Graphite piston for a radial air engine

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lensman57

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Hi everybody,

I am about to start the build of a 3 cylinder radial air engine based on Elmer's no11 design. I will machine the cylinders out of 1.25" brass rod as the square design of Elmer's does not appeal to me. I was thinking of using carbon graphite filled ptfe rod for piston mainly to reduce friction. I have a little stock of this material and was wondering if this was more suitable than either 2014 or 6082 Aluminium for this purpose. I was also wondering if the pistons required rings or a plain one as per Elmer's design would suffice.

Many thanks for your input,

Regards,

A.G
 

LindsayWood

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Hi,

Recently I started building my own version of the Elmer's 11, I kept some of the crankcase and pistons but the rest of the engine is my design, using a rotary valve of my own design, inspired by one of David Kerzel's engines.

Be aware that swapping out the square cylinders with round ones can make air delivery tricky. Best option is external tubes- there's a thread around somewhere covering this (and the multiple attempts to get there).

That material sounds suitable. I've used UHMW HDPE pistons in mine, and have used acetal pistons in the past without issue. They perform well with minimal friction and excellent sealing without rings, but be aware they don't handle temperature change well! Steam is absolutely a no go. Teflon tends to cold flow/extrude easily, be aware of this (although it should work fine). HDPE and acetal tend to be tougher and machine better than teflon, although they'll have slightly more friction. I found adding some graphite powder improved performance without the drag of using oil
 

Anatol

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Hi,

Recently I started building my own version of the Elmer's 11, I kept some of the crankcase and pistons but the rest of the engine is my design, using a rotary valve of my own design, inspired by one of David Kerzel's engines.

Be aware that swapping out the square cylinders with round ones can make air delivery tricky. Best option is external tubes- there's a thread around somewhere covering this (and the multiple attempts to get there).

That material sounds suitable. I've used UHMW HDPE pistons in mine, and have used acetal pistons in the past without issue. They perform well with minimal friction and excellent sealing without rings, but be aware they don't handle temperature change well! Steam is absolutely a no go. Teflon tends to cold flow/extrude easily, be aware of this (although it should work fine). HDPE and acetal tend to be tougher and machine better than teflon, although they'll have slightly more friction. I found adding some graphite powder improved performance without the drag of using oil
Lindsay
"a rotary valve of my own design"
did you post this design anywhere? how did it work?

"they don't handle temperature change well!"
so, in your opinion, is there any plastic/composite that lend itself to steam use?
thanks
 

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