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20PSI Bernzomatic Propane Tanks?

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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20PSI Bernzomatic Propane Tanks?

Unread postAuthor: Dornep » Sun Aug 19, 2007 6:23 pm

Ok guys I need some pointers.

I finished my 2nd combustion a few hours ago and for the last 45 minutes I've been trying to figure out why it only fires when it wants to. The first combustion I built last weekend is almost an exact replica to this one, except this one has interchangable barrels, and a fan control box that isn't so ghettoish as the first cannons box. I figured this one would go together just as easy and fire one the first shot just as the last did. Well it didn't..

I have three Bernzomatic propane bottles. The first one I used on my first cannon and it showed between 15-20PSI. I left that one on the first cannon all week and apparently it has a small leak as that bottle is empty now with 0PSI. The second bottle is my dad's and it shows around 15-20PSI on my meter regulator. The third bottle was one that I've had for a few months that hasn't been used until now, It shows around 15-20PSI also but feels much heavier then my dads. I've read on a few threads on Spudfiles that most Propane bottles come with around 90PSI. Keep in mind that I'm using two different regulators that each show the same pressure reading.

The Spudtoolonline told me that I needed around 40PSI in my meter on my first cannon which had a 12 inch meter pipe to get a 4.2% mixture of propane in my chamber. The Spudtool also told me that to use a 5 inch meter pipe on my second cannon I would need 40PSI in my meter pipe to get a 4.3% mixture.

When firing my first cannon I filled the combustion chamber 4 times with my propane meter pipe which caused it to fire the first time every time I fired it. With this cannon I've tried 1 time, 2 times, 3 times, all the way up to six times with it firing at random and seeming very weak when it did so.

The gun has a threaded end cap in a reducer bushing, and a threaded bushing for barrel switching. The ignitor and propane hookups have been setup so I can use 1 bottle of propane and 1 ignitor on multiple guns.

Do you guys have any ideas as to why this thing would suck ass so bad?

Here are some pics of the gun below before gluing.
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Attachments
DM5K01.jpg
Propane and BBQ Sparker disconnected
DM5K02.jpg
Propane and BBQ Sparker connected
DM5K06.jpg
Sparker electrodes
DM5K03.jpg
Chamber fan and quick release fitting for propane hose.
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Dornep
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Unread postAuthor: hi » Sun Aug 19, 2007 6:31 pm

is the meter pipe/hose the same diameter and the same length as the other one?
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"physics, gravity, and law enforcement are the only things that prevent me from operating at my full potential" - not sure, but i like the quote

you know you are not an engineer if you have to remind yourself "left loosy righty tighty"
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Unread postAuthor: Dornep » Sun Aug 19, 2007 7:43 pm

Yes my meter pipe is a 5 inch long section of 1/2 inch galvanized steel. The meter pipe on my first combustion is a 12 inch section of 1/2 inch galvanized steel. I'm using the same hose and regulator from the first cannon the only difference is the quick release fitting instead of a threaded adapter.

I've been playing around with it since my first post and it seems to fire on 2 meter pipes of propane into the chamber pretty consistently now only its pathetically weak. I do have major leakage around the sparker electrodes and the propane fitting going into the chamber, and most likely around the end cap and barrel threads also. I was using a burst disk from the plastic around a pack of cigarettes and it popped it a few times but it also ignited and slowly let the combustion pressure escape through the leaking areas a few times also.

I'm using the same hose and regulator from the first cannon
Yes I just quoted myself :)

As I was typing this I just now realized how retarded I might be.. The regulator which I attached to the propane tank is from an old antique camping stove. I don't imagine it would let 90 PSI of propane flow to the stoves burner as it would be like a cutting torch... There is a weird plastic thing on the regulator which might be an pressure adjustment of some type. I will see if it's adjustable or not, if not I will mod a torch head and see if thats the prob.

EDIT*****
I just took the tip of the torch head and hooked it up to my first gun and the regulator slowly started climbing. It was up to a about 45PSI when I started adjusting it so that was the problem with the pressure. I feel like a total asshat now but I feel much better all the same knowing that my cannons are going to be screaming tomorrow.. after some JB welding and thread tape of course. :D
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