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Regulator failure - theories?

Discussion in 'Regulators' started by resnick, Dec 6, 2014.

  1. redacted

    redacted Guest

    Some things to consider:

    Salt and crud in a 1st stage should be expected to result in uncontrolled gas flow, not the stopping of gas flow. Heck, an o-ring has to be just right to seal and even a hair will cause it to leak.

    No gas to the 2nds or the HP gauge suggests no gas in the HP chamber of the 1st stage.

    You were able to remove your "failed" regulator from the tank suggesting no pressure in the tank valve.

    Looking at the design of the ACD, it is not going to be able to stop gas flow once the reg is attached and working.

    Even a badly clogged filter will flow some gas, just not enough to breath well.

    The reg worked OK on other tanks for subsequent dives.

    I do not believe the primary problem was your regulator.

    When you tried another regulator on the tank involved in the failure, did you breath from it?
  2. resnick

    resnick Divemaster

    # of Dives: 200 - 499
    Location: Urbana, IL USA
    Good points. On your question:

    I used the purge valve on the second stage and it appeared to be working.
  3. Dive Right In Scuba 2

    Dive Right In Scuba 2 ScubaBoard Business Sponsor ScubaBoard Business Sponsor

    # of Dives: 1,000 - 2,499
    Location: Illinois
    Wasn't there a chapter in the book "Diver Down" where this occurred? Does anyone have a copy handy and can take a gander? My copy is at my other place.
  4. LeadTurn_SD

    LeadTurn_SD Solo Diver

    This is indeed a weird one, but my money is on the tank being the problem. Hopefully the dive shop pulled the tank from service, drained it, removed the valve and gave it a visual inspection.

    Complete failure as described, but then working on other tanks seems to point to the valve in the original "bad" tank, here is why:

    • The regulator worked on other tanks, and for the rest of the trip. I cannot visualize an intermittent problem on a diaphragm reg that would cause catastrophic failure... but then be ok again?

    • Water and corrosion in the 1st stage, despite the ACD intact and apparently functioning, may indicate the water was introduced from a tank with water in it. If that is the case, it is not a great leap to suspect a missing (broken, corroded off) dip tube, and possibly debris in the tank that could block the tank valve during the dive.

    • Failure of the ACD, as I understand it, probably cannot occur on a pressurized tank... tank pressure should easily overpower the ACD and allow air to flow into the 1st stage?

    • Other wear and tear and internal corrosion-related problems would generally result in freeflows or leaks, or diminished breathing performance, not a catastrophic failure.

    • When the tech serviced the reg after the trip, he found evidence of salt water intrusion, but no obvious defects in the regulator. This again seems to point to the reg being placed on a "bad" tank (one with salt water in it)... the ACD "should" prevent salt water intrusion during normal post dive soaking or washing, even if the diver forgets to replace the dust cap... although I would not count on it to do so :wink:.

    So, my money is on the tank as culprit. Even if the tank appeared to "work" again subsequently (a blockage that dislodged itself after the valve was turned off and the tanked bumped around a bit while being moved).

    Best wishes.
  5. keyshunter

    keyshunter Solo Diver

    # of Dives: 5,000 - ∞
    Location: Lower FL. Keys
    While I agree with your analysis in general, I think you can eliminate "failure of the ACD". The ACD does not operate off of air pressure as does Oceanic's DVT. It is held open mechanically by the pressure of its attachment to the valve. However, the DVT could be held partially open when soaking if used with an early flat dust cap that was not fastened tightly. Aqualung apparently noticed this and the later DVT regs come with a dust cap which will normally prevent this.
    LeadTurn_SD likes this.
  6. LeadTurn_SD

    LeadTurn_SD Solo Diver

    Thanks! I had thought it was air pressure that opened that ACD gizmo, not mechanical pressure. My bad.

    Still, it seems like it would either "work", or "not work", with regards to allowing air into the 1st stage.

    I'm not a fan of that "feature", but the design seems pretty "fail safe", and not likely to cause a catastrophic failure one dive, yet work fine thereafter without a hitch??

    That is what has me puzzled, and why I think it was probably the tank valve not passing air, versus the 1st stage failing in some fashion.

    Still curious about it because catastrophic failure is so danged uncommon, but we will probably never know with this one.

    Best wishes.
  7. Kunundrum

    Kunundrum Divemaster

    # of Dives: I just don't log dives
    Location: Ajax Ont. Canada
    Being a AL tech and having also worked on my fair share of Oceanic Regs, I can tell you that the only thing that the ACD and DVT share is their intended function, how they achieve this function is in two completely different ways. the DVT is reliant on tank pressure to open the valve (if i had this on my regs I would remove it too) the ACD opens once it's mounted to the cylinder and tightened with the Yoke nut/DIN.

    The inherent design of ACD If the 1st stage is still mounted to the tank valve the ACD can't fail.

    I seriously doubt the ACD component is at fault, based on the information given I would say lean on the side of the bad tank.
  8. Nemrod

    Nemrod Solo Diver

    Yes indeed, on the AL ACD the ACD is pushed open when it is mounted to the valve, it is physically pushed open, it does not require pressure to open, it is fail safe. There is no realistic way the first stage could be mounted to the valve and not have the ACD pushed open. N

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