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Is this good practice?

The water will lay in that piping just like it does in a sink drain trap.

A related problem with this is that the trap also acts as an air vent, letting the air out of the coil so steam can enter. The air is vented at some central location- most probably in the boiler room- and the water goes back to the boiler. With the "water pocket" in that piping, the air won't be able to get thru.

It is possible to get "in-line" F&T traps that don't have the outlet lower than the inlet. This may help to solve your problem. I think Spirax-Sarco makes these, and possibly others.

They might have cranked the boiler pressure way up to try to make it work. After you fix this, see how low you can go!


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  • Erik Z
    Erik Z Member Posts: 1
    Steam coil condensate drain.

    I am new to the field of HVAC, and am doing a survey for some hotel AHUs. I encountered the pictured set-up on the condensate drain of the steam coil. This is a 100% Outdoor Air unit. It would appear that condensate would have to flood the coil quite a bit to not only break open the steam trap, but also open the check valve. Not to mention, I see no vacuum break. Just wondering if anyone had any comments.

  • Brad White
    Brad White Member Posts: 2,393
    Unless (and even if)

    it is a vacuum system, that pipe arrangement will eventually freeze. As you perceive, the invert of the condensate line after the trap is above the coil bottom plus the lift required to flow past the check valve is of concern.

    The only thing that stands between the coil freezing is a freeze-stat (low-temperature, non-averaging capillary type is what we specify). This in turn should be hard-wired to the fan starter to shut down the fan and close the OA damper. If any return air is used (you said this was 100% OA but just offering) that damper should fail open.

    Add to this, your steam valve should fail open to keep the coil warm as much as can be done.

    If it is a vacuum system you would not have a vacuum breaker of course. Assuming this is standard gravity return, yes a vacuum breaker would be installed upstream of the trap.

    This could be and often is installed downstream of the steam supply control valve near where the steam enters the coil. I often put a separate one upstream of the trap, elevated to above the coil. These can be bona-fide vacuum breakers or two check valves in series mounted horizontally is an old-timers trick.

    Overall, I think you nailed it, Erik.

    The short-term solution is to make sure that the above noted safety devices and sequences are implemented and that vacuum breakers are installed.

    Long term solutions mean elevating the units (if and when replaced and if room is available) or to pipe the condensate and install the traps below the floor. If this is a basement, a pit may have to be created.

    I agree with your observations.

    "If you do not know the answer, say, "I do not know the answer", and you will be correct!"

    -Ernie White, my Dad
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