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Hammer & Water leg

Installation of new boiler and boiler feed pump has created a water leg.  In "The Lost Art of Steam Heating" it is suggested that solving a hammer problem you can add an air vent to a F&T trap. My existing F & T is a single inlet/outlet.  The outlet side flows to a "T" about 8 inches down stream.  Would an added air vent at the "T" work in the same manner as it would piped directly from a new "H" pattern F & T trap.  I'm trying to save a little money and time here.  By the way the existing F& T is a Dunham_Bush 30-5.  Could I or should I port an eliminate the steam trap that is part of the F & T and put an air vent in it's place.


  • Pulling a water leg

    Can you give a little more information on this problem?

    Is your system 1-pipe, or 2-pipe?

    A layout drawing would also help with the description of the problem.--nbc
  • Phil604
    Phil604 Member Posts: 4

    Hi,  This is a two pipe system and the F&T is at the end of a 100+ ft. steam main.  There are 4 of these trunks and the one in question seems to be the only one with hammer.  I rebuilt the Dunham 30-5 with a complete kit and hoped that would stop the hammer.  It helped but did not completely end the problem.  I don't know how to attach a drawing but I will take a picture or two and try attach them from my home computer this evening.

    On the Dunham 30-5 "face" where the piping enters and leaves there is also a Dunham radiator style steam trap protruding from the upper left corner.  Would it be a mistake to thread this out and put an air vent there?

    The 3/4 piping from the outlet of the F&T goes about a foot or so to a "T" that right angles on to further condensation collection points.  One side of the "T" has a plug that can be removed and an air vent could be installed there.  All of this piping runs on horizontal plane.

    Thanks for the response.
  • Phil604
    Phil604 Member Posts: 4

    Here are a couple of pics
  • height of waterline

    what height are those in relation to the boiler waterline. horizontals can create problems when they are too close to the waterline height.--nbc
  • Phil604
    Phil604 Member Posts: 4
    water leg


    crime in italy, i just wrote this long response and boom it disappeared.  the jist of it was.

    the boiler room is about 18 to 24 inches lower than other floor levels in the building.  the original wet return gave up the ghost about 4 years ago and I put in a small tank and pump at the point where the entire return for the building went into the floor rather than jackhammer about 40 feet of concrete and dig that 18 inches.  The return water was then pumped overhead the above distance into the boiler room to the original wet return pump.  2 years ago a new boiler (there are two) was installed along with condensate tank and boiler feed pump.  The system flooded a couple of times that winter as high as the lobby level and the hammer that developed then was attributed by me to that flooding.  And this hammer was mostly on the steam trunk this discussion is about.  I found the pictured F&T trap and valved drip leg in the recesses of the building and purged a LARGE amount of water from the line.  And lived with some start up hammer that year.  This year with some more understanding of what I have I rebuilt the F&T and reduced the hammer quite a bit more but water still builds up or back flash pressure at the point in question still is giving me problems.  I believe after reading Dan Holoran's book that the problem may be the water leg that was created  by me at the collection point mentioned above and the installation of the new return tank and pump.  So I'm going to buy an air vent and try that but would like some opinion about the install location.  If I'm way off base, I can take that news too.
This discussion has been closed.