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Unexpected rapid ascent

Discussion in 'Advanced Scuba Discussions' started by ladyfishdvr, May 12, 2014.

  1. scagrotto

    scagrotto Barracuda

    # of Dives: 500 - 999
    Location: Hudson Valley
    277
    204
    43
    Schrader valves open towards the pressure they are intended to contain, which means towards the 1st stage (or the tires on your car), so the pressure holds the valve closed. The higher the pressure, the higher the resistance to opening. Excessively high pressure might cause leaking or even complete failure (it's certainly not designed for 3000 PSI), but it wouldn't open the valve.

    I would assume that an Air 2 uses the same sort of inflator valve as others. Even if it isn't the same, it's still independent of the 2nd stage. They're just two separate valves attached to the same hose.
     
  2. ladyfishdvr

    ladyfishdvr Nassau Grouper

    # of Dives: 50 - 99
    Location: Rochester NY USA
    160
    79
    28
    One cannot control where the geese go, and there is some exposure to it when getting in and out of the water at the quarry. But consider that fish live underwater and have similar bodily functions and you dive in that!:cool2:
     
  3. Bob DBF

    Bob DBF Solo Diver

    # of Dives: I just don't log dives
    Location: NorCal
    7,338
    9,030
    113
    The Schrader valve is only used to prevent airflow when removed from the BC inflator. Air 2 and other integrated octo-inflator combo's do not use Schrader valves because they restrict airflow too much for proper breathing, and therefore use a connector similar to an air tool quick coupler which will provide the necessary air flow. The quick coupler is also only used to prevent airflow when the hose is disconnected.

    The inflator valve is under the button you push to inflate the BC.

    That is how my Oceanic version is built, but I haven't torn an Air 2 apart. It would depend upon whether the inflator was built to have IP hold the valve shut or a spring, lets say for simplicity, to hold it shut against IP. In the first case you would use pressure on the button to overcome IP and open the valve, in the second case the pressure on the button would overcome spring pressure to open the valve, but so would a high IP. The first example is safer as there is very little chance of an accidental inflation.

    We need a comment from someone who has had an Air 2 apart.



    Bob
    -------------------
    You only need two tools in life – WD40 and Duct Tape. If it doesn’t move and should, use the WD40. If it shouldn’t move and does, use the Duct Tape.
     
    ladyfishdvr likes this.
  4. scagrotto

    scagrotto Barracuda

    # of Dives: 500 - 999
    Location: Hudson Valley
    277
    204
    43
    I'm wondering if you're referring to the valve in the quick coupler on the LP hose, but that makes this puzzling:
    Maybe it's just a matter of terminology? There are three valves all together, and none are identical to the schrader valve on a car tire. I probably wouldn't have thought of any of them as schrader valves, other than hearing so many references to BC's using schrader valves. I'd describe them as poppet valves (Schrader being a type of poppet valve), but whatever term is used all three are fairly similar as I understand them.

    There's the dump valve (clearly irrelevant to the discussion), the valve in the quick coupler, and the inflator valve. If the LP hose is connected and there hasn't been some kind of failure then the valve in the coupler will be open whether IP is correct, incorrect, or 0 psi as a result of an empty tank.

    I was under the impression that the inflator valve is (at least similar to) a schrader valve. The only question is whether it opens upstream or downstream. The dump valve would also appear to be a schrader-like valve, though obviously larger than the standard tire valve. I haven't taken one apart, but the design certainly appears to open upstream against pressure in both cases. In that case too-high IP will close the inflator valve with more force rather than cause a free flow, which was the relevant point of my post.

    The quick coupler on every non-integrated BC I've seen appears to be similar to the one for my air tools. Though it doesn't apply to my equipment I'd be curious how the connector on an Air2 prevents airflow if it doesn't use a shrader valve or something that's quite similar.
     
  5. copter53

    copter53 Solo Diver

    # of Dives: 500 - 999
    Location: Panama City, Florida/ Gainesville, FL
    121
    6
    18
    Why are you diving with a bcd anyways when you can just use a backpack. Simplicity does not falter.


     
  6. Bob DBF

    Bob DBF Solo Diver

    # of Dives: I just don't log dives
    Location: NorCal
    7,338
    9,030
    113
    It's probably my explanation, it is hard to make a technical description quickly.

    The Schrader valve (also called American valve) is a brand of pneumatic tire valve used on virtually every motor vehicle in the world today. The Schrader company, for which it was named, was founded in 1844 by August Schrader. The original Schrader valve design was patented in the United States in 1893.The Schrader valve consists of a valve stem into which a valve core is threaded, and is used on virtually all automobile tires and motorcycle tires and most wider rimmed bicycle tires. The valve core is a poppet valve assisted by a spring.

    The Schrader valve is located in the inflator hose, and can be replaced by a tire tube valve. It is opened and stays open when connected to the BC, providing IP to the inflator valve.

