Help Building "V3" advanced combustion

Boom! The classic potato gun harnesses the combustion of flammable vapor. Show us your combustion spud gun and discuss fuels, ratios, safety, ignition systems, tools, and more.
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starman
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Fri Feb 13, 2009 10:42 pm

There's really no need to guess about your fueling..this is completely predictable based on your chamber and meter size. Are you familiar with how this works?

Your meter psi sounds really low meaning you it might be a little large. A meter size that requires 40-60 psi is about right and will let you load in cooler weather.
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roboman
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Fri Feb 13, 2009 10:48 pm

BTW: when you connect your wired to your battery terminals, it would be better to use crimp-on connectors, rather than soldering to a washer. It looks cleaner, and there's less of a chance of the wire breaking off.
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metallover
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Fri Feb 13, 2009 11:00 pm

starman wrote:There's really no need to guess about your fueling..this is completely predictable based on your chamber and meter size. Are you familiar with how this works?

Your meter psi sounds really low meaning you it might be a little large. A meter size that requires 40-60 psi is about right and will let you load in cooler weather.
I only have one ball valve and all the tubing going from the propane tank to the first ball valve acts as the part of the meter that gets filled up. I don't see a problem in this but if there is please correct me.
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starman
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Fri Feb 13, 2009 11:40 pm

OK I see it now, yeah that's a monster meter counting all that piping and hose. I assume you use the propane valve as the "front" meter valve.

It's really too big. You can help yourself my installing a regulator and a front side valve. Don't allow the hose to be used as part of the meter and that will help a lot.
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metallover
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Fri Feb 13, 2009 11:50 pm

How will it help? I can't see how it's any different as long as the right amount of propane gets into the chamber.
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Radiation
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Fri Feb 13, 2009 11:54 pm

Not to mention your "meter" isn't a meter at all. Basically all you have here is a giant cluster@#$ of tubing that's stopped by a single ball valve. Who knows how accurate your propane dump will be at any given time. Honestly it's basically a glorified spray and pray. You need to have a fixed and known length meter between two ball valves with an exact measure of PSI regulation. That is true metered propane. I hope this helps.

Example:
Image
This takes out the guess work and gives you a fixed amount at a useful PSI level such as 65 or more. 8 PSI may be ultra lean or ultra rich depending on a lot of variables.
Last edited by Radiation on Sat Feb 14, 2009 12:21 am, edited 1 time in total.
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metallover
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Fri Feb 13, 2009 11:59 pm

OK, OK. I'll go buy another ball valve next trip to the hardware store. I've been wanting to do that anyway...
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Radiation
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Sat Feb 14, 2009 12:02 am

lol Good on you! Check out this website before you go to the store so you can get the exact measurement of what sized meter you will need. Trust us, this will all be worth it in the end!

http://www.burntlatke.com/ft_live.html

EDIT: Also pick up one of these:
Image
Husky regulator No other brand is any good in my experience. The husky is dead on accurate, but it will cost you about $25. :shock: worth every penny. :D
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metallover
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Sat Feb 14, 2009 12:57 am

I think I'll hold off on the regulator until I really want to upgrade my cannon later this summer.

How much pressure can a propane cyllender consistantly put out? I'm using the camping 4" diameter ones if that makes any difference.
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Radiation
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Sat Feb 14, 2009 1:02 am

A propane cylinder can meter to 90-100 psi give or take. Usually people will tell you 90 psi. While true the problem is if you make your meter built for 90 psi and you go out on a cold day and can only get 75 psi you may have to get creative with your metering. If you regulate down to 60ish you will find that your gun works better in colder conditions. While not a perfect method I find it preferable to not being able to meter to 90 psi. Now remember this may require a slightly larger meter.
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metallover
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Sat Feb 14, 2009 1:08 am

What would you recommend I shoot for? Does 60psi sound good?
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Radiation
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Sat Feb 14, 2009 1:11 am

Sounds good to me. My gun is about 65 psi. I was actually shooting for 60, but realistically getting the meter calculation to be that accurate is near impossible. You will be better off shooting for a range between 50ish and 75ish. And don't surprised if you don't hit it the first time!
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metallover
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Sat Feb 14, 2009 1:20 am

Ehhh, I will have about 30 psi according to fueltool. IDK if that will be enough, or does it really matter? I can re-design my propane meter if it comes down to it.
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Radiation
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Sat Feb 14, 2009 1:24 am

I would, you want to be a little higher psi than that or you have a problem with getting a consistent amount in my experience. I don't know anyone that uses less than 50. Then again perhaps try it. If it doesn't work well you can always rebuild it. as long as you're safe this hobby is very forgiving.
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starman
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Sat Feb 14, 2009 1:53 am

Even without the hose, the meter looks a little largish so 30 psi sounds about right.

I agree with Radiation, get your meter psi up a bit...should be about half the volume.
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