Renovated 2-pipe system still has some water hammer

Steamhead (in transit)

a plugged return line could be causing water to back up into the main.

joe barone

renovated 2-pipe system still has some water hammer

We have changed or repaired all radiator traps in a building with a 2-pipe vacuum system (11 stories, about 300 radiators). All basement drip traps (about 45) have also been replaced or repaired, on a "1 for 1" basis (if it was an F&T, we put a new F&T, if it was thermostatic, we put a new thermostatic). Most of the drip traps in the basement are thermostatic (Mepco 1E's), the rest (5) being F&Ts. The system is working well, but there is still some water hammer, primarily on startup.

There is one somewhat odd thing about the system. The radiators in the first floor apartments are not served by the risers that serve the other floors. Rather, the are fed by 1" risers that branch directly from whatever main (say 2") is in the area to the radiator. Each first-floor radiator itself is trapped and connected to the return in the usual way. These risers, some 30 in all, vary in length but are typically 5 or 6 feet long with some horizontal and some vertical run and are not dripped or trapped in any way, so any condensate just falls back into the main.

My question: is it likely that sufficient condensate is dripping back into the mains from the first floor risers to cause the water hammer?

Thanks in advance for any replies - Joe

Steamhead (in transit)

Have you been able

to isolate the source of the banging?

That piping arrangement isn't so odd. If the first-floor rads were connected to the main risers, they'd get steam long before anything else on those risers since there are several other rads venting air from the riser. A very tall riser would have its own venting arrangement, possibly a crossover trap at the top.

"Steamhead"

joe barone

source of noise

The banging seems to be in the (horizontal) mains at some distance from the boiler (i.e., relatively close to the ends of the mains). By "somewhat odd," by the way, I meant that no provision was made to drip these risers, though on the other hand they are quite short. Hence my question. If there can't be enough condensate to matter, then there was no point in dripping them in the first place. I could be grasping at straws, but since everything is in such good shape right now, the only other thing I could think of was the pitch of the mains, and that really seems to be o.k.

Thanks a lot for the response - Joe