Love my new 0.25ci HPA tank

[nervoustrigger]

Thanks for the heads up Bob. I'm not much on assumptions when it comes to safety so thanks for the information.  I ordered spares so I can test by carrying it up to rupture pressure.  I did not know about the 40% overage on SCUBA discs so it sounds like what I ordered will not give me the desired result.  Of course if the threads are not compatible then all bets are off.  Oh well, either way it's a $30 learning experience. 

So frustrating that the 1.8k disks won't even let me get within 85% of rated, and come to find out other 3/8" discs are designed to sustain 140% of rated.

[rsterne]

My understanding is that paintball discs are supposed to be plus-minus 10% (or maybe only minus 10%), and I have certainly had some 1.8K let go at 1600, or at 1500 cold and then warmed up.... SCUBA tank discs, as I say, are apparently marked for the tank they are supposed to fit onto, and designed to rupture 40% higher than that, but 20% below the hydrotest pressure (which is 5/3res = 160% of MSWP).... The two systems of marking are different, it's not so much that one is under spec and the other over spec....

Bob

[Norton1]

If you have never tinkered with something trying to get it set just right, it involves a lot of taking it apart, adjust it, re assemble, test.
Then do it all over again until you get it where you want it.

Sometimes I thought my real job was taking apart and reassembling my air rifle.

I would be at work thinking,
 ok, if it wasn't this, then it has to be this, then when you get home, it is in front of you until you go to bed, you get to where you can assemble it in your sleep.

And you get to know every part by a four letter word first name basis..

So I m not the only one.... 

Nope - not even close -

[nervoustrigger]

I received the burst disks from onlinescuba.com yesterday.   They are indeed as Bob stated.  For example, the one rated for 2400psi working pressure is imprinted with "4000" on the housing (a 5/3 ratio) so they are not suitable for my purposes.  But it was immediately apparent that these were made differently; the diaphragms themselves are accessible and replaceable so I decided to test some common materials to failure to see if I could come up with something that will rupture around 2000psi.

The first candidate was a Coke can measuring 0.005" thick.  I used a hollow punch to create a small disk from it and assembled it to the high pressure side of the regulator and began pumping.  When the pressure climbed between 2000 and 2100psi, it ruptured.  I then repeated the test and the second one ruptured between 2000 and 2100psi as well.

Very nice.  I proceeded to replace the diaphragm and installed it on the regulated side of Andy's rifle and got it pumped up last night.  I checked this morning and the gun is still charged.   Neither of the 1.8k disks lasted more than a couple of hours so this is promising.  I want to be sure it will hold up to a temperature-induced pressure rise so I plan to let it heat up outside today and see if it holds.

If anyone else attempts to make their own burst diaphragm, please be sure you understand what you are doing.  High pressure air is very dangerous.  I would not assume another soda can (even of the same brand) to have the same ultimate tensile strength.  Definitely test to failure to confirm before you entrust your safety to it.

[nervoustrigger]

Looking good.  I placed the rifle in the sunshine for 1 hour to drive up the reservoir pressure.  It was the hottest part of the day...no clouds, sun beating down hard.  The metal parts were so hot that I did not want to hold them for more than about 3 seconds.  The burst disk held up beautifully. 

[rsterne]

Like you said, risky business, but better than using a 3K one, if you are confident in your testing.... It's not only the tensile strength of the can metal, though, but the diameter of the hole that would make a HUGE difference....

Bob

[nervoustrigger]

It's not only the tensile strength of the can metal, though, but the diameter of the hole that would make a HUGE difference....

Right, thanks for the reminder.  I meant to include that the aperture measured 0.153".

Also, for the sake of completeness I wanted to note I added a bleeder screw and an accompanying O-ring seat to the fill adapter.  A better solution was offered by bigtinboat which in an adapter has a built-in automatic relief feature when you back off the hand screw.  Only about $10 with shipping on ebay:
http://www.ebay.com/itm/CO2-FILL-ADAPTER-REMOTE-ON-OFF-DEGAS-WHEN-UNSCREW-AMERICAN-MADE-/271945664365?hash=item3f5139876d

[Buldawg76]

I have the same ASA with the built in bleed off and had to drill the knob to install a t handle to it to be able to rotate the knob to bleed off the pressure. at pressure over about 5oo psi it is had to turn and the threads will start to wear and deform even with extreme pressure lube on them. There is just to much pressure against the knob to allow it to rotate easily to bleed pressure.

Mike