Noisy capped pipe

Ferris

The capped steam pipe in my bedroom knocks when the steam stars to hit the radiators in the other rooms of my apartment. I had it capped last year by a professional plumber / steam radiator man.



The knocking isn't loud but it is bothersome. And since the objective of getting the radiator removed and the pipe capped was to keep it more quiet, this problem is quite frustrating.



What's making it knock? Is it the pipe expanding as it gets warm? Any advice is welcome.

Jamie Hall

It may well be

expansion, which can be a bit tricky to track down.  Also a bit tricky to get rid of, although if you can find anywhere where the pipe is rubbing on something -- such as where it comes through the floor -- that's a good place to start.



It could also be a minor water hammer; as steam gets into the pipe it condenses, of course, and that condensate has to go somewhere.  If that's it, it will be only at the very beginning of the cycle.  The trick there would be to figure out where in the pipe the condensate can get slightly trapped, and change the pitch so it can drain easily.