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Intermittent steam (water) hammer

briggs Member Posts: 3
Hello, We're having an intermittent problem of hammer in a riser from basement to second floor radiator. See attached drawing.
Hammering may occur on boiler start up or shutdown. Sometimes it is mild hammering, sometimes it's rather severe.
Boiler Pressure Troll is adjusted to it's lowest setting.
Boiler operating at between 5 & 7 lbs.
Sight glass is 7" long & water level is approx 3" from bottom during operation. No water droplets in the glass above water line.

This is a 2 pipe system & riser pipes are buried in the wall with no access.
What's causing the hammering & what can we do to sop it?


  • Jamie Hall
    Jamie Hall Member Posts: 23,280
    "Boiler Pressure Troll is adjusted to it's lowest setting.
    Boiler operating at between 5 & 7 lbs."

    That makes no sense. I don't know of a pressuretrol which can't be adjusted down to about 0.75 psi cutin/1 psi differential.

    So do it.

    5 to 7 psi is MUCH too high. If it hasn't already trashed your vents and traps, it will.

    Now on the hammer. You show two horizontal sections of pipe. My guess wold be that one of them -- or more than oone -- has gotten slightly off pitch. Wouldn't take much.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • bburd
    bburd Member Posts: 912
    Is the pigtail between the pressuretrol and the boiler clean, also the opening into the boiler itself? The pressuretrol cannot do its job if these are clogged.

    EBEBRATT-Ed Member Posts: 15,517
    You can't run a radiator on 1/2" copper never going to work.
  • briggs
    briggs Member Posts: 3
    Gentlemen, Thank you for your comments. Will follow up on them. Very helpful.Mr. Hall, Will go back to pressuretrol for proper adjustment. Ed, What are your thoughts on using 1/2'' copper? Why won't it work on a radiator?
  • Waher
    Waher Member Posts: 250
    1/2” copper doesn’t have sufficient volume to deliver steam while allowing condensate to return back beneath the steam. Steam radiator pipes are never less than 1” unless a very special two pipe vacuum vapor system. There’s simply not enough volume in the pipe for supplied steam to not get into a hammer fight with returning condensate in a one pipe steam system.
  • briggs
    briggs Member Posts: 3
    Ok Waher, This makes sense. Thanks for the explanation!