Nitrogen Tanks

[russyj]

What skeet says is generally right, however just thought I'd bust out a bit of physics coz I'm bored...

Co2 is stored as a liquid.
In order for it to turn from a liquid, to a gas, as it does when it expands, it pulls heat from the surrounding area, so making that area cold.

...

Its cleaner, more consistent, doesnt freeze things (the reverse in fact)

ANY gas expanding, CO2, air, nitrogen, fart gas (not sure how that'd work ) cools down, thus if you took air from a high enough pressure and expanded it quickly enough, you could freeze things. Not sure what gas they use, but thats one of the ways they attempt to reach absolute zero, by putting a gas under enormous pressure then letting it expand quickly. The reason you see it more predominantly with CO2 is because you have a higher latent heat of evaporation/expansion, i.e. it takes more energy to drop the pressure, thus taking energy from the surroundings, making them colder.

Because it is at high pressure, when it moves through small orifices, it moves very quickly, which generates heat through friction, which is why your tank gets warm when you fill it too fast.

Close but no cigar. While there IS friction, this is in no way accountable for the heat. The reason? Compressing gases causes them to heat up! Put your finger over the end of a bicycle pump and push, and the gas inside will heat up (though probably not enough to notice unless you're hulk hogan).
But, I hear you say, the gas inside the feed tank is already compressed! Yes [insert name], but the gas expands between the feed tank and the paintball tank, but is then compressed by the force of the rest of the gas in the feed tank trying to get into the bottle until they reach an equilibrium state (even if they are not on at the same pressure), where no more air enters the paintball tank. You could technically say the feed tank cools down, though I've never noticed this.
Finally, why does it heat up more when you fill fast? Well, [insert name again], if you slow fill the tank is heating up, but the heat energy is being dispersed to the surroundings, cooling it down again, meaning a minimal change in temprature. When you fast fill, it doesnt have time to get rid of all that heat, thus increasing its temperature. Dont worry though, the temperature increase no matter how fast you fill it (within reason) is minimal, you wont melt your tank.

Too deep for thursday morning? I hope so, but killed 15 minutes of work

 

[Marcus Geezer]

I bow down to your infinite knowledge....

We seem to have an expert here, so I thought I'd throw in a question or two.

I've always been advised flashfilling a tank is bad, for two reasons.

1) If you flash fill a tank it heats up and the air expands, so when you you take it off the fill rig and let it cool down, the psi you thought you had has gone down a touch.

2) Flash filling, causing heat, can cause moisture to condense on the inside of your tank, promoting rust, which is bad.

I think 1) is a given (?), but 2), well I await someones wisdom on that!

 

[russyj]

I must state before anything else that my knowledge on high pressure systems comes from engineering and industry, thus it is not paintball-specific before anyone calls me up on the little things...

1) If you flash fill a tank it heats up and the air expands, so when you you take it off the fill rig and let it cool down, the psi you thought you had has gone down a touch.

Thats true, but I cant say to what extent the psi will fluctuate. My advice on that would be that during a day at the field where you fill between games, dont worry too much, its only really a consideration if you're filling at the end of the day to take some air for teching at home. If it varied more than 200psi I'd be surprised.

2) Flash filling, causing heat, can cause moisture to condense on the inside of your tank, promoting rust, which is bad.

This is something thats interested me for a while. The reason you get condensaiton (in gas compression) is moisture in the air, or humidity, when the air cools down, which lowers its saturation point (how much water it can absorb), thus causing condensation, as the excess water is deposited. If you slowly cool air the saturation limit does not drop as much as if you quickly cool it, for reasons I can't remember (but probably should know). This causes the effect you're talking about.

From what I gather where I'm working, in industry the air is scrubbed, or dried, before compression so it has almost 0% humidity, thus the problem is avoided. With regards to paintball tanks, I've never seen dry air used, however the amount of moisture to which you're refering is minimal, far less than a droplet in one fill.

In a steel tank, this means even after a thousand fills the rust will be minimal, as a given amount of water can only rust a certain (small) amount of metal. This means if you leave the tank with a droplet of water for around a month, it will have rusted the same as if you had left it 5 years, thus time is a minimal factor. Also, it will be surface rust, thus the structural integrity of the tank will not be compromised (take a rusty object and skim the surface rust off - if its a thick-ish chunk of metal, you'll find clean metal underneath). Yes, the increased temperature when the tank is filled will propogate rust, but for such a short time that its not even a factor.

Also, air tanks are made to a safety factor of AT LEAST x5 (meaning they can handle 5 times the pressure they're meant to before they fail, or 22,500psi for a 4,500psi tank). Do not become overly concerned by the tank blowout publicised around here. Yes, oil in tanks is a danger and something to be very careful of, but do not doubt the structural integrity of air tanks, that one failed because an internal explosion would have caused phenomenal pressures instantly, too fast for the burst disc to compensate. Anyone who's seen a blown head cylinder in a car will appreciate what combustion can do to steel.

Aluminium on the other hand is even less of a danger with respect to rust, as in its processed form it will naturally have an oxide layer, or rust, which protects it against futher rust. Stako tanks... well, we all know plastic doesnt rust


Personally, its not something that would worry me, as I say the amount of rust will be minimal, and knowing the safety factors and the stringent testing anything with a PI or DOT certification must undergo, I'm never worried about my tanks failing. DO however be careful of oil - high pressure, high temperatue and fuel caused that poor guys tank to act like a diesel engine - not pretty.

 

[Big Mac]

I've never seen dry air used, however the amount of moisture to which you're refering is minimal, far less than a droplet in one fill.

i take it you have never been to elsham then

 

[russyj]

i take it you have never been to elsham then

hah, working in Brigg atm, was going down on friday to give my tanks a fill

 

[Big Mac]

hah, working in Brigg atm, was going down on friday to give my tanks a fill

well i went to fill from one - it had some sort of oring problem on the fill rig and i didnt know - so when i pulled the handle down all this cloudy, dirty water just kept spurting from it

needless to say i expect my tank is half filled with water

 

[JTD1993]

well i went to fill from one - it had some sort of oring problem on the fill rig and i didnt know - so when i pulled the handle down all this cloudy, dirty water just kept spurting from it

needless to say i expect my tank is half filled with water

Water ball

 

[russyj]

well i went to fill from one - it had some sort of oring problem on the fill rig and i didnt know - so when i pulled the handle down all this cloudy, dirty water just kept spurting from it

needless to say i expect my tank is half filled with water

Now THAT will cause rust... there goes your shelf life... you used it since?

 

[Big Mac]

we dont really have much option

im certain it aint as bad as im making out but - i aint buying a new bottle everytime i wanna train

 

[Skeet]

Now THAT will cause rust... there goes your shelf life... you used it since?

Tanks have Ali core.
Ali rusts in Air, not water.

Still not ideal though!