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h.p.a tanks geometric true value


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#1 BOBBYTUCSON

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Posted 09 January 2009 - 01:42 AM

i know this is a wierd wamble here , but there is a big debate in my shop and feild . 1/2 of us, including myself, are under the assumption that you will get more shots out of the 70ci/72ci stubby tanks that some brands make, than shots out of a 68ci. the other 1/2 of us beleive that there is the same amount of air , its just they think its just labled 70ci or 72ci because of its wider shape due to a compact profile. we believe that its the inside diameter were the air is stored that determines and equals the labled cubic inch size. they beleive that its not , and that the 70ci or 72ci tank holds the same amount of air as the 68ci , but marketed as 70/72ci for whatever reason, and beleiving that no tank maker would waste their time to just make a tank thats just 2 or 3 ci more than a 68, and on that point i could see. but... cockerpunk , please settle this for us , we would really like to know if the tanks have the same volume of air , or if the 70/72 cubic inchers really do get 2-3 more cubic inches worth of air!!

and if so , than how much?
any substantial amount?
and does the measurement in cubic inches = internal diameter where air is stored , or does it equall the outer diameter of the tank?

thanks cockerpunk , you rule!!!!!!
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#2 cockerpunk

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Posted 09 January 2009 - 01:46 AM

you could dip each tank in a bucket of water and see if they displace the same amount. only up to the reg though, unless they have the exact same reg. that wouldn't be internal volume, but it should work for determining if there is a difference in size.

idk ... 2 or 4 ci is just not that big a difference, it would be hard to detect. hard to measure anyway.
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#3 BenM

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Posted 09 January 2009 - 02:13 AM

If you guys have the tools, you could pull the regs off and fill the bottles with water. Then measure the volume of water each tank holds. Since the tanks are being evaluated by a regulating body chances are that the volume marked on the tank is actual internal volume. I wouldn't expect more than 25-40 shots extra on a 70 or 72 ci tank vs a 68.

#4 BOBBYTUCSON

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Posted 09 January 2009 - 02:14 AM

good piont , ima try that w/ the two tanks. ill let you know what the results are!!
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#5 wgp2002

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Posted 09 January 2009 - 02:14 AM

the thickness of the tank would come into play as well.. but still hard to measure..

maybe if you took the regs off 2 tanks and filled it with water or sand then measured how much was in it. i guess would be one way of testing.
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#6 BOBBYTUCSON

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Posted 09 January 2009 - 02:25 AM

I wouldn't expect more than 25-40 shots extra on a 70 or 72 ci tank vs a 68.


but that few extra cubic inches compressed at 4500psi leads me to believe that it will give you at least one and a half pod more worth of shots.
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#7 BOBBYTUCSON

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Posted 09 January 2009 - 02:37 AM

mathematically though , what would be the correct formula , im having a hard time determining the correct formula. i will use the ego's 1700 shot capability for the control . or -0/+0.

1700(shots) divided by .68(c.i) x 4500(p.s.i)= 11250000 ...so put a decimal in the ten/thousands place , and thats not right lol because ur pack can hold only 4 digits

or , 1700x.68 divided by 4500?

4500% devided by 1700x68?

either way , the first formula ended up with more shots with 68ci over the 72ci , so that aint right lol!
and i have no clue how to get the right formula.
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#8 Troy

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Posted 09 January 2009 - 08:43 AM

Just weigh them empty, then weigh them when they are all pressurized to the same pressure. A lot of people forget that air has weight, and a full air tank is heavier than an empty one. The tank that gains the most weight is the one that has the most volume. If you know the weight change, and the pressure, you'll be able to derive the true volume of the tank. Just keep in mind that you'll need a fairly accurate scale.

Edited by Troy, 09 January 2009 - 08:43 AM.

\m/

#9 Snipez4664

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Posted 09 January 2009 - 12:03 PM

The simplest answer is 5.9% more. If you get 1700 shots off a 68, you'd get 1700*1.059=1800 shots (even, i do love when numbers work out).

I assume they're buying standard tanks and the volumes are accurate.
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#10 BenM

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Posted 09 January 2009 - 02:34 PM

The simplest answer is 5.9% more. If you get 1700 shots off a 68, you'd get 1700*1.059=1800 shots (even, i do love when numbers work out).

