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Max velocity

Jason_13 Member Posts: 304
I know how to calculate velocity in a steam pipe but my question is, what is the maximum velocity in a steam main?


  • crash2009
    crash2009 Member Posts: 1,484
    Good question

    Try searching the wall for "maximum velocity"   http://www.heatinghelp.com/forum/search   Much has been written on the subject.  It appears that max velocity is dependent upon the pipe size.  Here is a quote from Boilerpro  Look in the lost art

    Dan has the charts in there, because the maximum recommended velocity varies with the pipe size. 12 fps was the old maximum, which generally is about 1/2 of the maximum at which water can fall back against steam. Also, individual boilers vary greatly in water carry over. Noel's Slant fins run bone dry steam at 190,000 input with a single 2 1/2 inch riser, while the same size Durkirk will have heavy carry over into the header with that size piping. Boilerpro
  • clammy
    clammy Member Posts: 3,091
    max velocity

    Dan does have the formula in the lost art ,I usually always try to get it down to below 12 fps and have never had a issue with any boiler that i have installed usually peerless.weil.utica and a few others.You will find that usually when wanting to obtain lower exiting velocities below 12fps you will be using both tapping and have a miniun of a 3 inch header this is a usually for below about 150 mbtu over that it's usually 3 inch risers into a 4 inch header.Also alot depends on how many risers you are conecting to the header over 2 risers connected to the header then think of up sizing like 3 to 4.The slower the exiting velocty the dryer the steam .I in the past have also posted question concerning this subject and did not get much reaction .So i myself started doing the math and came to my own conculsions and use that approach when i install steam boilesr and never have issues with carry over steam or wet steam or issues realted to improper near boiler piping.This of course always increases the price of the job and usually puts my price higher then others but it is cheaper to do it once then doing itthe second time  for free or to have the HO just live with it which is what alot do cause the contractors says thats the way steam operates .As always the best place to start when installing a new steam boiler is to take a look at the manafactures installation and operation instructions and there requirements for the near boiler piping and always remenber that there piping dimensionsare the minuin and when it comes to residental low pressure steam heating systems bigger near boiler piping is better  Peace and good luck clammy   
    R.A. Calmbacher L.L.C. HVAC
    NJ Master HVAC Lic.
    Mahwah, NJ
    Specializing in steam and hydronic heating
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