main sag with no water hammer?

arches

There's a section of my basement main that has a very perceptible sag in a 2.5" pipe (maybe sag is the wrong word...its more like an elbow has allowed the pipe to move downward - almost like a swing joint, creating a lowspot on the intended path to steam risers and the dry return).

Surprisingly, this produces zero water hammer effect. However, the apartments served by this main (there are 3 additional branches of the main - its a 25 unit apt building) are cooler than others.

Should this low spot be dripped back to a wet return? Does lack of hammer mean that water is not actually accumulating there? Can a drip be installed via drill and tap into the elbow?

djthx

Cast iron DWV pipe.

Are you sure that it's a steam line?  It seems to be a DWV (drain, waste, vent) line with shielded hubless sleeves couplers.  I've never seen those types of couplers used on steam heat piping (though in a pinch, I suppose they may be used to temporarily repair return lines). 

arches

bad labelling

Sorry my labelling and photography skills are lacking here. There is indeed a waste line in the photo...but the pipe in question is the white pipe in the foreground.  I should probably take a few more pictures to make it more clear.

Jamie Hall

Sags and hammer

Sags don't always cause a hammer, particularly in larger diameter pipe.  The picture isn't as clear as it might be (!), but if there is a clear opening on top of the accumulated puddle, it is possible for steam to get through without, necessarily, hammering.  But it will go very poorly.  Until the water is warm, the steam will condense right there, and even afterwards, there is a restriction.



The best way to fix the problem is to re-hang the pipe so that it has a consistent pitch from one end to the other.  If that can't be done, it could be dripped back to the wet return, but in my opinion (I've never been awfully good at tapping pipe, and you're looking at trying to tap a 1" or 1 1/4" pipe into a 2 1/2" pipe -- tricky at best) it would be better to do the job right, with fittings.  Just my opinion...  But I'd much rather re-hang the pipe if I could.  It can't have been that way when it was installed.  I hope...

arches

other pipes in the way

I think the sag was caused by a set of water and gas supply lines that someone no-so-wisely piped in direct contact with the steam main. Or maybe they were piped after the main sagged. Either way, the main can't be pushed back up towards the ceiling to create the proper pitch. I suppose lowering the low end would be possible, but its very difficult to access (it meets the dry return in a 18" tall space btwn the top of the oil tank enclosure and the ceiling).

I was thinking that maybe a 3/4" drip would suffice - since this is really a supplemental drip to the existing returns. LAOSH shows 3/4" drips for risers up to 1 1/2" (doesn't give figures for dripping a main directly though). I've never tapped anything over 1/2", to be honest...so 3/4" and up is a bit daunting. Afraid you are right...seems like its probably a job best suited for pipe fittings (and a professional, since i dont have tools large enough for 2 1/2" pipe work).

Jamie Hall

3/4 inch

might well do the trick.  It doesn't have to be all that big, I wouldn't think.  If so, you could probably get away with a weldolet on the pipe -- if you're welding skills are up to it (mine aren't), or a pro could probably do it pretty easily.