AirgunAdvice.net

[mcmike]

Some where along the way I picked up the idea of cascading scuba tanks. It was not my original idea and sorry I can't quote the source.

I did some interesting math this morning. Using the www.airhog.com fill calculator, I calculated the following:

1) Fills of a 400cc cylinder from an 88cuft 4500psi tank, filling from 1740psi/120bar to 3,000psi/206bar = 24 fills


Now the concept of cascading, you fill the 400cc cylinder from two tanks. One does the bulk fill and then the second tops it off to the desired pressure.


2) Fills of a 400cc cylinder from an 80cuft 3300psi tank, filling from 1740psi/120bar to 2550psi/175bar = 23 fills

Then cascade to the second tank:

3) Fills of a 400cc cylinder from an 80cuft 3442psi tank, filling from 2550psi/175bar to 3000psi/206bar = 24 fills


I used the two tanks mentioned above since that is what I have in the closet. Don't think I'll be lugging two cylinders out into the field but I thought the exercise was interesting since high pressure fills can be found about 30-45mins from my house and the local dive shop is 5mins from work. I bought my tanks from the local shop and they fill them for free 50% of the time. So for me, the lower pressure tanks are the path of least resistance.

I thought this may interest you guys who live in areas where high pressure fills are hard to find. You can replicate the fills of a high pressure tank with two lower pressure tanks.

Mike
_________________
"Talent hits a target no one else can hit, Genius hits a target no one else can see." Arthur Schopenhauer

[PortlandGuy]

What is the summary for cascading with a 300psi tank- sorry if I didn't follow it.

John

[-=ed]

.
can't you just consider the connected tanks as one single 176cf tank and make the calculation?

[mcmike]

PG,

The bottom line is ~24 fills for an 88cuft 4500psi tank and ~24 fills for cascaded 80cuft 3300psi and 3442psi tanks.

Ed,

Nope, if you just link the tanks together you get 16 fills at ~3371psi for a 176cuft tank. (avg. 3300 and 3442psi)

What you are doing when you cascade is using more air from one cylinder to do the bulk fill than you normally would. For example, you would normally fill the cylinder a number of times and then stop when the fill pressure falls below ~3000psi. With the cascading you fill all the way down to 2550psi on that same tank thereby taking advantage of much more air. The top off with the second tank which is using less air but and emphasis on finishing the fill to the required psi.

Obviously the Achilles heel is if you want to fill to 3300 or 3400psi all the time. In that scenario you need the 4500psi tank.

HTH,

Mike
_________________
"Talent hits a target no one else can hit, Genius hits a target no one else can see." Arthur Schopenhauer