I assume they're buying standard tanks and the volumes are accurate.


Yeah that's the same percent difference i found between a 68 and 72 ci, But I based the number of shots on a typical 1000 shots per tank as an average to account for all markers then subtracted about 20 since In mikes efficiency tests the final half pod tends to drop of significantly.

Edited by BenM, 09 January 2009 - 02:35 PM.


#11 Lord Odin

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Posted 09 January 2009 - 08:43 PM

Have you guys thought to just shoot the manufacturer an e-mail to see how they measure their tanks?

#12 BOBBYTUCSON

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Posted 09 January 2009 - 10:27 PM

^^ no , but damn good idea lol
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#13 MrSpit

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Posted 09 January 2009 - 11:30 PM

Ok, im Super glad i read this before i posted, because i had the same sort of question my self.

I really want a new Ninja tank, but i didnt want to wait for the 68c.i. to get the TC stamp (I live in Canada) so i thought about getting a 50c.i.
So i was wondering what the shot diff would be on my Vice.

So is it safe to assume the following.......
Mike's test got 14 pods (or approx 1960 rds) from a 68c.i. on 4000psi
The 50 c.i. is 18c.i smaller, or 36% smaller, and i would assume it would get 36% less shots
Thus, i would expect to get almost 9 pods (approx 1254 rds.)

Now i suppose this is a safe estimate???


Also, the tanks are measured in Cubic Inches, and the air is rated by pounds per square inch........is there a way to measure the volume of air under pressure?
That feels like a stupid question......
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#14 BOBBYTUCSON

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Posted 13 January 2009 - 11:42 PM

^^to measure the volume under presure would be linear , you cant really measure any other way except by a formula of wieght , as the tank is sealed off being under pressure.
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#15 meag8er

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Posted 14 January 2009 - 05:27 PM

Also, the tanks are measured in Cubic Inches, and the air is rated by pounds per square inch........is there a way to measure the volume of air under pressure?
That feels like a stupid question......


Assuming that the temperature is the same between the two pressures you would just use the ideal gas equation (we are assuming that air is acting as an ideal gas, this is perfectly fair for what we are doing).

Thus we are left with the equation P_1*V_1=P_2*V_2. Variables: P_2 = 14.7 psi (atmospheric), P_1 =4500 psi, and V_2 = 68 in^3. So using these numbers we get a volume of roughly 21,000 cubic inches of air at atmospheric pressure being compressed to 68 ci at 4500 psi.

Also to answer the initial question of whether or not you will get more shots out of a 70 or 72 ci tank over a 68 ci tank, yes you will, there is more volume. All of these tanks undergo a great deal of quality control by the manufacturer and the claims of the manufacture that the 70/72 ci tanks being what they say they are, are correct. Keep in mind that the companies like carleton, that make these tanks do not rely on paintball as their number one source of revenue, these tanks are used by the aerospace industry, military and others, so they can't afford to have bogus claims of volume. So I would say, don't even waste your time trying to measure the internal volume of these tanks, its already been done.

Thus with more air, you will see more shots, not a lot more as it is only 2 ci, but more nonetheless.

#16 brycelarson

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Posted 14 January 2009 - 05:40 PM

the manufacturer is your friend!


we use a strange system in paintball - I assume becuase the manufacturers assumed that we're not bright. In scuba the tank is indicated by the volume of 1 Atmosphere pressure air that needs to be shoved into the tank to produce that tank's specified pressure. For example, an "80" in diving is a tank in which 80 cubic feet of air will fill it to it's specefied pressure. They also rate the tank to a pressure, of course, since filling them doesn't depend on watching a gague for how much air you've put in.

the link I posted is to luxfer - who makes pretty much all the tanks you're going to see out there. notice they have a few specs - the one that is germain to the previous threads is the column labeled "capacity" - which is a listing of how many cubic feet of air you will shove into the tank to reach the desired pressure - in this case 4500/3000.

hope this info is helpful. So, I could reasonably call my 45/45 tank a "7" and be pretty cool - right? :)

#17 OnOppositeDay

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Posted 14 January 2009 - 07:43 PM

go to this website http://www.scubatoys...ntballshots.asp
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#18 BOBBYTUCSON

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Posted 15 January 2009 - 01:47 AM

scubatoys was an awsome link , thanks opposite day!!
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