Loving the irony of having a fire extinguisher being used in this project. Perhaps have a separate site where you can showcase a new video, because I would love to see it in a much more reliable state.

If this were to be a water pistol, it would be allowed. Just remove the video and I imagine it would be authorized. This is very well constructed, and I would love to see a video with a better ignition system. Well done on a good build!

Presumably so that he can market it as a tool rather than a toy. It is indeed a beast!
Best of luck to him, but constant spinning shots of the cannon in that video were frustrating!

I wound up going for the piezo BBQ igniter separately, then 8AA batteries in a purpose built enclosure for the 12v supply. It gives plenty of power and isn't too bulky. Attaching the gas to the metering system is still a bitch, have caved and bought a blowtorch and will be attaching it with some hose.

Depends on what pressure you want it to hold, and the diameter. Larger diameters and pressures require thicker walls.

Fair enough on ABS, I am in the UK and if I could get it, I would. I'll be honest, I hadn't really considered steel as being possibly lighter than PVC, my ABS/PVC combustion isn't excessively heavy* and I hadn't considered brazing, but in my experience malleable iron and other threaded parts are ver...

PVC is the worst of the commonly used cannon building materials. I disagree. Of the few materials available to use in pipe form, PVC is an excellent compromise between (for <10bar) saftey, price and weight. MDPE is strong and safe, but usually too large or small diameter and electrofusion fittings ...

I might well do that, although I now have 14 AA batteries, so I'll likely use them.
If it's too bulky or doesn't deliver enough power i might well have to splash out for a rechargeable 12v.

In other news, lots of parts for the fuel meter arrived today. Pretty excited!

I've decided to go for a piezo igniter, it's a great salvaged one, has at least 1cm spark!
As for the fan, it's 100mA, I'll have to test it with a 9v, but if it's pathetic, I will likely need 8AAs, or perhaps a 12v camera battery, maybe 2?

What's the best way to power a 12v fan and a 9v HV supply on a cannon. I'm thinking a 9v battery and 2(maybe 4) AAs, but will they give me enough power to run the fan properly?

Using a compressor with a crank is a nice idea but totally defeats the object of using a compressor instead of a pump!

8 AA batteries wouldn't be too hard to fit in a backpack, but I think the compressor itself would be the challenge.

A stirrup pump is good because you can use your weight over a medium area to get high pressure quickly. If you made a small hand-held stirrup* pump, you would have to make it a much smaller area to get the same pressure, which would happen very slowly. I tried using a shock pump to fill my smallest ...

Didn't want to budge, even with heat applied. Luckily, I have found a gas bottle adapter in the UK From either here or here This means I just need a 1\4" needle valve. The plan from there is to use a tyre valve on the cannon, and a female chuck on the meter system so it's detachable. Good idea? Will...

I guarantee a shock pump will not be worthwhile for a tank that large. My vote is definitely with a stirrup pump (aka bike pump). You'll have to use it when you get a chance to rest, but it's the only real option.

You can also use ctrl+mousewheel to zoom in Firefox. Handy for switching back and forth (images get pixellated when zoomed)

I like firefox because of the extensions and scripts, but chrome is pleasant to use for the less technologically adept.