Can someone please help me diagnose water hammering given this situation?

mgdpublic

Hey all, I’m hoping to get a little help diagnosing a water hammer issue with my steam heat. I’m not terribly familiar with all this but have done some research. I have a Carrier BS2 model 150 (number at end). I have a single pipe system with what I think is a wet return, hartford loop, etc.

In 52 years at this house I’ve never had this issue but it started about 2 months ago. I called my heating guy who said I was up for yearly service so he came and did a basic annual service on just the boiler. The hammering stopped for about 3 weeks but is back again. It happens about 2 minutes after the boiler starts (boiler usually stays on for about 5 minutes).

The sound comes from the horizontal return pipe right before the T junction to the vertical return pipe from one of the mains. It lasts for a minute or two. The water in the sight glass is still at the same level roughly and is about as dirty (maybe a little dirtier?) as it was when the service guy left (he said my pipes are old and the water will never be clean). The water color is a little lighter than tea with no oil in the top and it doesn’t surge it just bobs gently up and down about an inch or so.

Given that this came out of nowhere I thought the return was clogged at the T junction or something but I thought it was odd that it went away for a few weeks after the servicing. One other thing is that the main air vent preceeding the vertical return pipe that feeds into the horizontal one hammering, gurgles just a little while venting (I actually think it’s done this for a long while). It does not spew water - you can just tell there’s a little water near the valve. My mains are insulated.

I’ve added a few questions that I’m just curious about if you have the extra time. This whole steam heat thing is pretty interesting.

1. First off, what do you think I should try to stop the hammering?

2. Is that slightly gurgling main air vent a problem?

3. Curious, if this horizontal return that goes all around my basement is below the top of the hartford loop, then presumably it should always be filled with water, correct? Is this steam causing the hammering coming from the main return? I’m surprised it has the pressure to push into a constant stream of water in a full pipe to create that bubble but what do I know.

Thank you very much for any help you can give me.

-Mike

Jamie Hall

It may not be steam pushing down -- it's more like steam in the boiler pushing up. How far below the steam main and the vent is this pipe? How far below the water line is it?

Fred

Pictures would be helpful but from what you describe, it sounds like the horizontal pipe, near that vertical pipe has either lost its pitch or has a sag somewhere nearby causing it to hold water and when steam hits that puddle of water you get hammer. That could explain the gurgle you hear at the vent as well.
Check the horizontal and make sure it pitches towards the vertical drop (level is not good enough) and check the main to make sure there are no sags in the pipe.

mgdpublic

Jamie Hall said:

It may not be steam pushing down -- it's more like steam in the boiler pushing up. How far below the steam main and the vent is this pipe? How far below the water line is it?

Well, the return line is about 6 inches below the water in the sight glass while the boiler is firing if that helps. The main to return drop is about 3.5 feet. Thanks.

Jamie Hall

OK. What pressure is it running at?

mgdpublic

Jamie Hall said:

OK. What pressure is it running at?

Hmm I think my pressure gauge isn't sensitive enough because it goes up to 30 and mine is pinned at 1. I see some instrument where the cutoff psi is .5 Thanks.

Fred- These pipes are pretty well bracketed to the wall and can't see them moving much if at all. Also the hammering stopped for the 3 weeks after servicing so I don't think pitch is, at least the only, problem. Thanks.

Jamie Hall

Well... measurements are a little unclear, but if we assume -- and it's kind of a broad assumption -- that the pipe in question at the same level at the point in question as at the boiler, then any pressure over about 1.3 psi may back water up to that T -- which will then hammer quite happily.

Fred

@mgdpublic , water is being held somewhere or you wouldn't get hammer. The fact that it didn't happen for 3 weeks is not proof of anything. It is quite possible weather was mild enough that enough water didn't back into the problem area. It is very possible the wet return is nearly fully clogged and when the boiler runs often enough or long enough, water stacks in that vertical pipe and backs into the end of the steam main.

EBEBRATT-Ed

@mgdpublic

I would suggest a new pressure gauge make sure the pig tail and pipe connecting the pressure gauge and pressure control are clear.

If the connection to the gauge and pressure control are plugged you may be running with more pressure than you think.

More pressure in the boiler will cause the return water to back up into the dry return causing the hammering and your vent to spit water

Since it never did it before that is the most likely cause

mgdpublic

Fred said:

@mgdpublic , water is being held somewhere or you wouldn't get hammer. The fact that it didn't happen for 3 weeks is not proof of anything. It is quite possible weather was mild enough that enough water didn't back into the problem area. It is very possible the wet return is nearly fully clogged and when the boiler runs often enough or long enough, water stacks in that vertical pipe and backs into the end of the steam main.

