Canadian Airgun Forum

On the Hatsan pcp I own there is a small (maybe 1mm) hole drilled nearly through the air tube near the air inlet. I take it to be a safety burst valve which is comforting. I have a new pressure regulator installed and set on the high side at 150 bar. I'm now getting 18 shots and would like to up that to 2 magazines or 20. That would mean adding more air to the tube than the recommended pressure of 200bar. I believe that recommendation is in part because the velocity of the pellet will fall when filled higher. My question is how high can I fill the air tube without fear of a pending mushroom bomb?
Ed.

Instead drop your reg pressure to 100 bar
Over filling the tube not the best practice.

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Walter

Every time you over-pressurize the tube you stress it a bit more. The damage is cumulative. Some day, sooner or later, it might rupture. That's a polite word for a big scary boom with potential for shrapnel. Stick to the maximum safe working pressure. They don't 'suggest' those limits for giggles, it's a basic safety issue.

All true but I have no doubt there would have to be a considerable safety margin built in. For example I was filling the air tube a while back and when it got to 200bar instead of turning the scuba tank off I accidently turned it up. The burst valve didn't blow but my eyes nearly burst out of my head when I saw the gauge. The Benjamin Discovery has a recommended fill of 2000psi and I've read on this forum how even the most experienced tuners fill it to 2500psi. I'm talking about only a 220bar-3200psi fill and no more on the Hatsan.
I realize I'm playing the devil's advocate AGAIN and overfilling is a practice us mature responsible members don't want to encourage as a fool may take it too far.

You're a grown up, right? So you take responsibility for your own actions. It's up to you. If you want to dance with aluminum cyclic fatigue, fine, go for it. Yes, of course they build in a safety margin. Typically 3:1, burst strength to working pressure. Some may build stronger than that. Without certain, specific knowledge of the exact tube and end caps in your particular case, I would strongly advise against testing those limits. Of course it's not likely to explode if you do it once, or 10 times, or maybe 100 times. But some day that accumulated fatigue may result in a catastrophic failure. What if you're shooting next to a child when that happens? What if it costs you an eye or worse? For what, a couple of extra shots? Why not do as Walter suggests and simply drop your regulator preset, lose a tiny amount of power per shot, and get a higher shot count? But hey, it's your funeral. Metals fatigue every time they're stress cycled, that's basic engineering. You can live in denial and pretend it won't happen to you, fine, go for it.

Fatigue will happen even with 200bar fills. The difference between 200 and 220bar is 9%. I know it's not linear but basically if mine fails at 1000 fills, at 200bar fills it will fail at 1090.
As for being safe why not fill to 190 or 180bar? Why not drive at the speed limit of less. Maybe you do.

How do you know?
See you dropped your tag line?

Safety is no accident

Sounds like your mind is made up. BTW who set your reg so high? Why?

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Walter

Yeah, it really doesn't seem like your initial post in this thread was really a question. You wanted an argument, not advice. When you got an argument you didn't like it, but your rebuttals are all guesswork, nothing based on actual knowledge or math. You're decided that you want those extra couple of shots per fill at a very high regulator setpoint and no amount of cautionary advice from others is likely to change your mind about that.

And you'll probably get away with it. It seems unlikely that the tube will ever blow up in your face. Just like it's unlikely, to use your example, that driving over the speed limit will result in one's death. Heck, most drivers don't die in fiery crashes, so there's your proof! But those who do die in fiery crashes... if one could go and ask them, you know, their ghosts or something, do you think they'd express second thoughts about driving too fast? What about that idiot who didn't properly pin his valve in his modified HiPAC 22xx build, putting the valve body through his upper leg while dismantling the silly thing under pressure? Even in his follow-up video where he calmed down a whole lot on his blaming of others for his stupidity, he continue to justify his actions based on having done "over 200 builds with no failures" or something to that effect. Play stupid games, win stupid prizes. We've got bouquets of plastic flowers lovingly tied to cast iron light poles all over Vancouver as testament to the fact that ignoring posted speed limits is not a brilliant idea. Drive down any highway and you'll sooner or later see the little crosses similarly decorated.

