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1/2" piston valve bb gun (unfinished)

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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1/2" piston valve bb gun (unfinished)

Unread postAuthor: LCTChamp » Sat Apr 04, 2009 7:47 am

This is my first piston gun, and I decided to start small. The piston is made of hot glue and a bike inner tube for the sealing face. I am currently piloting it with a schrader valve, but eventually I will pilot it with a blowgun. It has 1/8" porting and once a I get a bb barrel will be a bb pistol. My tee and some of my fittings are pvc, and 1/2" pvc pipe is rated to 600 psi. Everyone always says the glued fittings will fail before this pressure. So what is the highest pressure in psi that can be used safely? Also what is the best lubricant to use to make the piston slide smooth? I thank you all in advance for any help.
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bb gun 002.jpg
The right part is the shcrader and the left is the 1/8" nipple.
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Unread postAuthor: spudtyrrant » Sat Apr 04, 2009 7:57 am

since you say its rated to 600, and since its pvc i would think about 200psi. even if its rated to 600 the glue will start to spring leaks above 200.
if you put epoxy at all the joints you may be able to go to 300psi but not very often.
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Unread postAuthor: LCTChamp » Sat Apr 04, 2009 8:00 am

Thank you! What is the best type of lubricant for the piston?
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Unread postAuthor: mark.f » Sat Apr 04, 2009 12:23 pm

spudtyrrant wrote:since you say its rated to 600, and since its pvc i would think about 200psi. even if its rated to 600 the glue will start to spring leaks above 200.
if you put epoxy at all the joints you may be able to go to 300psi but not very often.


A glued joint is stronger than the individual components themselves. If the pipe says it's rated to 600 PSI water, then it will take 600 PSI of water.

Only catch is you're using air, and there is an additional shock factor. Therefore, I would use maybe 200 PSI max for safety.

As for the lubricant, I would just use white lithium grease. Works fine for me and others.
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Unread postAuthor: LCTChamp » Sat Apr 04, 2009 12:27 pm

Can you buy white lithium grease at the hardware store? Thanks for the help.
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Unread postAuthor: Biopyro » Sat Apr 04, 2009 12:50 pm

Yeah you can. It's usually with the WD-40.
Air doesn't exert more force, but if it were to break, it contains a lot more energy, so unless it says on it 600psi, I wouldn't really take it past 200. Often store assistants will just make things up they don't know to please a customer.
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Those who would give up Essential Liberty to purchase a little Temporary Safety, deserve neither Liberty nor Safety. -Benjamin Franklin
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Unread postAuthor: mark.f » Sat Apr 04, 2009 12:56 pm

Biopyro wrote:Yeah you can. It's usually with the WD-40.
Air doesn't exert more force, but if it were to break, it contains a lot more energy, so unless it says on it 600psi, I wouldn't really take it past 200. Often store assistants will just make things up they don't know to please a customer.


Air doesn't exert more force, but the piston slamming back in the carriage is putting extra stress on fittings designed to hold non-critical fluids in a stationary setting.

1/2" PVC is rated to 600 psi.
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Unread postAuthor: LCTChamp » Sat Apr 04, 2009 12:58 pm

So with a sufficient bumper it would be safe at 250?
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Unread postAuthor: mark.f » Sat Apr 04, 2009 1:03 pm

I wouldn't like pushing my luck that much. I'd feel safer at 200 and below, but it's your decision.
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Unread postAuthor: LCTChamp » Sat Apr 04, 2009 1:07 pm

Alright then, thanks for the help. I'll let you guys know how this ends up.
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Unread postAuthor: MrCrowley » Sat Apr 04, 2009 4:56 pm

A glued joint is stronger than the individual components themselves.

Assuming, of course, that the joint has been correctly bonded and there are no imperfections whatsoever.

I agree with the others also, 200PSI sounds like a nice...round...number. :)
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Unread postAuthor: LCTChamp » Sat Apr 04, 2009 5:01 pm

Assuming, of course, that the joint has been correctly bonded and there are no imperfections whatsoever.


All of my joints are correctly bonded, and I didn't see any imperfections. I'll post this in the showcase when it gets finished (in the next 2 weeks).
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Unread postAuthor: Brian the brain » Sat Apr 04, 2009 5:16 pm

Just always keep safety in mind.
If you feel you need more power, go with metal or upscale the cannon.

There is no sense in pushing your luck when there are more sensible ways of achieving your goals.Moar power means more danger.Never forget that.

A lot of guys use high pressure these days, but 200 psi is still nothing to sneeze at.
You'll have a lot of fun with this one I assure you.Don't let them ( or me)get to you... :D


So..again...once this gets boring, it's time to upscale or use metal.
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Gun Freak wrote:
Oh my friggin god stop being so awesome, that thing is pure kick ass. Most innovative and creative pneumatic that the files have ever come by!

Can't ask for a better compliment!!
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