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Tapping Sound At The Beginning And End Of Heating Cycle

geoprell Member Posts: 19
edited January 2018 in Strictly Steam
Please help me diagnose a tapping (gentle knocking) that seams to echo through my pipes. It seams to be most prevalent during the beginning and end of the heating cycle, but I am hesitant to say that is the only time. It seams to mostly effect two of the branches off the middle of the Main. I never hear "Water Hammer".

My initial thought was it must be expansion and contraction of the pipes, but I am not sure if that could be the cause. I have raised the middle of my Main about 2" (it had a belly in it), in order to crate a constant pitch. The branches off the Main already have a good pitch. I have replaced the vents at the radiators (Jacobus/Maid-O-Mist), and have been experimenting with changing the different size orifices (sizes:5,6,C,and D). I don't know if their is a trade off between maximizing the heating of a radiator, and creating a quiet system (my original goal was to maximize heating up the radiators). At the end of the Main, I have a single vent (Durst) on a 6" riser (I am planing on adding two more vents on an antler design - read in a post for these basic vents, should add one for every 10' of Main).

The system is a 23' Main, with 8 radiators on 6 branches. The pipes have fiberglass insulation tubes.

Appreciate any advice.


  • nicholas bonham-carter
    nicholas bonham-carter Member Posts: 8,576
    I don’t know about the capacity of the Durst, but our rule of thumb is one Gorton #2 for each 20 feet of 2 inch main.
    Also check the tightness of the rod which may be holding the radiator sections together. It needs to have no play in it.—NBC
  • Jamie Hall
    Jamie Hall Member Posts: 23,310
    Almost certainly expansion noise. Now the trick is to find it. Pipe supports on the mains or runouts are suspects. Places where a riser goes through a floor are suspects. And then there are the radiators themselves.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • ImYoungxD
    ImYoungxD Member Posts: 130
    edited January 2018
    I'm having the same issue as OP.
    @Jamie Hall
    Jamie, a few days ago, I insulated my main and installed big mouth, I'm getting a lot of expansion noise in the beginning stage from a cold start. How do I fix it? I think it's the pipe risers.
    JUGHNE Member Posts: 11,061
    Your piping is just heating up and retaining the heat quicker than it did. Expansion that was always there is just occurring much quicker.
    Pipes coming up thru holes is the floor need a 1/4" clearance on all sides.
    Same for steam mains passing thru any walls, they should be able to float thru the wall with a sleeve or hanger on each side.
    Cut up milk jugs are used a lot to provide anti friction pads to allow easy movement.
  • geoprell
    geoprell Member Posts: 19
    You Guys Are So Good.

    I lifted up the carpet around the pipes that run from the basement to the second floor (visible-corner of room) and found two pipes that go through the first floor sub and finish flooring and found their is "0" clearance on one side. It is a tight fit, and since its the first floor, moving the radiator on the second floor will not help. I guess I will have to try and drill holes around the tight side.

    Perhaps the pipe supports are a problem also. As I mentioned in the first post, I raised the middle of the Main 2" (it had a "belly" in it ) in order to create a constant pitch. What I did was raise the metal strapping that holds the Main to the joists. The Main does not touch the joists, but the 1" wide steel strapping is tight around the 2" Main. Is their a better way to hang a Main that runs perpendicular to the joists?

    Thanks for the help.
  • KC_Jones
    KC_Jones Member Posts: 5,737
    Before you go cutting any wood, cut up a milk bottle and slide a piece of plastic in the hole between the pipe and the wood. This will allow the pipe to slide and should stop the noise.
    2014 Weil Mclain EG-40
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