Complete Plans for Advanced Combustion

[Pete Zaria]

A friend gave me $25 to draw him up complete plans for an "advanced" over-under combustion. I call it "advanced" because it has onboard propane metering/injection, a chamber fan, and stungun ignition. No fan timer, but everything else. It can be built for around $125 USD buying parts from local retailers.

I hope some of you can get good use from these plans. I've built a design almost identical to this (exact same design but not over/under, though my next will be over/under) and have fired it 500+ times with very few misfires and surprisingly consistent distance.

Edit:
I just realized, I didn't even mention what kind of pipe to use.

I use ABS for all my combustions. It's not pressure rated, but if it fails, it cracks clean and doesn't send shrapnel everywhere like PVC will. NSF-PW (pressure-rated) PVC would be the first choice, but getting pressure-rated fittings would cost an arm and a leg. ABS is better than non-rated PVC, however.

There's a disclamer on the bottom of the document, but I'll restate it here:

TREAT THIS CANNON LIKE A FIREARM! IT IS NOT A TOY! This cannon design is capable of putting potatoes (Let alone harder objects) through ¼” sheet metal. Do not EVER point it at a human or pet animal, loaded or unloaded. Don’t shoot it at anything you don’t intend to destroy. As far as I know, this design should be legal in any non-metropolitan area in the US. However, if you use it for malicious purposes, it will become illegal very quickly.
I, Pete Zaria, TAKE ABSOLUTELY ZERO MORAL OR LEGAL RESPONSIBILITY IF YOU INJURE YOURSELF, SOMEONE ELSE, YOUR PROPERTY, OR ANYONE ELSES PROPERTY WITH THIS CANNON. IF YOU BUILD THIS, YOU DO SO AT YOUR OWN RISK.

Let me know what you think.

Peace,
Pete Zaria.

[frankrede]

I printed it.

[Pete Zaria]

Cool, but what do you think?

Peace,
Pete Zaria.

[Tyro]

I like the idea. But I'm Not a combustion sorta guy. But OMG it is pretty good!

[mark.f]

Looks a little like Sgort's Blue Flame II.

I like combustions, (which is why I own two very powerful ones), but I'm done building em for a while. The only over/under I made ran off Right Guard, (I've still got a can that works), and barely shot 40 yards. Might be because it only had a 2" chamber, though.

[MisterSteve124]

These plans are great. Even if you don't use the whole design it has good plans to make a direct propane injection. All the other instructions for propane injection that I have seen are too confusing this just shows it to you in the diagram. Good Job

[sgort87]

Not bad, but I see a lot of things that should be changed.

[MisterSteve124]

like what? I'm just wondering cause I was going to make something like this.

[sgort87]

Well, I'll start off with the fact that it is using DWV parts which isn't BAD, but it isn't good either. PW parts or ones that at least resemble them are much better in quality and look much nicer.

This design allows no access to the inside of the chamber. Should something go wrong with the fan or electrode gap, you are royally fucked. I've had times where a spud chunk got stuck between the electrodes real badly and didn't allow any spark because it travelled right through the potato. With no access to the chamber I would not even know what was going on or be able to fix it without pulling the scews out. Something even worse is when the fan needs replacing or adjusting. A closed chambers is really bad in that case.

I don't like the electronics. Yes, it works, but it could be nicer. There should be an LED on there so you know when it is on. There should be a main on/off switch. Also, molex connectors are one huge pain in the ass to install. I stopped using them for that reason. They are ugly as all hell as well. I only use them if I absolutaly need multiple connections in one spot which this design does not.

The meter pipe could use some improvement. For a measly extra 10 bucks, you can put a pressure regulator on there instead of just a gauge. Also, the meter pipe should be 3/8 or 1/2, definately not 3/4".

The fan should be placed on the other side of the spark gap or it is at large risk of being blown apart.

The spark strip is overkill nad may just be too much for a newb to handle.

Also, there needs to be more detail on what the parts are and where to find them if you expect new people to understand this. I forsee many confusions on what's going on with this.

Very good start though.

[MisterSteve124]

Ok most of those things won't be a problem for me because I wasn't doing that. But if I shouldn't use 3/4" for the meter pipe then should all the sizes be increased like the ball valves and everything?

[sgort87]

Nah, the ball valves should be the same size as the pipe unless you really want them a different size for some reason.

[Pete Zaria]

Gort,
Thanks for pointing that stuff out.

First, you're right about the placement of the fan fan and size of the meter pipe. I'll change that.

In my defense, I figured if you used a good fan that would last a long time, and a spark strip (which could be removed through the 2" ball valve), you wouldn't need chamber access. I hate clean outs and end caps.

The fan circuit is definitely overly simplistic (that was actually the idea, keep it simple and reasonably low cost), and the molex isn't required but I don't see why you hate them so much... I've used them quite effectively.

Would you be willing to help edit this paper to make it more "n00b-friendly"? Or at least give me a list of things you think should be explained in greater detail?

Peace,
Pete Zaria.

Edit: OK, updated the file.

By the way, as to the DWV thing... All of my combustion guns (which is a long list, starting with hairspray and engine starter aerosol guns when I was 13 ) have been DWV or ABS. My current gun is this exact design but not over/under, made out of ABS. It's seen 500+ fires, no signs of wear on the inside of the chamber.
"Perfect", ideal propane combustion would produce 102psi. Achieving ideal conditions is nearly impossible, so a more realistic peak combustion pressure would be more like 85psi. This is an educated guess, though. But even if your cannon magically produced 102psi, DWV and ABS pipe can handle at least 125psi (I've pressurized it to this, for testing) for extended periods of time. 85 shouldn't be a problem.

Plus, finding all that pipe and fittings in NSF-PW (especially the 4" stuff) at any given local store can be tough. Home Depot, Lows, Ace (all the local hardware stores near Seattle, WA) don't carry NSF-PW fittings over 2". You have to go to a plumbing supply store (which usually don't sell to individuals) or McMaster, which is expensive as f%&@.

For these reasons, I think it's fine to use DWV pipe, ABS is even better. ABS won't shrapnel if it fails; it just rips down the side of the chamber, nice and clean. Yes, I've tried that, too.

As to the regulator, I tried hard to find any regulator locally or online that came to less than $25 with shipping included. I couldn't. My meter works fine without the reg, you just have to close the tank-side ball valve when the gauge hits the correct pressure. Doing so saves $25.

I'll draw out a diagram for a better control box. What else do you think needs work?

Peace,
Pete Zaria.

[MisterSteve124]

Cool glad everything is fixed. Good job I plan on using this in my gun.

Edit: A couple more questions. What do I use to connect the meter pipe to the hose? What kind of fitting is it? and What size hose should it be? Thanks

[POS]

Nice gun. At what pressure does it shoot, any idea on that ? (the pressure just after the combustion I mean)

[boilingleadbath]

POS, that's going to be dependent appon projectile weight.