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RE: Multi tank CO2 system



> Am getting ready to install pressurized CO2 system. I wish to run multiple
> tanks, approx. 25, of varying sizes from one system. Currently using
>
> Suggestions, other's experience. All input welcome.

IMO, refrigeration copper is a bear to work with.

The CO2 permeability of silicone tubing is 10132 (units:  10^-10
cc-mm/sec-cm^2-cm Hg).  A better choice is FEP (fluorinated ethylene
propylene) tubing (CO2 permeability:  5.9).  Cole-Parmer charges $23 for 25
feet of OD 1/4Ē, ID 3/16Ē FEP tubing.  You donít need the more expensive,
thicker tubing.  Iíve not seen this tubing degrade after many years of use
with corrosive gases.  Use brass compression fittings from Swagelok ($1 to
$3 each) and itíll never leak.  Cheaper compression fittings (Home Depot)
work almost as well -- just donít over tighten them.  I like to use
self-sealing quick disconnects ($11/set from C-P) instead of a valve at each
tank.

So, is it worth it to use FEP instead of silicone tubing?  Iíve wondered
about it myself, so hereís my shot at a calculation (Iím sure someone will
let me know if Iím wrong):

				English		Metric
CO2 flow rate		1 bubble/sec	0.06 cc/sec (my measurement)
Room pressure		14.7 psi		76.0 cm-Hg
CO2 Line Pressure		25.0 psi		129.3 cm-Hg
tube wall thickness	1/32 inch		0.8 mm
ID of tube			3/16 inch		4.8 mm
Area 1 ft of tube		7.07 inch^2		45.96 cm^2

Fickís Law:
Flow = Permeability * Area * (Pressure Difference)/ Thickness
= 10131*10^-10*45.96*(129.3-76.0)/0.8

Tube length		CO2 loss (silicone tubing)
1 ft			0.0031 cc/sec (ml/sec)
2 ft			0.0061
4 ft			0.012
8 ft			0.025
10 ft.		0.031
100 ft.		0.31

So, you lose about 20% of your CO2 with 4 ft of silicone tubing per tank and
virtually none with FEP.  With multiple tanks, the percentage loss is the
same, but the total volume lost is greater.  CO2 is cheap (I just paid
$13.65 for a 10# refill) -- but youíre also saving the cost (annoyance) of
getting your tank refilled more often.

Bottom line:  Cost recovery time for FEP instead of silicone, about the time
it takes you to use 5 tanks of CO2.

Joe K