Help - banging in return line in my new house

JonC

Firstly, I know very little about boilers but I bought a book and I've been reading. Here's the problem: once steam starts flowing, I get a very loud banging in one return line that lasts about two minutes then all is fine. I followed this return line and this is what I found. For one, this return line slopes towards the steam side - unlike the other lines which slope to the return side. I'm 99% sure that there is a semi-closed loop in the system that shouldn't be there - this involves the pipe that's sloped the wrong way. I follow the 3" steam output, it has a four branches going up to radiators and then goes directly back to the boiler as a return. This line has no other lines attaching to it (no returns from upstairs) - it "looks like" a return line going into the boiler but is actually a steam line. That can't be good. My radiators have steam in and water out. Here are some pictures:

ps the banging pipe gets hot, the other returns do not.

Snowmelt

Is this 2 pipe or one pipe.

JonC

Pics going from top left down and then top right down:

1. two of the returns -the 1/2' connectors connect to the third return. The pipe on left is banging -hot pipe.
2. steam pipe about 20 ft from boiler with branches going up. this pipe then returns to boiler.
3. the Two connectors (1/2') with traps connecting the 2 returns (black) to the larger return (white with air vent).
4. (668) the three returns - far left is the larger one in previous pic (white). One on far right is banging.
5. (675) exit of steam pipe into my shop - 4 feet from boiler.
6. blurry pic - steam exiting into shop, black return also seen
7. another pic of the returns

here's a pic of one of my radiators

JonC

I could also do a video walk-thru and put it on You Tube if you'd like.

JonC

It's a two pipe system - steam goes up one set of pipes and down another. If I understand it correctly, that's a two pipe sytem.

JonC

Actually, how do you tell if it's a one or two pipe system? Teh radiator has steam in and then a second pipe on the other side.
The boiler has steam out and a separate return.

neilc

it's the 2 or 1 pipes to your rads they are asking about,
sounds like you're 2 pipe.

DuggieFresh5

I had a similar experience with water hammer and I was also very new to steam at the time. Now I'm just mostly new. I also have a 2-pipe system.

If a return line is hot, you may have a failed trap on one of the radiators. I'm working on that particular issue with my system right now. If that steam is coming into contact with condensate, you have a very good chance of getting some dramatic water hammer.

I also had a return line that was pitched poorly. A repair or change done in the past had one of my lines pitched weakly and due to some other piping in the basement, I actually had a 90 bend in the return line that was a semi-low point. I say semi-low because I would get water hammer, but it was all mid-cycle and seemed to calm down once the pipes got hot.

Even if you are handy, I recommend as a fellow homeowner you get a steam pro in there to help you get to know your system and look at your system as a whole.

Jamie Hall

I think I see crossover traps in one of the pictures. This is a two pipe system -- and may have been a vapour system (very low pressure).

It would be very helpful if you could draw a line diagram of your system and post it.

In the meantime... you say that the return which is banging gets hot. Returns shouldn't get hot; warm, perhaps, but not hot. The banging is a symptom of some other problem which is allowing steam to get into that return. It may be aggravated by poor pitch (or even backwards pitch!) but without a clearer idea of the piping I wouldn't care to say at this point.

Check for two things: failed traps -- particularly a failed open crossover. This will also show up as poor or even non-existent heat in some radiators. Second, look at all the piping and figure out if you have a wet return or returns and, if you do, if they are safely below the water level in the boiler. That's a newer boiler, and it's not unheard of for the water level to get changed.

neilc

img 0671 shows 2 parallel lines to crossover traps behind that main vent,
looks like that closer middle line is sagging maybe just enough(?),
is that where you hear or feel the banging ?
(careful, hot !!)

nicholas bonham-carter

Is your hoffman vent now plugged with foam insulation? One of those will not be enough anyway to allow the air to escape.
Definitely check all the traps for hot pipes on the exit of the trap.
A diagram of the piping would make things more understandable, but work on the traps and vents, should be first. Take off the green Hoffman 75(6), fire the boiler, and you should not see any steam. If you repair the traps, you may be able to do without that main vent.--NBC

JonC

Thanks for the replies. The pressure is shut off above 2psi with elctronic shut-off. There are NO traps on the line that is banging. It goes from the boiler, carrying steam, gives off four lines, and then returns to the boiler as a return. That's a problem right?
- A line diagram would show a line leaving the boiler, giving off 4 1" pipes, and then returning to boiler (at the bottom - the return port). No valves, vents, or traps are in that line directly (only a trap on the connector that branches from it).
- The trap shown in the pics is on the 1/2" connector - there is a connection between the line I'm descibing above and another return and there's a trap on that 1/2' line ( same thing for a second return). There's an air vent on the bigger line that the connector goes to (there's probably a better word than connector). There are two connectors - one coming off each of two returns and feeding into a third (white pipe). It seems to be serving some kind of pressure balance purpose - but why have a trap that close to the boiler (should there be steam that far downstream?)

I'll go ahead and do a line diagram though -showing all I can see.

Other:

I don't see any vent that could be clogged with insultaion -just that one green vent.

