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Sealing face burn-out

Post questions and info about hybrid (compressed gas with fuel) powered cannons here. This includes discussion about fuels, ratios, ignition systems, build types, safety, and anything else relevant.
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Sealing face burn-out

Unread postAuthor: Fnord » Mon Apr 14, 2014 7:51 am

Hey, it's that guy that never posts anymore.


A few days ago I was testing out a project and made an interesting observation.
I had a piston made from a solid chunk of neoprene which developed sealing issues, after taking it out of the valve it looked as though it was vaporizing a little at a time around the port. This is the first time I've ever seen this happen, though there is a different chamber and valve profile in this gun than my past launchers had.

When was the last time you hybrid guys looked at your sealing faces? any similar issues?
This happened over maybe 20 shots.
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burnout.jpg
The lines are just there for depth reference. The area with the most damage was facing the chamber
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Re: Sealing face burn-out

Unread postAuthor: MrCrowley » Mon Apr 14, 2014 4:22 pm

I guess I've had similar results:
Image
Image

I had to change the sealing face several times because of this, I gradually started using thicker and harder rubber. The sealing face below was the last one used on that piston and was still working before I changed to the aluminium piston. The rubber I used for it came from a boat trailer roller, which is some really hard rubber.

You can even see how the heat has smoothed off the rubber along the body of the sealing face; notably the edge between the front of the sealing face and the body.
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Re: Sealing face burn-out

Unread postAuthor: POLAND_SPUD » Mon Apr 14, 2014 5:28 pm

I think I asked JSR to test whether it is possible to achieve lapping/sealing with delrin

Ohh found something on it though that's not exactly the right thread, but it has some info on it
spud-cannon-related/topic23893.html?hilit=lapping
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Re: Sealing face burn-out

Unread postAuthor: Fnord » Mon Apr 14, 2014 6:32 pm

I've made a different piston which should hopefully be immune to most of the carbonizing problems, though not sure when I'll be able to properly test it. I don't have much shooting space for this gun.
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The sealing face is recessed back into an aluminum housing, maybe this will create enough of a low air velocity vortex area to keep the heat off the rubber.
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