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Thermodynamic Steam Trap; Pressure needed to Drive

  1. Sep 10, 2015 #1


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    How much of a differential pressure does a typical thermodynamic steam trap need to discharge condensate?

    i.e. Say one needs to drain condensate from a shell under vacuum 310 mmHg abs, would a thermodynamic steam trap work correctly if I connected the discharge pipe to a vessel maintained at 210 mmHg abs i.e. A differential pressure of 100 mmHg i.e. 0.13 bar.

    This is a small 1/2" trap & the expected condensate isn't much. Approx. 100 to 250 Litres / hour. The discharge piping is very short (say 6 feet long) since the vessel is very close to the trap.

    An image of the trap type just for context.

    Last edited: Sep 10, 2015
  2. jcsd
  3. Sep 10, 2015 #2
    Not much delta-P is needed; however, you're indicating a higher pressure in the receiving vessel????
  4. Sep 10, 2015 #3


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    Arrgh! My bad. Messed up my spreadsheet. I've corrected the numbers now.

    And indeed I'm having a lower pressure in the receiving vessel. i.e. A higher vacuum in the receiving vessel.

    So, you think with just a 100 mmHg delta P the typical steam trap would drain condensate correctly? That would be awesome for my purposes. I was worried about having to mess around with the more complex and expensive "pumping steam traps".

    Last edited: Sep 10, 2015
  5. Sep 10, 2015 #4
    Well, 100mmHg is only about 4.5 ft of head so you'd have to make sure your elevation differences don't cause a problem. As usual, the final answer should come from your Armstrong or Sarco rep.
  6. Sep 10, 2015 #5


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    Any idea if they note the differential head needed on the trap spec sheets? I couldn't find it on any I have on file. Just wondering.

    Also, among the various trap types any idea which one can do with the least head requirement? Are there big variations? Or not really.
  7. Sep 10, 2015 #6
    I'm going to back-peddle. Your vacuum application and subsequent low temperatures might not work with thermostatic types. Float or inverted-bucket types are more positive-acting for these conditions. Yeah, the web sites talk about "up to" capacities but no curves. Talk to a rep.
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