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Loss of power

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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Unread postAuthor: Hubb » Wed Jan 16, 2008 5:59 pm

Using metered propane (or MAPP, or butane, or....) will be more efficient then dropping some alcohol or gasoline in the chamber. There are several threads here, along with several calculators in the wiki that will assist with any questions you have on that subject.

Another thing you could do is use some math and figure out how many drops to put in chamber (although building a meter may be easier, as gasoline and such have impurities that will affect performance).
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Unread postAuthor: ralphd » Wed Jan 16, 2008 7:14 pm

That reminds me of another problem I was having when I first built my launcher and it was "Spray & Pray"....After every shot I had to "hand" fan the chamber and barrel so fresh air would be there for combustion. If I didn't I wouldn't get good shots. The very reason I installed a combustion fan.
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Unread postAuthor: Kaotik Kustoms » Wed Jan 16, 2008 7:48 pm

Which way do i want to to vent my cannon? Should i have the fan vent towards the barrel or the back of the chamber?
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Unread postAuthor: sjog » Wed Jan 16, 2008 8:02 pm

vent to barrel,rear to front.
You will end up spraying the hair/deodorant stuff to the side of fan. Small fan will be fine.
The electrodes will have to be cleaned so keep that in mind when installing fan. The starch and goo from sprays will end up grounding electrodes.<a title="IMG_0095-1.jpg" href="http://s116.photobucket.com/albums/o12/sjogun/?action=view&current=IMG_0095-1.jpg"><img src="http://i116.photobucket.com/albums/o12/sjogun/th_IMG_0095-1.jpg" border="0"></a>
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Unread postAuthor: frogy » Wed Jan 16, 2008 8:48 pm

Propane is definitely THAT MUCH better and beyond... It can increase muzzle velocity over 200 miles per hour (about 300 fps) in some cases....

If your not ready for propane (you seen like your interested though), try adding a chamber fan first...

How are you spraying denatured alcohol and gasoline into the chamber? A regular spray bottle should atomize the liquids enough so that they blend decently with the air... Directly pouring them in definitely doesn't work (but you did mention spray).

After every shot try to thoroughly evacuate the exhaust fumes from the chamber so it is full of nice clean air... Blowing into the chamber with your mouth will most likely result in hot corrosive fumes blowing into your eyes and nose... Which for some reason doesn't bother me, but there's no way it's good for you :shock: :o .... From one of the most safety conscious people here :roll:

Normally smaller propane tanks are used, but it is possible for 20lb tanks to be used...

It matters on the size of your chamber really, but you do get quite a few (actually many) shots from even small camping size (1lb or 14.1 oz) propane cylinders.


edit: some people posted during my typing...

An added note on chamber fans... Covering the electrodes in hot glue\epoxy will help isolate them from corrosion and shorting, so take prevention measures before installing the fan, so you don't have to fiddle with it later.
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Unread postAuthor: Kaotik Kustoms » Wed Jan 16, 2008 8:52 pm

frogy wrote:Propane is definitely THAT MUCH better and beyond... It can increase muzzle velocity over 200 miles per hour (about 300 fps) in some cases....

If your not ready for propane (you seen like your interested though), try adding a chamber fan first...

How are you spraying denatured alcohol and gasoline into the chamber? A regular spray bottle should atomize the liquids enough so that they blend decently with the air... Directly pouring them in definitely doesn't work (but you did mention spray).

After every shot try to thoroughly evacuate the exhaust fumes from the chamber so it is full of nice clean air... Blowing into the chamber with your mouth will most likely result in hot corrosive fumes blowing into your eyes and nose... Which for some reason doesn't bother me, but there's no way it's good for you :shock: :o .... From one of the most safety conscious people here :roll:

Normally smaller propane tanks are used, but it is possible for 20lb tanks to be used...

It matters on the size of your chamber really, but you do get quite a few (actually many) shots from even small camping size (1lb or 14.1 oz) propane cylinders.



I was using a $1 store spray bottle but i would still have left over liquid that wouldnt burn.

