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Dry steam vs. velocity

clammy
clammy Member Posts: 2,739
Exiting velocity ofa steam boiler should be kept as low as possible at 26 fps that's way to fast for me i always try to make my header large enough so my exiting velocity is down to about 15 or lower at the velocity your getting some very dry steam and if the boiler is clean you should hardly any surging in your sight glass .At that slow of a exiting velocty the old layers of latex paint should be peeling away .Check the library i know there is a formulka for fiquring what size header pipes will give you your boilers exiting velocity .I will always go at least one pipe size larger then the exiting mains for my header example boiler 2 2inch riser system 2 2 risers this header should be at a mimuin a 3 and thats if the boilers output is only about 150 btus peace and good luck clammy
R.A. Calmbacher L.L.C. HVAC
NJ Master HVAC Lic.
Mahwah, NJ
Specializing in steam and hydronic heating

Comments

  • JIM W.
    JIM W. Member Posts: 16
    DRY STEAM VS VELOCITY

    DOES ANYONE HAVE INFO ON STEAM QUALITY AS IT RELATES TO STEAM VELOCITY. I HAVE READ ABOUT THE "ANTI-SURGE TANK" THAT SLOWS THE VELOCITY OF STEAM. IF SOME ONE HAS SPECS ON THIS I MAY BE ABLE TO GET SOME INFO FROM THAT. THANKS
  • mel rowe
    mel rowe Member Posts: 324


    FWIW, I have gone through this very question relative to my own boiler, during the last year. If you have access to Dan's very excellent book, you can use your boiler data and calculate the velocity of the steam leaving the boiler, etc. A few key numbers to keep in mind would be to keep the vertical risers from the boiler to the header a min. of 24 inches between the center of the gauge glass and the bottom of the header. This helps water droplets from being carried out with the steam. In addition the steam velocity should be kept below approx. 26 ft./sec. With my 299,000 btu boiler, improperly installed as it was, with only one 2 in. tapping, the velocity was 54 ft./sec. Recently I completed repiping the boiler myself by adding a second tapping and a 3 in. drop header and cut the velocity in half, of course. The result is dry steam and a much better overall result. Based on data in Dan's book, for a boiler rated at 760 EDR, and only one 2 in. tapping, you get a velocity of about 27 ft. / sec., so you can probably estimate where your boiler falls.
  • mel rowe
    mel rowe Member Posts: 324


    Just a point of interest, Clammy. In the case of my 299,000 btu boiler, I've now got two 2in. tappings into the boiler and a 3 inch header that is 34 in. above the centerline of the sight gauge. I have two mains off the header, one 2 in. and one 2 1/2 in. Even if I added tappings into the boiler and added a larger header, the velocity would still be the same in the mains. So I guess the answer is that the steam velocity in the mains is not a concern, but only the velocity as it leaves the boiler through the risers. Is this correct?
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