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valve question

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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valve question

Unread postAuthor: Mike_Hunt0420 » Sun May 24, 2009 8:02 pm

can any offer suggestions on a piston valve design that can handle 600-800 psi without machining a teflon piston? I don't have the tools to machine anything which makes me sad. :(
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Re: valve question

Unread postAuthor: Technician1002 » Sun May 24, 2009 8:12 pm

Mike_Hunt0420 wrote:can any offer suggestions on a piston valve design that can handle 600-800 psi without machining a teflon piston? I don't have the tools to machine anything which makes me sad. :(


I can't think of anything in that pressure range. That's very high. Are you planning on using unregulated CO2?

What tools do you have? For no tools, there isn't much that is simply bolt together in that pressure range.
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Unread postAuthor: Hotwired » Sun May 24, 2009 8:13 pm

Why would you make a piston from solid PTFE?

Something with low friction mebbe, but which is also tough is a better bet, HDPE or UHMWPE would do it.

Check out approximately every copper launcher with a homemade piston in here.

Most of the pistons are made with nothing more than hand tools.

There is nothing more to the basic design than what you see. As to the pressure rating... Steel, tough rubber, tough plastics - no PVC in there -_- are the basic materials for that.
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Unread postAuthor: boom_o_matic_2.0 » Sun May 24, 2009 8:16 pm

600-800? I"d say use steel pipe. and your piston would have to be something strong too but still light enough to move. you gotta kinda play around with it. maybe a wood piston with a big washer on the front of it with the sealing face covering that.
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Unread postAuthor: Technician1002 » Sun May 24, 2009 8:19 pm

boom_o_matic_2.0 wrote:600-800? I"d say use steel pipe. and your piston would have to be something strong too but still light enough to move. you gotta kinda play around with it. maybe a wood piston with a big washer on the front of it with the sealing face covering that.


I wouldn't use wood about maybe 200 PSI max. It may part company. Something without grain would be better to prevent the start of a high pressure entry point to blow it apart.
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Unread postAuthor: boom_o_matic_2.0 » Sun May 24, 2009 8:28 pm

what if you were to seal it? I'm not sure how. maybe laquor or coat it in epoxy
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Unread postAuthor: Technician1002 » Sun May 24, 2009 8:31 pm

boom_o_matic_2.0 wrote:what if you were to seal it? I'm not sure how. maybe laquor or coat it in epoxy


Wood gives under pressure. It will compress. The seal must not fail.
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Unread postAuthor: boom_o_matic_2.0 » Sun May 24, 2009 8:37 pm

Technician1002 wrote:
boom_o_matic_2.0 wrote:what if you were to seal it? I'm not sure how. maybe laquor or coat it in epoxy


Wood gives under pressure. It will compress. The seal must not fail.


are you talking about the barrel seal or the sealing of the entire piston I talked about with epoxy?
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tools and construction

Unread postAuthor: Mike_Hunt0420 » Sun May 24, 2009 8:50 pm

I am constructing the entire cannon out of steel, galvinized is all I can get easily but should suffice with a little polishing, and I have all sort of hand tools, drills, vices, etc., I was just lacking a laithe or any such niftyness. I had looked through most of the cannons in the forums and not many are in the pressure range I am shooting. I am running an hpa notrogen system regulated to as much as 800psi. I will play around with variations of this piston http://www.spudfiles.com/forums/self-cl ... 17609.html I think it should be up to it. any further info or advice is always appreciated, i'd hate to do myself an injury lol.
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Unread postAuthor: Technician1002 » Sun May 24, 2009 9:24 pm

boom_o_matic_2.0 wrote:
Technician1002 wrote:
boom_o_matic_2.0 wrote:what if you were to seal it? I'm not sure how. maybe laquor or coat it in epoxy


Wood gives under pressure. It will compress. The seal must not fail.


are you talking about the barrel seal or the sealing of the entire piston I talked about with epoxy?


Sealing the entire piston. If it has a void and the crack, pore, etc gets 800 PSI in it, when fired, it is likely to come apart.
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Unread postAuthor: Gippeto » Sun May 24, 2009 9:52 pm

You didn't give a barrel size,or pipe size so you're on your own for dimensions.

Just make the piston from all thread, nuts, steel washers, and rubber washers.

It goes like this, front to back, everything mounted on the all thread (duh!);

Nut, small steel washer (must fit inside barrel), rubber washer (sealing face), larger steel washer (backing), nut, appropriate distance to fit piston to design (gap with nothing on the all thread),nut, large steel washer (piston guide), nut, empty space, nut, smaller steel washer, rubber washer, larger steel washer (backer), nut.

Use a bit of sharpened pipe to cut the rubber washers to the correct size. The "large steel washers" should ideally fit inside the steel pipe with only a little gap.

It'll be a bit heavy, but it'll handle the pressure just fine. Use an adequate bumper.

If you ask Ragnarok nicely, I do believe he has a picture of something roughly similar, from HEAL.

Seems to me there are others using similar setups as well.
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Unread postAuthor: Mike_Hunt0420 » Sun May 24, 2009 11:15 pm

thank you kindly. I didn't give dimensions because I want to work everything out myself. just needed a couple pointers. thanks again.
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Unread postAuthor: Gaderelguitarist » Mon May 25, 2009 12:34 am

I do hope that by Galvanized steel that you don't mean the fittings from a home depot or Lowes. Those fittings can't hold that much pressure I'm pretty sure.

and go to Mcmaster.com to find a suitable material for your piston.

they sell plastic by the rod so all you need is a saw
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Unread postAuthor: Mike_Hunt0420 » Mon May 25, 2009 1:13 am

ah thank you. I will search around for more suitable mats then galvanized shouldn't be too hard, and thanks for the mcmasters tip.
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Unread postAuthor: Gippeto » Mon May 25, 2009 8:58 am

Those fittings can't hold that much pressure I'm pretty sure.


You're pretty sure are you? :wink:

I think you'll be surprised. :)


http://www.spudfiles.com/forums/the-fai ... 15393.html
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