Well isn't water always gonna be in the wet return? Just FYI the weather has been warmer here if anything. I'm not being contrary, just trying to understand. Also, I forgot to mention that the hammering happens almost right when the main vent shuts off. Does that tell you anything? Thanks again.

Jamie Hall

Yes, water is always in the wet return. In fact, that's kind of the definition... however, the question is... how high does the water stand in the pipe going up to where it's hammering? And that is determined by the local difference between boiler pressure pushing on the water in the wet return and steam pressure pushing on the water at the other end. When the vent is open, the pressure at the vent is atmospheric, while the boiler pressure at the other end is, I suspect, perhaps 1.5 to 2 pounds. That pressure difference has to be balanced by the water rising higher at the low pressure -- vent -- end of the wet return. By your elevation numbers, it is, in fact, going to rise up into the pipes above.

And hammer.

Your dimensions suggest that you have very little margin in terms of pressure at that location . It shouldn't have been piped that way, but it is what it is. Try keeping your boiler pressure below around 1.2 pounds; you may need a vapourstat instead of a pressuretrol.

Fred

@mgdpublic , yes, water should always be in the wet return, so long as that return isn't clogged or mostly clogged with sludge. Have you seen any pictures of the inside of a wet return that hasn't been flushed out in 20 or more years? It is not pretty and certainly clogged enough to cause water to move so slowly through that return that it will stack in the vertical drops. What Jamie says about the pressure is also very important. As to the hammering starting right when the vent closes, It tells me that's when steam has reached that location (vents close on steam) and it takes water and steam to cause hammer.

mgdpublic

Fred said:

@mgdpublic , yes, water should always be in the wet return, so long as that return isn't clogged or mostly clogged with sludge. Have you seen any pictures of the inside of a wet return that hasn't been flushed out in 20 or more years? It is not pretty and certainly clogged enough to cause water to move so slowly through that return that it will stack in the vertical drops. What Jamie says about the pressure is also very important. As to the hammering starting right when the vent closes, It tells me that's when steam has reached that location (vents close on steam) and it takes water and steam to cause hammer.

First off, thanks to you and the others for taking the time to help. I thought I’d upload a picture to make sure we’re on the same page. I put a box of hand warmers at the spot on the horizontal return where the hammering occurs just for reference. You seem to be saying the water is climbing that vertical return from reduced volume in the horizontal from corrosion. If the hammering is in that horizontal, how is the vertical water column contributing to the hammer? And just out of curiosity, how high would the water rise in that vertical At its peak in the cycle if things were working correctly? Lastly, how can steam penetrate that water column to create a pocket that low in the horizontal? Thanks so much!

pecmsg

We need some pictures of the piping at the boiler, far enough away, left & right to see everything.

Jamie Hall

The hammering occurs in that copper pipe? Where the hand warmer box is located?

I am NOT saying that water is climbing in the drip -- the vertical pipe -- because of reduced volume or corrosion. I was suggesting that it was possibly because of pressure. Reduced volume or corrosion may keep water from flowing -- but won't push it somewhere.

That said I'll go back to a question I asked earlier, which is even more important now that I see where that pipe with the hand warmers are located: What, exactly, is the difference in elevation between that location where the hand warmers are and the water level in the boiler? How many inches higher or lower?

To which I will now add another question: where does the pipe extending to the left horizontally in the picture go? I presume the pipe to the right goes -- eventually -- to the boiler?

dopey27177

WHEN YOUR HEATING GUY SERVICED THE BOILER DID HE FLUSH OUT THE WET RETURN, AND CHECK TO SEE IF THE PIPE THAT ALLOWS THE CONDENSATE BACK INTO THE BOILER IS CLEAR OF DEBRIS.

I ASK THIS BECAUSE YOU SAID THE WATER WAS DIRTY WHEN HE REFILLED THE BOILER.

AFTER THE PIPING IS FLUSHED OF OLD RUST AND DEBRIS THE WATER SHOULD BE NICE AND CLEAN FOR A LITTLE WHILE.

THE COLOR WITHOUT CHEMICAL TREATMENT SHOULD LOOK LIKE LIGHT TEA.

YOU MAY HAVE CRUD IN THE LOW END PIPING OF THE WET RETURN OR AT JUNCTURE WHERE THE PIPE REENTERS THE BOILER.


jAKE