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Why did I get a CO reading?

Discussion in 'Compressors, Boosters and Blending Systems' started by rhwestfall, Jul 17, 2019.

  1. rhwestfall

    rhwestfall Solo Diver

    # of Dives: 200 - 499
    Location: "La Grande Ile"
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    I have an in-line monitor for CO on my compressor. It is a tee in the line at the fill whip connection going through a flow reducer, then to a flow meter with a bypass check valve venting the additional flow. The back side of the flow meter is plumbed to a CO detector. With the flow meter, I am able to set the 0.5 lpm rate the detector (Sensorcon) is calibrated/designed for.

    I have run it in the past, and have been getting 0 for a reading all the time. I have usually hooked it up/turned it on a little into the run time, but this time I had the monitor on earlier. Today, upon start-up, I had a momentary spike to 6 ppm for 15-20 seconds or so, then went to 0, staying there for the duration of the hour run time. I started with the pressure in the system at basically zero inclusive of the filters as it had been sitting for a number of weeks since the last run.

    Any ideas what may have happened for that moment?

    P.S. - the end of this run was used to take an air sample that has gone out for analysis...
     
  2. rjack321

    rjack321 Captain

    # of Dives: 1,000 - 2,499
    Location: Port Orchard, WA
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    Zeolites (13x) offgas when depressurized. My best guess is that a tiny amount of CO was adsorbed on the 13x from hours of running, those multiple hours worth of (eg 0.25ppm) CO offgassed into the small depressurized tower housing, then ended up as a little detectable burp in your monitoring stream as that bolus of gas pushed through your priority valve.
     
    swamp diver and rhwestfall like this.
  3. davetowz

    davetowz Dive Shop

    # of Dives: 2,500 - 4,999
    Location: usa, Ohio
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    What co detector are you using?
     
  4. rhwestfall

    rhwestfall Solo Diver

    # of Dives: 200 - 499
    Location: "La Grande Ile"
    12,415
    11,164
    113
  5. davetowz

    davetowz Dive Shop

    # of Dives: 2,500 - 4,999
    Location: usa, Ohio
    648
    93
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    I agree with Rjack. The co came out of suspension in the adsorbant and that is probably why you saw the spike. What filters are you using?
     
  6. rhwestfall

    rhwestfall Solo Diver

    # of Dives: 200 - 499
    Location: "La Grande Ile"
    12,415
    11,164
    113
    After the coalescer, the first vessel is just 13x (re-purposed from the original filter that was just AC). From there, it goes to a 10" MAKO cartridge (13x, AC, Hop), then to NS Research/Ultra Filter hyper-filters (two micro particulate, and one AC).

    Low volume MAKO/Bauer 2.4 cfm compressor
     
  7. BRT

    BRT Giant Squid

    10,833
    6,754
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    For what it is worth mine does the same thing.
     
    rhwestfall likes this.
  8. rhwestfall

    rhwestfall Solo Diver

    # of Dives: 200 - 499
    Location: "La Grande Ile"
    12,415
    11,164
    113
    BTW - While this discussion was going on, I got a message last night that the air test I took on Sunday passes Grade E standards. Full results should be back to me soon.
     
    RyanT likes this.
  9. abnfrog

    abnfrog Tech Instructor

    # of Dives: 2,500 - 4,999
    Location: great white north
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    I would agree with the CO "burp" scenario I see it sometimes on my unit
     
    rhwestfall likes this.
  10. swamp diver

    swamp diver Barracuda

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    I agree with Rjack. The molecular sieve does adsorb small amounts of CO when pressurized and with the compressor sitting for a couple weeks the CO desorbs back into the airstream on start-up until the purifier is fully pressurized again.

    We have the same thing happen on both our compressors with the duration and magnitude of the spike on start-up related to the duration of the shut-down.

    I think Analox did some research into this and also confirmed that is what is happening. Just blow off the spike to ambient or if you have large storage banks it will be diluted down and the final concentration of zero will be insignificant.
     
    rjack321 and rhwestfall like this.

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