JonC

Onemore thing - I know that the green vent puts out steam because it has eaten away a part of the ceiling.

nicholas bonham-carter

If the green vent puts out steam, then it has failed, and should be replaced with one or two larger Gorton #2's
I see a trap on the return of the radiator, and that and or its brethren may be leaking. The crossover traps must be checked as well.
Your pressure control and its pigtail may have failed, and when you replace it, get a vaporstat, as these old vapor systems need just a few ounces of pressure. Put a 3 psi gauge graduated in ounces, on as well, so you can verify the settings.--NBC

JonC

Thanks NBC - I've never actually seen it put out steam but see the evidence of it. Could be that it has been replaced already so I may have jumped the gun on claiming it's putting out steam.

Could you explain the idea behind the crossover traps? Why are they needed? I assume it's to regulate steam in some way but why should there be steam that far down in the return system?

What do you think about the idea that the banging line is a steam-carrying line as shown in the little drawing I did? I must assume that this is on purpose and the boiler needs this returning steam for some reason. Is it ok for this line to be carrying steam back to the boiler as a return?

Jamie Hall

The crossover traps let air and condensate out of the ends of the steam mains. They serve much the same purpose as vents. Of course the dry return into which they discharge also has to be vented and dripped! That other line which is carrying steam back towards the boiler probably is also actually a steam main up to the point where it drops to the boiler, although I find it a little hard to tell from the diagram. If so, it should have a crossover trap to the dry returns on it.

I would check that line very carefully for pitch and sags. It must pitch smoothly towards a drip -- a pipe going vertically down -- to the wet returns. Doesn't matter whether it's toward or away from the boiler -- but it must pitch towards somewhere wher the water can drain, and there must be no sags or dips in it.

JonC

Here's another picture of the traps on the returns.

Geting confused here - let me ask this:

Is it normal to have a steam main return with steam to the return side of the boiler? Here are the returns (one being a steam main) - is that trap configuration correct? (the boiler return is down and on the far left).

What is the purpose of those crossovers? To carry steam out of the those bigger returns? Seems the steam could go down as well as up and then what happens when the crossovers fill up with steam and the traps are closed?



New Picture:

Jamie Hall

In that picture you just posted, the big black lines are steam mains -- which should be insulated, by the way. The black verticals on the left side are, I think, drips from those mains back to the boiler return connection. The smaller white lines above them are the inlet lines to the crossover traps, shown at the right. The crossover traps' outlets go straight down to the white pipe, which is a dry return,which is vented by that green antique.

That dry return should NOT be hot. Warm, possibly. Hot, no. If it is, somewhere on your system there is at least one failed open trap. Either that or the water line in the boiler is set much too low -- which I can't tell from any of the pictures.

The steam cannot or at least should not get through those traps. It will go down those big verticals until it gets to the water level, but it won't go any farther than that ,and that's perfectly alright -- so long as the water level is somewhere above the bottoms of those lines. They return condensate from the steam lines to the boiler.

JonC

Thanks Jamie, that helps. So the steam/air goes up those crossovers and empties into the white line as condensate.

So the steam in either the main black lines or the crossover lines is running up against water and causing the banging - does that sound right? The crossover lines should slope to the vertical returns and the steam lines (black) should also slope towards the vertical returns.


The white line does not get hot -the two black lines do, so that sounds right.

I have several failed traps in the system (assuming that's why the radiators are not heating).

Water level is halfway up the clear tube.

I just checked all the slopes again.

Found a slope problem!

Both crossovers have a good slope towards the black verticals. One the black lines is sloping toward the vertical but one of them is sloping away form it (the banging pipe)! So water would be sitting in that pipe and the steam is hitting hit and pushing it (or whatever happens) to cause the bang. ......I hope that's it.

So I'll fix the slope and let you guys know what happens.

Jamie Hall

Please do -- and good luck!

JonC

Couple of last things - you called that a "green antique", should I get a different vent? What brand? Which website store?
Second, my ceilling is plaster/lathe - any good ideas for securing a pipe hanger (?correct term)? My plan is to secure some adjustable pipe hangers and raise the pipe as far down the line as I can, "walking it" towards where the problem (as to not create a sag somewhere else in the line). Do you know of a good site that sells pipe hanger type stuff?

Fred

The Green antique is not really antique. That Hoffman 75 is now unpainted when you buy a new one but you can still get "New, Old Stock" that is green. Hoffman decided not to paint the vents maybe 8 to 10 years ago. Those vents can last 20+ years. The new unpainted ones are identical in design and function. The only thing I'd say is you need more venting than 1 Hoffman 75.

You can get pipe hangers of varying quality at almost any plumbing supply house. I definitely would not raise the pipe "Down the Line". Try to keep your corrections to the area that is sagged. Otherwise you will end up with everything out of pitch.
"Your ceiling is plaster/lathe" Under that plaster/lathe is a structure of floor joists that supports your floors. You need to maake sure the hangers are attached to those joists.

JonC

Update:

Working on the slope issue, I found that the old pipe hangers were completely loose and not holding. I replaced them (not real easy) and fixed the sag. No more banging!!!!!!!!

Thanks for all the help.

Fred

That's great!