I have no problem running propane if it is that much better. I just watched a vid on how to make a meter for propane.

How do i figure out how much propane i need to send to the chamber?
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Unread postAuthor: ralphd » Wed Jan 16, 2008 9:09 pm

That is why there are tools like Prometer. At the top right of this page under "Archive" is "Other". Click on that then Computer Applications. You must first determine the volume of your chamber only. You can calculate this or fill it up with water then empty it into a measuring cup. Figure about 4.3 percent propane. I tried more but I always use that. It will ask you to enter a desired pressure as well; I use 55psi but I also use 90psi. Ask around to see what others use. Enter the info in the spreadsheet, chose the diameter of the meter pipe you want and voila...you have the length. You then need some hardware and tools. It takes a while but you'll love the results. I'm now propane and I'll never go back
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Unread postAuthor: frogy » Wed Jan 16, 2008 9:45 pm

I believe this video tutorial at BCVids is pretty good, but you will have to make an account there to watch it...

http://www.bcvids.com/dload.php?action=file&file_id=24

Normally a propane meter is pretty cheap to make... All it requires is a few pipe nipples, a 90 elbow, a tee, a pressure gauge, and 2 ball valves to make the meter assembly... Plus a few more dollars to adapt it to connect to a propane tank.
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Unread postAuthor: Deterrent » Sat Jan 26, 2008 6:17 pm

frogy wrote:Propane is definitely THAT MUCH better and beyond... It can increase muzzle velocity over 200 miles per hour (about 300 fps) in some cases....

If your not ready for propane (you seen like your interested though), try adding a chamber fan first...

Whoa, should I be worried? I'm a first-timer who just slapped together an extremely simple combustion cannon using some generic 5 euro PVC pipe pieces and a PC fan, and so far I've only shot some potato pieces and such using deodorant.

Is it risky or something to start using propane?
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Unread postAuthor: frogy » Sat Jan 26, 2008 6:21 pm

If all your PVC parts are NSF-PW (Have a pressure rating or "NSF-PW" types on the side), they should be perfectly fine with propane...
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Unread postAuthor: DYI » Sat Jan 26, 2008 6:51 pm

NSF-PW SCH 40 PVC and solid wall SCH 40 DWV ABS are both fine for metered propane combustions. SCH 40 DWV PVC is kind of iffy, and cellular core plastic pipe of any kind is a bad idea.
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Unread postAuthor: Deterrent » Sun Jan 27, 2008 6:12 am

I have no idea what kind of PVC mine is...

Already with deodorant the spud gun is much more powerful than I expected - the spud is so fast that I can't see it in flight, and when shooting solid objects the potato only leaves a wet splat. I just hope the chamber doesn't blow up when I move on to a 50/50 butane and propane mix.

I have heard that PVC explodes into shards when it fails. Is it an "ouch" thing, or is it particularily dangerous? Will I be OK with just eye protection?
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Unread postAuthor: ralphd » Sun Jan 27, 2008 8:10 am

I have 1 piece of cellcore in my launcher. I used it, unknowingly, to hold the two pvc fittings that make up my combustion chamber. It's only as long as the shoulders of the two fittings but it's cellcore all the same. I think the only thing in my favor is that I don't go crazy with the propane. When I start buying for my next launcher I'll be more careful. Remember, just because Lowes carries pressure rated pvc in 1/2, 3/4 and 1 1/2 inch doesn't mean the 3 inch is pressure rated as well. My lesson learned was to read all the damn labels.

As far as eye protection, that's up to you. Don't hold the thing on your shoulder like a bazooka.
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Unread postAuthor: frogy » Sun Jan 27, 2008 9:33 am

I'm not sure how Europeans rate their PVC...

Deterrent can you please take a picture of the pipe your chamber is make out of? The writing on the pipe would help us greatly to determine if it is safe or not...
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Unread postAuthor: Ragnarok » Sun Jan 27, 2008 10:41 am

frogy wrote:I'm not sure how Europeans rate their PVC...

Absolutely appalling, that's why I use copper.

You can tell I'm in a very silly mood today.
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