one pipe steam Radiator vents

Karlv0179

a job that I visited today had the bullet steam vents on the radiator sucking air in. The homeowner is complaining about the banging. I could not find the "end of main" vent. quiet possibly covered up over the years and remodeling ect.
anyways, the "near boiler piping is not insulated, I know that at time this might cause the main vent to suck in air due to the vacuum, can this also happen to the individual radiator vents? and will this help the banging? it's not terrible, I have heard worse.
Thank you

Jamie Hall

Sucking air in? At the end of a cycle, when the boiler turns off? If it's really significant, that indicates that either there aren't any main vents -- or that they are not functioing.

You're going to have a nice time finding them... or finding where they should be.

However, that isn't likely to be the banging problem. That's much more likely to be a pipe -- or several pipes -- which are not pitched properly to drain. I hope the piping at least in the basement is visible...

ethicalpaul

I agree with Jamie and I'll say it this way:

Insulation or not, when the boiler stops firing, the steam will collapse and the vacuum will form. This shouldn't cause any banging. Something (possibly several things) is wrong. But it's not the insulation.

Karlv0179

Thanks guys, but this system is sucking air through the vents DURING the fire. couldn't this mean that the condensate is traveling back prematurely, by cooling off too fast at the boiler in this "one" pipe system?

Jamie Hall

Interesting. Is this a continuous suction? Or is it pulses at specific radiators. I honestly can't think of a mechanism which will create a continuous suction at a vent or even an open pipe so long as the boiler is firing, unless there is an eductor or vacuum pump on the system -- and that wouldn't be found on a one pipe system (and is rare on residential two pipe systems...).

If it's in pulses, and different at different radiators, there is a possibility that the problem has to do with pockets of trapped water in the piping, which could also cause the banging -- but that would only be very short pulses at specific radiators.

And... not that I doubt your observation, but double check. Are they really sucking, indicating a vacuum, or are they actually blowing?

mattmia2

It sounds like the banging and the sucking in air are likely symptoms of the same problem. Water is colliding with steam and producing a vacuum and water hammer when the steam collapses. Could be the boiler is priming or surging, could be because of issues with the near boiler piping, could be trapped water somewhere in a main, could be a water seal that was once below the water line that is no longer below the water line, could be excessive pressure, could be a number of other piping problems.

Karlv0179

Jamie,
Thank you, Yes, I put my lighter up to it because it caught me off guard as well. This is an old customer that I haven't seen in 20 years, someone else installed a new boiler. two pipe header, but everything is done in 2" header and the piping. a Burnham boiler maybe 5 or 6 years old. I was just there to reconnect a radiator after a bath reno. and got into all of this. I do realize steam is tricky and Dan has been my hero for years.. this is why I came here because I have never had this situation.

mattmia2

The header in to a tee that goes to the equalizer and to the riser to the main isn't right. It might work if everything else is perfect but the water is going to want to follow the bullheaded tee up the riser with the steam when it hits the side of the tee and has to make a decision.

Karlv0179

mattmia2,
Thank you, This is what I am thinking. I lowered the pressure from 2 lbs to a hair less than a pound ( I know this is still to much for a row house in D.C. ) still, But do you think that insulating the near boiler piping could help the issue. I also agree with with jamie and ethicalpaul that the main vent may very well be covered and or not working.

Karlv0179

Karlv0179

mattmia2.
I agree that this may be the cause of the noise, but not the vacuum. am I right?

ethicalpaul

Nothing in these pictures would cause a vacuum during production of steam. Insulation won't affect this issue (and wouldn't affect nearly any issue anyway)

To add to what mattmia said about possible surging, what is your water level doing during a call for heat?

dabrakeman

Seems like the owner is going to have to consent to light demo in order to to be able to verify pipe pitches and main vent functionality. If either of these are not in order then can't see how banging and vent noise issues are going to get solved. I guess you could go around raising and lowering what appear to be problem radiators but it would be a degree of shooting in the dark.

I didn't see any returns in the photo so assume the returns are wet returns?

mattmia2

dabrakeman said:

I didn't see any returns in the photo so assume the returns are wet returns?

Or it is counter flow and missing the drip which will make the incorrect header piping worse.

Karlv0179

It is a wet return.. Thank you all for your help. cheers