Click here to Find a Contractor in your area.
Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit

steam traps

jfgh Member Posts: 3
Is it possible to over size a steam trap? Case in question is an airhandling unit with a condensate load of 900lbs/hr at full load with a pressure diff. of 6psig. Steam is controlled via a modulating valve. Supplier is trying to sell be on a trap which is has a safety factor of almost 8. His reason is as valve modulates closed you no longer have a diff. press of 6#s. This is true but you also don't have a full condensate load either. Am I better off with a larger trap or smaller one with a safety factor of 3 or 4.?


  • Robert O'Connor_3
    Robert O'Connor_3 Member Posts: 272
    steam trap

    there is no advantage in oversizing a steam trap. air handlers are ok with a 3 to 1 safety factor. be sure you have a vacuum breaker installled. tp tunstall
  • Walt Deacon
    Walt Deacon Member Posts: 5
    sizing on coils

    Here's the scoop:
    The temperature control valve has the capability to be 2/3's open, delivering steam at 2/3's of full load, and the coil is in a vacuum!
    It doesn't matter that your steam supply is 8 psi. The valve is controlling the pressure to match the temperature it needs. If it needs 205 degree steam, it can do that!
    That's why you'll see SHEMA ratings in older trap catalogs (like Dan's excellent books). Those ratings built in a 2:1 safety factor at about 1/2 psi differential, which looks like 6:1 at 8 psi.
    See, the coil will be in a vacuum, the vacuum breaker will open, and you only have the static head of the water to drain the coil (hence the 1/2 psi differential).
    The SHEMA ratings were an agreement by the equipment manufacturers on how to rate traps so that coils wouldn't freeze. The ratings accounted for wet steam, modulation of the valve, and a likely drop in pressure when "design days" hit. The SHEMA group are all "dead guys" now, but the lesson lives on...
This discussion has been closed.