Atomic o-ring sizes

[guruboy]

Putting together a list of the Atomic o-rings for the service kits. Sizes seem to be embedded in the atomic part numbers.

Am hoping to get confirmation on the durometer values.

Starting with the 1st stage-
(6) LP port plug -010 70D
(2) HP seal -010 90D
(1) DIN/Yoke retainer -010 90D
(2) HP port plug -011 90D
(1) HP seat -013 90D
(1) Seat retainer -015 80D
(1) DIN nipple -111 90D
(1) Swivel -016 70D
(1) Piston -019 80D
(1) Swivel -021 70D
(1) Body -024 70D

 

[guruboy]

The seat retainer and piston are the ones I'm not sure about. They don't feel like 90D.

 

[halocline]

I really have no idea what Atomic uses for o-ring duro, so please take my reply with a grain of salt. I can tell you what SP uses in their balanced piston 1st stages (very similar design) and I can tell you what I think might be appropriate based on my experience working on my SP regs. I don't know if it will be helpful.

First, I think SP is using 85 duro EPDM o-rings for the HP piston, HP seat, and maybe DIN/yoke retainer o-rings, and 70 duro for everything else.

Second, I suspect that the only one that really has to be a higher duro is the HP piston o-ring. I wouldn't worry about the port plugs. I do use higher duro o-rings for the HP seat and DIN/yoke retainer, but unless there's a real chance of extrusion I wouldn't consider it critical. On the older SP balance piston 1sts without the bushings (MK5/10) a 90 duro polyurethane o-ring performs very well. But the shelf life is limited, and with the bushings that the MK25 (and certainly atomic) has, the tolerances are tighter and supposedly the HP piston o-ring doesn't have the same problem with extrusion and increased friction.

So if the HP piston o-ring in your kit doesn't feel stiff enough to be a 90 duro, try an 85 and see if that feels more like it. I can feel a difference, I bet you would be able to as well.