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First Combustion, PVC Questions...

Post questions and info about combustion (flammable vapor) powered cannons here. This includes discussion about fuels, ratios, ignition systems, safety, and anything else relevant.
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First Combustion, PVC Questions...

Unread postAuthor: Dornep » Fri Aug 10, 2007 9:57 pm

I've been cruising around Spudfiles as a guest for the last few days soaking up all the info I can find on Combustion cannons.

I built an all steel pneumatic a few years ago but for some reason I've just gotten the itch to build a combustion. My mind is pretty much set on what I want and don't want as I've already started shopping.

I'm looking to construct a Metered propane, dual electrode stun gun ignition, with a chamber fan.

My combustion chamber pipe is 4" SCH 80
My barrel is 2" SCH 40
My stun gun is 150,000 volts and its in the mail.
My chamber fan is a 12 volt 80mm with a brush less DC motor

My propane meter is complete save for 2 fittings, which I will pick up tomorrow.

My main question to you pro's is about my end cap and 4"x2" reducer for the chamber/barrel. I checked my local Ace Hardware for any type of pressure rated reducer for my chamber but all they had was NSF-dwv.

I then made a 45 minute drive to the nearest Lowes to get the reducer with the proper pressure rating only to find they had the same exact NSF-dwv type crap. Both the end cap and reducer were available only in DWV. So I went ahead and picked them up. Now.. I've read on certain threads which I probably can't find now, that some people claim that DWV is not a bad thing as long as its solid core. Then on other threads people swear on the Holy Bible that its dangerous and should be avoided at all costs.

Which do I believe and if it is no good how am I to find the correct reducer and end cap. I would rather not order them from the internet since I would like to start working on the gun itself asap..
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Unread postAuthor: rednecktatertosser » Fri Aug 10, 2007 10:02 pm

DWV is fine for combustions, i believe this is because of the short low pressure spike.
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Unread postAuthor: sjog » Fri Aug 10, 2007 10:08 pm

4x2 reducer you want is a" flush bushing"
On the IPLA logo above^ have flush bushings
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Unread postAuthor: origin unknown » Fri Aug 10, 2007 11:23 pm

Welcome to Spudfiles! If you don't mind, would you post your all steel pneumatic?
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Unread postAuthor: frankrede » Fri Aug 10, 2007 11:42 pm

I would suggest checking your local ewings irrigation supply store for the right fittings.
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Unread postAuthor: Dornep » Sat Aug 11, 2007 12:17 am

If DWV is fine for combustions I will start calculating everything and begin tomorrow. Also if there is no difference performance wise between the "flush bushing" and the normal reducer, I would rather go with the reducer I have now since it looks so much cooler.

@:origin unknown
The pneumatic was pretty basic, nothing fancy and the only reason it was steel was because I was paranoid about PVC explosions. I would attach pic's but I don't have any of it and its in my brothers garage at the moment.

@:frankrede
I've checked all the local hardware stores in town but everything I've found is dwv. I work for one of the largest plant nurseries in Florida, our pipe room is nearly as big as my house and has just about every type of pipe and fitting imaginable from 1" up to 10" (this is where I "acquired" my chamber and barrel) but when they stock up on a certain fitting its for a few pounds of water pressure, not a near super sonic tater... :)

I will continue to search but I will go ahead with what I have now. If I find what I need I guess I will have to shorten my chamber and barrel a bit...

Thanks for your suggestions guys
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Unread postAuthor: frankrede » Sat Aug 11, 2007 1:08 am

http://www.ewing1.com/general/ews_loc_florida.htm

check this site for a location nearest to you.
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Unread postAuthor: Dornep » Sat Aug 11, 2007 8:31 am

Tallahassee is a little further then I would like to drive (184 miles).

I do have another question about my pvc cleanout cap. The cleanout caps outer diameter is about 4 1/2", but my chamber is also 4 1/2". Which means I will need a straight coupling to use to cleanout cap. Would this be safe or should I go with cap that slides over my chamber's wall?

