OP
Compressor theory--is there an ME in the house?
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pescador775
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Belmont, the NG compressor does not require a filtration system, a fixed cost on breathing air compressors. However, the point is well taken, if there were a broader market for a mini compressor then production of scale could reduce price of the mini. I tried to suggest to the OP that he should look into commercial oxygen compressors used in medical oxygen transfer units but it didn't take. Maybe that is because the cost savings could only be realized if the concentrator/compressor were bought on the surplus flea market. He wants to justify a preconceived notion but getting a working unit from existing sources might be a little pedestrian.
Belmont
Contributor
I just googled "CNG compressor" and got this amongst other interesting leads: Oil free SCUBA compressors, nitrox, helium, heliox, nitrox cylinder filling compressors, diving compressors.
OP
WetCell
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I just stumbled across your posts last April titled "very small compressor". Interesting thread. Of course, lots of guys jumped in with their $.02 of why it won't work or why you shouldn't bother.
Anyway, I also just located the Phill (USA), that I had seen before and forgot about, and the Gasfill (UK) systems. Essentially, they are wall mounted units for your garage that "slow fill" your car with natural gas overnight to 3000 PSI from your gas main. AH-HAH! So, why not fill your scuba tank the same way. The downside is that these units run $4K. My guess is that all the special issues surrounding a flammable gas may be why the price is high for a "slow fill" unit. Anyway, I'm going to try to find out what compressor these babies use.
Getting closer!
pescador775
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Flammability has nothing to do with it. NG is only flammable when in the presence of oxygen and that element is very scarce inside a gas compressor. A real, breathing air compressor is expensive and always will be. Those little medical oxygen units boost gas in two stages and raise pressure from a couple hundred psi to 3000. Output is about 1 liter/minute or two cfm/hr.
OP
WetCell
Contributor
Well, that isn't entirely true--but immaterial now to the new data. A bit of further research has revealed that the paintball guys have multi-stage handpumps that get to +3000 PSI. One company marketed a motor connected to a handpump via a cam--but they no longer sell it. That is now the direction of my work with this.
A couple of issues now arise:
1) Why did the power-driven hand compressor get discontinued? Was it too expensive for the paintballers? Is power driving a hand pump too much for the technology to bear?
2) What about air quality, since that is not a major issue with the paintballers since they aren't breathing the air.
My answer to the first issue is that, like scuba divers, the paintballers are in a hurry to get their fill and the power driven unit was too much for the pump. You have to think outside of the box here (see some of the other posts--not TOTB) AND have patience. My goal is a cheap system. To get that, I have no problem letting it run all night if necessary--just like the NG systems. The UK NG compressor uses 800 watts, so that is about a buck (with my elec rates) over 8 hours. You cycle the pump[ i.e., it runs a bit, it waits, it runs a bit, it waits. I am even thinking about temp cycling it, since apparently that is the bugaboo of the hand pump. In other words, a temp sensor lets it run until the pump reaches a certain temperature, then cuts off the motor, then lets it cut on, etc. A pressure switch shuts the whole thing off when the tank is full.
To the second issue, there is one pump that has an air drier system, since the PBs do have a concern for dry air. I don't see a big issue with putting a filter on the output, but that may be a challenge. The other issue has to do with how these pumps are lubricated. One site indicated that it may be silicon grease, which is more benign than oil, but a concern nonetheless in a scuba air fill.
MDE ( or something like that),
a french company, developed engines running on HP air, may their compressors would meet your needs. It seems the latest model of their engine doubles as a compressor refilling the HP air cylinders at night.
you could google for HP diaphragm compressors, single stage low volume high pressure, which could putter away at night refilling your scuba tank while you sleep.
Shil
a french company, developed engines running on HP air, may their compressors would meet your needs. It seems the latest model of their engine doubles as a compressor refilling the HP air cylinders at night.
you could google for HP diaphragm compressors, single stage low volume high pressure, which could putter away at night refilling your scuba tank while you sleep.
Shil
pesky, while we are on this subject, I am wondering if some real outside of the box thinking could be a solution, removing the question of practicality and other little details does make it easier. If we define the goal as to compress air to fill an 80 cu ft tank within 8 hours, what alternatives to the traditional compressors can we come up with? Hydraulic powered Haskel style boosters? Better yet, here is one I would like someone to poke holes into (pun intended). Excluding the massive waste of electricity in this design, let me ask why this would not work:
Basic concept is a home water well style pressure tank in reverse in a 2 stage cycle
Have a high pressure accumulator tank with a HP neck on each end (lets say around 20 cu ft at 3000 psi, exact size is not important as we could cycle this system to fill a tank if needed) we place a rubber bladder inside (the bladder is to keep excess moisture out of the compressed air)
Stage one, We then pressurize the rubber bladder to around 100 psi with a small oiless air compressor through a priority valve to prevent back flow.
