YAFS (Yet Another Fill Station)

[Genesis]

Bill of Materials:

1. Alkin 3.5cfm 220V, single phase compressor. (Damn nice unit, by the way.)

2. Backpressure regulator and check valve, plus a hex nipple and 90 degree elbow, for the compressor (to keep the filter stack pressurized and thus improve its efficiency when filling a near-empty tank), along with preventing any backflow into the compressor from a tank when it is connected.

3. Second fill whip w/valve (used to connect to the Hyperfilter)

4. Lawrence Factor Hyperfilter, 7,000 cuft capacity (to the right.) I removed the original whip that came with the compressor, O2-cleaned it, and installed it on the output of the LF unit - its a much nicer whip than the separate one! Note that this is NOT an Oxygen whip (in fact, none of these are)

5. I also added a digital pressure gauge to the whip for final pressure monitoring. It is more accurate than the one on the hyperfilter. This is a 1% gauge - not a precision 1/4% unit. Accurate enough - within 50 psi.

The reason for the hyperfilter is that I am partial-pressure Nitrox blending. Not shown is the O2 tank and whip - the whip is current complete EXCEPT for the handwheel and nipple, which, of course I need to hook up to the bottle. Should have been here today, but its not yet - probably will be here Monday.

The O2 tank itself is chained to a hand truck (which is chained to the wall when not in use, so it cannot fall over), and for filling use will be rolled out into the driveway.

Why? Two reasons:

1. IF you are going to have a problem with a partial-pressure fill, odds are it will happen when putting the O2 in the tank. If you have it outdoors and away from the building, you have the option of running. That is not an option if its in your garage and lights it on fire! (Putting an O2-enhanced fire out if you can't get to the valve is likely to be flatly impossible.)

2. The risk of a problem while adding the AIR is controlled by (1) pressurizing the whip above tank pressure BEFORE opening the tank valve (thus pure O2 never passes above the valve seat) and (2) using hyper-filtered air.

I considered continuous entrainment ("stick" nitrox mixing) and for the time being have decided not to go that way. I am just not convinced that it is safe and doesn't lead to excessive wear of the compressor hardware itself. I may revisit this if I end up dumping a lot of half-full tanks, but Lawrence Factor specifically does not recommend running enriched air through the hyperfilter, and, for that matter, neither do any of the compressor makers (although lots of people do indeed do it!)

Fill time is a bit over 20 minutes from 500 - 3000 psi; the first 2-3 minutes or so are spent pressurizing the hyperfilter stack before gas actually starts to flow into the tank - a consequence of the considerable volume of the Lawrence Filter stack and the priority valves fitted in the system. If you're filling multiple tanks that obviously only has to happen once, which helps a great deal.

The Hyperfilter and check valve on the compressor are my anal side on safety issues showing through - many people will say its not necessary, and they may be right. On the other hand even with the cost of using it a Nitrox fill will cost me about 1/4 of what I pay for them at any of the local shops.....

 

[Aquamaniac]

Very Pretty

 

[Genesis]

about this compressor is that it does not have to be hard-wired. In fact, it came with a 220V/20A plug on the end - making it truly PORTABLE! I would have preferred a twist-lock plug, but that's ok - I don't leave it plugged in anyway, since I have a kid around (actually, I turn off the feed breaker in the panel AND unplug it - double safety )

You could actually make up an adapter to an electric dryer (30A typically) outlet if you wanted to, and run it portable. Its only about 120lbs wet, so while its not "light" its definitely "2-man portable."

The Hyperfilter setup from LF is a completely stand-alone device. I like it. Since its just yoked onto the compressor, you can break it down when not in use and don't have to run hard-line.

I considered re-rigging it permanently, but that removes my option of filling regular air (not O2-clean) bottles easily, and forces me to burn Hyperfilter volume for all fills. Right now all my tanks are O2-service rated, but in the future I might have a couple that I keep around for "weenie dives" on straight air, and there is no reason to spend the hyperfilter capacity on those.

 

[The Curly One]

Those little compressors really are heavy duty units and I am very pleased with them. In my opinion the ALKIN is the best portable compressor made. The only real drawback to the compressor is that it is pretty heavy. Glad to hear you are pleased with the compressor, that is a significant purchase and I want you to feel you got the best. I think you did. Thanks, Curly

 

[Genesis]

that I have gotten is how COOL the gas is going into the filter stack.