***************************************************************

Edit.. Ok I have played with a few numbers with the Spudtool at AdvancedSpuds and with Burnt Latke's ratio calculator and fuel tool. My section of 4 inch SCH80 for the chamber is 23" long. The Spudtool says I will need to shorten my 2 inch SCH40 50" barrel pipe down to 30" to get a 1.5:1 C:B ratio. Does this seem right to you guys and is my chamber too long for a good fuel mix?
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Unread postAuthor: boilingleadbath » Sat Aug 11, 2007 1:15 pm

DWV is not pressure rated; combustions create pressure; ergo, no DWV for combustions!

Now, you may get away with it, and you may not... I personally have gotten away with clean-out plugs on pneumatics - but that's a dumb thing to do.

Just buy the damn fittings online, at say, mcmaster. It doesn't cost much more and ensures your safety.
*************

Further, I don't know what's up with spudtool... I'm calculating a barrel length of 52" for a C:B ratio of 1.5:1... but, personally, I wouldn't make it that long.
40" would be a lot easier to handle. This is strictly from an ergonomics Point Of View. (on the other hand, if that 50" barrel isn't bothering you... don't bother.)
**********************

I don't know if a 23" chamber of that diameter can be mixed well enough without a chamber fan. It doesn't matter, because you should - and do - have one anyways. I'm fairly confident that, with a chomber fan, you won't have fuel-mixture problems.
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Unread postAuthor: jimmy101 » Sat Aug 11, 2007 1:18 pm

Dornep wrote:Tallahassee is a little further then I would like to drive (184 miles).

I do have another question about my pvc cleanout cap. The cleanout caps outer diameter is about 4 1/2", but my chamber is also 4 1/2". Which means I will need a straight coupling to use to cleanout cap. Would this be safe or should I go with cap that slides over my chamber's wall?

That is called a "spigot" fitting. "Spigot" is a fitting that has the same OD as a piece of pipe.

This approach is OK.

Nearlly all combustion guns are built with NSF-DWV fittings. Pressure rated fittings are very rare.
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Unread postAuthor: frankrede » Sat Aug 11, 2007 2:08 pm

I wouldn't care much about the fittings, its the pipe I would worry about, if its cell core that is.
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Unread postAuthor: beebs111 » Sat Aug 11, 2007 3:03 pm

i see a much larger risk in fittings rapidly detaching from pipe because of bad glue jobs than your pipe actually turning into flying shrapnel. avoid cleanout caps at all costs, they are the most common piece to fail on a combustion. use a 2" ball valve instead, they are rated for like 1000psi and are simpler to operate. bell reducers are bad, not pressure rated, use couplers and a reducer like is on the ipla logo.
sch80 might be slightly overkill for the pipe, but it sure as hell wont burst.
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Unread postAuthor: DYI » Sat Aug 11, 2007 3:14 pm

A 2" ball valve rated for 1000psi would cost more than his entire cannon.
It would be better to just use a 2" PVC ball valve for an exhaust vent.
There are such things as pressure rated bell reducers, they are just hard to find. I have never had a cleanout cap actually fail on a combustion (unless you count the Oxy-MAPP gun incident), but I would agree that a PVC ball valve is safer.

And overkill on safety is never a bad thing.
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Unread postAuthor: frankrede » Sat Aug 11, 2007 3:32 pm

I have a 4" cleanout with a ballvalve threaded into it and it hasn't failed.
The ball valve is 1.25" too.
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Unread postAuthor: Dornep » Sat Aug 11, 2007 7:38 pm

Thanks for the input guys. It's much appreciated. My stun gun from Ebay arrived DOA. So.... I'm going old school with a bbq lighter for the time being. I'm not too worried about the end cap since I wont be directly behind the gun. Both the end cap and reducer seem sturdy and are a bit on the heavy side.


I'm going to be working on my electrode placement and chamber fan position tonight and will hopefully start the gluing process tomorrow. I will post pic's when it's complete.

About my C:B Ratio.. I have figured it up to be 1.5:1 with the Spudtool, but this is a first for me and math was never my subject so if you guys have any info or suggestions I should try please let me know.

Thanks
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