Filling tanks with Cheap-O Air Compressors on eBay?

[yle]

A lot of replies in this thread are obnoxious hand-wringing. OP asked about these compressors, he didn't promote them as the next big thing in DIY fill stations. I also want to know. Instead of hearing about the cleanliness of the compressor, or seeing an analysis of said compressed gas, we get replies like "Don't". Nobody was going to actually use these for diving, we just wanted to know more about them. It may be that they cannot be used, or it may be that they are suitable for breathing air with some modifications and suitable filtering.

It's okay to think about it.

There are plenty of replies on this thread that explain why the compressor in the original post is not suitable for scuba. As I replied earlier, that compressor is designed for paintball, which uses small, 4500 psi cylinders.

Scuba compressors include very important filtering, as the air being compressed will be introduced to someone's lungs and bloodstream. The air breathed will still be compressed to higher than atmospheric pressure, which amplifies the physiological effect of impurities in the air. This is basic scuba knowledge, which is why most replies here are short and simple: don't do it, you will die. Because the people replying assume the OP either has basic scuba knowledge (because they are a certified diver) or does not have basic scuba knowledge and just needs to be told "No, you will die." (The implication being that the OP should get basic scuba knowledge before even thinking about doing anything scuba.)

Scuba compressors serve two important functions: they compress the air to a higher pressure, and they filter the air so it is appropriate for breathing. The compressor shown in the original post only performs the first function.

Can you modify the compressor shown to be a suitable scuba compressor? Absolutely, just like I can modify an old VW bug to look exactly like a new Ferrari. I would just need to buy a new Ferrari, remove all the parts, and then bolt the Ferrari parts onto the VW. Follow up question... does it make any sense to do this? No.

If you want a scuba compressor, buy a scuba compressor. The companies that make them have already done the hard part for you.

 

[yle]

Well, my original question was "Has anyone here tried these?" The clear answer is no, no one who responded has used one. There are people out there who have, though, and as I mentioned before, "Minidive" is out there packaging one up with a pony bottle and a reg, so logic would follow that if you could fill a very small tank, you could probably fill a larger one. I think we've we've sufficiently covered the risks, and I wouldn't even consider "Minidive" as a safe system, but I point it out only because it exists, people are using these compressors, and I was wondering what the experiences of anyone had been.

The Minidive people state this about the compressor:

" it have been specially designed by MiniDive to filter humidity, moisture, oil residues and oil smell for a clean air. Filter change is advised after every full tank filling. The nominal power of the MiniComp is 1800 W. An American plug is included for all MiniComp shipped to North America."

The difference between the $1400 "Minidive package" with its compressor and the $200 compressor on ebay is the filtering system. Granted the $1400 package also includes the little breathing cylinder (i.e. essentially a 3 cu ft spare air), but you're still paying about $1000 for the little compressor. Which is about right for a small (very small?) scuba compressor.

It says the compressor takes 3 minutes to fill the 3 cu ft cylinder... so it would seem it would probably take 90 minutes or so to fill a standard aluminum 80... if the compressor didn't overheat.

 

[djbclark]

The difference between the $1400 "Minidive package" with its compressor and the $200 compressor on ebay is the filtering system. Granted the $1400 package also includes the little breathing cylinder (i.e. essentially a 3 cu ft spare air), but you're still paying about $1000 for the little compressor. Which is about right for a small (very small?) scuba compressor.

So as far as I can tell the difference in the filtering system comes down to smaller cotton plus molecular sieve and carbon beads in the little cylinder that comes off the hose and goes next to the tank instead of just cotton. And using an appropriate oil. All of which are consumables you can purchase from their store.

Mini dive products - Scuba diving equipment - Compressor - Oxygen tank

Discover our products, scuba spare air, refillable mini scuba tank and 300 bar diving compressor. Check out the mini scuba tank review of our mini dive users.

www.minidive.com

However in chatting with them something interesting came up: they claim that the Yong Heng and similar looking compressors are Chinese intellectual property theft from them. Brief searching for dates makes this seem plausible: Minidive mentions go back to 2016, but earliest mention of Yong Heng compressor I could find was 2018. If that is true it's possible the compressor you get from them is actually higher quality, even though it looks the same as the others.

