Here's what happens during a "hydro" test

Forums Air Tanks, Pumps, Compressors, & Filters Here's what happens during a "hydro" test

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    Tominco
    Participant
    Member

    I had an opportunity to watch some FD bottles get hydro’d so, I thought I’d share the process with all of you. 
    The first thing the tech will do is perform a visual inspection of the outside of the tank. 

    The next thing is to jot down the bottle info for his company’s records. 

    Then he pulls the valve off the bottle and takes a peek inside. (sorry no pic but, there’s not much to see. They’re silver inside.)
    The next step is to fill the bottle with water and attach it to his lift assist. They’re not particularly heavy but, this keeps them upright for filling with water and avoids an accidental drop. 

    Down into the dunk tank it goes. The water will be topped off and the lid locks in place. 

    Now he pressurizes the tank to ~7500 psi. DO NOT ATTEMPT! These bottles will not hold for very long at those pressures!
    When he does this, the bottle expands. 
    There is a hose that goes from the outside water to a little measuring cup on his workbench. When the bottle expands it pushes a small amount of this water out and up the tube. He notes the level of the water before the pressure, then he notes the level of the water during pressurization, and once more when he lets the pressure off. He’s only at 7500psi until the expansion of the bottle settles. Then he cuts the pressure off. This is only takes about 3-5 seconds. 

    Now the attachment comes off the bottle and it is turned upside down to drain the water out. There’s tubes blowing warm air into the bottles to speed up the process. 

    Once that is completed, he writes up a label and epoxies it to the outside of the bottle. 

    The o-ring gets replaced and the valve is screwed back on. 100ft lbs (If I remember correctly). (That little brass tube is the reason why turning the bottles upside down and opening them will not drain them.)

    The bottle is now hydro’d! Ready for a fill and another 5 years of service. :)
    Thanks goes to Bob and best wishes for your retirement! 
    Tom

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    JohnL57
    Participant
    Member

    Very informative, I’ve wondered about the process. Thanks for posting it!
    John

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    Oregun
    Participant
    Member

    Cool post, Tom!
    Does anyone know the ~cost of a hydro test?  

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    Tominco
    Participant
    Member

    (Obviously, prices may vary.)
    I think I paid ~$30 last time I got a bottle hydro’d.

    Thanks guys, I’m glad you enjoyed it and were able to learn new information. 
    I’m after my 4th dot so, feel free to + away! lol! :) 
    Tom

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    bltefft
    Participant
    Member

    Very interesting.  I wonder if taking the tank up to 7500 psi has any negative impact on the integrity of the tank?  I mean, does that lessen the life-span of the tank.  Maybe that’s why they only have a 15-yr life span – enough to do two hydro tests – one at 5 years of age and the second at 10 years of age – no third one, because the tank is “dead”.

    I’d think a tank was more likely to fail the 2nd hydro.  Just wondering.

    Bobby

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    jlc
    Participant
    Member

    I had two steel scuba tanks hydroed, took them to the facility myself, 21 dollars each., 3 day turn around during Xmas week.  

    Take them to a dive shop the price will prob be doubled and the turn around time tripled.  

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    iride
    Spectator
    Spectator

    I would like to know what % fail and the age of the tanks that fail
    I know over the big pond the life of a Carbon fiber tank is a lot longer.
    Mike

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    bltefft
    Participant
    Member

    “iride”I would like to know what % fail and the age of the tanks that fail
    I know over the big pond the life of a Carbon fiber tank is a lot longer.
    Mike

    
I don’t know, but do you happen to know the life expectancy of a carbon fiber tank over there?

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    Tominco
    Participant
    Member

    I’ve heard they’re good for 30 years across the pond. But, I have no proof of this. 
    There are 30 year bottles available in the states but, they cost twice as much. They also go through a different testing process at their 15th year, which has a good chance of taking them out of service, on top of the normal hydro every 5 years. I got this info from talking with “Bob”.
    In my opinion, it’s not worth it. 
    Tom

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