Where is Urethane Required for CO2 Use?

[Toestr]

I have a couple of expansion chambers that came stock with buna seals. Buna would make sense for HPA use since it's a static seal and it won't turn to goo like urethane. But since they're made explicitly with CO2 in mind, it seems odd that buna would be chosen over urethane. Does anybody have some sort of practical 'guideline' for where urethane is required with CO2 vs where buna will do?

[Jonnydread]

I would imagine you would want urethane where the co2 is most likely to be in liquid form. So I would want urethane where the co2 enters the expansion chamber, but towards the outlet buna is probably fine. Just my guess.

[Trbo323]

Kind of depends on the design of the expansion chamber but I would want to put a urethane anywhere that is sealing between expansion chamber and the outside air as those will have a pretty big pressure differential

Most expansion Chambers are divided to have separate Chambers internally those ones can run Buna o-rings because the worst case scenario is one of them cracks and lets a small amount of CO2 between each chamber which really will not affect anything

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[Chappy]

You really only need urethane where expansion is occurring. While this is an x chamber , so it is obviously occurring there, it’s not occurring at or on the seals. I’ve never seen urethane seals in an x chamber, though I’ve only opened a few. In my experience you only need urethane on a valve face in a blowback or pump running liquid.

EDIT Also a thought. I have 30 year old blowbacks that still have factory urethane seals and function. Did Montneel and Tippmann just know where to get better quality seals back in the day? Your turn to goo comment for me thinking on this.

[BrickHaus]

I think its more of the oils used by people over the years. Many oils murder o rings, and back in the day any old oil worked.

[Toestr]

Yeah it seems to happen with cheaper STBBs. Tippmann orings just seem to dry out and solidify.

[Shane-O]

Urethane seals are somewhat "Newer" technology in paintball. Buna was used for millions of CO2 guns without issue. Urethane became more popular once they become less cost, and some designs used them for a reason. A good quality Buna o-ring works fine with CO2.

[Toestr]

Really? The VM68 used urethane, as did older Tippmanns.

[glaman5266]

My understanding is that urethane is more useful in areas with a lot of friction/movement. If the o-rings are just sitting there sealing something I see no problem with using buna. Would I use buna on a Spyder bolt & hammer? Probably not.

[Toestr]

Yeah urethane has the best abrasion resistance of all oring materials. Buna has poor abrasion resistance. If you've gotten a pin prick in a nitrile glove you know that glove will be shredded in a minute. Buna is good because it's cheap and solvent resistant.

[Jordan]

Oh, buna still turns to goo... every Palmer gun I've cracked open had black sludge instead of seals in them.

I've seen urethane tank orings absorb CO2 so I wonder how good urethane actually is for CO2 useage... it's definitely good for high-wear locations on or in a marker - ICD Freestyles come to mind, as do Automags.

[Toestr]

I've never seen that. When I get a gun with a mix of the two the buna orings are almost perfect while the urethane ones have long turned.

[Shane-O]

I would guess its due to age and oil used in the gun. Ive used Buna with Tri-Flow, Hoppes #9 (Tippmann recommended), ATF and air tool oil. Have not had any of those affect the Buna o-rings. Things like Regulator pistons is where Urethane works well in my opinion.

[Myrkul]

I've found that urathane works best in high wear locations. I had a mech ion once that loved to eat buna seals quickly on the bolt assembly, so I replaced all the seals with urathane and it never had an issue again.

[Cunha]

I miss the days when people bought typhoons strokers and blazers because they wanted an automated cocking gun that -just worked-

it was a glorious time.