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Help with my first piston valve

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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Help with my first piston valve

Unread postAuthor: omgimonfrie2 » Mon Oct 15, 2007 10:58 pm

I need help making my first piston. Most of the existing guides require sheet PVC or O-rings, I have neither. I was planning on making it out of sevral cicular cut-out sections of wood, then cutting up on of the rubber bike innertubs I have lying around, then epoxing it to both ends. Will this work?
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Last edited by omgimonfrie2 on Tue Oct 16, 2007 12:14 pm, edited 1 time in total.

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Unread postAuthor: knappengineering » Mon Oct 15, 2007 11:11 pm

i suggest using 2 pvc end caps that fit inside the pipe u are using with a sealing face and a bumper on the ends. it requires no machining just putting a good sealing face on it. good luck with ur first piston they can be tricky and mine still need some work but thats the design i use. I have a one and a 1/4" T with 2 3/4" end caps put together and a rubber sealing face and bumper on each end.
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Last edited by knappengineering on Mon Oct 15, 2007 11:16 pm, edited 1 time in total.
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Unread postAuthor: homedepotpro » Mon Oct 15, 2007 11:13 pm

what size is the piston, 2''?
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Unread postAuthor: hi » Mon Oct 15, 2007 11:15 pm

i have made 4 piston valves, all of them work and none of them have O rings or sheet pvc.

i would not recommend using wood because i used wood that i turned on a lathe and because it was so heavy it cracked the tee that i built it into.

what works best is to mold the piston out of either epoxy or hot glue. i use hot glue and it works very very well. i suggest that you mold it. its fast cheap and easy and it works.

if you look at jack's guns he uses pistons made from epoxy. he to never uses O rings.

some people argue that O rings improove proformance, but if you mold it right it really doesnt matter.

by the way, to get sheet pvc all you have to do is cut a pipe down the side, heat it up, then flatten it out on the ground.

edit- if you make a piston and find out that it is too small you can just wrap it in painter's tape or duct tape until it fits.
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Unread postAuthor: MrCrowley » Mon Oct 15, 2007 11:21 pm

Do some searching next time, there is plenty of topics about wooden pistons.

This is my sheet pvc/o-ring free piston guide:
http://www.spudfiles.com/forums/how-to- ... 10381.html
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Last edited by MrCrowley on Tue Oct 16, 2007 12:00 am, edited 1 time in total.
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Unread postAuthor: omgimonfrie2 » Mon Oct 15, 2007 11:33 pm

knappengineering wrote:i suggest using 2 pvc end caps that fit inside the pipe u are using with a sealing face and a bumper on the ends. it requires no machining just putting a good sealing face on it. good luck with ur first piston they can be tricky and mine still need some work but thats the design i use. I have a one and a 1/4" T with 2 3/4" end caps put together and a rubber sealing face and bumper on each end.


I was going for 2.5. I've already found that my home depot has the 2.5" pipe, but its the gray stuff thats made for sunlight resistance. I tried to read it for pressure ratings but it was too high.

So on the piston you made with the endcaps you used, for examlpe, say 1.5" caps joined with a VERY short section of 1.5" pipe. Then added rubber to the rounded ends? I can do that.

And something I've always wondered is in pneumatics does it really matter about the postioning of the barrrel, valve, air tank? In the combustion world it makes a huge difference. I have no clue about pneumatics.

Will a ball valve work for sprinkler valve acuating? That's for another project I want to complete, a marshmellow sniper rifle.
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Last edited by omgimonfrie2 on Tue Oct 16, 2007 12:11 am, edited 1 time in total.

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Unread postAuthor: hi » Mon Oct 15, 2007 11:53 pm

the problem with using an end cap is that the psiton has to be an absolutly perfect fit in the pipe. if you use and end cap you will have to wrap it in tape, which is ok, but you will have to take the old tape off and put new tape on after every 50 shots or so.

there are two types of grey pvc that i know of.


there is electrical conduct pipe, its kinda light grey. it is bad for making cannons, and there is SCH80, which is dark grey. SCH80 is ecellent for cannons and if you can use it i strongly recommend it over sch40., but if you cant get it then sch40 is just fine.
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Unread postAuthor: omgimonfrie2 » Tue Oct 16, 2007 12:14 am

Its light grey. An endcap covered in melted rubber could fit perfectly. 1" caps fit EXACTLY into 1.5", I use to use them as ammo. I didn't even need wadding. I'm sure there's a pipe size that comes close enought to free improvise it.

EDIT: I posted that, but forgot to metion that if I can find 1.5" SCH-21 pipe I'll use it instead.

I think I found a way to make the tape stick: I have a bunch of heatactivated wing covering from my RC plane left over. I'll tape up the piston and seal it on with that stuff.
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Last edited by omgimonfrie2 on Tue Oct 16, 2007 12:13 pm, edited 1 time in total.

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Unread postAuthor: BC Pneumatics » Tue Oct 16, 2007 10:27 am

Glad to hear my hot glue piston method is hard at work :)
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Unread postAuthor: williamfeldmann » Tue Oct 16, 2007 11:36 am

Depending on where you are planning on using the pipe electrical conduit can be an excellent option.

I have used conduit for barrels many times with excellent results because of the sunlight resistance. However, conduit IS NOT PRESSURE RATED. Do not attempt to make a air chamber ot any other part of the gun out of conduit.

Pistons that are made of wood are often too heavy to work properly. They will either crack the pvc due to their weight or not fire correctly. Hot glue and epoxy will give you a very lightweight piston but can be somewhat difficult to mold.

If possible make a molded piston. You are not out anything if it fails except hot glue and time. I have had good luck using a 2 inch cap (for a 2 inch tee piston, adjust accordingly) with a wax paper lining as a mold. I stuck a piece of foam inside the piston as I was making it to lighten it as well. Then you just sand it or lathe it down till it fits.
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Unread postAuthor: omgimonfrie2 » Tue Oct 16, 2007 3:35 pm

I just realized how simple the could be. I'll get a small section of pipe that fits into the t connector, then put some pingpong balls in it, cover on end with some paper, fill it with epoxy, then cut up the inner tube and superglue a few layers to both ends, After removing the paper. Will 3 or 4 layers of the inner tube work as a bumper and a sealing face?
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Unread postAuthor: jrrdw » Tue Oct 16, 2007 4:48 pm

A cut up tennis ball seems to be a bumper of good choice. I would think that one thick seal would seal better then multi layered.
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Unread postAuthor: omgimonfrie2 » Tue Oct 16, 2007 11:46 pm

I can see a tennis ball working. What would you suggest for a sealing face?
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Unread postAuthor: Hubb » Wed Oct 17, 2007 12:03 am

Try to find some neoprene. Also, check out the thread I made a while back:

http://www.spudfiles.com/forums/piston-valve-improvement-t10720.html

It may be of interest to you.
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Unread postAuthor: Pilgrimman » Wed Oct 17, 2007 12:11 am

I make all of my pistons out of suave deodorant caps and I use VERY old (Like 15 years or so, my dad says it's been sitting around that long, and the adhesive is worn out) insulating tape with the foil removed for the sealing face. The caps fit perfectly in 2" SCH-40 tees. It takes all my breathing power to get the piston to move, so the fit is THAT good, and best of all, it's practically free! Best of all, if it breaks, just sweat a bunch so that you have an excuse to buy more deodorant!
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