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Urethane Rod for pistons.

Post about things you have launched or thought about launching. Also post about various materials used for building cannons. No posts about explosive projectiles!
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Unread postAuthor: inonickname » Wed Aug 26, 2009 7:46 am

Can you read the topic? He's looking for a sealing face and piston solution.

Gippeto has had success with teflon.

I can testify that nylon will not crack in this use. (with a bumper, from experience anyway)
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Unread postAuthor: qwerty » Wed Aug 26, 2009 7:49 am

yes i did read the topic and kevler could be a solution for a strong, long lasting piston.
About the sealing face i would do something like farcrys idea.
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Unread postAuthor: Mr.Sandman » Wed Aug 26, 2009 8:56 am

qwerty wrote:yes i did read the topic and kevler could be a solution for a strong, long lasting piston.
About the sealing face i would do something like farcrys idea.

Hell, if it can withstand bullets then it would work really well but its expensive as hell it cost like 140 bucks for just the powder :shock: 6 ounces. But i agree urethane should work because as tech said it is able to take the impact of some dude jumping down 20 feet of stairs. And gippeto uses o-rings to seal in his high pressure hammer valve coaxial so im pretty sure it could handle the decimator.
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Unread postAuthor: Technician1002 » Wed Aug 26, 2009 9:37 am

psycix wrote:Machine a piston that seals inside the porting with an o-ring instead of against the pipe.


At his pressure, air gets under the o rings and removes them. Unless he has a guide to retain the rings they will be shot out the barrel. It is one of the reasons the QDV has metal remaining between the breech and barrel. It is to keep the o rings from being peeled off the piston.

With a polished valve seat and machined piston face of HDPE, the pressure will seal that very well. If you can get the gaskets they use for the CO2 bottles used in the soft drink industry, you will see what I mean. It's hard plastic and seals well under pressure.

Edit, found a picture of the fiber gasket for CO2 regulators. They are called fiber, but they appear to be hard plastic.
Image
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Last edited by Technician1002 on Wed Aug 26, 2009 12:44 pm, edited 1 time in total.
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Unread postAuthor: Gippeto » Wed Aug 26, 2009 10:07 am

As mentioned, I have used teflon for sealing faces with excellent results. I've also used nylon for the piston itself, with a neoprene (fairly hard stuff) washer cut to look like an oversized tap washer for a bumper.

I've had no trouble with pistons changing shape (mushrooming), sealing faces extruding, or bumpers coming apart to date.

I use quad rings in my co-ax to seal off the chamber, not as a sealing face.

Jeep, I have a piece of 1.5" nylon you can have if it's long enough.

Let me know, and it's on the way. :)
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Unread postAuthor: jeepkahn » Wed Aug 26, 2009 12:09 pm

You know, even though I know that there's 1000lbs of force on the sealing face(causing face destruction) I forget that with 1000lbs of force will seal nylon/hdpe/uhmw against a smooth breech...doh... :roll:

Thanx for the offer Gippeto, my local fastenal has some in stock for like $.83 per inch... I'll let you guy's know how it does...
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Unread postAuthor: Technician1002 » Wed Aug 26, 2009 1:02 pm

jeepkahn wrote:You know, even though I know that there's 1000lbs of force on the sealing face(causing face destruction) I forget that with 1000lbs of force will seal nylon/hdpe/uhmw against a smooth breech...doh... :roll:

Thanx for the offer Gippeto, my local fastenal has some in stock for like $.83 per inch... I'll let you guy's know how it does...


The force is relative. The force can be spread out over a larger area. With enough area, the force per Square Inch can be kept in the material strength and not be damaged. A wider valve seat may be all that is required to prevent destruction from pressure.

My Mouse Musket used a very wide valve seat. It used a coupler glued onto a 1 inch pipe so the seat was thicker than the end of the 1 inch pipe. I grooved both the pipe and coupler to take an o ring in between to complete the valve seat seal.
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Re: Urethane Rod for pistons.

Unread postAuthor: velocity3x » Wed Aug 26, 2009 1:18 pm

jeepkahn wrote:Has anyone used manufactured urethane rod for pistons???


Not me. I strictly use Acetal. I fire a 2.0" dia piston with 1.8" of travel and an o-ring is machined into the piston face. I'm using 300-400psi carbon dioxide and never had a piston or o-ring failure. I'm moving up to 1000psi helium in a few months and I don't view the piston as any potential problem. I guess when it comes to material selection, it's just a matter of what you have the most success with. Personally... Acetal works for me.
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Unread postAuthor: THUNDERLORD » Wed Aug 26, 2009 1:26 pm

I don't see aluminum piston being much heavier than those types plastic(???)
Since a shorter piece could be used.
Even if the "piston" was a flat piece of thick steel somehow with rubber sealing face.

Also, On (atleast) one of JSR's designs the rubber sealing face was on the valve seat and not the piston.

BTW, Been thinking of a co-axial with a large flat diaphram sealing the barrel with large valve seat.
Design has rubber sheets with leather glued in between,
same diameter as chamber with equalization slots,
filled from behind diaphram,
a large valve seat back of barrel and up to atleast 300psi action.
Got me wondering about flatter, shorter (lighter) pistons.
tech wrote:...The force is relative. The force can be spread out over a larger area. With enough area, the force per Square Inch can be kept in the material strength and not be damaged. A wider valve seat may be all that is required to prevent destruction from pressure. ...

Makes sense. 8)
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Unread postAuthor: velocity3x » Wed Aug 26, 2009 1:50 pm

THUNDERLORD wrote:I don't see aluminum piston being much heavier than those types plastic(???)


Actually...Acetal / Delrin is .05lb per in^3
Aluminum is .10lb per in^3
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Unread postAuthor: Biopyro » Wed Aug 26, 2009 2:04 pm

Acetal is 1.2g/cm^3 and HDPE is 0.9 iirc. Aluminium is 2.7. It may not seem a lot but it sure adds up for larger diamters!
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Unread postAuthor: THUNDERLORD » Wed Aug 26, 2009 2:14 pm

Finally somebody mentioned delrin.

My point though, how does it's strength to weight compare?
Are those figures mentioned relative to it's strength???

Because depite it's density/ weight difference, if a smaller (shorter) chunk of aluminum can be used (because it's stronger)...not much difference(?)
IDK.

BTW, off topic, but anyone's guesstimate how much pressure a two part epoxy filled 1/2" pvc piston could handle??? Thanks fellas! 8)
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Unread postAuthor: dewey-1 » Wed Aug 26, 2009 3:50 pm

Also keep in mind that polymers like Nylon, Teflon, HDPE, UHMW, Acetal and others have a "self lubricating" property.

It means they are very low on friction losses. Slippery in other words.
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Unread postAuthor: THUNDERLORD » Wed Aug 26, 2009 4:01 pm

dewey-1 wrote:Also keep in mind that polymers like Nylon, Teflon, HDPE, UHMW, Acetal and others have a "self lubricating" property.

It means they are very low on friction losses. Slippery in other words.


Females have a self-cleaning property.
G*d i LOVE WOMEN!!! :P
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