N/A Help me out with the Math! If i have a 1000cc 300bar bottle filled- how many times can i fill my 700cc gun bottle at 250bar?

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grzech2005

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Dec 23, 2024
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Hi Guys

another dumb question from a newbie- my fx dreamline will get a 700cc carbon bottle which i fill 250bar, no more. If i get lets say a 1000cc carbon tank to feed my smaller 700cc bottle off of it- how many times can i fill until the 1000cc tank has to little pressure to fill the 700cc bottle again...

i understand it like this- i have the reg set at 150bar and i fill the 700cc bottle only 250bar so i am only using 100bar and i bounce off the reg and need to refill the gun again..

but how does that correlate to my 1000cc tank which is filled at 300bar?

am i taking every time 100bar from the 1000cc tank? but i am taking cc from the tank, not bars and the tank is filled with 300bar and not with 250bar...

i don't get it..

the 700cc bottle has always still 150bar when i refill it so those 150bars inside are resisting the compressed air coming from the 1000cc tank- so where is the limit, when will the 1000cc tank be unable to fill up the 700cc bottle with another 100bars... this is too much for me..

how to calculate that air usage?
 
sorry
grzech2005 said:
its not working.. doing something wrong
Click to expand...
sorry- did it wrong.. 1000cc tank is only 0.035 cf but under pressure of 4500psi its 9.5cf

but its still not making any sense because it says that i will get 0.8 fill so not even 1 full fill although i am filling from bigger 1000cc tank at 300bar into smaller 700cc tank at 250bar... weird

ScreenShot_27.12.2024_03_21_56.png
 
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Until your tank is equal to the pressure of the filled vessel..... duh ..... :D

Those calculators will get you really close, but the best way is to just fill and see what happens. Remember that it will depend on how low you get your tank on the gun as well. And typically we don't fill at the EXACT same pressure each time.
 
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woogie_man said:
Until your tank is equal to the pressure of the filled vessel..... duh ..... :D

Those calculators will get you really close, but the best way is to just fill and see what happens. Remember that it will depend on how low you get your tank on the gun as well. And typically we don't fill at the EXACT same pressure each time.
Click to expand...
but in this calculator one puts in the exact amount at which the gun bottle will be filled from the tank- in my case at 150bar, no sooner and no later..

i don't get it why a bigger 1l tank at 300bar will fill a smaller 0.7l at 250bar tank only 0.8 times 🤒 it should me more like 1.3 times or something like that.. it makes no sense but ok, lets just leave it at that..

you guys are right- i will know once i fill.. i asked because i don't have the gun yet, i bought it online few days ago and will get it in few weeks..

i just wanted to know it so that i can buy now a bigger tank from which i would fill the gun bottle and i don't know how big should the main, larger tank be- 3l or 6.8l or, or...

to many unknowns.. i don't want to be buying twice, they are not cheap mistakes to make
 
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grzech2005 said:
but in this calculator one puts in the exact amount at which the gun bottle will be filled from the tank- in my case at 150bar, no sooner and no later..

i don't get it why a bigger 1l tank at 300bar will fill a smaller 0.7l at 250bar tank only 0.8 times 🤒 it should me more like 1.3 times or something like that.. it makes no sense but ok, lets just leave it at that..

you guys are right- i will know once i fill.. i asked because i don't have the gun yet, i bought it online few days ago and will get it in few weeks..

i just wanted to know it so that i can buy now a bigger tank from which i would fill the gun bottle and i don't know how big should the main, larger tank be- 3l or 6.8l or, or...

to many unknowns.. i don't want to be buying twice, they are not cheap mistakes to make
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There is a law of diminishing returns when it come to a gas filled into a pressurized vessel. It is not a linear 1:1 math formula unfortunately.

www1.grc.nasa.gov

Boyle's Law | Glenn Research Center | NASA

Air is a gas which has various properties which we can observe with our senses, including the gas pressure (p), temperature, mass, and the volume (V)
www1.grc.nasa.gov www1.grc.nasa.gov
 
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MongooseV8 said:
There is a law of diminishing returns when it come to a gas filled into a pressurized vessel. It is not a linear 1:1 math formula unfortunately.

www1.grc.nasa.gov

Boyle's Law | Glenn Research Center | NASA

Air is a gas which has various properties which we can observe with our senses, including the gas pressure (p), temperature, mass, and the volume (V)
www1.grc.nasa.gov www1.grc.nasa.gov
Click to expand...
i did not know this- thank you for explaining...

but tell me this- will i be good served with a 6.8l or 6800cc carbon scuba tank for 219euro? is it good size or maybe too big or too small?

i might get only 40-50 shots with my .30 cal using my 700cc bottle so reffiling will become an issue

ScreenShot_27.12.2024_13_29_49.png
 
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Since you asked for the math, I'll offer a link where I explained it in pretty good but simple detail to somebody asking about regulators, with the key part of it being the unit we use for this of the "bar-cc" to address the air stored and used. Read it if you want to dive into more of an understanding: https://www.airgunnation.com/threads/plenum-volume-confusion.1323483/page-3#post-1866085

It applies here, and amounts to the product of the pressure in each vessel in bar times the "water volume" of the vessel in cubic centimeters. That gives you a very close approximation of the relative amount of "air molecules" held or used in each case - it is not perfect as air no longer acts as an "ideal gas" once it gets up over about 230 bar or so, but it is linear below that and the "curve" only shifts about 7% above it, so it is a good approximation without diving deep into the weeds (known as accounting for the intermolecular "van der Waals" forces). There is no need for all that cubic foot of standard pressurized air silliness this way . . .

