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Chamber fan question.

Posted: Mon Jun 25, 2007 3:15 pm
by Jumpin Jehosaphat
I'm planning on making a metered propane combustion, and I want to use a chamber fan.

The pictures of cannons with fans confuse me. Aren't the fans exposed to the combustion when it is ignited? How do you prevent damage to a chamber fan?

Posted: Mon Jun 25, 2007 3:37 pm
by psycix
I dont know the answer but i think chamber fans dont get damaged by the combustion, they just get warm. (correct me if im wrong)

I would like to add aswell:
What if the fan SPARKS inside!? Ehhh BOOM?

Posted: Mon Jun 25, 2007 3:40 pm
by Flying_Salt
The fans are supposed to be in the chamber. They are exposed to the combustion, but don't get damaged, unless it's a crappy cheap fan that gets clogged with hairspray or something. But you'll be using propane so it'll be fine.

Posted: Mon Jun 25, 2007 3:47 pm
by lukemc
psycix wrote:I dont know the answer but i think chamber fans dont get damaged by the combustion, they just get warm. (correct me if im wrong)

I would like to add aswell:
What if the fan SPARKS inside!? Ehhh BOOM?

that is why you use computer fans they are brushless and dont produce sparks

but yea they stay intact because is only a split second of combustion

Posted: Mon Jun 25, 2007 8:09 pm
by jrrdw
Mount it in the end cap/clean out plug. Thats what i plan on doing.

Posted: Mon Jun 25, 2007 9:47 pm
by Scotty
You could do as i have done and mount it in the middle of the chamber using silicone. Then just drill out a hole for the wires and silicone that up.
Silicone rocks!!

Peace
Scotty

Posted: Mon Jun 25, 2007 10:16 pm
by SpudBlaster15
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Posted: Tue Jun 26, 2007 4:25 am
by psycix
Another question:
Doesnt the fan block some explosion or airflow from the explosion?
It may divide your chamber into 2.

I once saw a few frame by frame pics wich showed he had 2 seperate combustions in his gun (though very very short after each other i kno) First one in the front, then one behind the fan.
It worries me....

Posted: Tue Jun 26, 2007 7:06 am
by TwitchTheAussie
Put the fan in the back. I had no problems destroying my cannon by mixing butane with it :lol:

Posted: Tue Jun 26, 2007 8:45 am
by mark.f
psycix wrote: Another question:
Doesnt the fan block some explosion or airflow from the explosion?
It may divide your chamber into 2.

I once saw a few frame by frame pics wich showed he had 2 seperate combustions in his gun (though very very short after each other i kno) First one in the front, then one behind the fan.
It worries me....
The fan may block the actual flame front slightly, but the pressure rise will still be pretty much the same. The raise in reaction rate due to the consistent mixture and turbulence would easily make up for any obstructions to the flame front.

Posted: Tue Jun 26, 2007 9:12 am
by psycix
If i put the fan completly in the back, does it have any use then?
I can imagine that a fan in mid-chamber mixes more effectively..

Im thinking about fitting a very small fan (60x60mm) in my future gun so it blocks less and still can be mid-chamber, good idea or should I take the hugest fan that fits in?

Posted: Tue Jun 26, 2007 11:45 am
by Jumpin Jehosaphat
Thanks for all the tips guys, It seemed like fans are exposed to flames in most cannons that use them, but I just wanted to be sure.

@ psycix: It seems like a big fan will mix faster, but a small fan will obstruct flow the least. There is a trade off, you could always go with a mid sized fan.

Posted: Sat Jun 30, 2007 4:09 pm
by SnowFlox
how much does a fan increases the combustion ?

Posted: Sun Jul 01, 2007 4:05 pm
by jimmy101
SnowFlox wrote:how much does a fan increases the combustion ?
I don't think anybody knows the precise answer to that. Besides, a fan really does three things in a combustion gun.

1. It mixes the gases. This all by itself may well double the velocity that the gun shoots at. If nothing else, it will reduce the shot-to-shot variablity from perhaps 50% to ~10%.

2. If the fan is running during firing it should boost the burn rate and increase the muzzle velocity. Exactly how much is hard to say. An increase in muzzle velocity of perhaps 20% would seem reasonable.

3. The fan helps to air out the chamber between shots. That means you are much less likely to have CO2 and water vapor carrying over from shot to shot. Any CO2 or water vapor in the chamber displaces a like amount of oxygen.

Posted: Sun Jul 01, 2007 4:23 pm
by iPaintball
Just mount the fan behind your spark gap to minimize obstruction of the flame front.