"1/2 PSIG" regulator

[iknowmy3tables]

some regulator I found a long time ago says "1/2 PSIG on it, the spring is very weak so maybe it does actually regulate to .5psi. its used I found is from some about to be scraped system attached to old 1/2" threaded pipes and fittings, along with a directing solenoid valve. The regulator has some rust and corrosion in it but should still work.

anyways I haven't had a good use for it, but I was thinking, could I use this regulator for automatic fuel injection? would adding propane or or other fuel until the chamber gained more or less 1/2psi of pressure create a proper fuel air ratio environment

[jimmy101]

could I use this regulator for automatic fuel injection? would adding propane or or other fuel until the chamber gained more or less 1/2psi of pressure create a proper fuel air ratio environment

Yep, if you trust the accuracy/reproducability of the regulator. For adding propane to a closed chamber;
(14.7 PSI)(0.042)=0.62 PSIG

So, set the reg to 0.62 PSIG and your're good to go.

Probably want a short pipe with small ID between the reg and the gun's chamber.

I wouldn't be surprised if the reg wasn't all that accurate. But, it might be reproducable which is more important anyway. You might try tweaking the setting up and down a bit to see what works best.

[iknowmy3tables]

thanks, this could turn out to be a pretty cool thing, I'll probably regulate the pressure before the gas hits the .5 psi regulator

but makes me wonder what the heck would a .5psi regulator be used for?

[SpudFarm]

a REALLY small hybrid

[jimmy101]

iknowmy3tables, a regulator before the "1/2 PSIG regulator" is probably a good idea. I think there is a good chance that a regulator with such a low outlet pressure probably wasn't designed for use with a high inlet pressure (like a propane tank).

[Ragnarok]

So, set the reg to 0.62 PSIG and you're good to go.

I think it's a bit more complex than that. If we assume the chamber is not completely air-tight, gases will slowly leak from it. As they leak in rough proportion to the mix of the gases, then air will leak with the propane.
This leaking will lower the pressure - which will be diligently topped up by the regulator, destroying any pretence at an accurate mix.

So, to do it, there will need to be a shut off valve between regulator and chamber. I would hope that there was one anyway to protect the regulator, but it's doubly important with respect to an stoichiometric mix.

[jimmy101]

Rag, well of course there has to be a valve between the reg and the chamber, there is always a valve there (well there always should be).

Leakage can be a problem but it depends on how bad the leak is. Easy enough to test, pressurize to 0.6 PSIG, close the valve to the propane source and leave the reg connected, let the gun sit for a while. Does the reading on the reg's gauge change? No significant change means leakage is not a problem.

Combustion guns, in general, tend to be leaky buggers. Few people even test for leaks becasue there isn't any easy way to do it. (You would have to glue a cap onto the muzzle, use a "bung plug", ...) Cleanout plugs and threaded couplers are often leaky. The cleanout plugs are extra leaky because they are removed for every shot and it's a PITA to do that if you crank'm tight enough to not leak.

[iknowmy3tables]

if leaks became a huge issue but the regulator was acurate I'll use it to make a sorta smart hybrid, with a standard mix chamber that compresses the air into a smaller high tolerance chamber like the hydro-pneumatic thiny only probably with a pump