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Very short water hammer

Our one pipe steam system is usually very quiet. I went around and adjusted the vents on our radiators the other day by increasing the ones on the largest radiators and decreasing the ones on the smaller ones. 
We have all mains vented with big mouths. 
Over the last few days I’ve noticed that after the system has run for about 10 minutes, there are usually 2 sharp raps of water hammer and maybe a third not as loud one. Then the system is quiet for the remainder of the time it is running. 
What would cause it to happen like that? It’s very hard to pinpoint exactly where it’s coming from because it stops so quickly. Thanks 

Comments

  • Maybe you could restore the radiator venting back to where it was, and see if quiet returns. As they have said for a long time, “vent your mains quickly, and your radiators and risers slowly.” As you observe the system operation, you can then increase the venting of any slower radiators. Monitor your low pressure gauge like a hawk, and make sure the mains vent at under 2 ounces.
    The goal is for steam to hit them all at the same time.—NBC
  • Don_175
    Don_175 Member Posts: 75
    Thanks guys 
  • STEAM DOCTOR
    STEAM DOCTOR Member Posts: 1,485
    Could be expansion noise. 
  • Don_175
    Don_175 Member Posts: 75
    It sounds like someone hitting the pipes with a metal object. We have the ticking expansion noises in the radiators 
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 12,010
    @Don_175

    The above posts are correct. First take a level and make sure all the radiators are pitched correctly. Then check to make sure the steam mains and run outs are pitched correctly with no sags.

    If you don't find anything, try venting the larger radiators a little more slowly
    ethicalpaul
  • Don_175
    Don_175 Member Posts: 75
    So I turned all vents down to 2. I noticed that there was more air noise coming from the vents. In the master bedroom this morning, the Castray radiator was making this weird moaning sound. Sounded like when someone is letting the air out of a balloon and pulls the sides apart to make that weird high pitched sound. I thought it was coming from the vent so I put my finger on the top. It was not the vent. It was the inlet part of the radiator. 
  • Jamie Hall
    Jamie Hall Member Posts: 18,953
    Is the inlet valve on that radiator fully open? That can cause all manner of odd noises -- bangs, gurgles, whistles...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Don_175
    Don_175 Member Posts: 75
    Valve under radiator is all the way open. One thing I’ve noticed is that when the boiler is off, water level is right where it is marked on the jacket. When the boiler is running, the water level in the glass will bounce a half inch or so 3-4 times in a row and then supply drop 3 inches before coming right back up. It repeatedly does this. No water hammer at that point, but the probe LWCO will sometimes shut it down and then it comes back on and runs runs until the thermostat is satisfied. 
  • chuckadoo
    chuckadoo Member Posts: 30
    Whistle on inlet valve could be stem packing, try tightening packing nut. For the drop in sight glass, I’d guess boiler is oversized? After increasing vents, this may have allowed an increase in steam velocity, which is dragging moisture into pipes?