Pneumatic piston ring design

[_Fluffy_]

Hi everybody
I was asked to select/design appropriate sealing for a pneumatic jack. I looked up for handbooks and design guides, I have found good sources for designing plastic sealing including tolerances and fittings and groove sizing... but for metal rings I have found nothing comprehensive telling me which material is appropriate for each usage, how many rings should I use and other things.
Where can I get the info?
Specifically:
A (horizontal) pneumatic jack is to absorb energy, it's moving with approximate speed of 40m/s compressing air from 40bar to 70bar moving about 1 meter. The cylinder should be precharged with a (low flow) compressor to 40 bar of pressure which means the ring(s) should work statically as well as dynamically. What should I use (I have found carbon-graphite augmented materials capable of tolerating high pressure and speed but I know nothing about them (as well as appropriate shape for rings, number of them, distance between theme, tolerances ...), just saying).

 

[Hidromar]

Hi, Fluffy!

I guess you have considered using floating seals, as soon as speed is high. In this case, you can almost use both plastic and metal seals since pressure is not such higher.

For plastic, and depending the counterface material, I would use PTFE+Ekonol, or PTFE+PI (being the first more common) Nevertheless, and for testing purposes you can find, also, PTFE+Carbon.

I would not use a compressive (automatic) seal here as far as speed is high and sudden movement at such speed will tend to produce a failure on the (contacting/primary side) seal

For installation, as as soon as this will work as a pneumatic Jack, my suggest is to install a mínimum of 3 seals at a distance of 5mm between them. As always, please, bear in mind that this is empirical, and tests should be run before production to ensure this will work for your needs

Have a nice day!

http://www.hidromar.es