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Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Unread postAuthor: Ragnarok » Mon Nov 19, 2007 11:15 pm

The gauge won't fly out that fast. The bigger problem is the pipe fracturing.

Still, wear goggles if you're bothered by it.
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Does that thing kinda look like a big cat to you?
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Unread postAuthor: elitesniper » Mon Nov 19, 2007 11:16 pm

Im only in the 8th grade D: and yea im only looking at it when im pumping its faceing the side when i shoot so its ok:D. safety googles always on sir :D
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Last edited by elitesniper on Mon Nov 19, 2007 11:18 pm, edited 1 time in total.
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Unread postAuthor: ShowNoMercy » Mon Nov 19, 2007 11:17 pm

And to really get you going, the gauge itself is a safety flaw, jar it once or twice and you could be looking at shards of plastic flying into your precious eyes.
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Unread postAuthor: elitesniper » Mon Nov 19, 2007 11:19 pm

Um what does jar mean? Like the pickle jar or does it mean somthing else?
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Unread postAuthor: ShowNoMercy » Mon Nov 19, 2007 11:22 pm

No like rattle it, drop it on the ground, jar it, you know like hit it with something hard? I don't know, its late I have way to much coffee today and my mind hurts from statics.
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Unread postAuthor: elitesniper » Mon Nov 19, 2007 11:25 pm

Oh ok, you, sir ,should get some rest:D
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Unread postAuthor: ShowNoMercy » Mon Nov 19, 2007 11:27 pm

Nah, to much caffeine in me to sleep now so I will continue to prowl this site. Such an awesome life I have.... lol . You got any more questions?
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Unread postAuthor: elitesniper » Mon Nov 19, 2007 11:32 pm

hmm, naw thats all for my safety concerns now , i gotta go brush my teeth Lol
ill have more questions when i add on or fix my launcher. A luacher is never complete for me i just keep adding on it to make it better or safer lol, im wierd o.o :lol:
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Unread postAuthor: jimmy101 » Tue Nov 20, 2007 11:19 am

As folks have posted their are really two things you are worried about when you drill a hole for a gauge (or any other accessory).

Will the hole weaken the pipe (fitting, joint) and act as a nucleation site for a catastrophic failure of the gun?

Will the threads in the hole be strong enough to keep the gauge from being fired from the gun?

For the second question it is easy enough to test. Figure your typical "1/4 inch NPT fitting" actually uses a hole pretty close to 1/2 inch in diameter. The area of the hole is (Pi)r<sup>2</sup>=(3.14)(0.25)<sup>2</sup>=0.19in<sup>2</sup>
If you are using a shop compressor, then the maximum pressure in the chamber is about 120 PSIG. That means there is (120PSIG)(0.19in<sup>2</sup>)= ~24 pounds of force pushing on the gauge when the gun is pressurized. Really not all that much. You can grab the gauge and pull hard and easily put that much force on it. If you can rip the gauge out of the gun with you hands then the mounting probably isn't strong enough.

There are a couple reasons for drilling into joints instead of just the pipe. Strength is certainly an important one. Another reason is that you want the threads to seal. Imagine threads through a curved piece of pipe wall. If the wall thickness and diameter of the pipe is small enough then you won't have very many threads (perhaps none at all) that actually make a full revolution in contact with the pipe.
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Unread postAuthor: jimmy101 » Tue Nov 20, 2007 11:53 am

As folks have posted, there are really a couple things you are worried about when you drill a hole for a gauge (or any other accessory).

Will the hole weaken the pipe (fitting, joint) and act as a nucleation site for a catastrophic failure of the gun?

Will the threads in the hole be strong enough to keep the gauge from being fired from the gun?

Will the threads actually create an air-tight seal?

For the second question it is easy enough to test. Figure your typical "1/4 inch NPT fitting" actually uses a hole pretty close to 1/2 inch in diameter. The area of the hole is (Pi)r<sup>2</sup>=(3.14)(0.25)<sup>2</sup>=0.19in<sup>2</sup>

If you are using a shop compressor, then the maximum pressure in the chamber is about 120 PSIG. That means there is (120PSIG)(0.19in<sup>2</sup>)= ~24 pounds of force pushing on the gauge when the gun is pressurized. Really not all that much. You can grab the gauge and pull hard and easily put that much force on it. If you can rip the gauge out of the gun with your hands then the mounting probably isn't strong enough.

There are a couple reasons for drilling into joints instead of just the pipe. Strength is certainly an important one. Another reason is that you want the threads to seal. Imagine threads through a curved piece of pipe wall (see the attached image "thread_in_pipe"). If the wall thickness and diameter of the pipe is small enough then you won't have very many threads (perhaps none at all) that actually make a full revolution in contact with the pipe. Without at least a couple full revolutions of the threads they won't seal very well. The double pipe thickness you get at a joint helps get more threads actually seated in the plastic. This helps both the strength and reduces leaks.

If you really want to beef up a place where you are installing a gauge you can use a triple layer of PVC. Take a piece of pipe a couple inches long and cut it in half lengthwise (so it looks like a "C"). Boil the piece in water for a minute or two then remove it from the boiling water and, while still hot, force it around the fitting on the gun and clamp in place. Let it cool to room temp. Remove the piece, dry it thoroughly (water will prevent the glue from bonding properly), prime and apply glue to both the piece and the fitting, reinstall the piece and clamp in place until the glue is dry. You need to allow at least 12 hours (24 is better) for the glue to dry. If you drill and/or tap into it before it is fully dry you'll rip the piece back off the fitting.

You now have a triple thickness of pipe wall. For 3"D sch40 PVC the triple thickness is about 0.7 inch thick.
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Attachments
thread_in_pipe.gif
(Hmmm, looks like a fitting with left-handed threads.)
thread_in_pipe.gif (3.69 KiB) Viewed 297 times
tripple_layer.jpg
The PVC thickness is about 1/2&quot; where the gittings are tapped.
EDIT: Engrish
Should read &quot;The PVC thickness is about 0.7&quot; where the fittings are tapped.&quot;
tripple_layer.jpg (33.22 KiB) Viewed 297 times
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Unread postAuthor: nivekatoz » Tue Nov 20, 2007 7:39 pm

Why don't you use steel or tempered aluminum...That way the threads will be worry proof if you tap them.......
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