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Radiator noise when cooling

We have a one-pipe steam system in our 80 year old house. Most of the radiators work well except for one in our dining room that makes a lot of noise when it is cooling. I have done a lot of research and have read a lot about water hammers. I am not sure this is a water hammer because the noise happens between heating cycles when the radiator is cooling. It's one or two loud bangs - enough to make me start. I have pitched the radiator, replaced the valve and tightened all connections.

A friend suggested that it could be that the rod connecting the fins is loose and is banging when it contracts. Has anyone ever heard of this?

Does anyone have any other suggestions? Should I try flushing the radiator?

Re: Radiator noise when cooling

Tell me more about the results of your research.

Why is this one rad causing problems & not the others.

Have you checked the operation of the rad during the heating cycle & is it doing the same things the others are doing??

Have you checked that the on/off valve is all the way open?

It's hard to believe that a loose connecting rod could make such a noise, but anything's possible.

Have you checked that the air is being expelled out the rad vent, that the little bellows inside the vent is closing & steam is filling the rad??

Remember, water hammer is caused when steam is smacking against the returning cooler water condensate trying to get back to the boiler.

Is this rad on its own branch circuit all the way back to the boiler??

The Heating Help site says to check the Hartford loop piping near the boiler---the sound may be occuring there & transmitting back to the dining room rad; the hartford loop (if you have one) may be clogged, or the wrong fittings were used on it when installed.

Also check any branch vent in the cellar to make sure it too is expelling its air at the beginning of the heating cycle.

Is the water level at the proper level on the boiler glass indicator---1/2 way or 3/4 up the glass indicator---too much water in the system can cause water heammer.

Is THIS rad hotter than the others at the end of the heating cycle, when the others have cooled off???

Something like this may be causing a meeting of cool condensate & steam even AFTER the heating cycle.

Most of the diy forum sites have a "search" box where you can enter such short phrases as "water hammer", "water hammer after heating cycle", "Water hammer cold rads", etc.

If you start your search at Google with just "water hammer" you will get tons of sites that deal with this problem; you can then narrow your search to those sites & forums that deal exclusively with steam systems; keep changing & modifying the search words you enter into the search engines, while keeping "water hammer" in quotes, & adding & subtracting other related words not in quotes.

Be assured that others are experiencing the same problem as you, but it takes time to find the relevant info.

The Heating Help site has a lot of articles on steam rads; click onto "system" at the top of the page, then onto "steam", then onto "There's water hammer near the end of the heating cycle"
The author of this site, Dan Holohan, has widely written on steam systems & is considered an authority; he talks of "dead men", as a reference to the long- ago people that pioneered the steam/hot water heating industry.

The NYT article and High Performance sites are also helpful.


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