o-rings and duro

[Downunder_WPB]

I ordered a bunch of O-rings from a website. I purchased 90 duro and 70 duro versions of the same type.

I was under the impression that the higher the number the better, however, I can't remember where, but someone said in a forum not to use 90 duro all the time (something to do with pressure and elasticity). I am replacing all my o-rings so I was wondering if a) what I read was the correct and b) if the following image is accurate in terms of what O-ring duro I should use per application

To me it seems as though all high pressure applications are 90 duro, and low pressure are 70. is this an accurate assessment?

 

[Nick Ruberg]

One isn’t “better”. 90 shore is harder and resists extrusion better at higher pressures. 70 shore is softer and offers a slightly better seal at lower pressures because of its softness. Think of how soft a camera o-ring is for absolute sealing (can’t have any leakage whatsoever) at relatively low pressures.

Generally the low pressure stuff will use the 70 shore whilst higher pressures and heavier duty usage will use the 90 shore.

 

[Nick Ruberg]

Is there a reason why you are replacing all the o-rings? Is this on older gear?

Be aware that some of the original o-rings may be polyurethane or EPDM maybe. What make of gear?

 

[Downunder_WPB]

Is there a reason why you are replacing all the o-rings? Is this on older gear?

Be aware that some of the original o-rings may be polyurethane or EPDM maybe. What make of gear?

By all I mean the ones on the spg swivel, hoses, and ports. It is Oceanic circa whenever the px2 was made. Some gear I got from a friend that needed a bit of love.

 

[Pao]

Not better, but different. Use what the manufacturer specifies, especially for critical dynamic O-rings. I converted a 1st stage for O2 service using Viton 90 O-rings (original spec was fro EPDM 80). Gas delivery was notably not as "smooth" (subjectively) even when IP and cracking pressure were the same.

 

[Scubagaskets]

One isn’t “better”. 90 shore is harder and resists extrusion better at higher pressures. 70 shore is softer and offers a slightly better seal at lower pressures because of its softness. Think of how soft a camera o-ring is for absolute sealing (can’t have any leakage whatsoever) at relatively low pressures.

Generally the low pressure stuff will use the 70 shore whilst higher pressures and heavier duty usage will use the 90 shore.

In general, the Sh70 is more suitable for low pressure (under 100 bar) while the sh90 can handle higher pressure and friction than the sh70. Nevertheless, many gear manufacturers don't follow that rule so at Scubagaskets you can find all Viton EPDM NBR and Polyurethane o-rings in 2 or even 3 different hardness in order to meet manufacturers specifications.