Tank Compressors
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People sometimes did these conversions using surplus air compressors from the military. The Cornelius, Kidde and GE aircraft compressors were light weight and pumped high pressure (3000 psi) which made them suitable for homebuilts. The changeover required that the builder fabricate a mounting stand or frame, a motor mount, pulleys for belt drive, or modifying an engine drive shaft and engine crankcase for direct drive. Then, he had to find a filter canister, blow off valve, and appropriate tubing and fill whip with yoke connector and gauge. A fair amount of practical engineering knowledge is necessary. Yet, as I say, quite a few were built during the 50's-70's.
The compressors themselves had built in failsafe valves or discs which minimized the explosion risk. However, handling compressed air is always potentially hazardous so a project like this must, of necessity, be approached thoughfully and carefully. The key is finding a good compressor at a cheap price, and that requires research and some luck. Not as easy as it used to be when you could buy the compressor and conversion instructions prepackaged, or could buy a surplus compressor for a hundred bucks.
Unfortunately, the "standard" compressor is not suitable for this. The supply pressure is too low. You need a three or four stage unit which can supply at least 3000 psi. It's not a bad idea, even today. It's possible, with the internet advantage, that a suitable block could be found. The trick is knowing which one is in good enough shape to use. That ain't easy and is mostly a matter of luck.
Believe it or not, some guys make a living from converting and selling old MIL compressors, even today.
http://hometown.aol.com/protecair/
The compressors themselves had built in failsafe valves or discs which minimized the explosion risk. However, handling compressed air is always potentially hazardous so a project like this must, of necessity, be approached thoughfully and carefully. The key is finding a good compressor at a cheap price, and that requires research and some luck. Not as easy as it used to be when you could buy the compressor and conversion instructions prepackaged, or could buy a surplus compressor for a hundred bucks.
Unfortunately, the "standard" compressor is not suitable for this. The supply pressure is too low. You need a three or four stage unit which can supply at least 3000 psi. It's not a bad idea, even today. It's possible, with the internet advantage, that a suitable block could be found. The trick is knowing which one is in good enough shape to use. That ain't easy and is mostly a matter of luck.
Believe it or not, some guys make a living from converting and selling old MIL compressors, even today.
http://hometown.aol.com/protecair/
Isn't it too expensive to operate and maintain a compressor as a home user?
I would love to fill my own tanks but I think the cost would be prohibitive.
I would love to fill my own tanks but I think the cost would be prohibitive.
Gorji, Yes, it is expensive. If every diver had the money and motivation to fill tanks then we would see a lot more of this. Reasons for doing so are as diverse as the divers themselves. In my case, it was the hassle factor. No need to make a run to a distant dive shop with inconvenient hours or to deal with hot fills, low fills, or inspections. It used to be that special equipment was needed to remove a valve. Today, anybody can twist off an O ringed valve and check for rust, etc. If I need to fill a clean but out of date tank, it gets done. Nobody is going to ask if my Nitrox marked tank already contains a partial fill of O2; that's because I am the tank monkey doing the fill. If a tank is just 300 psi low, no run to a shop; it gets topped off right now, and no charge, no hassle.
Compressed air is used for more than tank filling; having it available at all times is really nice. Try filling a boat trailer tire to 60 psi with a hand pump. Try operating air tools without an air source. With a small dive tank, harness and air tools, you can bring the solution to the problem, and if more air is needed, it's available anytime.
I bought a Bauer Capitano, new, in 1974, for $1580. I've had virtually no problems with it. Today, this type unit costs $6000. I've filled tanks every year since. Was it a good investment? You tell me. I've also owned a home made portable from 1976 which cost $1200 and has been overhauled once, for $200 in parts. It has done duty on many boat trips to far away islands. A compressor owner can become very popular. With a compressor aboard, everyone is relieved of having to lug tanks ashore on some little island where the dive shop is open every other day from noon to four. Of course, if your dive trips are canned (packaged), there is probably no need to do this sort of thing. It depends on the diver. Saving money was the last thing on my mind when I went this route. However, as it turns out, our expeditions have not only been infused with the thrill of discovery, but the overall costs has been less than some packaged tours treading the beaten path. As a compressor owner and experienced diver, I'm one link in the chain of expertise required to untertake a venture of this sort. If you can put together a group with experienced in yacht handling, navigation, cooking, provisioning, dive gear, spearfishing, fishing, first aid; you're pretty much set to start a plan.
So, the question of expense is relative and must be weighed in context.
Compressed air is used for more than tank filling; having it available at all times is really nice. Try filling a boat trailer tire to 60 psi with a hand pump. Try operating air tools without an air source. With a small dive tank, harness and air tools, you can bring the solution to the problem, and if more air is needed, it's available anytime.
