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too humid?

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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too humid?

Unread postAuthor: uncomplientspud » Fri Jun 06, 2008 7:12 pm

well i have spent the better part of an hour and a half hunting down my problem and to be honest, there isn't one. Everything is fine. Good spark, fan and propane but no boom?

So i have narrowed it down to two issues:

1 too humid out
2 the spark is in front of my fan, could that my starving the fuel mix near the spark?

any help would be great thanks
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Unread postAuthor: frankrede » Fri Jun 06, 2008 7:31 pm

Humidity probably isn't the problem
Your fuel mixture is probably off, run your calculations through the calc again and double check your meter
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Unread postAuthor: psycix » Sat Jun 07, 2008 5:27 am

A fan does not mess up fuel mix near the spark, it just improves it. If you are unsure you could try firing it without the fan on.
You probably made a mistake in your fuel calculations. Maybe post your specs over here so we can have a look at it.
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Unread postAuthor: jimmy101 » Sat Jun 07, 2008 5:39 pm

A fan can inhibit the firing of the gun. High gas velocities at ignition require higher ignition energies (at least according to a reference I was just reading).

So, run the fan to mix the fuel then turn it off. If the gun fires then it is the high gas flow. If it doen't then it isn't the fan.

Humidity can wreck havoc with high voltage systems. It is possible that the humidity is giving you a short somewhere. I wouldn't think it is very likely but it is possible.

Is this a new, never before fired gun or a gun that used to work but has stopped working?
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Unread postAuthor: starman » Sat Jun 07, 2008 5:49 pm

I've experienced BBQ igniters failing to spark when the humidity rose to 100%...was basically trying to spud out in a light rain on a muggy southern summer night. It fired great the afternoon before and then again the next day when it was dry. Literally the only difference was the atmospheric conditions. You'll find piezo lighters won't light very well in high humidity either. Found that out during July 4th fireworks shooting efforts.

I haven't tried a stun gun ignition under those conditions.
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Last edited by starman on Sat Jun 07, 2008 5:51 pm, edited 2 times in total.
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Unread postAuthor: Darkside 6ix » Sat Jun 07, 2008 5:50 pm

yea guys, have the same problem, but with a mini, and obviously without a fan. I get a big blue spark and there isnt any shorts. But when I take my axe, and spray it, it just wont fire. I have gotten it to fire once out of a million times. Please help.
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Unread postAuthor: uncomplientspud » Sat Jun 07, 2008 8:23 pm

alright, i will consider the fan. Heres a question which i hav enever had answered. How long should the fan be for? 5 sec? 10 sec? 15 s?

and here are the numbers so you guys can crunch them, see if i made some mistakes. I have 21 inches of chamber with an ID of 4 inch. That is 265 inches cubed of chamber

i have 12.7 inches of meter, so if the psi is at roughly 60 it work no?

well from 60 all the way to 45 today i got nothing. Just two for no reason ignitions

any help would be great thanks
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Unread postAuthor: starman » Sat Jun 07, 2008 8:50 pm

Just start the fan and let it run. It will mix the fuel while firing and evacuate the chamber after the shot. 5 - 10 seconds will evacuate the chamber properly if you have a fresh air inlet.

Yep you're in the right neighborhood on the ci of the chamber.

Would need to know the ID of the meter pipe you are using to calc its volume. Anyway, use the water method to measure you meter volume. Fill it with water and measure it. Then you can get down to biz on your meter psi.
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