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Air Tanks And Psi

...related to volume...

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#1 Murdock

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Posted 13 September 2004 - 02:53 PM

I was wondering if anyone had proven, whether by formula or actual tests, what is the best type of air tank.

Obviously you want a lot of PSI, so I would think a smaller tank would be best. The smaller the tank, the harder to pump. I have made both guns with full stocks for their air tanks, as well as guns with a 2" diameter section for a small airtank, and don't seem to notice much difference in them.

--In theory it seems that you could have a small tank and pump it once, or a large tank and pump it 10 times, and get the same amount of PSI in both.--

How far off am I?
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#2 THIRST

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Posted 13 September 2004 - 03:21 PM

The thing is with using one pump and a small tank, you will have a lot of pressure, but the volume wont be sufficient to propel the dart. You want a nice mix of volume and pressure, pressure mostly. Maybe a small airtank with 3 pumps? If you want equations, Cx is the guy for this.

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#3 cxwq

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Posted 13 September 2004 - 03:22 PM

--In theory it seems that you could have a small tank and pump it once, or a large tank and pump it 10 times, and get the same amount of PSI in both.--

Well sure, the PSI would be the same but you need to consider the pressure drop associated with the barrel volume. A good ratio to start with is about 2.5 tank volumes to 1 barrel volume. By barrel volume I mean everything between the valve and the tip of the barrel, including dead air space behind the dart.

Anything less than 2:1 and the pressure drop by the time the dart gets out of the barrel is too large to maintain your velocity. Anything much greater than 3:1 is just a waste of pumping time and will contribute to fishtailing.

All that said, it's not an exact science because it is dependant on your barrel material, dart size, and valve flow rate, as well as any porting you may have done. Start with 2.5:1 and mess around with your barrel length till you get optimal results, then you know how close you were to the best tank size.
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#4 AirApache

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Posted 13 September 2004 - 05:00 PM

^^ And this, is why he is our admin... ^^

I wish I was smart enough to add to that...
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#5 xedice

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Posted 14 September 2004 - 04:15 PM

I remember in high school chemistry and physics, I would use all these equations I found in the book and try to find a good airtank size.

After I got out of high school and smartened up, I found that building and testing it yourself is a lot faster and more fun than math. Yes, teachers would hate me for saying that, but which would you rather play with, numbers or pvc? I choose pvc.

What I am saying is experiment yourself with it, you'll learn a lot more that way than reading stuff on a forum / message board in my opinion.

Edited by xedice, 14 September 2004 - 04:17 PM.

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#6 Murdock

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Posted 14 September 2004 - 04:26 PM

Thanks Cx.
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#7 Viper

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Posted 15 September 2004 - 08:32 PM

That's true, what cxwq said for the most part, but if you mod a squirt gun you'll find that it has a large airtank that ends up being beneficial because it has a relatively slow air release system by which air can get behind the dart. With a long barrel, you can use this air release mech to put constant pressure behind the dart, making it go very far. As far as porting goes, if it fishtails I'd try putting a ring of ports around the area close to the valve on the barrel, and it that doesn't work, use a muzzle break like porting system or spiral porting. Spiral porting makes the dart spin a little making it more accurate usually as long as your precise with measurements.
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