Aluminum stress cycling fatigue is a very thoroughly established phenomenon. Many steels are much more durable, and some aluminum alloys are more resistant than others. Rolling the dice has nothing to do with basic physics in this question. When expert airgun builders perform hydrostatic tests on tubes, the reports read pretty clearly. Deformation doesn't happen... doesn't happen... doesn't happen... then suddenly happens and the tubes fail. Which doesn't factor in the other elements such as thread engagement and material integrity of other parts under the same pressure. Did Hatsan build their tube to a much higher spec than normal? I doubt it. Why would they? To cost their customers higher shot counts? To spend a bit more money by using superior alloys and more metal? If they'd ever had a failure then perhaps their lawyer would recommend building in a 4:1 safety margin, but that probably hasn't happened. Again, go ahead and do what you were planning to do anyway. I'll shut up as you aren't listening, but post this because it just might discourage some other airgunner from blowing up his gun someday.

Aged - why not reduce the reg. setting to 100 Bar, 125 Bar or even at your current 150 bar, then do recognized & recommended work on the rifle's valve or hammer system to get your requisite # of shots & the velocity you desire. There is so much information for this sort of work, right here on CAF. The "Search" is your friend.

Or, perhaps you are simply attempting to get someone to recommend your foolishness so you will have a legal case against them if your actions result in damage. I keep having the "retirement' poll come to mind - the poll in the USA noted that 43% of the baby boomers polled expected to have a law suit fun their retirement, while in Canada, the numbers were lower - in the 20's.

CYA comes to mind along with giving what is normal for this site, being safe advice.

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Best Wishes
Daryl

I set it that high because I wanted the maximum consistent power for 2 magazines.
I've been working on my third tag line. How do you like it?

I've done valve an hammer spring adjustment in the past. It seems no matter how you get the desired power you pay the price in more air used. Increasing efficiency like the 5 screw mod is something I've been considering.
No I don't think about suing people. I just thought I'd hear from others who also over fill a little and I believe it happens often but everyone's so hush hush about it.

Metal fatigue is NOT linear, the closer you are to the failure point, the fewer cycles it takes to reduce the tensile strength until it coincides with the stress you are applying.... Once they are the same, failure occurs.... Steel and aluminum have completely different response curves to repeated stress cycles.... A vessel operating a 1/3 of it's calculated yield may go indefinitely (millions of cycles) before failure.... while the same vessel operating at 1/2 it's failure point, when new, may fail after 1000 cycles.... even less if there is a "stress riser" such as a sharp edge or crack to start with....

Bob

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Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal; Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!

Looks good
Tell me more of your setup. Whose reg? What fpe are you atnow?
As to the tube, the Hatsans have the worst tubing I have worked with so far. And they seal at a larger diameter so thinnest wall is where it seals. Compounding that the axial force is higher pushing on the threads.
I do not recall Hatsan or any other pcp with a safety valve.
Cheers

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Walter

If it's alum then is it safe to assume it's one of those small removable tanks like paintball use, like a mini scuba tank? If so then they should be cheap and you could just replace them if you felt the need, plus they can be pressure tested to give you an idea of their condition. I personally wouldn't worry about that pressure diff, but people rarely consider me a safe type. For example I always filled my Mrod to 3200 vs the 2900 max. Fyi I once had an 1800psi alum scuba tank that I had filled by a dive shop, when I connected the reg it read 3k! Now that concerned me and I released some pressure... My only real fear was dropping it like that. I assumed it would be ok if it didn't see abuse but Murphy's law dictates that would be the tank to have some bizarre accident and blow. Steel tanks I don't worry about nearly as much, carbon fiber or other misc wrapped tanks I fear above all but may be irrational.
I would work on getting the thing dialed in to max efficiency, like a hammer debouncer which gave my Mrod a LOT of extra shots. That gun also had the option of an extended tank which I had as well, so maybe they have one for yours? Or if an alum threaded mini scuba tank tehn maybe a larger one is available? I'm diggin the new Hatsan with two tanks, which I'm glad they did but wonder why it took so long? They also have mini CF tanks now, so a 4500tank with a reg would be the ultimate!? Imagine a nice fat CF of say 400cc regged to 2500. Yum...
Maybe rsterne has one, or can chime in on the possibilities and shot count?
rsterne: Every time I see your name I can't help but think of this in Heavy Metal: http://tinyurl.com/o3xolej Great scene!

Seems likely he's talking about one of these Hatsan cylinders, not a bottle gun at all:
http://store.airgunforum.ca/product_inf ... ucts_id=67