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O2 clean system?

Discussion in 'Compressors, Boosters and Blending Systems' started by surfsidedav, Jul 22, 2009.

  1. surfsidedav

    surfsidedav Instructor, Scuba

    # of Dives: 200 - 499
    Location: Myrtle Beach, SC
    187
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    On another thread someone was asking if the LDS I'm tied to has an O2 clean system for nitrox fills. Normally we use a blender box (at least that's what I call it) for normal mixes or we can partial pressure blend. I've heard about O2 clean tanks and compatible regs, etc, but never an O2 clean system. Does this mean the entire system, ie fill lines, banks, etc have been cleaned or what?
     
  2. dannobee

    dannobee Instructor, Scuba

    # of Dives:
    Location: SF Bay Area
    2,480
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    48
    Yes. Any time pure oxygen at pressure is used, the tubes, lines, valves, fittings, bank bottles, etc, all need to be cleaned and prepped for oxygen service. Also, the system should not be cross contaminated with non-O2 cleaned gas.
     
  3. Salmonboy97

    Salmonboy97 Loggerhead Turtle

    # of Dives: 200 - 499
    Location: Hernando County, Florida
    1,293
    6
    38
    Here is another question. At what pressure can O2 be safely used at witout having to O2 clean the system? Assuming the system is clean enough for use @ 40% to 4500psi.
     
  4. oxyhacker

    oxyhacker Loggerhead Turtle

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    There really isn't any good number. Most of the "official" sources will say any system holding 02 should be O2 cleaned and compatible, period, and may define oxygen as any mix above 23.5% or so.

    There's an old rule of thumb which says that under 500 psi or under 50% you can treat it like air, but this is just a crude approximation, and has no real science behind it.

    The risks increase as pressure and % increase, but they never go away completely as you head in the other direction, at least, not until all the O2 is gone.


     
  5. surfsidedav

    surfsidedav Instructor, Scuba

    # of Dives: 200 - 499
    Location: Myrtle Beach, SC
    187
    11
    0
    Ok. So if we're doing a partial pressure fill, I get that the line, connectors etc must be clean, but are you saying that the top off gas must come from a clean source also?
     
  6. dannobee

    dannobee Instructor, Scuba

    # of Dives:
    Location: SF Bay Area
    2,480
    53
    48
    Two things, one, the top off gas must be clean enough for oxygen, otherwise the tank and valve can be contaminated with hydrocarbons and such.

    The lines must be isolated if using OCA air and Grade E air. Usually with one way check valves and ball valves.
     
  7. oxyhacker

    oxyhacker Loggerhead Turtle

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    This has been one of the great debates in tech diving for many years now, just how clean the top up air has to be. And like all mixing questions when O2 is involved, there is no exact answer. You choose your level of risk and take your chances.

    Since most compressors output filthy air which then must be cleaned up enough to make it breathable, the whole system cannot be clean, so usual practice is to add enough filtration at the output end, to clean up the air before it is dumped into an O2-primed tank. Some very knowledgeable people argue that if the air is good enough to breathe it is good enough to PP mix with; others insist that another stage of filtration, usually called a hyper filter, is necessary.

     
  8. CraigAClark

    CraigAClark Instructor, Scuba

    # of Dives: I'm a Fish!
    Location: South Florida
    569
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    Hey Vance,
    I've always wondered about this when it comes to CCRs. My understanding is that Grade "E" or equivalent is what the manufacturers are ok with. I don't dive CCR myself, but have seen several CCR students and the instructor charging with that standard air. Seems whether you are PP blending or using a CCR, both involve mixing air and O2. With a self regulated industry, you're probably right about risk and chances.

    Craig
     
  9. oxyhacker

    oxyhacker Loggerhead Turtle

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    I hadn't heard that the manufacturers approve Grade E, though it seems fair common practice to use it. Most dilutant mixes for rebreathers are prepared exactly the same way as mix for OC diving, with similar degrees of cleanliness. But one can argue that since the dilutant is at ambient pressure when it mixes with the O2, plain old scuba air would be fine when air is being used for the purpose. The only problem with this is that the possibility exists that using dirty air could contaminate the dilutant delivery system, and cause problems later on should a higher FO2 dilutant be used. But then who uses >50% dilutants in a CCR anyhow?

     
  10. diverdowndude

    diverdowndude Solo Diver

    # of Dives:
    Location: Mid Atlantic
    90
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    You meant to say: SLOW OPENING BRASS NEEDLE VALVES - didn't you?

    Adding ball valves in an oxygen system will increase the risk of adiabatic compression which may result in explosion or fire..... one of the reasons for oxygen cleaning the system is to reduce the possibility of foreign particles in any oxygen system causing adiabatic compression which may result in a explosion or fire.

    Hydrocarbons from any source in a oxygen system may contaminate the breathing air by creating undetected combustion resulting in carbon monoxide and/or carbon dioxide in the breathing gas or cause a fire and or explosion....

    Inexpensive Blending Courses are available from the best TDI etc. you might want to look into one of these..

    :wink:
     
    Last edited: Jul 26, 2009

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