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Thread: HPA from Scuba tank Many questions

  1. #1
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    HPA from Scuba tank Many questions

    I am thinking about getting the new end cap/ foster valve for my QB78 and investing in a scuba tank for HPA refills.

    Can someone here please help me get a list together of everything I will need (valves, gauges, transfer hoses ect ect)

    How many PSI will the stock tube SAFELY hold?

    Are extended tubes that hold up to 3000 PSI still available?

    Lots of questions. I am in no rush but want to educate myself a bit more.

    Thanks all.

  2. #2
    Moderator rsterne's Avatar
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    I would recommend that any HPA conversion of a QB7X incorporate a 1.8K burst disc to limit the pressure to 1800 psi.... That means you will be limited to a regulator setpoint of 1500-1600....

    Bob
    Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
    Airsonal: Too many to count!

  3. #3
    Senior Member remtom1200's Avatar
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    I put a 3k burst in my 13ci ninja thinking I was gonna be operating at 1800psi. Turns out my operating psi will be 1600 so back in goes the 1.8k. I am using the original Qb tube cut with a bottle adapter block.
    For every mile of road, there's two miles of ditch

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    Please bear with me...

    Burst disk?

    Please understand I am a TOTAL newb for HPA conversions.

    I just saw how cheap scuba tanks are new and they come with 20 fills!

  5. #5
    Moderator rsterne's Avatar
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    A burst disc is a small disco of copper mounted in a hollow bolt that will rupture if the pressure is above a certain value.... They are commonly available in 1.8K (1800 psi), 3K, 5K, and 7.5K (7500 psi) and normally they are used at about 5/3 of the rated pressure of the tank, which is also the pressure they are hydrostatically tested to.... eg. a 3000 psi tank is tested to 5000 psi, and has a 5K burst disc fitted to prevent it ever being filled beyond that....

    The QB series guns were designed for CO2, which can reach ~1900 psi at 120*F, and even at that level they are being pushed, as they normally run about 850 psi.... It is therefore pretty widely accepted that the stock tube on a Qb should be protected by a 1.8K burst disc on the outlet side of the HPA regulator....

    Bob
    Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
    Airsonal: Too many to count!

  6. #6
    Senior Member remtom1200's Avatar
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    For an actual display of how a burst disc works....roll up you windows in your minivan on the hottest day of the summer, throw a fully charged C02 tank on the front seat and watch and listen what happens in a short amount of time. On your tank(neck) will be little bolt like brass or chrome things with a bolt like head. If you look closley you will see stamped 1.8K, or 3K, and a 5K for 3000psi tanks. A 4500 psi tank will usually have a 1.8K, or 3K, and a 7.5K stamped on the little bolt like looking things. The lower number one is the output psi safety, and the larger is the input psi safety. If any one of these are subjected to psi close to what is stamped on them they rupture and vent the air before harm to bystanders.
    For every mile of road, there's two miles of ditch

  7. #7
    Senior Member remtom1200's Avatar
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    Sorry, took too long here on dialup
    For every mile of road, there's two miles of ditch

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    Senior Member SeanMP's Avatar
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    Pharoah
    I'm going to suggest a slightly different setup first. The reason for this is QB tubes fill so fast that it's hard to fill them straight from a 3000 psi tank using the time honored whip the valve closed at 1600 psi technique. Obviously it is do-able and you can put a tiny metering orifice inline to slow the fill down as well but....filling a regulated buddy bottle from the SCUBA I think is the easiest way to go. A full buddy bottle is also very portable and good for about 500 shots.

    So here is a list of what you need to do that in the order they fall inline.
    1. SCUBA Tank
    2. Fill yoke http://www.ebay.ca/itm/PAINTBALL-BRA...1#ht_510wt_906
    3. Whip hose http://scopesandammo.com/storefront/...-30-inch-p-309
    4. Buddy bottle http://www.ebay.ca/itm/PAINTBALL-BRA...#ht_1820wt_906 (You would install your 1.8K burst disc in the provided spot on the regulator http://scopesandammo.com/storefront/...st-discs-p-313 )
    5. Buddy bottle to gun hose http://scopesandammo.com/storefront/...oil-hose-p-274
    Where possible I have used scopesandammo links but Eric's policy is if its not in stock he takes it off the website so I used Ebay links to items he has carried in the past.
    Last edited by SeanMP; Feb 18 2013 at 01:31 AM.
    Sean

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    Thanks Sean.

    This REALLY gets me looking in the right direction. I think you are right with a remote tank.

  10. #10
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    SeanMP..

    You said I should get about 500 shots from a buddy bottle. What size bottle?

    I am looking into some of the Ninja brand adjustable regulator bottles and they come in various sizes.

    they come in 13/35/48 cubic inch bottles. approx what cubic inch size bottle were you referencing when you said 500 shots?

    Thanks!

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