The pipe going into the compressor filter stack is cool to the touch! That amazed me - of course the one coming out of the 3rd stage is hot, but by the time its gone through the cooling coil, its back to near room temperature. Pretty good.

The other BIG difference from other compressors I've seen is that thus far I've gotten ZERO condensate out of the filter stack drain. There is a LOT coming from the condensor after the second stage, but it appears that condensor does an absolutely amazing job, because essentially no liquid water is discharged at all from the stack drain when I crack it at 10 minute intervals. Now its been pretty dry humidity-wise here the last week or so, so I don't expect that stellar record will hold through the summer, but it is amazing nonetheless.

I'm going to run flexible tubing to a "crap trap" for the condensate, just to keep it off the top of the cabinet.

I don't consider this thing heavy - 110 lbs or so - its not bad at all. Plus, it has rollers/wheels on one end, and a lifting handle on the other, so moving it on a flat surface is a single-man job.

 

[Dryglove]

ok im jealous Nice set up.Can i have it when you get tired of it

 

[Genesis]

Tired of it eh? Let me think about this..... Nitrox for roughly $2/tank in costs, .vs. buying it for $10.... hmmmm.... I wonder when I'll get tired of that

 

[Waterborne]

That's quite a setup you have going there Genesis. Maybe when I sell a kidney on ebay I could afford one myself:wacko:

Seriously though, it seems like it would be an excellent investment. How long is it gonna take the cost to savings grid to equal out?

 

[redacted]

But is that bungeed phone DIR?

 

[Genesis]

Here's the breakdown:

Total investment - approximately $4,000 (including O2 whip pieces and parts, compressor, hyperfilter, miscellaneous parts that I added such as the priority and check valves, wall box, socket, wire, breakers, etc)

Differential .vs. buying EAN - $7.50/tank for AL80s, about $7.00 for HP120s (at one shop - the others all charge more for larger tanks, so its actually about $8.00 for the larger tanks at others)

Time before the hardware is fully paid for: 570 fills.

Expected hours on compressor at that time: 280 (based on HP100s)

Time to first overhaul on compressor, based on scheduled maintenance list in the book: 1,000 (cylinder head valves)

Oil changes required (first one is free as its supplied when the warranty card is returned): 4 (based on six months, not hours - 100 hours will not be reached first)

Value of setup at time of full amortization - likely almost "as new".

Therefore, depending on how you run depreciation/amortization of the hardware, the hardware is in fact "free" from the first fill, in that its value does not materially decline during the payback period. If you get out of diving and eBAY the hardware you are likely to get almost everything back you put into it.

Opportunity cost on the money (at 10%, compounded annually, in the S&P 500 index, assuming approximately 250 tanks/year): $840.00 This you CANNOT logically ignore, because its real no matter what you do.

Net savings over two years, assuming near-zero depreciation of the hardware, opportunity cost of the money, and filling 250 tanks/year with EANx32: $2,910.00

The hardware, including opportunity costs, is fully paid for (assuming 100 dives/year for you and a buddy) in just over 2 years, at which point your per-fill cost is under $2.50/bottle, all-up.

If you're filling just AIR, and don't use the hyperfilter (and its expensive stack) or O2 the cost is under a buck a tank. HOWEVER, if you do that realize that you shouldn't stuff that gas in a nitrox cylinder that is O2 service rated - I will be running all my breathing gas through it, because all my tanks are O2 service rated and I want the option to put Nitrox in any of them at any time. So in that case a fill of air, through the hyperfilter, costs about $2.

Do the math - you're nuts not to own one of these if you, and a buddy, are doing more than about 50 dives annually and using Nitrox Assuming the maximum "payback" period for the hardware you will tolerate is five years, the "breakpoint" in terms of wanting one of these setups happens somewhere around 50 dives annually, as that load will require changing filtes slightly more often than at filter capacity due to time expiring (six months) before gas consumption requires it.

In South Florida where you can get fills of EAN for $3-4 it makes no sense to buy your own other than for convenience. If you're paying $8-10 for those fills then you're simply insane not to "roll your own", not to mention the convenience of being able to fill tanks whenever you want (e.g. come in from diving this evening, want to dive tomorrow, shop is closed, you can still fill your own tanks.)