O-Ring friction

[65CCJ]

Question about o-ring frictionz;

1) Is friction higher at temperature or ambient considering factors like thermal expansion of gland? O-Rig Material is Viton 90 and Virgin Peek back-ups
2) High temp is 350F
3) Gland has 32 RMS and 14%-20% squeeze
4) Fluid is hydrocarbons and then acid

4) I understand that pressure friction is much greater than static friction so with 1,000 to 2,000 psi across o0rings the friction would be much higher than static friction.
5 is there a program that will calculate these values?
6) Are there steps that can be taken to reduce the squeeze ad make it more consistent?






Thanks,

War Man

 

[Hidromar]

Hi!

All replies are inside a book that is being written during these days but there's no right answer for this as son as materials on production of seals are very different.

Nevertheless, please, consider the following:

1) As soon as an O-Ring is a (said) automatic seal (need to be compressed to do its job) changes will, definitively, affect the behaviour of the O-Ring. So, temperature changes will do so as soon as this will increase compression of the O-Ring -> Increase of friction. If this affect the product (energy/power consumtion and/or damage of gland) you need to run tests at optimal working conditions to find your best O-ring material (think you've, even, got low-friction Viton) and best compression/squeeze

2) 350º (depending on Viton grade) could be a critical temperature. Usual Viton Works nice up to 390º, but mechanical properties at these temperatures might not be the optimal (in case you've got high pressures)

3) squeeze between 14-20% depends on working conditions mainly. But this range of squeeze is too huge if you are worried about friction

4.1) Ok if used with proper concentration (please, try with an O-Ring directly exposing on these fluids for about 72 hrs mínimum

4.2) Replied...as soon as static means no movement so no friction.

5) a "program" is not practical as all as soon as materials, working conditions...are different from one application to another. If you find it this will bring you to a statical approach...but I guess this is not what you need.

6) squeeze on an O-ring is necessary to do its job. Think more squeeze requet formore power, and very low squeeze will tend to resist less pressure on the system


...the point that surprised me is why are you using PEEK back-up rings

I hope this helps you

http://www.hidromar.es

 

[BrianE22]

I assume this is a dynamic seal. If so, then you would also need to consider the relative expansion of the parts (piston/cylinder?).

 

[johnchrc]

Why are you surprised with Peek Backups for Viton T-Seals?
Temp range 275 and 350 F
3 seals see 2,000 psi DP
1 will potentially see 10,000 psi and it could e unloaded under pressure so I have a special PEEK backup/diffuser ring that will not allow pressure to unload inti t-seal is protected in reduced squeeze gland.
The squeeze is based on Vacuum Seal Gland form parker and a mil spec and is 9%-14% but my Elastomer vendor will have final say on gland dimensions while sealing.

keep in mind there is 15% HCL solution so HNBR type materials are out and next step up would be Chemraz or Kalraz.

I am able to reduce squeeze during closing og vent valve by reducing squeeze on toe t-seals that don't need to seal until the pass equalizing ports on vent valve. Still i used 400 psi activation pressure forvent valve to obtain friction of 60#. So i'm using a 363# spring load at L1 with 1.1 sq inch piston area.

I am looking at ave springs in series to reduce rate in 1/2 to keep P2 and L2 under 415# and rectangular compression spring with same load at L1 and 435# at L2 with MP35N material and stress under 56%of tensile so life cycle should be high. The crest to crest wave springs are surprisingly more difficult to work in.

My stroke is fixed at 1.284" somy rate should be 50#/in or 100#/in with spring in series or less.

I am wondering if I need to but xylan bushing between springs so they will not rotate relative to trapped gland with rectangular ring and with crest to crest wave springs.

Contact with fresh Acid will be limited to under 24 hours in most cases. I JUST DON'T HAVE ANY CLUE HOW MUCH THE FRICTION IS REDUCED FOR A T-SEAL WITH SAME SQUEEZE AS O-RING OF AMD=ME MATERIAL AND SURFACE FINISHES. DOES ANYONE KNOW?

Also, my static friction will be greatly reduced so the 3X the friction to get moving is overkill for 4 t-seals. It may be appropriate for teo t-seals. Also, the vendor is making these t seals fit in cross section that is less than standard for o-ring groove. Don't know why yet..


- CJ

 

[Compositepro]

Dynamic O-ring seals must be lubricated. Often the fluid being sealed does this but if the lubricant properties are poor you may need a separate lubricant that is compatible with your elastomer and fluids.