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.
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.