Banging in one-pipe steam system

mmoresco

I moved in a 1920, 6-condos, 3-story building last summer. A few weeks before I moved in, a new boiler was installed. We started running the boiler in November, when temperature got colder. We are hearing loud banging in several the radiators. I think the radiators are fine, they are all properly pitched, and we replaced all the valves and vents as soon as we moved in. The noise comes from the underlying pipes (in fact, the noise continues whether I shut the valves on or off). The noise occurs towards the latter part of the heat cycle, but not the beginning. Also, the banging is more severe in the radiators that are most downstream from the boiler. The wet return pipe is made of steel, and looks old. My side of the return pipe is quite long because the boiler is located on the other side of the building, perhaps 200 feet. The first 100 feet seem properly pitched but has several bends. The last 100 feet of the pipe runs almost flat near the floor and makes a couple of bends until it reaches the boiler through a Hartford loop.

Last week, the technicians realized that the bottom part of the riser was stone cold. The cold area was located near the end, where the riser connects to the wet return pipe through a 90 degree bend. We replaced the cold portion of the riser with a brand new copper pipe. Unsurprisingly, when we inspected the old pipe segment, the region near the bend was clogged with rock solid dirt. Unfortunately, replacing the pipe segment had no effect on the banging.

We also installed a valve at the far end of the wet return pipe, which we then used to flush the entire length of the wet return. The direction of flushing was from the far end of the line towards the boiler. We saw some mud on the other side, but not too much. To make things worse, after flushing the wet pipe, some of the more upstream radiators began the bang. Before the flush, those radiators had never banged.

All I know about steam systems and more generally about plumbing I learned in the last two weeks, at night, while the banging was keeping my awake. From what I read, it seems the problem is in the wet return. My theory is that flushing the return pipe moved some of the dirt upstream, which caused the water to creep up in other risers, in addition to those located downstream near the far end of the wet return. This would explain why we are experience banging in more radiators now.

Does that make sense? Should we replace the entire length of the wet return with copper, or should do targeted replacements? Other possible causes/solutions?

Jamie Hall

Banging -- hammering -- in steam systems is almost always a situation where water is trapped in steam mains or horizontal (more or less) sections of runouts. If that wet return is solidly below the water level in the boiler for all 200 feet of its length, it is unlikely to bang.

However... if that new boiler has a water level lower than the water level in the old one, and that newer water level is lower than the wet return line for all or part of its length, it can and almost certainly will bang. So that would be the first thing to check.

If you flushed the wet return and water ran through it it's unlikely to either need replacement or to be clogged enough to cause a problem in that regard -- although the increased banging in radiators may simply mean that the weren't getting steam previously, or not as much.

As a start, I'd suggest at least getting the book "We Got Steam Heat", available from the store on this site.

JUGHNE

Can you show us the sight glass and pressure control settings?

Actually the entire boiler floor to ceiling piping would help.

mmoresco

See photos below:

mmoresco

Jamie Hall: a substantial portion of the wet return appears to be above water. Consider the first pictures below, which shows one of the shorter wet returns (about 60 feet long). The water line is about 20 inches below the naked pipe, which goes through the wall. Once it passes the wall, it drops by 30 inches (see second picture). Overall, I'd say 50% of the wet return (counting only the naked pipe, not the risers above it) is above water, 50% is below water. Is this a problem?

Jamie Hall

Potentially. It depends a great deal on what -- and when -- pressure changes in the steam mains and the dry returns. The risk is simply that boiler pressure will try to push water back into the dry portion of the wet return, unless it is opposed by an equal pressure at the other end. If there are dry returns involved that equal pressure isn't there.

Two things can happen -- first, it can cause quite a drop in water level as the boiler pressure rises. Second, if the timing isn't in your favour, it is quite possible for water to be forced back at speed, causing rather intractable water hammer.

There are two solutions: the best, in my view, is a false water line (consult The Lost Art for sketches and details). This raises the effective water line in the wet return,, and is otherwise quite passive.

mmoresco

Thanks! From the pictures above, do you think my boiler already has a false water line?

nicholas bonham-carter

Is this a one-pipe system, or two?
What floor are you on?
Was there a reason to change the steam inlet valves? If the new valves are taller than the old, enabling any horizontal feeding them from under the floor, to go out of pitch, there may be hammering in that pipe.—NBC

Jamie Hall

mmoresco said:

Thanks! From the pictures above, do you think my boiler already has a false water line?

Honestly, I'd have to walk through the piping... from the pictures, I don't think so, but I wouldn't care to say firmly.

mmoresco

NBC, it's a one-pipe system and I'm on the third (last) floor. We replaced the radiator valves because the gaskets were gone when we moved in. Not sure about height. Is there an easy way to test whether there are water pockets in the pipes immediately below my radiators?

mmoresco

JUGHNE, do you see anything unusual in the boiler piping?

JUGHNE

My guess is that the water level of the boiler changed enough to cause problems. For me it is hard to follow the return piping, as Jamie said would have to just about be there.

In addition the wet return could still be partially plugged.
Was an isolation valve installed at the far end of the returns to keep the flush water from backing up towards the radiators?

And what pressure is the boiler running at?
Was the boiler skimmed?

mmoresco

Yes, we have an isolation valve at the far end of the return line, at the base of the most downstream riser. However, there are no isolation valves at the base of the upstream risers.

The pressure is about 1-1.5 PSI

The boiler was skimmed.

mmoresco

Does anyone have any recommendation for a contractor in Boston who might be able to help with this issue?

Jamie Hall

@New England SteamWorks

mmoresco

As a quick follow-up, I measured the height of the water line. See attached diagram. It seems I have a 2" A dimension. No wonder we have banging. Is my understanding correct?

Jamie Hall

Ugh. That bit of pipe where you have the red arrow is a problem -- possibly the problem. Can you either lower it to match the rest of the wet return or raise it to the height of the steam mains?

mmoresco

Moving the pipe down is going to be very difficult. It's almost 50 feet in length. Besides, the diagram illustrates only 1 of 4 branches. We'd have to reposition 4 return pipes. I'd much rather install a false water line. Does that make sense?

ethicalpaul

Can you raise it?

Also, 4 return pipes? How are they all tied in? Can your diagram be updated to show them?

MilanD

mmoresco said:

As a quick follow-up, I measured the height of the water line. See attached diagram. It seems I have a 2" A dimension. No wonder we have banging. Is my understanding correct?

Yes. I believe your easiest fix would be a false water line. Something like this. I'll let others comment on placement, but I believe this would be correct.



Also, check that the equalizer is tied in properly. Per your scetch, it's tied into a floor wet return. It may be just a sketch mistake. It's tied into the boiler and Hardford loop ties into it.

mmoresco

Attached is a top view. Not sure how to show all the branches in cross section.

Jamie Hall

The false water line should work -- with the equalizer tied properly, as shown in @MilanD 's sketch.

May I suggest, however, that you check the condition of those wet return pipes while you are at it? If there is going to be a system leak in a steam system it's going to be in the wet returns, and it would be a shame to do a good deal of work -- and discover that the wet returns needed replacing anyway...

mmoresco

Thanks. Yes, the equalizer feeds into the Hartford loop. Just a sketch mistake

MilanD