is that while you have capital costs with your own fill system, you get rid of ALL of the Dive shop BS at the same time you save money.
The compressor really doesn't depreciate much. Yes, it costs money to maintain, and time, but what doesn't?
The "we need a day to fill your tank" crap completely goes away. So does the driving (which costs money, natch.) You can make your own custom mixes, to the limit of your ability or willingness. If you want to dive Trimix, you can make that too. You want to fill your own O2 bottle? Cool - have at it. No BS required. None of it is really difficult, and its also not REALLY that dangerous, if you pay attention. Oh sure, its not zero risk, but how many people use welding gear (with O2 in there - oxyacetylene torches) all the time? If you stand around at the fill station while the shop fills your tank, if your tank explodes you're just as dead as if it happens in your garage. No difference there at all.
On top of that its cheaper. Possibly a LOT cheaper. Figure refillable cartridges good for 3000 cuft can cost $20/shot, and the "throwaways" are in the $30-35 range. That's 10 cents/cuft, or about $1 for each HP100. The O2 to make Nitrox for an AL80 is about fifty CENTS. Power is inconsequential; with a 3kw motor each AL80 costs you perhaps a dime to fill (at 6c/kwh) So your "per fill" cost is under $2 for "recreational" EANx mixes, ignoring depreciation on the hardware.
Can you reasonably do that? Sure. The typical compressor will run 1,000 hours before you have to pull the heads and replace the valves. Oil changes are every what - 100 hours or so? Each hour on a 3.5cu/ft FAD compressor will pump 210 cubic feet of gas, or 21,000 for each oil change, and 210,000 for each head overhaul. That's 210 HP100 tanks for each oil change, and 2,100 tanks for each head overhaul!
That's a LOT of diving.
Let's look at the math.
Say you buy an Alkin W31 ($2500), the pressure-maintaining valve for it (its not included) for another $50 or so, make up an O2 whip ($100) and buy a couple of decent digital gauges ($225). You have about $3,000 in the set-up.
Ok, how long before the compressor is FREE?
Let's say that we allow $0.50/tank for oil and maintenance. That's WAY conservative - the real value is probably closer to a dime.
Your actual cost of a fill of EANx is about $2 in power, O2, and filter media. You would pay $10 for that fill, plus tax - call it $11, which is pretty close.
Ok, so you save $8.50 for each fill.
In 352 fills the entire setup is paid for - completely amortized.
If you dive 100 dives/year, you pay for the entire filling station in under four years, have gone through four oil changes (time, not hours), roughly 10 filter cartridges, and the heads are due to come off in about another six years for the first "top end" job. The compressor is barely broken in.
If you have a buddy who dives with you and goes in on the gear with 'ya, then cut that time in half.
If you add a Lawrence Factor "zerofilter", to get OCA (which you might want to do if you're going to do PP blending), then add $1,000 to the capital cost and about a buck a fill to the per-tank costs. What you save is the more-frequent teardown and cleaning of your tanks to remove accumulated contamination.
Gee, this is tough to figure out. NOT!
