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HP drop on inhalation

Discussion in 'Regulators' started by Gyula Fora, Jul 21, 2020.

  1. Gyula Fora

    Gyula Fora Angel Fish

    # of Dives: 100 - 199
    Location: Sweden
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    Hi all!

    Yesterday I used a slightly older Apeks reg and I noticed that the HP gauge dipped considerably every time I inhaled.

    I double checked that the tank was completely open and the reg seemed to give enough air as far as I could tell.

    Is this normal with some first stage designs?

    Thanks!
     
  2. tbone1004

    tbone1004 Technical Instructor ScubaBoard Supporter

    # of Dives: I'm a Fish!
    Location: Greenville, South Carolina, United States
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    absolutely not normal and you should not dive a regulator that's exhibiting that behavior. Check it on another tank as it may be something in the dip tube. If it stays with the regulator, then it needs service and is likely in need of a new filter
     
    abnfrog, Bob DBF, wnissen and 3 others like this.
  3. rsingler

    rsingler Scuba Instructor, Tinkerer in Brass Staff Member ScubaBoard Sponsor

    # of Dives: 500 - 999
    Location: Napa, California
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    Typically a first stage will show a dynamic drop of 8-20 psi on purge/max flow. On inhalation, it is usually much less.
    An IP drop indicates inadequate tank gas getting to the first stage, or markedly increased internal friction from a HP oring, perhaps.

    If the tank valve was wide open (or on two tanks, to rule out a valve problem), then I would think either a very blocked sintered metal filter where tank air first enters (like from grease or verdigris corrosion from salt water), or a component about to fail.

    Lol, tbone beat me to it!
     
    Hoyden, taimen, Bigbella and 2 others like this.
  4. halocline

    halocline Solo Diver

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    No it's not normal. It's probably not a regulator issue unless (I guess) it could be a clogged filter. Try a different tank, then if you are able to remove the filter for testing it, try it without the filter. If it still does it I'm stumped.
     
    couv likes this.
  5. couv

    couv Instructor, Scuba

    # of Dives: 1,000 - 2,499
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    Damn kids type too fast for me.
     
  6. Gyula Fora

    Gyula Fora Angel Fish

    # of Dives: 100 - 199
    Location: Sweden
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    Thanks guys for the info, I will try it on a different tank and see what happens! I will post the outcome
     
    RainPilot likes this.
  7. herman

    herman Divemaster

    # of Dives: 500 - 999
    Location: Raleigh,North Carolina
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    Not likely I know but I'll throw it out there just in case. That is normal if you are using a J valve in the dive position. I see it fairly often but then I often use vintage tanks with operable J valves a lot of the time. Otherwise, I agree with the above.
     
    jgttrey, Bob DBF, halocline and 4 others like this.
  8. Gyula Fora

    Gyula Fora Angel Fish

    # of Dives: 100 - 199
    Location: Sweden
    32
    10
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    That is exactly what I was using, it’s a very old tank/valve. So it could be a valve problem then, interesting. Why would it happen with the J valves?
     
  9. herman

    herman Divemaster

    # of Dives: 500 - 999
    Location: Raleigh,North Carolina
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    Dang, that was your issue. :)
    That is NORMAL for a properly working J valve in the dive position. When in the dive position, the valve has a seat that closes under spring pressure and is opened by the differential pressure when you breath. There is always some pressure drop across that seat, the amount depends on what the tank pressure is and the design of the valve. At some point, usually around 300-500 psi breathing will become difficult by design, which was your warning to end the dive. In the early days of diving there were no SPG's so this was you low pressure warning. If you set the tank to reserve (down position if it's set up correctly) it should not show a pressure drop if it's working properly. This may help.

    I dive vintage tanks and use these valves fairly often so it's something I see more than most people, Couv may have to be removed from the vintage dive community for missing this. :) Dive the tank in the down position with modern regs and you will be fine.....or dive it as intended, ignore the SPG swings and see how it works to warn you of low air when your tank gets low.
     
    HKGuns, buddhasummer, Kupu and 7 others like this.
  10. Gyula Fora

    Gyula Fora Angel Fish

    # of Dives: 100 - 199
    Location: Sweden
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    10
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    Thanks a lot, this is pretty sweet info, highly appreciated!

    It’s always nice to learn how the the designs have evolved over time to meet the requirements.
     

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