Anyways, your tank at 1000cc and 300 bar holds 300,000 bar-cc of air, but we are only able to use the air above 150 bar (the regulator set point is the lowest we can go), so that is half of 150,000 bar-cc of air.

Your goal to refill is to transfer 700cc at 100 bar or 70,000 bar-cc out of the tank to your gun. So the math is simple: in perfect conditions you would get 150,000 / 70,000 or about 2.1 fills. Of course things are not perfect, as you have to fill the lines and that air is wasted on each fill, and while small it matters (if it is 15 cc and we have to fill to 250 bar, we then vent our the full 3750 bar-cc with every fill). So call it two fills from that tank.

You can use the math to decide how big a tank you want to get for your needs . . . .
 
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AlanMcD said:
Since you asked for the math, I'll offer a link where I explained it in pretty good but simple detail to somebody asking about regulators, with the key part of it being the unit we use for this of the "bar-cc" to address the air stored and used. Read it if you want to dive into more of an understanding: https://www.airgunnation.com/threads/plenum-volume-confusion.1323483/page-3#post-1866085

It applies here, and amounts to the product of the pressure in each vessel in bar times the "water volume" of the vessel in cubic centimeters. That gives you a very close approximation of the relative amount of "air molecules" held or used in each case - it is not perfect as air no longer acts as an "ideal gas" once it gets up over about 230 bar or so, but it is linear below that and the "curve" only shifts about 7% above it, so it is a good approximation without diving deep into the weeds (known as accounting for the intermolecular "van der Waals" forces). There is no need for all that cubic foot of standard pressurized air silliness this way . . .

Anyways, your tank at 1000cc and 300 bar holds 300,000 bar-cc of air, but we are only able to use the air above 150 bar (the regulator set point is the lowest we can go), so that is half of 150,000 bar-cc of air.

Your goal to refill is to transfer 700cc at 100 bar or 70,000 bar-cc out of the tank to your gun. So the math is simple: in perfect conditions you would get 150,000 / 70,000 or about 2.1 fills. Of course things are not perfect, as you have to fill the lines and that air is wasted on each fill, and while small it matters (if it is 15 cc and we have to fill to 250 bar, we then vent our the full 3750 bar-cc with every fill). So call it two fills from that tank.

You can use the math to decide how big a tank you want to get for your needs . . . .
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Thank you! that is exactly what i wanted to understand better.. i figured that from 1l tank transfering to 0.7l bottle should give at least 1.3 refills (and not only 0.8x like the calc said) but also was hoping it would be more because i am filling from 300bar to 250bar..

so it is around 2 refills- good.... now i get the 6.8l tank and i can expect around 7x that which is 14x refills..

now i can round it up (or down) to 12 refills and i am happy with that to..

so do you think that 6.8l tuxing tank is a good idea to buy or is it maybe too big?
 
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While I agree with AlanMcD's analogy I don't think it takes into account the "fill" level of 250 bar. This is where the fill calculator is accurate and the above description needs some refinement.

The 1000cc tank is only good to refill until it's pressure equalizes to the pressure of the 700cc tank. The gun fills to 250 bar - so you only have 50 bar x 1000 cc = 50,0000 bar-cc until your source reaches the fill pressure of the gun. At this point you've only filled 50k bar-cc of the required 70k bar-cc for a single fill. It's all downhill from there and I would expect you'll even out around 225-230 bar. Taking into account losses from heat and fill tube air losses I think the original 0.8 time from the fill calculator is accurate.
 
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grzech2005 said:
Thank you! that is exactly what i wanted to understand better.. i figured that from 1l tank transfering to 0.7l bottle should give at least 1.3 refills (and not only 0.8x like the calc said) but also was hoping it would be more because i am filling from 300bar to 250bar..

so it is around 2 refills- good.... now i get the 6.8l tank and i can expect around 7x that which is 14x refills..

now i can round it up (or down) to 12 refills and i am happy with that to..

so do you think that 6.8l tuxing tank is a good idea to buy or is it maybe too big?
Click to expand...
Sorry my man - see my reply above. Trust the calculator - it is correct here.
 
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ctshooter said:
While I agree with AlanMcD's analogy I don't think it takes into account the "fill" level of 250 bar. This is where the fill calculator is accurate and the above description needs some refinement.

