lifetime of an o-ring 4

[offonoff]

I thought i posted this already but an hour later it isn't in the forums. Must have pushed the wrong button or something.

We've got a 6" port that needs sealing on a 1500 psi, under 100 C vessel full of super critical carbon dioxide and dissolved oils, terpenes, ethanol and others. A grooved flange and an o-ring is the likely solution.

the port will be opened daily and under these conditions i am curious how long before the o-ring will need replacing. The chemicals involved limit our material choices. Teflon and Viton (a fluoroelastomer) seem to be the options. Any other materials to consider?

both are similarly priced. any ideas about expected life times under daily seal breaking and making? Pressure builds over the course of a minute or so, and discharges more slowly (~10 minutes).

 

[Woko]

The problem with CO2 is not its "agrresive nature" its the fact that as you change its temperature and pressure it has the ability to "change" its solubility effect, so that by selecting the right critera (pressure and temperature) you can selectively dissolve most organic compounds (or swell elastomers)with CO2.

With any elastomer you have to consider that generally gasses double their volume with a halfing of pressure, if the temperature cannot change. Its this that "blisters or splits" the o-ring materials. So the slower you can reduce the pressure in the final stages of depressurisation <150 psi typically the greater the chance for the meida to permeate out of the elastomer before it can do damage.

On the subject of life you may want to talk about compression set as, even if you get a decopression regime which does not damage the o-ring this will provide a better criteria to "life" your seal.

I would take btrueblood's advice and talk to Greene, Tweed.

 

[diskullman]

No one has mentioned Quad rings in place of o-rings. They are a slight upgrade from orings, and still quite affordable and available in the same standard o-ring sizes.

http://www.marcorubber.com/quad_rings.htm

Russell Giuliano

 

[offonoff]

I've sent an inquiry to green, tweed but have not heard back.

Dsheets05, I dont understand your seal design. is the bottom portion containing the o-ring actually two pieces, or do you squeeze the oring to get it in there? how do you get it back out to replace it or check for wear? also, where does one get a ptfe cap?

We are considering a radial seal now over a face sealing flange. Does your option apply to either type?