SCBA carbon tanks

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@steve-l Considering that your profile states that you’re in Europe, I don’t know of a lot of options for you to shop for a bulky item of this size. This is the best online retailer I can think to suggest to you at the moment. https://www.krale.shop/us/sport-shooting/shooting-accessories/charging-cylinders/
9L is the largest common size I can think of hearing about for a carbon fiber SCBA tank that airgunners tote or cart around. I use a 74CuFt/6.8L tank. There’s a post I read recently I’d like to find to share with you on SCBA tank sizes. Give me a moment to locate it. 
Here’s the thread I had in mind https://www.airgunnation.com/topic/a-guide-to-compare-carbon-fiber-tank-sizes/

While searching for it I came across other threads, one of which you’ve already commented in.

Hopefully the maths in this post https://www.airgunnation.com/topic/please-help-me-do-the-math/ can help answer your current question and the issue you took with the OP’s explanation of a relative question in this post https://www.airgunnation.com/topic/carbon-fiber-air-tank-liter-to-cubic-feet-conversion/
 
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Currently I use two 12 liter scuba tanks. I would not like to go smaller. I do most of my shooting at home and I have a Bauer 4 cyl. compressor to charge them. The issue is the weight of the tanks, they are heavy. At home neither the weight or the max pressure is not so much of an issue. Now, 12 liters of 235 Bar air will allow me to shoot all day with my .25 Crown or almost a month shooting 20 rounds a day with my PP700. However, toting these tanks around in and out of a car and on to a range is a real PIA. I don't see any value in higher pressure in my case. It puts unnecessary stress on the guns for just a few extra shots, but the weight difference between 18 kgs. and 7 kgs is significant. KRALE does carry 12 liter steel tanks, but not CF larger than 6.8. liter. I did find 12 liter CF tanks being sold, but they are very expensive, around $800 delivered with duty and taxes. I was hoping for a better deal.
 
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@steve-l I see. Sounds like you have a nice setup. Yes, I saw the steel tanks Krale offers. As for shooting at a higher pressure, you raise an interesting point. I’m not so knowledgeable on how fill pressures can stress airguns. Hopefully some of our European members in proximity to you come up with some suggestions you can use regarding larger carbon fiber tanks. $800 for a 12L CF SCBA tank after shipping, duty, and taxes doesn’t sound so bad to me. Smaller tanks here go for around $700-$850 after shipping and taxes. I’m glad I read this post. I learned a few things. Good luck in your search. 
 
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Ezana4CE,

If I charge my .25 Crown to 235 Bar , I get 74 shots before my tank pressure reaches my regulator pressure of 135 Bar. If I charge the Crown to 200 Bar, I get about 60 shots. I recharge the Crown from 135 Bar to 235 Bar in under 30 seconds. I do this all day from my 12 liter Scuba bottle and my bottle is still above 135 Bar. I then take the bottle to my Bauer compressor and recharge the bottle back to 235 Bar in less than 20 minutes, much less actually. I'm being conservative. I don't see a significant advantage to use higher pressure. The higher the bottle pressure, the more stress there is on the regulator to bring down the pressure to 135 Bar. That is why FX has implemented the second regular along with the new gun bottle pressure of 300 Bar. I don't know what that does to the total shot count, maybe in my case perhaps 100 shots? I suspect increasing the chamber volume and decreasing the regulator pressure would keep the same pellet performance and increase the shot count more effectively. I spend far more time placing pellets in my magazines than I do charging the gun. I mean to me there is little advantage in recharging the gun after 74 shots or 50 shots, if recharging time is only 30 seconds.
 
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Ezana4CE,

If I charge my .25 Crown to 235 Bar , I get 74 shots before my tank pressure reaches my regulator pressure of 135 Bar. If I charge the Crown to 200 Bar, I get about 60 shots. I recharge the Crown from 135 Bar to 235 Bar in under 30 seconds. I do this all day from my 12 liter Scuba bottle and my bottle is still above 135 Bar. I then take the bottle to my Bauer compressor and recharge the bottle back to 235 Bar in less than 20 minutes, much less actually. I'm being conservative. I don't see a significant advantage to use higher pressure. The higher the bottle pressure, the more stress there is on the regulator to bring down the pressure to 135 Bar. That is why FX has implemented the second regular along with the new gun bottle pressure of 300 Bar. I don't know what that does to the total shot count, maybe in my case perhaps 100 shots? I suspect increasing the chamber volume and decreasing the regulator pressure would keep the same pellet performance and increase the shot count more effectively. I spend far more time placing pellets in my magazines than I do charging the gun. I mean to me there is little advantage in recharging the gun after 74 shots or 50 shots, if recharging time is only 30 seconds.
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I think I better understand what you mean now. It seems as if you’re specifically talking about higher pressure fills putting stress specifically on the regulator. So for you, it appears that you prefer to fill your gun at a lower pressure (235 bar as opposed to 300) and have a relatively decent shot count (around maybe 15-25 less than a 300 bar fill?). Then if you want to increase your shot count, you elect to alter your tune by decreasing your reg pressure to increase shot count. Am I understanding you correctly? If so, do you also adjust your hammer spring each time you adjust the reg?
 
