50 Bar Piston O-ring shore hardness

[Poorpaulus]

Hi everyone,
I'm working a piston that will see about 50 bar, but will also see approx 1 bar vacuum. It has a stroke of only 25mm, a 18mm dia and a linear speed of only 2mm/sec. This change from pressure to vacuum will occur over a matter of just a few seconds.

I've been asked by the Chief Engineer to investigate if there's any advantage to increasing the shore hardness of the o-ring from 70 to 90. His concern is that the "shock" of the sudden change from pressure to vacuum will have an effect on the o-ring, causing it to fail.

Any thoughts on this would be appreciated.

 

[Tmoose]

Is this a new design or adapted from another mature and successful product?

Regardless, I'd study the Parker Handbook ( available to download online), and then talk to the folks at Parker.

I think you will find that 50 bar/750 psi is nominally well within the range for O-ring sealing.
Details like backer rings or the gap between components to prevent the o-ring from extruding into the gap are important.

Will the poor o-ring being asked to slide while managing 700 psi?
I think I'd want some lubrication if I were that o-ring.

 

[Poorpaulus]

It is a variation of a legacy design which has worked for years. I thought that the question concerning shore hardness was a valid one, but I can't find any information concerning my original question.

 

[hydtools]

You might consider a quad ring seal in 70 durometer. Less likely to spiral fail.

Ted

 

[Tuckabag]

My first thought is that the seal could suffer RGD damage from the rapid pressure swing, however that will be highly dependent on the process media/temperature and o-ring compound.
For the sake of the cost of an o-ring, I'd probably go with the harder duro, or preferably an RGD resistant compound.
Note that there will be an increase in stiction going to a higher duro o-ring, going with hydtools suggestion of a quad ring will help negate this and as he mentioned reduce the likelihood of roll fail.

 

[Poorpaulus]

Thanks for your thoughts, everyone. Most informative.