Stage two, using a modern 3000+ psi plunger pump (either quality unit, or cheap import) found in pressure washers fill the area outside the rubber bladder in the accumulator tank with water thereby pressurizing the air in the bladder
Repeat, with forcing the water out into a storage tank
Add plumbing and valves as needed to the basic concept
Basic concept is a home water well style pressure tank in reverse in a 2 stage cycle
Have a high pressure accumulator tank with a HP neck on each end (lets say around 20 cu ft at 3000 psi, exact size is not important as we could cycle this system to fill a tank if needed) we place a rubber bladder inside (the bladder is to keep excess moisture out of the compressed air)
Stage one, We then pressurize the rubber bladder to around 100 psi with a small oiless air compressor through a priority valve to prevent back flow.
Stage two, using a modern 3000+ psi plunger pump (either quality unit, or cheap import) found in pressure washers fill the area outside the rubber bladder in the accumulator tank with water thereby pressurizing the air in the bladder
Repeat, with forcing the water out into a storage tank
Add plumbing and valves as needed to the basic concept
pescador775
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I don't know about the water accumulator, I thought that sprayers only generated about 1500 psi.
The hand operated booster has been around a long time. Hacker mentions it in his book. They are used to raise the pressure of small volumes of air or oxygen. I believe RB divers were interested in them and had actually imported one or two from Russia. Some kind of ram with oiless seals might work. It could be driven by hydraulics or by a lever working off an eccentric, and water cooled. Let's say the internal, swept volume was 1/10 liter, with one stroke per second and not figuring blowby, the rate would be 6 liters per minute or .2 cfm.
The hand operated booster has been around a long time. Hacker mentions it in his book. They are used to raise the pressure of small volumes of air or oxygen. I believe RB divers were interested in them and had actually imported one or two from Russia. Some kind of ram with oiless seals might work. It could be driven by hydraulics or by a lever working off an eccentric, and water cooled. Let's say the internal, swept volume was 1/10 liter, with one stroke per second and not figuring blowby, the rate would be 6 liters per minute or .2 cfm.
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mhinagoya
Registered
Please be tolerant. I'm working from memory.
When I learned to dive back in the 1960's, someone was marketing a single cylinder scuba compressor. It would only pump to about 2,500 psi. It was tiny and fairly inexpensive.
If I recall correctly, it had a piston about half an inch in diameter and took several hours to fill a steel 72. Mako comes to mind, but I wouldn't swear that they had marketed them.
I actually saw one once. It wasn't in serviceable condition. Evidently, the single piston and cylinder would get outrageously hot. The heating and cooling cycles would crystallize the piston and cylinder and in a few hundred hours, it would go bang. It was a great idea, but with affordable materials, it simply wouldn't work. I guess that something similar could be made today, using materials like inconel, 9 nickel cobalt, and beryllium copper alloys, but the cost would be insane.
The point here is that anything can be done, given sufficient money. If there was a way to build a small, inexpensive compressor to fill scuba tanks, someone would be all over it. The market is ready.
Technology is available to do virtually anything that can be imagined. In the end, it will always come down to cost. The military compressors cross the cost benefit line by a substantial margin. They are vastly better made than the commercial units of similar size. Cost was a consideration in their design, but only in a secondary sense. Longevity, reliability, and weight took top honors.
In many cases, economy of scale will drive costs down but not with the materials I mentioned. Some things are so difficult to machine that very few people on the planet can even do it (9 nickel cobalt is one of those materials). In those cases, economy of scale is just a dream.
You can have it good, cheap, quick. Pick two.
I work in the aerospace industry. We face these decisions on a daily basis. We do not resort to exotic materials if any reasonable alternative exists. This is just reality and the same reality that compressor designers and manufacturers have to consider.
Bill.
When I learned to dive back in the 1960's, someone was marketing a single cylinder scuba compressor. It would only pump to about 2,500 psi. It was tiny and fairly inexpensive.
If I recall correctly, it had a piston about half an inch in diameter and took several hours to fill a steel 72. Mako comes to mind, but I wouldn't swear that they had marketed them.
I actually saw one once. It wasn't in serviceable condition. Evidently, the single piston and cylinder would get outrageously hot. The heating and cooling cycles would crystallize the piston and cylinder and in a few hundred hours, it would go bang. It was a great idea, but with affordable materials, it simply wouldn't work. I guess that something similar could be made today, using materials like inconel, 9 nickel cobalt, and beryllium copper alloys, but the cost would be insane.
The point here is that anything can be done, given sufficient money. If there was a way to build a small, inexpensive compressor to fill scuba tanks, someone would be all over it. The market is ready.
Technology is available to do virtually anything that can be imagined. In the end, it will always come down to cost. The military compressors cross the cost benefit line by a substantial margin. They are vastly better made than the commercial units of similar size. Cost was a consideration in their design, but only in a secondary sense. Longevity, reliability, and weight took top honors.
In many cases, economy of scale will drive costs down but not with the materials I mentioned. Some things are so difficult to machine that very few people on the planet can even do it (9 nickel cobalt is one of those materials). In those cases, economy of scale is just a dream.
You can have it good, cheap, quick. Pick two.
I work in the aerospace industry. We face these decisions on a daily basis. We do not resort to exotic materials if any reasonable alternative exists. This is just reality and the same reality that compressor designers and manufacturers have to consider.
Bill.
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