O-Ring life 3

[nanobot29]

I'm trying to figure out the life of an o-ring under the following conditions:

1. Temperature will range from 70 to 300 degF
2. Air pressure in contact with o-ring will not exceed 5 psi
3. radially compressed to less than 1/4 of its strength
4. the only liquid in contact may be some condensation.
5. O-Ring thickness is .25 inches and made of silicone rubber


These conditions dont seem harsh at all. is it safe to assume an infinate life scenario or is it recommended to replace the o-ring periodically? i would really like to get atleast 10 years out of it.

thanks

 

[MikeHalloran]

Is it a static seal?
Or does it rotate?
Or does it reciprocate?



Mike Halloran
Pembroke Pines, FL, USA

 

[nanobot29]

its a static seal. there's no rotaion

 

[MikeHalloran]

>>>radially compressed to less than 1/4 of its strength<<<
I understand "radially compressed", not the rest. Squeeze is normally expressed as a dimension or a percentage.

The low 5 psi pressure is actually a problem; it's not enough to force the o-ring into location.

If the joint is assembled with some good silicone-compatible grease, and the squeeze is within Parker's recommended limits, the seal should last indefinitely.



Mike Halloran
Pembroke Pines, FL, USA

 

[nanobot29]

Thanks Mike, as you can tell i dont have much experience with seals. the o-ring will be compressed between two steel parts and squeezed down to 20-40%. So it'll be in compression even without the presence of the air.

 

[MikeHalloran]

Download Parker's o-ring handbook:

http://www.parker.com/portal/site/P...N=O-RINGS&iden=&stpoint=K&fromSource=&fromId=

or

http://www.google.com/url?sa=t&source=web&cd=1&ved=0CB0QFjAA&url=http://

http://www.parker.com/literature/OR...-vKwU9UlZ0z3mkcNg&sig2=Ya_1sqL_c9vtcXfwRk5zlg

Read it all.



Mike Halloran
Pembroke Pines, FL, USA

 

[israelkk]

There is no need for 20% to 40% squeeze for 5 psi pressure difference. The 20% difference dictates too large dimension tolerances. See PARKER handbook for recommended squeeze and dimension tolerances of the mating parts. As to the life of the seal, the very low pressure of 5psi and assuming more reasonable and much less squeeze, leaves only the life of the silicone rubber which is normally guarantied for 5 to 10 years. You need to check the actual spec of the seal rubber for guarantied life.

 

[MikeHalloran]

I think the real service life will be governed by how long you can keep the steel from rusting.



Mike Halloran
Pembroke Pines, FL, USA

 

[ornerynorsk]

As Mike said, get the Parker book, it's one of the best reference sources for gland dimensions and other related information.

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

 

[IceStationZebra]

Depends on the material type. 300°F is too high for NBR or HNBR long term.

You may also need to consider ozone as it degrades rubber materials. A common non-chemical source is electrical arcs such as welding and motors.

ISZ

 

[nanobot29]

Thanks everyone! the info you guys provided has been very helpfull. It seems like the life of the sillicon rubber is my only concern now. I'd like to get 10-15 years out of this but its doesnt look like sillicon rubber can get me there.

 

[dgallup]

Good quality FKM (fluorocarbon) can easily handle the temp, compression set and life requirements.

 

[nanobot29]

dgallup, thanks! ill look into that material.

 

[btrueblood]

Silicones can do 300F in air easily.

 

[ornerynorsk]

Some grades up to 500F, if memory serves.

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.