O-ring material questions

[lmorin]

How important are the material and hardness of replacement o-rings for the standard yoke valve? I can readily find o-rings made of Viton and EPDM in 70 or 75 hardness, or Nitrile o-rings with a hardness of 90, which I gather is preferred. However, I also gather that Viton or EPDM are preferred for nitrox use, but I have been unable to find a source for either with a 90 hardness. I know there is lots of advice lurking out in the ether. I'd appreciate reading it. Thanks.

 

[captain]

75 hardness EPDM

 

[Dan Gibson]

www.marcorubber.com

I have been unable to find a source for either with a 90 hardness.

 

[bradshsi]

The hardness of an o ring will affect primarily the extrusion resistance.

To minimize the possibility of extrusion, harder is better.

However, nothing in life is free. As you increase the hardness of the o ring rubber it becomes less able to seat against imperfect or rough surfaces. Very hard o rings require extremely good surface finishes to effectively seal.

75 to 80 IHRD is a good choice for most applications, including yokes.

EPDM is the best choice for oxygen service. I would not recommend Viton due to it's more limited temperature range and poorer physical properties.

Hope this helps

 

[rockjock3]

Well I don't know about what limited temp range viton would bring with it but here I was I found at an online O-ring store.

Viton -20 to +400 degrees F, $6.50 a bag of 50
Viton Extreme -5 to +400 degrees F $11.00 bag of 50
EPDM 70 -65 to +250 degrees F, $12.00 a bag of 50.

 

[bradshsi]

My concern with Viton is it's low temperature limit.

People tend to refer to Viton as a generic term when there are many different grades produced using different material combinations and curing techniques.

Some of these grades have relatively high glass transition temperatures which can lead to hardening and leakage when they are used at temperatures "approaching" the low temperature limit claimed by the manufacturer. These manufacturers limits are often rather optimistic in my experience.

In the case of 1st stage regulators which can get quite cold during operation, IMO it's better to err on the side of caution and use EPDM.

 

[Dan Gibson]

Also, Viton are the toxic ones when they burn.

My concern with Viton is it's low temperature limit.

People tend to refer to Viton as a generic term when there are many different grades produced using different material combinations and curing techniques.

Some of these grades have relatively high glass transition temperatures which can lead to hardening and leakage when they are used at temperatures "approaching" the low temperature limit claimed by the manufacturer. These manufacturers limits are often rather optimistic in my experience.

In the case of 1st stage regulators which can get quite cold during operation, IMO it's better to err on the side of caution and use EPDM.

 

[pt40fathoms]

EPDM is the preferred O-Ring, for the reasons stated above.

No sense in restating what has already been clearly stated...