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Piston Hybrid Questions, O Ring/Design

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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Piston Hybrid Questions, O Ring/Design

Unread postAuthor: WizardNoodle » Fri Aug 18, 2017 12:48 pm

Hello everyone, I haven't posted in a while because I took a break from designing the cannon, but now I have some questions regarding my hope to make a Piston Hybrid!

I was looking over my spreadsheet list of parts for my future cannon, and I noticed that the O-Rings that would go on the piston were only rated to 275 Fahrenheit, and the pressure rating was not listed. (The Durometer was 90A)
I don't think it's a good idea to use that O Ring in the cannon, which will be subject to temperatures above 2400 Fahrenheit and pressures above 2600 PSI (according to HGDT)
Does anyone have a suggestion for a more favorable O Ring, or where to find them?

Also, looking back, I am not sure if I am happy with how the breech system for the cannon looks.
Does anyone have any better ideas/improvements to the design, or would it work if I selected the correct materials?

Thank you for helping.
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Re: Piston Hybrid Questions, O Ring/Design

Unread postAuthor: mobile chernobyl » Fri Aug 18, 2017 9:03 pm

I'd take a look at a good ol silicone o-ring for starters (Silicone Rubber -> High-Temperature Silicone Rubber O-Rings)
https://www.mcmaster.com/#o-rings/=190271j

Something in the 1/8" width like this guy would be good - you'll obviously need to size based on your application though
https://www.mcmaster.com/#1283n445/=190298x

I've used them on the sealing face of a Hybrid I used a while back (note: this was a static application, piston's are going to be dynamic). Albeit not a piston hybrid - silicon o-rings are, in general, a great solution for this application. Size it right and you should be good!

The temperature you are seeing in HGDT is very short lived - not something you will need to worry about unless you've cracked the code to making a 1 round per minute or greater hybrid setup and plan on sustained firing sessions!
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Re: Piston Hybrid Questions, O Ring/Design

Unread postAuthor: jackssmirkingrevenge » Sat Aug 19, 2017 9:20 am

mobile chernobyl wrote:The temperature you are seeing in HGDT is very short lived


This is the important point, the temperature and pressure spike in a hybrid is very brief.
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