matteusz
10-04-2007, 08:43 AM
So I asked once before and got some wonderful info on how many fills I would get off one scuba tank. pneumagger gave us this:
PV=nRT
Assume nRT = constant
Assume V(s) = internal volume of scuba
Assume P(1) = Pressure in scuba before fill
Assume P(2) = Pressure in scuba and pb tank after fill
Assume V(t) = internal volume of paintball tank
State 1 = value before fill
State 2 = Value after fill
-----------------------
You can see the tank pressure drops with each tank fill and you will have to determine an "acceptable" minimum level of fill before you consider it in need of refill. With the above assumptions, P(1)*V(s) = P(2)*V(2) quickly simplifies to for your case:
P(1)*V(s) = P(2)*(V(s)+V(t))
Tabulated out, assuming a 3000psi filled 80CF cuba filling a 68/3000 tank, while taking dropping scuba pressure into account we see that...
Fills....Scuba Pressure...Tank Pressure
0.......3000.000000.....0
1.......2729.083665.....2729.083665
2.......2482.632551.....2482.632551
3.......2258.437314.....2258.437314
4.......2054.488127.....2054.488127
5.......1868.956663.....1868.956663
6.......1700.17970.......1700.1797
7.......1546.644216.....1546.644216
8.......1406.973822.....1406.973822
9.......1279.916425.....1279.916425
10.....1164.333003.....1164.333003
11.....1059.187393.....1059.187393
12.....963.5370043.....963.5370043
After 11 fills, the bulk tank fills the 12th tank at under 964psi and only filled the first tank to 2729psi. Factoring in quick or frequent filling (allowing the bulk tank to cool off) which is more representative of an adiabatic situation, the fill efficiency will worsen. So I'd say your looking at about 10-11 fills while maintaining at least 1000psi.
SO now I am thinking of getting a second tank and a cascade to connect them. Can anyone do a little more math or share their experience with me on what you can fill with two tanks instead of one? Your help is greatly appreciated.
Mat
PV=nRT
Assume nRT = constant
Assume V(s) = internal volume of scuba
Assume P(1) = Pressure in scuba before fill
Assume P(2) = Pressure in scuba and pb tank after fill
Assume V(t) = internal volume of paintball tank
State 1 = value before fill
State 2 = Value after fill
-----------------------
You can see the tank pressure drops with each tank fill and you will have to determine an "acceptable" minimum level of fill before you consider it in need of refill. With the above assumptions, P(1)*V(s) = P(2)*V(2) quickly simplifies to for your case:
P(1)*V(s) = P(2)*(V(s)+V(t))
Tabulated out, assuming a 3000psi filled 80CF cuba filling a 68/3000 tank, while taking dropping scuba pressure into account we see that...
Fills....Scuba Pressure...Tank Pressure
0.......3000.000000.....0
1.......2729.083665.....2729.083665
2.......2482.632551.....2482.632551
3.......2258.437314.....2258.437314
4.......2054.488127.....2054.488127
5.......1868.956663.....1868.956663
6.......1700.17970.......1700.1797
7.......1546.644216.....1546.644216
8.......1406.973822.....1406.973822
9.......1279.916425.....1279.916425
10.....1164.333003.....1164.333003
11.....1059.187393.....1059.187393
12.....963.5370043.....963.5370043
After 11 fills, the bulk tank fills the 12th tank at under 964psi and only filled the first tank to 2729psi. Factoring in quick or frequent filling (allowing the bulk tank to cool off) which is more representative of an adiabatic situation, the fill efficiency will worsen. So I'd say your looking at about 10-11 fills while maintaining at least 1000psi.
SO now I am thinking of getting a second tank and a cascade to connect them. Can anyone do a little more math or share their experience with me on what you can fill with two tanks instead of one? Your help is greatly appreciated.
Mat