to add flanges before and after valves?

Thanks,

No. Our valve/flange database is loaded with flanged components. Your "End Type" selection determines if the mating flanges are included - FLG adds a pair of flanges to the overall weight & length of the rigid element & NOFLG does not.

Thanks Dave.

So the weight and length given by valve/flange database include the two weld neck flanges and the flanged valve itselft. Is this right?

Just to remain clear...

"End Type" = FLG, yes, you are correct
"End Type" = NOFLG, no mating flanges included in length & weight

(Actually, there will be some added length & weight for the two gaskets as well when "End Type" = FLG.)

Just try it. Run an unflanged Gate Valve, then a single Falnge, and then a flanged Gate Valve. The relationship between lengths and weights should be obvious.

Thanks a lot.