Do you need O2 o-rings?

[Claus Qvist Krüger]

I was trying to find some 005 Viton o-rings for my Poseidon Sitech inlet valves and I came across the following from a dive gear supplier:

This made me wonder if I should change to normal NBR and then service them once a year instead or I should keep up the fight of trying to find Viton 005 o-rings every two years.
The unit has been serviced at an Poseidon service partner in Denmark, and it looks like the o-ring inside the inlet valve, have been bitten off, full of holes and one is broken.

Poseidon don´t have these inlet valves any more, so to change them is quite costly.

I would like your take on it.

Br.
Claus

 

[lizardland]

I can guess what Poseidon themselves say but just based on my last 20 years of rebreather diving, I've not used viton anywhere that doesn't see pure O2 and even then only where it is high pressure. It's not really a cost thing (they are peanuts if you buy from a supplier like Polymax), it's just the practicality of what I have as spares.

 

[Mobulai]

what kind of inlet valve is that? Is that for DIL, o2?

Technically you can use the NBR even for o2 HP, just be careful to open the tank slowly; but let’s choose safety (and viton)

I think you might be able to find the 005 in Viton at scubagaskets

 

[Maxco]

I only use viton O rings for the first stage and SPG......... as its the only high pressure O2 part.

Everything else is low O2 pressure and I use normal O rings.

 

[Snusmumrik]

FKM o-rings on aliexpress are cheap... So, i use it.
For 005 see "fkm o-ring 6,13x1,78" according to AS568 O-Ring Size Chart | Standard USA O-Ring Sizes

FKM Green Fluorine Rubber O Ring CS 1.78/2.2mm OD 5.34~136.63mm O-Ring Sealing Gasket Washer Oil Resistant Acid&Alkali Resistant - AliExpress 13

Smarter Shopping, Better Living! Aliexpress.com

aliexpress.com

 

[JackZwykle]

FKM is objectively more O2 resistant. Will you get away with NBR? Yes in most cases, with HP O2 being the most at risk.
I use NBR for ambient pressure pure O2 (I can't find that one specific oring in FKM) and FKM for everything else, especially HP O2.

Overall the savings are so small that it's not even worth talking about.

 

[happy-diver]

I used to use nbr for everything and then switched to epdm then mixed them up and use anything for everything

I choose not to use viton for anything as over the years from quality suppliers I have not found a real consistency

O2 grease for 1st stages, silicone for low pressure, loop

Also I use silicone 111 on the threads and things outboard of sealing orings for corrosion reg opening protection
also on 100% o2 regs

Not wet runny silicone but with Molycote111 you will never pull a better negative positive rebreather sealing test

 

[Geo7]

Great info in this thread. I'd like to add an off-topic consideration: My preference for EPDM is based on taking apart regs that have been sitting for 3 years, and the EPDM o-rings look pristine, while the Buna o-rings got squished and stay deformed. The Parker O-ring Handbook has tons of info on the mechanical properties and longevity (including shelf-life).

 

[happy-diver]

Shure is more likely to effect deformation no matter if hose and port plug rings did not come out deformed, torn

there would be something out with the axis of the world


I might pull apart some brand new never opened assembled 60yrs ago regs dude, that I would readily dive today

and check the orings dude

Now that's a test

Yeah good idea, as a distraction from the other things I'm doing when I have a break, thanks