I bought a Bauer Capitano, new, in 1974, for $1580. I've had virtually no problems with it. Today, this type unit costs $6000. I've filled tanks every year since. Was it a good investment? You tell me. I've also owned a home made portable from 1976 which cost $1200 and has been overhauled once, for $200 in parts. It has done duty on many boat trips to far away islands. A compressor owner can become very popular. With a compressor aboard, everyone is relieved of having to lug tanks ashore on some little island where the dive shop is open every other day from noon to four. Of course, if your dive trips are canned (packaged), there is probably no need to do this sort of thing. It depends on the diver. Saving money was the last thing on my mind when I went this route. However, as it turns out, our expeditions have not only been infused with the thrill of discovery, but the overall costs has been less than some packaged tours treading the beaten path. As a compressor owner and experienced diver, I'm one link in the chain of expertise required to untertake a venture of this sort. If you can put together a group with experienced in yacht handling, navigation, cooking, provisioning, dive gear, spearfishing, fishing, first aid; you're pretty much set to start a plan.
So, the question of expense is relative and must be weighed in context.
DevJr: Great Post I found it educational. Well done.
scubatrader
Registered
I own a junior II by bauer. LOVE IT. No more hot fills and I can do what I want. I paid about $2500 for it 2 years ago. Got it on e bay. I would like to add a better filter system to it. The one it has is fine. It cost $1.00 a fill less the 2500. buy I had to drive 30 miles each way to get a fill and had to leave it over night or sometimes days to get a short fill. Worth EVERY penny! If you buy one get a name Mako, Bauer, IR, something like that. I fill right off the compressor no bank bottles. Banks are just more tanks to get hydroed. I do not fill NITROX. It is a gas compressor which is GREAT for brining on the boat. But not to good around O2 if you want to fill nitrox get a electric one.
if you are going to home fill the biggest thing is air quality.. good filtration is a must.. If you fill your own tanks, count on spending at least $400 a year on filter media (assuming you are doing a reasonable amount of fills).. Your media probably wount be exhausted but the only other alternative to know how good your mix is is to have quarterly testing, and thats around $340 a year, just get good filtration and change it routinely. If you are doing a home system don't use a compressor that fills very fast, opt for a slower fill since compressors rated for fast fill rates require considerably better filtration.
If you plan on doing P.P. nitrox fills air testing is very important.. You must know if your gas is O2 compatible..
If you plan on doing P.P. nitrox fills air testing is very important.. You must know if your gas is O2 compatible..
Lost Yooper
Guest
Ah, just think of filling as a hobby and don't worry about the cost.
Mike
Mike
pescador775
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Four hundred dollars worth of filtration for the Junior II would fill 350 100 cf tanks. Do home users actually do this? If so, the cost could be cut in half by buying in bulk and hand filling the over priced Bauer inserts.
The whole business of micro filtration is overblown hype. The Bauer PO condenser/filter produces grade E or better and is acceptable, if not technically perfect, for PP topping off. For decades, the Navy UDT/EOD/SEAL used the Cornelius portable compressor for breathing air; this had only a condensator, no chemical filter whatsoever. Until recent years, even the smaller Bauer units used only condensers and a tiny refillable charcoal cartridge, and cost practically nothing to operate. None of this caused any notable problems with air quality although the very old Bauers would occasionally pump moist air. That was essentially cured with the introduction of back pressure valves.
A good condenser and small charcoal filter is really all that most portables need. Those that fill tanks in the LA Basin should probably have the full blown triplex cartridge with hopcalite. Ice divers should use filters with added dessicant like "13X". Beyond that, I doubt that anyone really needs the so called "polishing" filters that are being hyped around today. That is a diveshop concern for liability reasons. Any diver that gets a cough could sue the shop.
Aside from the above, gas engines produce noxious exhaust gas and dangerous CO. Appropriate precautions ARE necessary when filling diver tanks.
The whole business of micro filtration is overblown hype. The Bauer PO condenser/filter produces grade E or better and is acceptable, if not technically perfect, for PP topping off. For decades, the Navy UDT/EOD/SEAL used the Cornelius portable compressor for breathing air; this had only a condensator, no chemical filter whatsoever. Until recent years, even the smaller Bauer units used only condensers and a tiny refillable charcoal cartridge, and cost practically nothing to operate. None of this caused any notable problems with air quality although the very old Bauers would occasionally pump moist air. That was essentially cured with the introduction of back pressure valves.
A good condenser and small charcoal filter is really all that most portables need. Those that fill tanks in the LA Basin should probably have the full blown triplex cartridge with hopcalite. Ice divers should use filters with added dessicant like "13X". Beyond that, I doubt that anyone really needs the so called "polishing" filters that are being hyped around today. That is a diveshop concern for liability reasons. Any diver that gets a cough could sue the shop.
Aside from the above, gas engines produce noxious exhaust gas and dangerous CO. Appropriate precautions ARE necessary when filling diver tanks.
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