It is a requirement of NFPA 13 for the frame arms of upright sprinklers to be aligned parallel to the branch line to minimize obstruction by the pipe itself. I have seen pendent sprinklers (both directly attached to branch line piping and recessed in ceilings) that have their frame arms aligned with the piping above as general practice, depending on the fitter. I have also heard of this being done so you have a general idea of which direction the piping runs without having to look above ceilings.
There is no need to align the frame for pendent sprinklers.
The reason behind (always try to understand why) the alignement for upright sprinklers is to limit obstructions.
Frame arms create an obstruction. So does the pipe located underneath an upright sprinkler. So if you align the frame arm with the pipe, you have an obstruction only along the pipe. If not, you have an obstruction along the pipe + an obstruction from the frame arms.
With pendent sprinklers, there is no obstruction from the pipe. So no need to align (unless you are looking for aesthetic...)
Good clarification, Franck. I didn’t mention the obstruction caused by the frame arms themselves.
The reference for uprights can be found in 22.214.171.124 of the 2013 & 2016 editions of NFPA #13.
When I was in the field we lined up the pendent head frame arms with the branch lines only to be able to tell the direction the branch lines were running after the ceiling was installed.
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