Scubapro O-ring Sizes

[Timmyjane]

Deleted

 

[passedoutwookie]

I am late to the party here but this thread is a GREAT resource. Many thanks to all who contributed. Can someone tell me what the N and D stand for in the o ring chart and sheet?

 

[buddhasummer]

N likely Nitrile (material)
D likely Duro (hardness)

 

[passedoutwookie]

N likely Nitrile (material)
D likely Duro (hardness)

I assumed that as well, but there is already another column for material and hardness. Check out the mk20 column on this chart. It has “N” for o rings that are marked as viton in the material column.

 

[buddhasummer]

Nitrox

 

[passedoutwookie]

Nitrox

So those are required only when servicing for nitrox use, otherwise they do not need to be replaced? I am planning on going back with all viton anyway (I don't see any reason not to based on price). Any reason not to just replace them all with viton that I am not aware of?

 

[rsingler]

Any reason not to just replace them all with viton that I am not aware of?

Yeah. Viton is just not the best seal. It has lower tensile strength and most important, it permanently deforms much more quickly than either Nitrile or EPDM. That results in a failure to seal much earlier than an oring that retains its "springiness". IMO, this factor essentially eliminates the value of the extended lifetime of the compound, unless you're just storing them on the shelf for a decade.

After a decade of riding on the FKM bandwagon, if you are not using high pressure oxygen I no longer see much advantage in the o-ring. And even then, the benefit is present primarily where adiabatic heating is of concern. If you have red hot particulates impacting your oring, ANY of the compounds can burn.

 

[mr_v]

@rsingler, what's your take on "super resilient" Viton o-rings, as described by McMaster Carr:

"These durable Viton® fluoroelastomer O-rings bounce back to shape after repeated compression better than other types of Viton® fluoroelastomer O-rings. They resist a wide range of chemicals, including boric acid, butyl alcohol, and ethylene glycol. These O-rings have a round profile and are suitable for both static and dynamic sealing applications. They have shelf life, cure date, and traceable lot number printed on the bag."

These are Dura 75 in McMaster's catalog.

 

[rsingler]

@rsingler, what's your take on "super resilient" Viton o-rings, as described by McMaster Carr:

I've used them just once - in @Kupu's experiment in replacement of the D400 seat, where they did fine.
You have an excellent point - since loss of long-term elasticity is one of my pet peeves about Viton. I'll have to look to see what the breadth of sizing is for this compound, but I'll start experimenting with them.
One great place to stay would be with the HP seat seal in the Mk10, Mk25 and Atomic pistons. That 90 duro oring always gets squashed flat, and how quickly it becomes square would be a good test. Same thing with a 2-010 duro 90 piston shaft seal.

Great question!!

 

[mr_v]

@rsingler , thank you for the answer. Those rings are pricey though... I've been getting away with 70 Dura buna rings for the applications you've described, but I also check my regulators at least 2x / month and haven't seen any issues to date. Although, my MK10s are bailout regs, so they're lazy.