Butterfly valve face to face dimension

[Aj59]

Difference between short pattern and long pattern valve is face to face dimension changes, but on what basis we decided we need short patter or long pattern

 

[bcd]

Long pattern is used when you want to replace a gate valve with a butterfly valve. Short pattern is used when only a a butterfly is specified and used, such as new plant construction.

 

[JStephen]

You made me curious. I find a couple of older posts with essentially the answer above. However, if you look at, say municipal water valves, the laying lengths of gate valves do not match up to either the long or the short body butterfly valves. (There's also a wafer valve, which lacks the full flanges.)
With the short-body style, the disk can actually extend beyond the flange face when open, so you can't necessarily fully open a short-body valve with a blind flange attached. But then again, I'm not sure why you'd need to do that, either.

 

[mk3223]

With the short-body style, the disk can actually extend beyond the flange face when open, so you can't necessarily fully open a short-body valve with a blind flange attached.

The butterfly valve is intended to work as removed the blind flange and connected to the pipe.
It's a good lesson learned that the design should confirm the disc of the wafer type butterfly valve to be fully open in operation without interference. If it's a concern, a long pattern butterfly valve can be specified.