Also it would mean that the compressor was, in fact, initially designed for small scuba tank refill use. By a French company under EU regulations.

Personally I'm trying to figure out if I'd trust either of them plus maybe something like a Tuxing Separatory Tower and Coltri Personal Filter to produce Grade E air.

As far as I can tell no one, including minidive, has done testing to see if this is the case. The testing is relatively expensive, but in going with the crowdfunding idea of the minidive, if we could get 6 interested people it'd only be around $50 each.

So DM me if you are such a person, and let me know if you already have the equipment or not, and if so which brand and the history of oil types you've used.

 

[djbclark]

I actually found a person who tested a Yong Heng's air quality. It failed, however if I'm understanding it correctly this could easily have been attributable to using the wrong oil.

So a result with the oil minidive sells and recommends - "Special alimentary oil" - or some other scuba-breathable-air-rated oil would still be useful.

 

[lowwall]

I actually found a person who tested a Yong Heng's air quality. It failed, however if I'm understanding it correctly this could easily have been attributable to using the wrong oil.

So a result with the oil minidive sells and recommends - "Special alimentary oil" - or some other scuba-breathable-air-rated oil would still be useful.

Alimentary means you can eat it. It does not mean that it's safe to breathe.

 

[djbclark]

I just looked up the data sheet for
that oil.. It contains this actual line
"Mobil Rarus 427 is not intended
recommended for use in air
Compressors for breathing air
applications" :-(

Asked Minidive rep what's up with that, haven't heard back yet.

 

[lowwall]

I just looked up the data sheet for
that oil.. It contains this actual line
"Mobil Rarus 427 is not intended
recommended for use in air
Compressors for breathing air
applications" :-(

Asked Minidive rep what's up with that, haven't heard back yet.

As a former reference librarian, I can't help from anticipating where your research into shallow water swimming with scuba gear is going to take you next.

I suspect you will eventually find your way to home oxygen concentrators and boosters. There's been a few posts on them. For example, look at this post and the follow-ups such as post #14.

Workbench Update!

Inline adjustment tools are amazing. I haven't been able to/had to use one for many years diving Poseidons, and the one from VDH is great, especially for the price. Too bad they are currently OOS on those. First on I have seen without a gauge on it.

scubaboard.com

I want to warn you in advance that this is dangerous. Both because of the risk of fire in the regulator and because too high a partial pressure of oxygen will cause convulsions. Mitigating these risks requires knowledge which normally comes from the formal training you seem to be eager to sidestep.

 

[djbclark]

As a former reference librarian, I can't help from anticipating where your research into shallow water swimming with scuba gear is going to take you next.

I suspect you will eventually find your way to home oxygen concentrators and boosters.

Nah, I've become convinced of a lower-tech solution: a 2-4 used 80s (with up to date testing etc) and some quality rolling luggage, with ~monthly fill runs.

Would rather something less bulky and annoying to bring to the pool, but this seems to be an infuriating area of reality where the real solutions are either very expensive or insanely expensive.

 

[TrimixToo]

Missing from the responses (at least apparently so in my quick scan) is that breathing air filtration is not magic. There are hazardous compounds that can be created in a compressor that will pass right through the filtration system without being diluted in the slightest, and they can kill you. Breathing air compressors designed by reputable manufacturers are not cheap. There are sound reasons for this.

Anyone embarking on the journey towards one's very own compressor system need to google this and read it. Several times. Until it sinks in, in its entirety: Understanding SCUBA Compressors and Filtration by Ted Green

 

[CG43]

Hello : Why never use these cheap 2 stage compressors for 200/300 bar breathing air.

When you must not exceed a certain air temperature during compressing, you have to limit the compression ratio per stage .
For examble a proper value is 7 .
Three stage : after 1 stage 7bar ; 2 stage 49 bar , 3 stage 343 bar .
Attention, after first and second stage it needs an effective intermediate cooling because heat is produced again at the next stage.
With two-stage 300 bar compression, the compression ratio is 17.3/stage and there is only one intercooler possible . Under these conditions, it is almost impossible to keep the air temperature so low that it does not burn too much lubricating oil. In the net you can see videos of the second stage with a lot of soot.
A filter system that turns this toxic air into breathing air would cost some times more than this compressor.

greetings Rainer