How to Stop Radiator Hammer?

aidenbc

Howdy. We are considering moving into an old office building with cast iron steam radiators. Only problem is that one of the radiators makes a really loud sledgehammer sound at least 1-2x a day. It's on the 9th floor of a 10 story heritage building.

Question is - will turning off the radiator using the black knob on the right stop the banging? We are fine using space heaters if we can just get rid of or dampen the noise. Any help or suggestions would be appreciated :)

Sounds just like this but louder: https://youtube.com/shorts/FcTvb9DFHsU?si=9PXpxDl1T1FPe4Wz

Jamie Hall

I don't like the pitch of that return pipe. It will trap water — unless the building is off level! — and that will hammer from time to time. For that matter, the pitch on the supply is none too good either, from the look of it. That might hammer more on startup — but could any time.

Can you raise the radiator enough to get some pitch on those pipes? There seems to be clearance under the window.

AdmiralYoda

@aidenbc Shutting the radiator off by closing the valve isn't a good solution. Steam and condensate need to be separate. In a two pipe steam, dry steam comes in the inlet and condensate drains out the outlet.

If the pitch isn't correct condensate can build up where it shouldn't be and when enough of it gets in the way of the steam it will cause a bang.

As @Jamie Hall mentioned, 99% of the time it is because the pipes are not sloped correctly. This can happen over time as older buildings settle or if work had been done elsewhere and shifted things a bit.

An easy fix is to elevate the radiator an inch or two or three to correct the slope. The more the better but don't force it, and with those long supply/return pipes there won't be much risk of over-doing it.

But because pictures can be deceiving, the best first step would be to put a level on the pipes and see if there is no slope or negative slope. If our suspicions are correct…just raise up the radiator. 2x4's and boards can work to try it out and fine tune it….then once you are satisfied you can find a fancier solution like some metal pucks or something. 👍️

aidenbc

Thanks so much for this advice. @AdmiralYoda does it matter that the sound mostly comes from the pipes to the right and not from the radiator itself? The sound does travel into the radiator, but it sounds like it originates in that long stretch of piping in the photo. Will raising the radiator still help? Unfortunately the heat in the building is off right now so I can't test it.

EdTheHeaterMan

How to Stop Radiator Hammer?

Take away its tool box!

EdTheHeaterMan

oops

Steamhead

@aidenbc , it looks like that trap might be an orifice or disc type. These are not good choices for low-pressure steam systems. The wrong trap can cause banging. Can you post a close-up of the top of the trap so we can see for sure?

Also, the shutoff valve looks kind of unique. I found it here:

https://www.dahlvalve.com/products/radiator-valves/regular-pattern/regular-pattern-11021-4112.php

but there is no mention of what that nub is opposite the radiator connection.

There is a name on the radiator itself but I can't make it out.

What pressure does the system run on?

Where are you located? Does BC mean what I think it means?

aidenbc

Hi @Steamhead thank you for your help. I'm in British Columbia Canada. Vancouver to be exact!

I don't know the pressure unfortunately but I did take close up photos or the radiator as requested. Do they help at all?

Steamhead

@aidenbc , Gurney was a very old name in radiator manufacturing. I think here in the States, they were absorbed into National Radiator Corp at some point.

The trap looks like a thermostatic type according to the literature, but it's rated for 230 PSI. This means the orifice which is part of the trap seat is smaller than a low-pressure trap would be. I doubt your system is running that pressure- the radiators can't take it. So, condensate is slow to leave the radiator, and this can cause banging. You will want to verify what pressure the boiler is running, but it can't be that high.

Spirax-Sarco does make a straightway low-pressure trap, the RTH, but there is too much drop between the inlet and outlet to maintain slope on the return line. See:

https://content.spiraxsarco.com/-/media/spiraxsarco/international/documents/us/sb/steam_trapping_overview-spb1009-us.ashx?rev=e3bf974729f24b9bad463747884f0fb3

and scroll down to page 15 to see it.

A better bet would be the Barnes & Jones #122S:

https://barnesandjones.com/wp-content/uploads/2023/09/Thermostatic-Traps-VAC-125PSIG.pdf

aidenbc

Hi @Steamhead thanks so much for this investigation and expertise! I am a total rookie - are you advising that switching the trap to the B&J 122S may help with the condensation/ banging?

Steamhead

https://forum.heatinghelp.com/discussion/comment/1802844#Comment_1802844

I believe so. You should be able to get them in the Great White North. Try changing the trap on the worst one and see if it helps.

aidenbc

Thanks so much @Steamhead