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Piston Questions

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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Piston Questions

Unread postAuthor: pvcmaster » Tue Aug 07, 2007 6:13 pm

I am working on a piston valve with a 2" chamber port and 1.5" barrel port, and I am having some trouble finding answers to my questions. First of all, what is the best way to create a perfectly square sealing face on the barrel? I also need some help sealing the area between the 2" pipe inside the tee and the removable plug in the back. I was looking for something like a rubber gasket that sits around the rim of the 2" pipe, but i cant seem to find it. What size screws are typically used to fasten the plug to the back of the valve? One last question: What kinds of things could i use for a bumper besides a tennis ball? I don't think that it is suitable for an endcap piston because only the rim of the endcap would impact the back of the valve. Sorry for all the questions, and i would really appreciate any help i can get.
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Re: Piston Questions

Unread postAuthor: Modderxtrordanare » Tue Aug 07, 2007 7:06 pm

pvcmaster wrote:First of all, what is the best way to create a perfectly square sealing face on the barrel?


A chop saw, or a hack saw and a sort of jig to keep your cut flush. Follow that up with some sanding (orbital sander might be good idea too) and you'll be set. :wink:

pvcmaster wrote:I also need some help sealing the area between the 2" pipe inside the tee and the removable plug in the back. I was looking for something like a rubber gasket that sits around the rim of the 2" pipe, but i cant seem to find it. What size screws are typically used to fasten the plug to the back of the valve?


It doesn't really matter what kind of bolt/screw you use to secure the plug in the back as much as how many screws you use. I would go with 4 to 6 screws. 8 screws might cause too much stress, but I could be wrong.

As for the sealing aspect of that question, you can lathe in an o-ring groove. You can also rig it up to a sanding drum with some tape to compensate for the gap in the OD of the sanding drum and the ID of the plug. You just wedge the plug onto the tape/drum apparatus, and put the drill in a vice. (Drill press would work too) While it's spinning you use a cutting tool as if you were using a lathe and cut a groove out.

You could also try to smear liquid teflon (or teflon tape?) all around the plug so when you stick it in and bolt it down it's air tight. I don't know how well that would work though, I only tried it once and it didn't work that well. But I didn't apply the liquid teflon very liberally.

pvcmaster wrote:One last question: What kinds of things could i use for a bumper besides a tennis ball? I don't think that it is suitable for an endcap piston because only the rim of the endcap would impact the back of the valve. Sorry for all the questions, and i would really appreciate any help i can get.


How much travel does your piston have? My pistons don't have very much travel (d/4) so I don't use a bumper. (light spring in them too)

You can take a short (inch or two) section of semi-large diameter hose, fold it in half and stuff it in the plug. That should work, if you even needed one at all. I like a light spring from in a pop-up sprinkler personally, because I can cast it in the piston with expanding foam.
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Unread postAuthor: pvcmaster » Wed Aug 08, 2007 6:27 am

Thanks for all your help, but i dont think that i could manage an o-ring groove on the plug, and i need to find some sort of rubber washer, gasket, or o-ring that would fit against the rim of 2" pipe, i would appreciate anyones help.
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Unread postAuthor: noname » Wed Aug 08, 2007 10:25 am

You can use silicone sealant to glue it in, because it will seal well, but all you need is a pipe wrench and a vice to get it apart afterwards.
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Unread postAuthor: pvcmaster » Fri Aug 10, 2007 4:17 pm

Ok thanks, that sounds like an easier solution. I have one last question. My valve is almost finished, but I was planning to use a 1 1/2" slip x thread coupler to make barrels interchangeable, but that means that my valve will not be completely inside the tee. How can I make this connection flush with the tee? Will 1 1/2" pipe fit into the unthreaded part of a 2" x 1 1/2" spigot x thread bushing?
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