VL_Newbie

do they make tanks that are 3500 0? im looking looking at buying a scuba tank and that is the max psi. thanks for the help.

Peter

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Alpha

You can fill a 3500 PSI tank to 3000 psi.

Its interchangable..

Like this.. Say you have a barrel holder that fits 3 barrels . You can put 3 barrels in it. But then again, you can put two barrels in it and it will work fine.

Yuo can have a 3500 PSI scuba and when you get it filled, ask them to fill it to 3000 PSI.

Or you can just get a 4500 PSI nitro tank and you can fill it to 3500 every time.

You dont have to fill your HPA tank all the way every tiem. Am I makign sence?

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Huey69

Not quite. It will only fill the tank up to 3500 the first time, after that it will fill lower and lower. I know this.

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Alpha

Not necessarily.

You have a HPA tank at 3000 PSI and its 68 cubic inches.

You have a scuba at 136 cubic inches and 3000 PSI

You will be able to fill your HPA tank to 3000 PSI twice. Beucase your taking 68ci from the scuba, and putting it in the HPA tank.

Now a 136 cubic inch scuba is unrealistic and probably doesn't exist, but its just an example. But oyu get what I'm syaing?

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Angered Fists

No, that is incorrect. You don't take 68 ci of air at 3000 psi. You need to have some grasp over the ideal gas laws to understand this precisely, but I'll try and explain it.

The ideal gas law is pv = nrt: pressure x volume = number of mols x gas constant x temperature.

What happens is you take a certain number of molecules of air and allow them to enter into your hpa tank. Based on the gas laws, that number of molecules of air at a certain temperature and volume, will be contained under a certain pressure. So you don't take 68 ci of 3000 psi air, you take a certain number of mols of air, the volume is set at 68 ci, the temperature should be the same as the temperature it is being stored at, and it gives a resultant pressure.

The problem with using a scuba tank though, is that you can't just pump as much as you want into the tank, you just connect the scuba tank to your hpa tank, and the air goes from an area of high pressure, the scuba tank, to an area of low pressure, your empty hpa tank. It just balances out, it doesn't pump in, so now you have the same number of mols of air contained in a slightly larger container than when it was just the scuba tank, because your hpa tank has become part of the system. So everytime you fill your hpa tank, you decrease the pressure in the scuba tank slightly because it has less mols of air in the same size tank, so every fill is less and less psi than the previous fill until finally you can't get a decent fill off your scuba tank.

This is what air compressers are for, and why they cost so much, they make every fill a complete fill.

In response to the initial question, I don't believe that they make 3500 psi tanks, but if you fill a 4500 psi tank up to 3500 psi it will be fine. I'm not sure what would happen if you connected a 3000 psi tank to a 3500 psi fill station, because I don't know what sort of safety measures they implement in order to prevent over filling, but I would imagine there would be something in place.

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VL_Newbie

so, ur saying i can fill a N2 with an air compressor? does the size of the tank matter? thanks.

Peter

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You can fool some of the people all of the time, and all of the people some of the time, but you can not fool all of the people all of the time. Abraham Lincoln

Alpha

I dont quite understand what your getting at AF. What happens to the rest of the air in the scuba. I mean, if you start with x amount of air, put it into a few different containers, you should still have x amount of air total.

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Angered Fists

You can fill your tank with a compressor, but you need a much better compressor than I would imagine that you have just lieing around. I think most common compressors can only fill up to like 200 psi, certainly not much more than 1000 psi, which isn't enough for more than a couple of shots. If you get a high powered compressor then you're in business. Have you got a few grand burning a hole in your pocket?

Alpha: When you fill your scuba tank, lets say as a completely made up number you have 10 000 moles of air in it. Then you hook up your hpa tank. Between your hpa tank and your scuba tank you now still have 10 000 moles of air, but the combined volume of the hpa and the scuba system is greater, albeit slightly, than the scuba tank alone, so the pressure is reduced, do you understand why? Same amount of air, in a larger space results in less pressure. It will still be very close to 3000 psi, but not as high as it was originally.

You then disconnect your hpa tank which now has a share of the 10 000 moles of air, as another completely made up number lets say it has 500 moles of air in it, these numbers are important, because the ratio will remain the same. As the air expands from the scuba tank into the hpa tank, it expands uniformly, which is why the ratio remains the same. I give the example 20:1 meaning that the scuba tank is 20 times as large as the hpa tank. So now the scuba tank has 9 500 moles of air and your hpa tank has 500 moles of air.

You use up all the air in your hpa tank and bring it back to the fill station. Before when the fill station had 99 500 moles of air in it, it was at 3000 psi, now it has less moles of air, so the pressure is reduced. When you connect your tank again the complete system shares 9 500 moles of air. Now when you disconnect again, your tank won't take 500 moles of air again, it will take the same ratio 20:1, so the hpa tank will take 475 moles of air leaving the scuba tank with 9 025 moles of air. This cycle continues. Does that help explain it a little bit better?

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Alpha

Gotcha now. The pressure decreases becuase there is less quantity of air inside the scuba, and since theres more space then air, the air evens out. I ge what your saying now.

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HP_lovecraft

The short version: Say you have 2 100ci 3000psi scuba tanks.
One is full, and one is empty.

If you used one to fill the other, you would end up with 2 100ci tanks both at 1500psi. This is why it is hard to get a full fill at most fields at the end of the day.

It is not like Co2, where the pressure is self-regulating. To fill HPA tanks effectively, you often need a cascade of HPA tanks to do the "main" fill, then the "top off".

Thank god for boosters.

Nick

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VL_Newbie

can i get a "booster" for a scuba tank? what exactly does it do? thanks for the help so far.

Peter

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You can fool some of the people all of the time, and all of the people some of the time, but you can not fool all of the people all of the time. Abraham Lincoln