300 psi pneumatic, a couple questions

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wdr0
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Wed Jul 30, 2014 1:06 am

Hello, I am working on building a relatively powerful pneumatic. I am using all sch 80 PVC for construction
With a 2" barrel and 4" for the chamber. it will have a piston valve, and should be good for 300 psi max depending on temperature. I do intend to pressurize, and fire it remotely due to the pressure involved and it being PVC. Now I am trying to determine how to pilot the piston valve which will be based in a 4" tee. I was considering a QEV but was not sure if I could push it to 300 psi. So mainly I am looking for suggestions on how big, and what type of valve to pilot the main piston valve with.
Also I think I came up with a good way to get a 300 psi fill in a reasonable time for cheap. I was looking into it and came across the fridge compressor method, which obviously would take a ridiculous amount of time to fill that much volume. (4" x 10' pipe). So at first I thought I would use multiple fridge compressors, I asked a friend what he had and he had no fridge compressors but had a central ac unit. Got the ridiculously heavy compressor out, simplified the wiring, and by luck it puts out 300 psi while running below rated amps with 120 psi in, with quite a bit of flow. Only major draw backs are the oil like the fridge compressors, and you need access to 240v power. But hey it was free!
fenrir
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Wed Jul 30, 2014 9:52 am

Welcome to spudfiles! Are you sure the PVC can handle it? I never seen a 2" PVC pneumatic hold 300psi lol. Nighthawkinlight has a good tutorial for beginners on YouTube. Google "coaxial" and his name. Good luck!
wdr0
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Wed Jul 30, 2014 5:02 pm

Well the sch 80 pvc is rated 300 psi with glued joints only at 72 degrees Fahrenheit. But no, I am not sure it will handle the pressure which is why I am going to fill and fire it remotely.
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jrrdw
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Wed Jul 30, 2014 7:09 pm

What is your remote set up going to be? How far away?
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wdr0
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Wed Jul 30, 2014 8:03 pm

I am not entirely sure, it depends how I pilot the piston valve which I still need to figure out. Was considering a ball valve with a spring as the pilot, but I am not sure if it would open fast enough for the most power. I could then have a rope tied to a pin, or even a small air cylinder to pull out the pin. I was also considering an electric solenoid, or a qev with an extended pilot air line, or in conjunction with the solenoid. I don't know if the ball valve or plain solenoid will open fast enough. And I don't know if a qev will handle 300 psi. Does anyone have any experience with the max pressure of a qev? I am also certainly open to other ideas.
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jrrdw
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Wed Jul 30, 2014 10:41 pm

You don't need a whatchyamacallit contraption to shoot your cannon. QEV's have rateings to fit your needs. Use a air line to vent it.

Here's a tech tip every new spudder needs to learn: K.I.S.S. Keep It Simple Stupid! We all learn it, you should to. lol
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wdr0
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Wed Jul 30, 2014 11:56 pm

Yeah, I know. I am always torn between is this too simple to work, or is it more complex than necessary with projects. My first plan was what you suggested, qev with a long airline. But all the ones I found were rated 150 psi, I guess they would probably work for 300.
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jrrdw
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Thu Jul 31, 2014 12:19 am

Start out at 100psi then increase by 25psi and see how it acts...
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wdr0
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Thu Jul 31, 2014 12:24 am

That sounds good to me. I have to wait for my pipe and fittings. Getting it from the local supplier, but they have to order it in. It does give me plenty of planning time.
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Thu Jul 31, 2014 12:41 am

Be sure to get pics during the build and keep us posted.
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wdr0
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Thu Jul 31, 2014 12:47 am

Certainly, the pipe should be here by the end of next week, so that is when I plan to start the build. In the mean time I am working on setting up the big hermetic compressor, I'll post some pics of that as I think it could be useful to others.
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noname
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Thu Jul 31, 2014 2:43 pm

Sounds like you're making a rather expensive pneumatic grenade :wink:
I've experienced PVC exploding on a couple occasions and it's never fun. Schedule 80 pipe might be able to handle 200 psi (might!) but I'd be very skeptical/terrified of 300 psi...
wdr0
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Thu Jul 31, 2014 4:21 pm

Yes I am definitely aware it may turn out to be more grenade than cannon. I am going to pressurize and fire it from at least a hundred feet to the side so that I am out of range of shrapnel, and the piston if it decides to take flight. Even if I get only a few shots, I will have built a large, medium pressure pneumatic from pvc. I think it may do okay. I am using all glued joints, except for the pilot connection which will be a glued bushing to 1" which retains the 300 psi rating when threaded. I plan on bracing it well to prevent excess stress on the joints. And like I saw somewhere on here I am going to use a small piston on the back of the main piston to block the pilot opening as it opens forming an air cushion to slow the piston with less stress on the housing. But yes, I plan to take precautions to mitigate the hazards of an explosion, and I am entirely aware I may only be buying an expensive learning experience.

i will definitely document the build, and I will video the testing so at least I will have any exciting incidents on film.
Last edited by jrrdw on Fri Aug 01, 2014 6:44 am, edited 1 time in total.
Reason: Double posting.
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Solar
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Fri Aug 01, 2014 5:36 am

Why not buy two sets of everything and test one to destruction so you will know not to approach that pressure with the second build. Otherwise you will not know know close to failure you are which could be bad in the future, especially of you are compromising the sctructure over time.
wdr0
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Fri Aug 01, 2014 7:52 am

That's a good idea. I will already have extra pipe since they only sell 20' sections. I think I will build this one first and see how it does, that way I can make design revisions if there are any obvious problems. Although assuming it does work at 300 psi, testing to failure might be difficult because my compressor won't go much higher I think.
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