The 1000cc tank is only good to refill until it's pressure equalizes to the pressure of the 700cc tank. The gun fills to 250 bar - so you only have 50 bar x 1000 cc = 50,0000 bar-cc until your source reaches the fill pressure of the gun. At this point you've only filled 50k bar-cc of the required 70k bar-cc for a single fill. It's all downhill from there and I would expect you'll even out around 225-230 bar. Taking into account losses from heat and fill tube air losses I think the original 0.8 time from the fill calculator is accurate.
Click to expand...
That's a great point - I got too fast for myself as I had to go do something else, so I apologize for the math error. I am duly embarrassed . . . .

@grzech2005 - The correct answer should have been that you won't get any full fills, but will get a few partial fills . . .

While 150,000 bar cc is "usable" in the 1 liter tank, only 50,000 of it is above the fill point you want to take the gun up to, and it takes 70,000 bar-cc to fully get there. That first fill, as ctshooter noted, would be less than a full fill because the two cylinders when connected would equalize below your desired fill point. That would occur at 238 bar, which is 88% of a full fill, but losses would bring it down a bit, so I think about 85% max.

The math looks like this for the first fill when you hook up the full tank to the 150 bar gun:
(1000 cc x 300 bar) + (700cc x 150 bar) = 300,000+105,000 = 405,000 bar-cc of air available, and this will balance out to an equal pressure in both tanks of:
405,000 bar-cc / 1700 cc = 238 bar, or about 85% fill after losses

Your second fill would degrade a lot, as seen below:
(1000 cc x 238 bar) + (700cc x 150 bar) = 238,000 +105,000 = 343,000 bar-cc of air available, and this will balance out to an equal pressure in both tanks of:
343,000 bar-cc / 1700 cc = 202 bar, or roughly 50% of a fill

Sorry that I misled you - I hope you had not placed an order yet. If you did, the 6.8L tank is a good tank anyways. It's hard to get a lot of fills when you are filling that big 700cc bottle.

I'll go take my "time out" for my math error now . . . :)
 
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ctshooter said:
Sorry my man - see my reply above. Trust the calculator - it is correct here.
Click to expand...
Great info! thank you so much for accurate data.. the other pcp friend just made a calculation mistake somewhere, its all good - happens to all of us!

so i should still get 0.8 refill with 1l tank but with 6.8l tank that should be around 6.8 x 0.8- 5.44 or just shy of 5.5 refills right??
 
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AlanMcD said:
That's a great point - I got too fast for myself as I had to go do something else, so I apologize for the math error. I am duly embarrassed . . . .

@grzech2005 - The correct answer should have been that you won't get any full fills, but will get a few partial fills . . .

While 150,000 bar cc is "usable" in the 1 liter tank, only 50,000 of it is above the fill point you want to take the gun up to, and it takes 70,000 bar-cc to fully get there. That first fill, as ctshooter noted, would be less than a full fill because the two cylinders when connected would equalize below your desired fill point. That would occur at 238 bar, which is 88% of a full fill, but losses would bring it down a bit, so I think about 85% max.

The math looks like this for the first fill when you hook up the full tank to the 150 bar gun:
(1000 cc x 300 bar) + (700cc x 150 bar) = 300,000+105,000 = 405,000 bar-cc of air available, and this will balance out to an equal pressure in both tanks of:
405,000 bar-cc / 1700 cc = 238 bar, or about 85% fill after losses

Your second fill would degrade a lot, as seen below:
(1000 cc x 238 bar) + (700cc x 150 bar) = 238,000 +105,000 = 343,000 bar-cc of air available, and this will balance out to an equal pressure in both tanks of:
343,000 bar-cc / 1700 cc = 202 bar, or roughly 50% of a fill

Sorry that I misled you - I hope you had not placed an order yet. If you did, the 6.8L tank is a good tank anyways. It's hard to get a lot of fills when you are filling that big 700cc bottle.

I'll go take my "time out" for my math error now . . . :)
Click to expand...
its all good- we all make mistakes but you corrected it and the other pcp friend found it for you and me and its correct now.

i did not purchase yet but i am still getting this big 6.8l tank because with a smaller one it will be hassle
 
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Depends on two main variables:

- Initial pressure of the rifle; and

- Initial pressure of every refill.

You compensate pressures when filling from a squba tank.

Every time you refill your rifle you do the following:

Volume of air rifle deposit divided by volume of the squba = z

Volume of the squba = y

Then:

Total amount of air you are playing with: = z+y

Suppose your rifle is at 200 bar and you want it to be 250 bar what you should do is to make an operation of multiply the difference in pressure of actual pressure of the bottle of the rifle and the pressure in the squba by the fracción that the bottle on the rifle is in regard of the squba. The result will be the loose in pressure in the squba after the refill.

Suppose that the squba is at 300 bar, the rifle is at 200 bar and the rifle is a tenth of volume of the squba. Then that refill will imply to loose in the squba 50 (difference in bar on both) times .1 (10% of the volume of the squba).
 
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