calculating tank pressure...

[TheJester]

i'm looking to get a fill station, and i want to know if any 1 out there knows a formula or what ever to calculate the remaining presure in the scuba tank, after filling my gun tank, not sure if that makes sense, but i basicly want to know if any 1 knows how to figure out the presure of the scuba tank after each fill...any ideas?

[Kevmaster]

P/V = P/V

if its 100% full at 3000psi in say 5000ci and you take away 3000psi of 68ci, then it would be (for example) 3000psi in (5000-68). but since the volume is constant...it would be 2800 in 5000psi. all numbers are ficticious and are made up off the top of my head

[Spray Painter]

kevmaster-how could a 3000psi tank go to a 5000psi tank(i think it's a typo)

[virus]

there is no magic formula..... if i understand you want to know how much psi will be left in your tank after you do a fill.....

to be blunt in this case.... all things are equal.....

meaning... if you have an 80 cubic foot 3000psi scuba tank that has a full 3000 psi in it.... and you take any size hpa tank for paintball.... no matter what psi it is at as long as it has less then 3000psi..... when filled by the scuba the pressure in both tanks will equal out....

as an example.... 3k in scuba, 2k in on gun tank.... the fill would come out to about 2900psi give or take a few......

work the tank back down go fill again... now you are looking at 2900 in scuba and 2k in the on gun tank (using 2k as an imaginary base for now)
when you fill they will even out at about 2800psi give or take a few.....

the psi they level out at depends on how full/empty your on gun tank is and how full/empty the scuba is....


so to kinda answer your question.... to tell you can go top off a tank.... what ever pressure it fills to is how much psi is left in the scuba

[Evil Bob]

There is an easier way that does not require math...

1) Get yourself a fill adapter that has a gage on it.
2) Pick up a spare male adapter quick release and cap it so it's air tight.
3) Connect the male adapter plug into the fill adapter, close the bleed valve and open the main tank valve and you know precisely how much air pressure you have left.

-Evil Bob

[battlegroup]

Virus is right.

Whatever the guage of the last tank filled reads is the pressure in the scuba tank. Nuff Said.

[luke]

Evil Bob gets the prize!!

[Kevmaster]

first, i was talking about pressure sometimes(PSI) and volume(CI) other imes.. the 5000 was cubic inches...but i just reread what i wrote and it made no sense


however virus is right. whatever you have in your tank will be what you have in the scuba tank

[TheJester]

virus...if that's the case, why can you get like 2 or 3 full 3000 psi fills out of a scuba tank? my thoughts are it all goes back to mass...68 ci of air, at 3000psi, say has a mass of to keep number simple, say has a mass of 5, there fore, just adjust the numbers, a 80 cuf tank and 3000psi would have a mass of roughly 70, so if you take a mass of 5 out of the scuba tank, to take it down to 65, that meand you have a full paintball tank now, but a mass of 65 in an 80 cuf volume would have very little presure change relitivly speaking to the paintball tank, if everything were eqauls, you would only get 1 fill per scuba tank. did any 1 follow that, cause i'm not sure if i did, i guess in other words, because the volum of the scuba is greater than that of the paintball tank, the removal of x amount of air is very little in the eyes of the scuba tank, where the adding of x amount of air to the paintball tank is alot for it...hmmm, trying to think of a better way to explain this, i don't know, see if that makes sense, and evil bob, the reason i want to know is i found a 80 cuf tank 3300 psi, and i want to know how many good fills i can get out of it, not just how many

[luke]

[Kevmaster]

Jester:

If a scuba tank is filled to EXACTLY 3000 psi, and you connect your bottle to it and fill it, it will NOT fill to EXACTLY 3000psi. it WILL be below 3000psi. the bigger your bulk tank is the closer it is to 3000psi, but it will not be 3000psi.

why? the formula i mentioned earlier(this time with real math)
**3000psi is the inital pressure in a scuba tank with 500cubic inches of volume**

Pressure(1) * Volume(1) = Pressure(2) * Volume(2)

3000psi*500ci = 1,500,000 = Pressure(2)*Volume(2) = Pressure(2)*(500ci + 68ci) = Pressure(2)*568ci
--> Pressure(2) = 1,500,000 / 568 = 2640psi

hope that makes sense...

[TheJester]

yea, that makes sense, i'll play w/ that some, but sorry if i made it seem like i was saying the scuba tank wouldn't drain any, i know that it won't fill to exactly 3000, but i was saying the drop was prolly very little, do to the volume, that's why i wanted the volume, maybe i'm just better off asking does any 1 know how many good fills a 80 cubic foot tank, 3300(not 3000)psi tank will give a 68ci/3000psi tank? by good fills i mean 2400psi+

[Kevmaster]

yeh, i know, just pointing that out...