O-rings for CO2

[ScarletFire186304]

what material are you guys recommending/using for #113 replacement o-rings for fill caps and valves on CO2 (XS60C, QB78)?

i've tried a urethane 90 on the cap a couple days ago and it turned all white and odd looking. 

i've got the valve apart on a QB today and the o-ring there is shot (had to pound it out, could not get it to turn/loosen) 

thanks, bob

[SeanAT]

Where did you get the U90 from? I use cast U90 whenever possible for CO2 have never had a problem.

Make sure you're not buyin millable gum urethane or low quality cast.

[SaltwaterSlick]

In our gas booster systems we use HNBR or Buna-N o-rings. Worst is Viton... It swells and comes un-manufactured in CO2 (unless it is Viton-GF).

[fivestar45]

1st choice for co2 is mil spec nitrile. you can get them from McMaster-Carr ..

[ScarletFire186304]

i was using standard (not cast) U90 from the O-ring Store.

they turned from opaque to white. is that normal?

should i be using the cast U90 or Buna-N 70 or 90?

thanks,  bob

[Bullit]

A bag of Buna-N (nitrile), in a 70 durometer is cheap.  The U90 Urethanes (90 durometer), may not be sealing well, and not working out for you since they are so much harder.  A U70 may work better, and it's still tougher than Buna-N.  These Orings are a consumable, so just have a spare on hand.  McMaster Carr is a good vendor.  You may also be able to find them from your local Pneumatic/Hydraulics Industrial Supplier.   They can size them for you if you're not sure.

[SeanAT]

i was using standard (not cast) U90 from the O-ring Store.

Ah, that's the problem. Their cast urethane is very high quality and it's what I use.

I don't care for Buna-N or HNBR in a situation like a cap o-ring; urethane will last much longer.

[ScarletFire186304]

with all due respect to my elders, please bear with me.

in all my valves it looks like they are urethane (opaque) and kind of flexible (thinking 70 hardness)

and i'm just asking here,

with reference to the valve o-ring, would it be an upgrade to mil spec nitrile (buna-N) 70?

i,ve just never seen a black o-ring on any of my CO2 factory valves (granted i've only seen 4)

just trying to figure it out before i go and order the wrong thing again, Duhh!!!!!

respectfully submitted, 

bob

[ped]

i use edpm for co2 guns
ped

[Bullit]

Bob,  The urethane oring is tougher than the Buna-N oring.  Tear and impact damage resistance. 
I wouldn't worry about color changes, if it is conforming to it's seat, and sealing up well.