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Steam Humidifiers Trapping Requirements

I have been involved with steam humidification problems during the past several months - specifically the humidifiers depending on their mood, back up condensate and "rain" in the ductwork. I have end of the main runs @ 12psi and humidifier traps @ atmospheric pressure. The kicker is they are all tied into one condensate return line back to the reciever. I suspect flash steam is pressurizing my atmospheric traps? I am in need of a "dead man" to put my mind at ease, am I headed in the right direction? Any comments welcome


Mike Scelzi
ETI - Richmond VA
804 355 3230


  • Art Pittaway
    Art Pittaway Member Posts: 230
    Are they F&T traps?

    If they are not, install them, anything else backs up condensate or won't work with variable flow. If it's a horizontal unit see that the duct tube is tipped correctly per mfg. installation guide. Look at the run to vented reciever and see what is tied into it that would be blowing through, repair it. 12 psi is not that high for flash steam (broken trap blow thru is not flash) troubles, make sure the return is large enough (1/2" is not), drains DOWN with no lift, and open. But, the pressure does seem high for a humidifier, make sure the humidifier makers spec's and control valve is closing against that pressure, and is designed for 12#. Then make sure the reciever is actually vented. Just like relief valves, all it takes is one manager to not like the "smoke" coming from a vent, and have it capped by someone that hasn't a clue, and you have a pressurized vented?? reciever. If your looking for data Spirax/Sarco makes some great publications on sizing and piping practice. It might be worth putting a 0-10psi gage on the condensate return line to see what it reads. Years ago I went to an industrial site with all kinds of control and lack of process heat problems. 80# steam at boiler, put a gage on the return line, it read 60# at one point. Good luck, Not dead yet. Art
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