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New Device - Thanks Jimmy!

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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New Device - Thanks Jimmy!

Unread postAuthor: mark.f » Sat Apr 28, 2007 7:29 pm

It was quite a while ago that Jimmy gave me a link to a CDC website showing the making of a simple peak pressure recording device employed to record methane explosions in mines. He had the idea of using it on spudguns to measure the peak pressure. I still can't gather from context whether or not he did it or not, but I built one.

<img src="http://www.markfh11q.net/images/peakindicator.jpg">

All it is is a 1/4" elbow, a 1/4" close nipple, and a cheapo 0-120 PSI pressure gauge gotten from some company called "Lil' Auto Parts". I bored the nipple out to 3/8" with a drill, cut the head off the gauge, and roughed up the edges. Then, I simply epoxied the stem into the nipple.

I've got to wait overnight for the epoxy to dry, but I'll get some data up tomorrow hopefully.

Anyways, thanks Jimmy!

And Clide...
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Last edited by mark.f on Sun Apr 29, 2007 8:29 am, edited 1 time in total.
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Unread postAuthor: Flying_Salt » Sat Apr 28, 2007 7:49 pm

Yeah when I heard about wanting to know the max pressure, I immediately thought of a tire gauge. I was wondering how to connect them though. Now we will know what pressure our combustions are at! Mua ha ha ha!
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Unread postAuthor: ArticWolf » Sat Apr 28, 2007 9:13 pm

Sounds like an Idea, I might have to make one when I futher mod my resent cannon that I have now. I am almost done with it, wiring it up to work remotely. (Stun gun ignition and chamber fan) But back to topic That a good idea keep up the work new stuff alway's help's.
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Unread postAuthor: clide » Sat Apr 28, 2007 10:00 pm

Hmm, I don't think it was me that gave you the link. Somebody started a thread about this over at spudtech and I mentioned that I also had the idea awhile ago when my Dad found a heavy duty tire gauge with a head that unscrewed to reveal 1/8" NPT threads, but thats about it. I would have used it if I had a combustion, but I don't have any combustions.

Anyway, nice way to adapt a standard one to guns, looking forward to hearing the results. I don't think I've ever actually heard results from somebody using one.
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Unread postAuthor: Velocity » Sat Apr 28, 2007 10:37 pm

What, other than price, is wrong with using a check valve in combination with a pressure gauge? Is the problem that once the combustion is complete, the energy stored in the pressure gauge section will drop due to heat loss?
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Unread postAuthor: sgort87 » Sat Apr 28, 2007 11:30 pm

There's a huge pressure decrease after the heat drop (which happens in an instant) and a check valve closes too slow to get a decent reading.
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Unread postAuthor: mark.f » Sun Apr 29, 2007 8:28 am

clide wrote:Hmm, I don't think it was me that gave you the link. Somebody started a thread about this over at spudtech and I mentioned that I also had the idea awhile ago when my Dad found a heavy duty tire gauge with a head that unscrewed to reveal 1/8" NPT threads, but thats about it. I would have used it if I had a combustion, but I don't have any combustions.


You're correct. I checked the archive, (didn't find it before!), last night and found out it was jimmy.

Don't know if jimmy is on these forums, but if he is I'll throw out my thanks. Gotta edit and change stuff now... feel kind of stupid. :?

EDIT: and I'm gonna get those readings soon. My family's still sleeping right now, so I'm not gonna be a jackwipe and wake them up.
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Unread postAuthor: jrrdw » Sun Apr 29, 2007 8:41 am

sgort87 wrote:There's a huge pressure decrease after the heat drop (which happens in an instant) and a check valve closes too slow to get a decent reading.


I agree, even without the heat you still have to maintain a static pressure on those type gauges, as soon as you take it off the tire valve it looses 5 psi, the stick slides back in.
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Unread postAuthor: mark.f » Sun Apr 29, 2007 10:16 am

Well, I can't get a reading. I think that the piston inside the body is snagged up on the end of the tube where I cut it, therefore not allowing it to move forward. I'll try it again some other time with another cheapo tire gauge. Maybe next time I'll use tubing cutters 'stead of a hacksaw.
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Unread postAuthor: jackssmirkingrevenge » Sun Apr 29, 2007 10:31 am

markfh11q wrote:Don't know if jimmy is on these forums, but if he is I'll throw out my thanks.


yep, he is ;)
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Unread postAuthor: jimmy101 » Mon Apr 30, 2007 12:12 pm

markfh11q: I'm bummed that it isn't working.

Looks like you came up with a great way of plumbing the meter to the gun.

Does the meter scale still move easily or can you feel it hanging up near zero PSI on the scale?

Since this one isn't working, you could try to shorten up the spring a bit so the "zero point" of the gauge is actually at a few PSI on the scale. That will get the gauge's piston away from the distorted part of the gauge body and perhaps it will work?

Another possibility is that this type of gauge just responds too slowly for use in a spud gun. They work great for recording the peak pressure in mine explosions, but I would think things happen a lot slower in a mine than they do in a spud gun combustion chamber.

BTW, DR had a great idea of using this type of gauge on a fuel meter. With a bit of effort you might be able to make a complete fuel gauge for say $5. The tire pressure gauge is only a buck or two and could replace the much more expensive regulator and/or pressure gauge used in most meters.

It would also be really easy to convert this type of gauge to a "pop-off" type safety valve. Just drill a hole in the body that corresponds with the pistons position at the target pressure. Should be an easy way to use this type of meter with a bare propane tank without having to worry about overpressurizing the gauge pipe.
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Unread postAuthor: jackssmirkingrevenge » Mon Apr 30, 2007 12:33 pm

How about a spring-loaded piston attached to some sort of marker that hits a graduated scale (that would be easy to calibrate with known pressures of compressed air) to record peak pressure?
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Unread postAuthor: jimmy101 » Mon Apr 30, 2007 1:26 pm

jackssmirkingrevenge: That is exactly how the cheapo tire pressure gauges work. (well, there are a few minor changes, tha scale itself moves instead of being stationary...)

The piston is a rubber cup that also seals the cylinder. There is a return spring. The marker (scale) is not attached to the piston so when the pressure drops and the spring forces the piston back to its starting position the scale stays at the maximum reading. (see http://auto.howstuffworks.com/pressure-gauge3.htm.)

It is a very simple design, and cheap to make. You can pick one up at Kmart for $2 or less. Many have a 50 PSIG upper limit. If you hunt around a bit you can usually find ones that max out at 100 or 120 PSIG.
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Unread postAuthor: jackssmirkingrevenge » Mon Apr 30, 2007 1:29 pm

right, sorry for reinventing the wheel hehe
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Unread postAuthor: mark.f » Mon Apr 30, 2007 8:38 pm

The one I got for around five bucks read up to 120 PSI. Too bad I cut it wrong.
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