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need help with propane meter

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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need help with propane meter

Unread postAuthor: darknes » Thu Oct 04, 2007 6:37 pm

hi, i have just finished building my first propane cannon and i need help with the meter pipe. i have a meter pipe made that is 14 inches long and made out of 1/2 in sch 40 pipe. my total combustion chamber size is 462 cubic inches. i cant seem to get a pressure that will ignite. if someone could help me get an idea of what pressure to use that would be great. also if you need any more info just say so and i can get it to you.

thanks,
David
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Unread postAuthor: silverdooty » Thu Oct 04, 2007 6:46 pm

a nice online tool to use for this
http://www.burntlatke.com/ft_live.html
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Unread postAuthor: darknes » Thu Oct 04, 2007 6:56 pm

i have tried using that calculator and the pressures it gave me didn't work. i don't know what the problem is the ignition works fine, it has been checked numerous times. i just don't know what the problem is.
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Unread postAuthor: spudgunnerwryyyyy » Thu Oct 04, 2007 7:19 pm

Make sure you take into account the volume of the fittings in the meter. They can make a huge difference in the pressure needed.
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Unread postAuthor: Dornep » Thu Oct 04, 2007 7:36 pm

Have you tried filling your meter pipe with water to get an accurate volume measurement? Fill your meter with water and then dump the water out of it into a measuring cup. If you have a syringe, that will come in handy too.

What size pipe are you using on your chamber? The reason I ask is that 462 cu. in. is rather large... You will probably end up having to inject your meter pipe into your chamber twice or three times to get the perfect mix.

Like spudgunnerwryyyyy said you have to take into account the extra volume your ball valves and other fittings create in your meter. If you just use the volume formula on a 14"x1/2" piece of pipe your gonna get a bad mix.

I'm building a cannon now that has a 429 cu in chamber with a 23.6 cc meter pipe. I'm going to have to inject 180PSI of propane into the chamber, which means I will either be injecting 2 shots of 90PSI or 3 shots of 60PSI to get the right mix.

Once you get the right volume measurement, you can use that on BurntLatkes fuel tool instead of just going by pipe diameter and length.
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Unread postAuthor: darknes » Thu Oct 04, 2007 8:08 pm

i have done a liquid displacment test on my chambers and it is 462 ci (i am using 2.5 in sch 40 pvc), but i have not done a displacement test on my meter pipe. also, some of the pressures i have tried so far are 17, 60-70,90, and 110 psi. are those pressures too low, or do you think i need to put more in like Dornep has to do with his. i will try to do the displacment test on my meter and post the results. thanks
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Unread postAuthor: Dornep » Thu Oct 04, 2007 8:21 pm

How long is your chamber? Also how long is your barrel?

If your chamber holds 462 cu in of liquid, that would make it about 98 inches long..???

Have you tried using the Spudtool at advancedspuds.com? If you haven't this is the link.

http://advancedspuds.com/SpudToolonline.htm
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Unread postAuthor: darknes » Thu Oct 04, 2007 8:48 pm

my barrel is about 6-1/2 ft long and i think its 2-1/2 in thin wall (pop-can barrel), also my chamber is a dual chamber (side by side) so all of the fittings and pipe combined probably come out to about 98 in, but i do know the displacement of the combined chambers is 462 ci because me and my buddy measured it by means of liquid displacement. thanks
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Unread postAuthor: BigGrib » Thu Oct 04, 2007 8:56 pm

have you built in or would you need a crossover pipe between the chambers
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Unread postAuthor: Dornep » Thu Oct 04, 2007 9:11 pm

Well... I'm no expert on the subject, but I'm guessing your giganticus chamber is probably the biggest problem. Long slender chambers don't perform as well as short fat one's.

Do you have a chamber fan?

Are you waiting after you inject the propane or trying to fire it immediately?

When you get a chance try injecting 35PSI of propane and letting the cannon set for a minute or two before you try and fire it. Letting it set for a bit will allow the propane and air in the chamber to mix better.

I would like to see this gun if there is any way you can get a picture or two.
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Unread postAuthor: spudgunnerwryyyyy » Thu Oct 04, 2007 9:33 pm

Yah, on my 3"x24" chamber I have to wait at least 30 seconds for the propane to mix with the air. Take the pressure the calculator gave you and minus like eight psi and see how it works.
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Unread postAuthor: darknes » Fri Oct 05, 2007 8:08 am

i do have a chamber fan in the cannon and i let it run while i inject the propane and while i am trying to shoot it. i will try to get a picture up so you can get an idea of how it works.
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Unread postAuthor: darknes » Fri Oct 05, 2007 2:37 pm

hope you guys like my first cannon.
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Unread postAuthor: Dornep » Fri Oct 05, 2007 3:20 pm

Holy Crap Batman!

That's an awesome cannon dude. Even more reason to get it firing! From what I can see in the pic it looks like your propane injection point is a good distance from your spark gap/s. I'm also guessing that your fan is near the front of the chamber also..

Also how big is your fan? Do you know how many CFM of air it moves? If it's very close to the end cap it might not be blowing hard enough to force the air towards the propane injection point. Which means your propane is just setting there, it will mix eventually but it will take forever.

My suggestion's would be multiple spark gaps if you don't already have them. And maybe another chamber fan, one per chamber side. Get that meter pipe volume measurement and I'm sure we can figure out the right mix for your gun.

It's a great looking cannon and it looks very well built. The control box looks great too... BTW are you sure this is your first cannon? :wink:
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Unread postAuthor: darknes » Sat Oct 06, 2007 11:41 am

ok everybody, i figured out the volume of the meter pipe, it is 79 cc. i do have a chamber fan and yes it is very close to the end plug but it still moves a little air, but i don't know how many cfm it moves because my dad found it in my grandma's old computer and gave it to me. also, thanks on the compliments on my first cannon, i didn't want to overlook anything.
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