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My First Piston Valve Launcher

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: acs2997 » Mon Jul 16, 2012 8:06 pm

i actually have already watched that one! thanks a ton though, ive looked all over youtube as well as this website. i think i have all the info and instructions ill need. theres only two more thing i was wondering about: how long does it take for the air to travel through the hole in the piston and into the chamber? and can i just use a female and male adapter behind the piston? is there a need for all those screws?
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Last edited by acs2997 on Mon Jul 16, 2012 8:09 pm, edited 1 time in total.

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Unread postAuthor: MrCrowley » Mon Jul 16, 2012 8:08 pm

Well unless you're using o-rings, don't put a hole in your piston. There will be adequate space around the outside even though it may not seem like that. Your chamber should fill normally, the piston isn't much of an obstruction to the air.
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Unread postAuthor: acs2997 » Mon Jul 16, 2012 8:14 pm

and the need for the screws?
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Unread postAuthor: mattyzip77 » Mon Jul 16, 2012 8:22 pm

Thats just one way of doing it. you can use a female adapter and a mip x fip threaded bushing.
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Last edited by mattyzip77 on Mon Jul 16, 2012 8:56 pm, edited 1 time in total.
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Unread postAuthor: MrCrowley » Mon Jul 16, 2012 8:22 pm

Yes, it would be better to use male and female adapters rather than screws which may weaken the structural properties of the PVC. Make sure to find the socket type of female threaded adapter which requires a piece of pipe to attach it to the tee. This means the piston can be housed inside this piece of pipe and can be removed by unthreading the male adapter. There are some female threaded adapters which will prevent this as their inside diameter constricts at a certain point inside the fitting; preventing the piston from being removed.

The ones I'm talking about are like this:
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Unread postAuthor: mattyzip77 » Mon Jul 16, 2012 8:26 pm

And one of these which is a mip x fip threaded bushing


http://www.plumbingsupply.com/images/pv ... sxfips.jpg
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Unread postAuthor: Technician1002 » Tue Jul 17, 2012 12:14 am

Image
May I suggest using a really good bumper with PVC? Trust me on that one. I found ABS does better in that department. Use the proper glue to attach ABS to PVC. I eventually retired that cannon and built one entirely from ABS using the same piston.
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Unread postAuthor: MrCrowley » Tue Jul 17, 2012 12:46 am

I've had the same thing happen when I forgot to re-insert the bumper in my PVC piston cannon as well. Half a tennis ball will usually work well for a couple dozen shots.
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Unread postAuthor: acs2997 » Tue Jul 17, 2012 1:22 am

so you dont reccomend aq half tennis ball?
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Unread postAuthor: MrCrowley » Tue Jul 17, 2012 2:04 am

Half a tennis ball will usually work well for a couple dozen shots.
In other words, use a tennis ball hemisphere and make sure to check it every few dozen shots for signs of wear, deformation, cracks or failure.
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Unread postAuthor: Technician1002 » Tue Jul 17, 2012 5:31 pm

I recommend dense open cell foam rubber.

The current bumper is just behind the golf ball for the ABS cannon. This works well.
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