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Ezana4CE,

I think keeping a constant pressure is the goal regardless of your tune. It stands to reason that your standard shot deviation will be best regardless of your tune, if your regulator pressure does not move around. The lower the differential pressure is between the chamber and the bottle, the better the regulator will function. That is what I am saying. It is often more efficient to increase the chamber volume and decrease the chamber pressure (reg. pressure) maintaining the same shot velocity as opposed to just playing with reg. pressure. As the efficiency increases, so does the shot count. On the new FX Impact M3, they also increased the chamber volume to do just that.
 
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Well with my Maverick it went from 66 shots to 100 which is 66% more and that's what they advertise is 66% so that's what I'm going with. This is .30 cal at 85 fpe 

That being said I only air to around 220b
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@18-13 Maths isn’t my strong suit, but here’s what I was thinking about these numbers. You increased your shot count by 34 shots, from 66 to 100. If I divide 34 by 66 I come up with .51515 or approximately 52%. Is this not the correct way to determine the increased shot capacity?
 
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The gas laws state that there is a linear relationship between volume, temperature and pressure. What is done in the air storage end of the gun does not affect the volume of air used per shot on the other end of the gun beyond the regulator assuming the temperature does not change and the reg. is working correctly. That said, as the bottle pressure rises so does the temperature (temporarily) and the amount of air squeezed into the fixed bottle volume on a linear basis. So the effective volume of air based on atmospheric pressure contained in a fixed volume is done at the same ratio of pressure change, which is 300 - 250 = 50 or 6/5 or 20%. So what ever number of shots you were getting at 250 bar, you will get 20% more with the same tune using the higher storage pressure. 

Increasing the bottle size is another way to increase the amount of air stored, but it also increases the weight and balance of the gun, but the net advantage of increased storage capacity anyway you do it is moot if it only takes 30 seconds to recharge your bottle.
 
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Is it just me, or is there a whole lot of confusion going on? Please forgive me if I've misinterpreted something. The OP asks about CF tanks, but then the conversation shifted to the gun's bottle (& tune) pressures. A CF SCBA-style tank is rated to 4500psi/310bar, vs. the 3400psi/235bar of the SCUBA tank. Since (per other threads) I don't know what the capacity in cubic feet is for the 12L SCUBA, I can't use the on-line calculators to determine the number of fills, but I would hazard to guess the 9L CF tank at 4500psi will handle a LOT more gun fills from 135 to 235 bar, than the 12L SCUBA at 3400psi. It will also weigh much less, and possibly be smaller. Guns are designed to be filled from sources of at least 4500psi, so that's a non-issue.
 
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TN-Yankee, yes you are confused and it is understandable. The reason the thread went off track was due to the questions asked of me, the OP. In a nutshell, the advantage of a CF tank is weight and pressure rating. My interest is weight alone, not pressure because I feel there is a minimum advantage is usable capacity with the increased pressure of the bottle. Then others chimed in with exorbitant estimates of the number of additional available shots with the increased pressures. Then the overall understanding of bottle volumes between American standards and Metric standards arose, again understandably. All of this because I use a service pressure less than my gun maximum for my reasons stated. So for all you nerds that really want to know, I offer the following explanation:

The Metric rating of bottle volume and service pressure is different than the American methodology. So they are not comparable. The Metric system is wet volume with a pressure rating at 15 C temperature. The American system is compressed volume of atmospheric air at the bottle's service pressure at 70 F temperature. The formula to convert physical volume to the American rating is below:

References: Gay-Lussac's law of pressure and temperature (ideal gas), 1 liter = 28.32 ft3, 1 Bar= 14.696 PSI absolute, Z Factor = 1.0532 (air is not an ideal gas. It is a mixture of many gasses).

Wet volume in liters / 28.32 (ft3) x service pressure (PSI) / 14.696 (PSI (1 Bar)) x 1.0532 (Z Factor) = American service volume rating in ft3. More confusing is that the service pressure standard used for rating the effective volume is NOT the pressure rating of the bottle, but the Faber DOT US Spec rating for a steel bottle 3442 PSI. This also just happens to be about 235 Bar and the max service rating I choose to use. So, if you do the math a 12 liter bottle is rated at 100 ft3. So, the lesson offered boys and girls, is use only physical volume in your calculations, it is much less painful.


 
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