    You are correct.

    The ones I have pulled apart open upstream and, in that way, act like Schrader valves. In that case too-high IP will close the inflator valve with more force rather than cause a free flow.

    Externally the Schrader connector looks like the air tool connector, but notice on the male connection there is a tab, which also would restrict airflow, that engages the Schrader valve in the female connector, except the Schrader valve restricts the air more. On an air tool male connection there is no restriction and as you look into the female connection there is no schrader valve mechanism, they use a different valve in order to pass more air that is necessary to run the tool. It is the same in function as a Schrader valve but is different in design and use, however this type of connector is used in Air 2 type applications because of the need for greater airflow.


    Check out this manual for the inflator:
    http://www.aqualung.com/militaryandprofessional/product_information/Powerline_DualValve_rev09_09.pdf



    Bob
    ---------------------------------
    There is no problem that can't be solved with a liberal application of sex, tequila, money, duct tape, or high explosives, not necessarily in that order.
     
  7. scagrotto

    scagrotto Barracuda

    # of Dives: 500 - 999
    Location: Hudson Valley
    277
    204
    43
    It's largely my unfamiliarity with the finer details (I'm mechanically inclined but not a service tech), and interpreting your first response as more of a correction to my point about pressure closing the valve than an explanation of the finer details. My first post was correct about the function of a schrader valve, but I intended to describe the functioning of the inflator valve, and not the valve in the LP hose.

    That's the important distinction that I missed in your first post. Since we're discussing the valves I thought you were describing some restriction in the female fitting. Of course now I'm curious about the minimum cross sectional area in the the female fitting, too. It looks like it's about the same as the male, but has the valve mechanism which I would expect to significantly reduce area. Maybe I'll have to tear apart one from a leaky tool hose.

    As it happens, I'm in possession of a friend's (ancient) Air2, so I looked at that, and everything I can see in its assembled state appears (of course) to be identical to my air tool fittings. I also took a closer look than usual at the connector on my own LP hose. I never knew that little pin was down there. I'd be slightly embarrassed that the external appearance made me [-]think[/-] assume it was essentially identical to the air tool connector if I wasn't comfortable that if it works I don't need to know and a real service tech can fix it or I can buy anew one if it doesn't work. Of course I'm glad to learn these details.

    I expect that different companies may use slightly different designs, but on page 10 of the manual, picture 13 shows what looks very much like a schrader valve (though not just the core) as the functional part of the inflator valve. In the parts list it's called a valve core, as is the valve in the female quick coupler, though they have different part numbers and obviously aren't identical. Perhaps it just comes down very specific terminology and exactly how specific the definition of a schrader valve is. Schrader International (and other companies, I'm sure - "Schrader valve" appears to no longer be a trade mark) markets a lot of valves for different purposes that have similar appearance and seem to work in a very similar fashion to the tire valve. It looks to me like it's mostly a matter of putting a core that functions the same as a tire valve core into various assemblies to make a complete valve body.
     
  8. Bob DBF

    Bob DBF Solo Diver

    # of Dives: I just don't log dives
    Location: NorCal
    7,338
    9,030
    113
    That's the ticket, a Schrader valve has a very specific definition and is the same now as it was when he invented it, regardless of manufacturer. The pin you saw in the connector was the tip of the valve.

    As for the inflator valve, it looks and probably is very similar to the Schrader, however that part was not in the inflator I rebuilt. The link was found at random and sent to show the internals to you so I didn't look through the manual well before I sent the link. My bad, good catch. Keep your eye out for some cheap or free junk gear and start taking it apart and try to fix it, you would probably have a ball and it all translates to new gear in time.



    Bob
    ---------------------------------
    Always use the right tool for the job. A hammer is the right tool for any job. Anything can be used as a hammer.
     
  9. ladyfishdvr

    ladyfishdvr Nassau Grouper

    # of Dives: 50 - 99
    Location: Rochester NY USA
    160
    79
    28
    Well I had the BC checked out and the air 2 was in perfect working order. So the regulator froze, it came out the air2 first inflated the BC then free flowed from my second stage.

    On the upside, I was able to get the profile of the dive downloaded finally on my windows 8 pc and it appears I was successful in slowing my ascent down from 80 feet up to about 20 feet and only then at 20 feet did I shoot up too fast. That coupled with the shortness of the dive was in my favor.

    Lessons learned are to not dive a BC with an air2 in water in the low 40s and to use a cold water sealed regulator to prevent a freezeup.
     
    j yaeger likes this.
  10. j yaeger

    j yaeger PADI Pro

    # of Dives:
    Location: Canton, New York, United States
    1,501
    310
    0
    i ice dive with my air source (sea quest)
    it's the 1st stage that needs to be suited to the cold water!
    have fun
    yaeg
     

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