The piston is lubricated but its not at all volitile (it doesn't seem to be putting off any fumes that I can smell). I hooked an ohmmeter up to the spark gap leads and read some resistance so I thought that there may have been a short but once I redid the leads and their entry into the chamber it st...

It's somewhat impractical to try and fire with volumetric metering (chamber is about 2''x32'' [51mm x 810mm]). I've just tried firing it at a 1x, 2x, and 3x mix, loading the propane in first on the latter two and then the air as well as just trying to let it sit for a minute for the gases to mix, bu...

Oh no, I mean I have two leads coming out of the chamber for the spark gap, and while under pressure I connected one lead to one end of my module and then held the other lead ~1mm from the other end of my module to see if a spark would jump (as I assumed that it would mean I was getting a spark in t...

I forgot to mention, my spark gap is around .5-1mm before I inserted it (I don't know of it shifted when i installed it). I tried filling the chamber with 90 PSI of air and it seemed to be sparking in the chamber (at least it was sparking off the leads going into the chamber).

I've fired it as a pneumatic a few times to test that the piston fits and the seals are good, for ignition I'm using a dc step up module similar to this one (https://m.ebay.com/itm/DC-3V-6V-to-400kV-400000V-Boost-Step-up-Power-Module-High-voltage-Generator-/222522245188). I haven't thought to try 1x...

After much delay I finally found time to finish my piston valve hybrid cannon, but after 4 attempts at a test fire I can't seem to get it to work. I've went through and looked at all the joints for leaks (w/soapy water) at much more pressure than it would see post fuel and air injection and I can't ...

What size is the sprinkler valve? If it's one of the smaller 1'' ones then I think the flow is going to be pretty constrained (I bet the projectile leaves the barrel before the chamber actually empties). I would try and make a piston valve if I were you, I'm not sure what fittings you have available...

Another angle... Like it or not but 20 years ago if you were playing around with things that went "boom" you were just a rambunctious kid. Now you're a budding terrorist. And while the kids themselves may not realize this reality their parents do, thus, they are less inclined to even tacitly suppor...

So I'm sorry that this is a really dumb question, but I was looking at the load mix calculator on HGDT and it said that the chamber pressure after the fuel injection (using propane at a 10x mix) was only 5.89PSI whereas it's been stated throughout the thread that 6.44PSI's the proper pressure, am I ...

I'm amazed and grateful for the offer, thanks! As far as burn rates go it usually depends on the pressure that I set the tank to, the last time I melted I had it set to 10 PSI and the gallon of oil lasted over an hour (although I didn't actually think to time it, that and I don't have a hole cut in ...

Thanks! I'm pretty fond of siphon nozzles but I couldn't afford one, hence my rudimentary system :) . I haven't been filtering any of the oil, although this last burn I guess there was a clog in the nozzle that blew the flame out near the end of the melt, but it re-lit itself after a few minutes. I ...

The cast Monday was fairly large at ~8 pounds, although I made the mistake of not including vent holes for the gases so as I was pouring it formed some pretty aggressive bubbles (sadly, I didn't get to take pictures of the pour or mold).

Sorry about the crappy picture quality, but the point of the foundry itself was to be as cheap as possible (the only expense was the exhaust duct, $4 and not shown). It's made from a dirt mound that was once a fallen over tree. The side walls and roof are made of concrete blocks (horrible idea, I kn...

Just finished my waste (motor) oil burner It's basically just a nozzle with an oil line and an air line attached, the oil tank is pressurized to force the oil to the nozzle. It seems to runs best when the tank pressure is set to 20 psi (regardless of how open the air line is). The pictures below sho...

I realize this is a bit late but if you wanted too you could download two programs called HGDT and GGDT. With the former you could roughly estimate your competitions' range and with the latter (seeing as how you want to go pneumatic) you could figure out what dimensions and pressure would put you ov...