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Pressure gauge install

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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Pressure gauge install

Unread postAuthor: xboxteen01 » Sun Jan 27, 2008 1:35 am

I searched far and wide for the answer to this but came up empty handed, so here goes. I have a 1/4 NPT pressure gauge for my pneumatic cannon. I read once that the gauge should be installed through 2layers of overlapping PVC pipe, example of this is through the endcap. Is this necessary or can i just drill a hole and install into the chamber. I just want to do this right the first time
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Unread postAuthor: Pilgrimman » Sun Jan 27, 2008 2:07 am

What I do is buy a bushing that reduces to 1/2", put it on the chamber, then buy a brass bushing that goes from 1/2" to 1/4".
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Unread postAuthor: rna_duelers » Sun Jan 27, 2008 2:12 am

What seems like a better thing to do?Have the hole drilled through two layers of PVC or one?Two layers is the logical choice for safety reasons. :wink:
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Unread postAuthor: BigGrib » Sun Jan 27, 2008 2:16 am

Simple answer to your question yes install it in a douple layer. More explained answer For a 1/4 NPT fitting drill a half inch hole and then thread the fitting pvc using the fitting to cut the threads in the pvc. once you have it screwed into the pvc take it back out and apply epoxy in and around the hole you just drilled and tapped and reinsert the fitting back into the pvc. Let the epoxy set and the install the guage into that fitting using lots of thread tape to seal it all up.
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Yea, that's definitely going to get you at least a tazer.

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Unread postAuthor: Ragnarok » Sun Jan 27, 2008 2:25 am

As I've said elsewhere, a perfectly round hole in a flat plate will reduce it's failure load by a factor of 3.
A threaded hole in a chamber wall has even worse stress concentration, of the order of 4 times weaker than the unmodified chamber wall.

Tapping through a double layer helps to counter this loss of strength - the double strength of the wall means the hole is around half the strength of the regular wall. Still not great, but a lot better than a quarter of the strength.
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Unread postAuthor: limbeh » Sun Jan 27, 2008 10:12 am

Hey,

I'm thinking of doing this in 4" JIS AW PVC, which has a pressure rating of 10 bars (150 psi). My planned operating pressure is 110psi (120 max), would it still be safe to try installing a pressure gauge (same goes for a schrader / pilot valve) into a double layer of PVC (fitting + pipe)?

What if we get a female thread to socket adapter, drill an appropriately sized hole in the double layed of PVC, stick the adapter in (and solvent weld it), then thread the gauge in? Would it be any stronger than drilling a hole and using the gauge itself to thread through the hole?

Thanks.
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Unread postAuthor: BigGrib » Sun Jan 27, 2008 11:23 am

yeah your fine with installing a gauge on that. i get my 1/4 npt male fittings to 1/8 npt female which i screw the gauge into and merely screw the fitting into the drilled hole see my how to above. but dont try to solvent weld a brass fitting into plastic cause that's useless. get some 5 minute set epoxy for like 5 bucks and mix a little up and epoxy the hole so that the epoxy will cover the threads as the fitting goes in. it's gonna make it so if something happens like you drop your gun and the gauge breaks you just unscrew the gauge from the fitting and replace it.
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Yea, that's definitely going to get you at least a tazer.

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Unread postAuthor: jimmy101 » Sun Jan 27, 2008 11:33 am

If you really want to install a gauge in the chamber, and not a fitting, you can double up the chamber wall where you install the fitting.

Take a hunk of pipe the same diameter as the chamber that is perhaps 2" long. Cut the piece of pipe in half (or so) lengthwise. Boil the c-shaped piece of pipe in water to soften it, press it against the chamber and hold until cool. If the piece springs back too much when removed from the chamber then repeat the process.

Thouroughly dry everything. Prime/clean and glue the piece onto the chamber. Clamp at least overnight for the glue to dry.

Drill and tap your hole through the double layer.
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Unread postAuthor: BigGrib » Sun Jan 27, 2008 11:37 am

man, that's a lot of pain in the ass. i tend to stick with an easy method that does what it needs to
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Yea, that's definitely going to get you at least a tazer.

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Unread postAuthor: xboxteen01 » Sun Jan 27, 2008 7:40 pm

alright thanks for the help guys
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