Pics Update 1/2" copper cannon

Show us your pneumatic spud gun! Discuss pneumatic (compressed gas) powered potato guns and related accessories. Valve types, actuation, pipe, materials, fittings, compressors, safety, gas choices, and more.
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Lentamentalisk
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Mon May 19, 2008 10:13 pm

My QEV from McMasters arrived today, and after hours of fiddling with fittings trying to get them to seal, I finally got my first non-sprinkler-valve pneumatic sortof working.
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Specs:
Barrel: 5'x1/2" copper pipe
Chamber 5'x1/2" copper pipe
Valve: 3/4" QEV from McMasters

valve area
Image
Image

The 3/4" nipple between the chamber and QEV is leaking so much that I can't pump it over 120psi. I tried tape first, and then used the pipe goop paste stuff, several times over, but to no avail. Do you guys have any suggestions?

The QEV wasn't seating on its own, so I improvised a miniature spring to help it seat, which works perfectly.

At 120psi, despite the leaks I decided to shoot it off, and got some incredible results. You may have noticed it in the picture, but I was shooting into the packing tube of a lava lamp, filled with plastic bags. Shooting over my chrony I read 670.2fps at 120psi with a small piece of wood that I hollowed out to make as light as possible. Later, when the seal was worsening and the pump was dieing, and could only sustain 115psi, I got 556.5fps, with a larger piece of dowel that I hadn't hollowed out.
Last edited by Lentamentalisk on Wed Jun 11, 2008 9:07 pm, edited 2 times in total.
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rp181
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Mon May 19, 2008 10:25 pm

Make sure you wraped the teflon the correct way, if its wrong, then it unrolls as you screw.
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Lentamentalisk
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Mon May 19, 2008 10:32 pm

ya, I'm 90% sure I wrapped it the right way, but I have no clue why the goo didn't work... I smeared sooo much on, and did it so many times without it working! It really angers me...
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lockmanslammin
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Mon May 19, 2008 10:46 pm

Lentamentalisk, I don't see any marring on the elbow or the bottom of the QEV, such as the kind that would have been left behind by a pipe wrench. I would tape it, hold the flat areas on the QEV with a large crescent wrench and grab the rim of the elbow with and adjustable pliers or a pipe wrench and torque that baby down good and tight.

Weird that it leaks, as I don't believe I have ever had metal on metal threads leak on me when using teflon tape as long as the connection was nice and tight.

Hope you get it figured out, it will be a lot more fun to play with if you didn't have to be irritated with it.

Good luck,
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Lentamentalisk
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Mon May 19, 2008 11:35 pm

Well, on the joint that was leaking I undid it, took out all of the goop, and retaped it. When I filled it back up, that leak was gone, but a new one had sprung up... also in a gooped fitting. I removed that goop and retaped it, and yet again it worked... I am glad everything is logical today... [/sarcasm]
Next fill, I was able to fill it all the way up to 180psi before the female shraeder (how the hell do you spell that anyways?) on the pump popped off... That is the way my day has been.
I am going to see if I can borrow a compressor with a quick-connect from a friend tomorrow.
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psycix
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Tue May 20, 2008 10:36 am

Nice QEV gun!
Any chance that you are going to present us with a vid? :D
hraeder (how the hell do you spell that anyways?)
"schrader", I think.
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prospudder
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Tue May 20, 2008 11:17 am

i would use some epoxy putty just be careful because once its on it'll stay on :wink:
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Lentamentalisk
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Tue May 20, 2008 8:22 pm

B wouldn't use some epoxy putty because once its on it'll stay on :wink:


I finally got all of the seals good, and mounted it to a 1x6 to keep the barrels from warping and all, and stuck that up on some 2x4s to put it the level of the chrony when I set them down on a level surface.
Image
Image

I tested it at 180psi (my current max) and with the heavier ammo, managed to get 675.5fps.
Image

It appears that the weight of the ammo has a huge effect on the speed. The lighter ammo that I lost was about 1/2 the length of this one, and was almost completely hollowed out. I will have to make more of those.
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Lentamentalisk
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Wed May 21, 2008 10:01 pm

Now presenting you with my high pressure air source:
Image
HPA Fireman's air tank, fills to 3000psi, currently at ~2000, and I am working on getting a regulator to bring it down a tad. This should satisfy my air needs for a while I think...

The friend who has all of the compressors doesn't have any that go over 150psi, but does have several filled HP air tanks... Fun! Fun! Fun!

edit: by the way, that tank is a full scale backpack sized tank, and just walking the block from his workshop to my house I was already getting back pains... poor firefighters! At least they get the newer carbon fiber ones...
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Antonio
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Thu May 22, 2008 1:26 pm

some high velocities here...damn!

edit: Nice ammo btw (its a good way of getting the center of gravity forward while putting the center of pressure back and givin it a good aerodynamic shape)
Last edited by Antonio on Thu May 22, 2008 2:41 pm, edited 1 time in total.
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MrCrowley
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Thu May 22, 2008 2:15 pm

Cool cannon, clean and powerful. :)

I'd trust that QEV easily to 300psi, I've taken the same one to 240psi and some member has tested them to 850psi where they start leaking.
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SpudFarm
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Thu May 22, 2008 2:37 pm

that is a really clean and nice copper gun.!
also you got some good velocities there.
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al-xg
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Thu May 22, 2008 3:14 pm



8g projectile accelerated to something near 885fps :)
Looking forward to HPA eh ?
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Lentamentalisk
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Thu May 22, 2008 6:12 pm

well my ammo is around 1g or less, as it doesn't even register on my digital scale that can measure to the gram. I was just going to use the QEV at around 300psi. The current regulator doesn't work, it takes it from the 2000psi down to about 1-2psi (I can stop the flow with my finger) so I will need to get another one today.
Do not look back, and grieve over the past, for it is gone;
Do not be troubled about the future, for it has not yet come;
Live life in the present, and make it so beautiful that it will be worth remembering.
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Lentamentalisk
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Thu May 22, 2008 10:07 pm

Ok, several things
1) my friend just brought me over a broken fridge, that runs but doesn't cool, meaning its lost it's freon. I will be converting that on Monday or Tuesday if I have time.
2) I am doing this for a science project, which I am presenting on Wednesday (hence me being so rushed and trying to get the pump done by Tuesday) and I was wondering if anyone had an animation of a piston valve that I could use in my presentation. I have plenty of diagrams that I could use, but it would be infinitely cooler if I had an animation.

Lastly, thanks for all of the positive responses!

edit: sorry for the double post
Image
Do not look back, and grieve over the past, for it is gone;
Do not be troubled about the future, for it has not yet come;
Live life in the present, and make it so beautiful that it will be worth remembering.
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