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Filling and Humidity

Discussion in 'Compressors, Boosters and Blending Systems' started by ATJ, Jul 9, 2020.

  1. ATJ

    ATJ Barracuda

    # of Dives: 1,000 - 2,499
    Location: Sydney, NSW, Australia
    I was chatting to the owner of the company that services my gear, hydros my tanks and sold me my compressor about when it is ok to fill tanks. He said I should not fill my tanks if the relative humidity is greater than 75%.

    When I first thought about it, it made sense. The less water there is in the air, the less the molecular sieve has to extract and the drier the air in the tanks.

    I thought about it some more and wondered what happens in tropical locations where the humidity would be high most of the time.

    I also wondered whether relative humidity was a good measure as it is dependent on the temperature: 75% @ 10ºC has around the same amount of moisture in the air as 40% @ 20ºC. But, is it harder for the molecular sieve to pull out moisture at 10ºC versus 20ºC? The filter stack heats up anyway during the filling process.

    Do others worry about humidity when filling their tanks?
  2. BRT

    BRT not a soft touch ScubaBoard Supporter

    No question that dry cold air is easier for the moisture trap and filtration to work with. My little compressor is set up to drain more often with high humidity and or high temperature.
    AfterDark likes this.
  3. KWS

    KWS ScubaBoard Supporter ScubaBoard Supporter

    # of Dives: 500 - 999
    Location: SE TEXAS

    I do not. I think my compressor has an upper limit of 95% or so. My guess is that if it is a 3 stage you have no moisture removal between stage 1 and 2. Just a guess. Id read the book and try to figure it out or call the maker for an explanation.

    humidity is part of the compressors cooling. From the first moisture separator on it is 100% RH in the system. as pressure goes up more water gets wrung out in the mechanical separator and drained leaving 100% to go to the next stage or component. From stage 2 on it should have drains so the issue has to reside prior to the output of the first separator stage most likely on the out put of stage 2 compression. I will guess that under the right conditions the output of stage one could have too much water in it that stage 2 could try to pull water and try to compress it if inlet moisture is higher than 75%. stage 1 may not raise temp high enough to allow more vapor it. The first stage could have a large step up in PSI that it cant handle more than 75% without pumping water from condensation. an other factor may be that if you drain every x minutes greater than 75 would over flow into the suction of the next stage. perhaps drain more often when over 75. that could be a real factor if you have auto drains.

    what kind of compressor do you have?
    AfterDark likes this.
  4. ATJ

    ATJ Barracuda

    # of Dives: 1,000 - 2,499
    Location: Sydney, NSW, Australia
    I have a Bauer PE100. It has manual drains which I do every 10 minutes (the manual says every 15).
    AfterDark likes this.
  5. rddvet

    rddvet DIR Practitioner

    # of Dives: 50 - 99
    Location: Florida
    That’s total bs. Just fill whenever. I live in Florida. If I had to wait till under 75% humidity I’d never run my compressor.
    AfterDark, rjack321, couv and 3 others like this.
  6. kelemvor

    kelemvor Big Fleshy Monster ScubaBoard Supporter

    # of Dives: 200 - 499
    Location: Largo, FL USA
    He's full of it. If that were true, tanks couldn't be filled in Florida ever. Nowhere in the Caribbean for that matter.

    As others have said, the moisture gets removed during the fill process if you are using a compressor with a proper filter.
    AfterDark and Johnoly like this.
  7. James79

    James79 Reinventor of Wheels ScubaBoard Supporter

    # of Dives: 50 - 99
    Location: Lower Alabama
    Should not and can not are two different things... I know some filter media will be effected by the relative humidity (for example the Bauer Junior 2 manual has you record the temp, humidity and run time and do a an adjustment based on temp and humidity to track filter change interval). That may have been what he was referring to.
    AfterDark likes this.
  8. captain

    captain Captain

    High humidity does increase fill time and more requires frequent drains but here in south Louisiana I would never be able to run my compressor 11 months of the year if I only fill below 75%
    KWS, AfterDark and couv like this.
  9. tbone1004

    tbone1004 Technical Instructor ScubaBoard Supporter

    # of Dives: I'm a Fish!
    Location: Greenville, South Carolina, United States
    seconded in the Carolinas. If the water traps are doing their jobs, the molecular sieves shouldn't be doing any extra work. Sure you'll have to purge them more frequently but that's it.
    KWS, AfterDark and Dark Wolf like this.
  10. Yawana-Dive

    Yawana-Dive Dive operator in the Solomon Islands ScubaBoard Supporter

    # of Dives: 2,500 - 4,999
    Location: Solomon Islands
    I’m filling tanks every day here in the Solomons where the humidity probably never drops as low as 75%. I purge the valves every 5-10 minutes. Never had any problems with moisture in the cylinders.
    KWS, AfterDark, couv and 1 other person like this.

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