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PostPosted: Tue Mar 08, 2016 6:11 pm 
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Additional information, March 2015....

Recently one of our GTA members, Ribbonstone, noticed a slight bulging of the end of the tube on his QB79, in the thin area adjacent to the screw holes for securing the tank block.... The gun was operated for a time at 1250 psi.... In response, I have done an analysis of the tank block attachment, which is detailed in this thread....

http://www.gatewaytoairguns.org/GTA/ind ... pic=105712.

If you are building a QB79 HPA conversion of any kind, you should read that thread.... If you are using more pressure than the 1100 psi factory setting for a Ninja SHP regulator, I am now recommending that you pin the tank block with two additional 4mm or 8-32 screws, or a 5/32" shear pin, between the O-rings.... If you want to be more conservative, you might want to pin the block when using the SHP regulator.... or even with a standard 850 psi Paintball regulator.... Complete information is in that thread....

Bob

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PostPosted: Thu Mar 10, 2016 10:58 am 
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A comment here.
The so called "web" incorrect wording, it is known as a "TEAR OUT" when apllied to a pressure description. The tear out was engineered to fatigue cycling from Co2 pressures not that of compressed air in excess of 850psi of a standard operating pressure. Which mulitiplies and compounded ever time the pressure tube is refilled. Pressure tubing was designed for Co2 applications not high pressure as that used under compressed air applications. Tube body thickness comes into play here as well. The average being 0.062 - 0.068 for Co2, thicker for PCP aplications.

I have repeated this before upon tear out. If a #8 high tensle fastener is 0.162" in dia then tear out must be 1 1/2X that dia. Equating to 0.243" a safety factor almost never taken into an account by those who want to modify. To error more upon caution is a safe thinking practice. Thats MHO, here.

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PostPosted: Thu Mar 10, 2016 12:46 pm 
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Not quite sure I understand.... Are you saying that using 850 psi air, which is more likely to stay at that pressure indefinitely, because of the regulator, is harder on the tube than using CO2, which will go from zero to 850 psi, and much higher in hot weather, every time you refill the tank?.... My understanding of fatigue was that it is due to cycling, not a constantly applied force.... If I have that wrong, and 850 psi of HPA is somehow harder on the gun than using CO2, which not only fluctuates in pressure but in temperature, please explain.... I'm talking about having a 1.8K burst disc fitted in the regulator, of course....

I agree that the tearout length needs to be improved on the QB79, which is why I have recommended pinning the tank block if you are using more than CO2 pressures.... It appears we agree on that point.... It would have been great if the QB79 had been engineered for a 3.5:1 safety margin at 1900 psi, which CO2 can hit on a hot day.... but unfortunately, that does not appear to be the case.... at least from my calculations....

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!


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PostPosted: Fri Mar 11, 2016 1:46 am 
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I expect Kim is largely talking about non-regulated setups with higher pressure (1,500psi and more) and about regulated bottle setups where the setpoint is higher than 850psi. Doubt he's talking about the particular gas mixture involved, though plainly the CO2 on a hot day scenario is something one needs to factor in with this stuff. Some guys insist on setting their regulators for 1,400psi or even 1,500psi, resulting in something getting close to double the 850psi standard operating pressure with CO2. Burst disc or no, that can spell trouble with inexpertly pinned inserts, especially when the remaining steel beyond the pin becomes too shallow. Seems to me that quite often more attention gets given to bumping up the pressure and maximizing plenum volume than to this basic safety concern.

It is good however, seeing the renewed interest in safety cropping up with QB** mods and 22** mods since a couple of incidents have brought to light the potential hazards, within the past year. Perhaps such events might help bring hobbyists a sharper understanding of the real dangers involved with pressure vessels and home made adaptations, encouraging more study before getting out the hand drill etc.


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PostPosted: Fri Mar 11, 2016 2:06 pm 
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rsterne wrote:
Not quite sure I understand.... Are you saying that using 850 psi air, which is more likely to stay at that pressure indefinitely, because of the regulator, is harder on the tube than using CO2, which will go from zero to 850 psi, and much higher in hot weather, every time you refill the tank?.... My understanding of fatigue was that it is due to cycling, not a constantly applied force.... If I have that wrong, and 850 psi of HPA is somehow harder on the gun than using CO2, which not only fluctuates in pressure but in temperature, please explain.... I'm talking about having a 1.8K burst disc fitted in the regulator, of course....

I agree that the tearout length needs to be improved on the QB79, which is why I have recommended pinning the tank block if you are using more than CO2 pressures.... It appears we agree on that point.... It would have been great if the QB79 had been engineered for a 3.5:1 safety margin at 1900 psi, which CO2 can hit on a hot day.... but unfortunately, that does not appear to be the case.... at least from my calculations....

Bob


Well while scratching my head in reading this over. I fail to understand where your mind is to come up with IMO fabricated implication as to what I posted :?:

IMHO the 2 most dangerous platforms that have come to be are the QB and the 22xx. There has become far too much misrepresented information upon the web. Having budget minded tinkers to add to the mix only time will tell upon what accidents or close calls really get reported upon forums. Is my take upon the subject already.

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PostPosted: Fri Mar 11, 2016 2:15 pm 
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Whitewolf wrote:
Well while scratching my head in reading this over. I fail to understand where your mind is to come up with IMO fabricated implication as to what I posted :?:


My apologies. Seems I've offended you, but all I was trying to do was clarify. Guess I misunderstood completely your intention... and your comments today do nothing to un-muddy the waters for me. Oh well, I'll shut up about what you said as you plainly speak for yourself (or not so plainly as the case seems to be from my end, and Bob's I guess). If you're saying no one but 'professional' tinkerers should play with QB/22** airguns, well, good luck stopping hobbyists. Not going to happen.


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PostPosted: Fri Mar 11, 2016 2:28 pm 
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Kim, I didn't mean to get your back up.... but I truly don't understand what you are trying to say.... I was merely asking for a clarification of your post.... Believe me, I'm not trying to put words in your mouth....

Please read what you wrote, my questions regard it.... and reply if you care to.... If I understand something incorrectly, I want to know why....

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!


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PostPosted: Fri Mar 11, 2016 3:27 pm 
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The way I read it, I believe that WhiteWolf's comments were aimed at the "1250psi" and "1100psi" figures from your "update" post. . .

I feel it that your comments, and expressed concerns, are parallel. . . .

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PostPosted: Mon Mar 14, 2016 12:44 pm 
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Gerards first expressed statement is on par with what I posted. As to your added assumptions are not. Bob we have seen the increase of safety margins and continued changes upon your builds over the last few years.
From my world in the Oil & Gas Industry this is just second nature of 30+ yrs in the industry. My earned arrogance as some may interpret.

Fluctuations in pressure create cycling fatigues. That of a consistant pressure only contributes a stress upon the metals operational safety margin.
As for the modding tinkers', just a matter of, HAVE RESPECT FOR YOUR WELL BEING when taking the path of high pressure air apllications upon engineered Co2 platforms. There is alot of poor misinformation or interpreted out there. Doing some research will never hurt you, a poor choice of the information may.
Thats my opinion upon the topic of which many can not dispute.
SAFETY FIRST. Which is that of this posting upon this, tis it not.
Regards

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PostPosted: Tue Mar 15, 2016 4:54 am 
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This is brilliant. I guess the only thing to figure out now is where to find a QB79 in Canada. :cry:


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