Correct o-ring materials?

[--ped--]

pu90 doesn't absorb co2 so when it is exposed to atmosphere it won't swell like all the other seals do
silicone only absorbs it a little but is very soft and will be damaged easily
epdm if smothered in silicone oil is ok but will swell then go down
viton will swell and i find will them break easily
nbr will swell
the interesting thing with compatibility charts is they don't take into account exposing the o ring to atmosphere after it has been in contact with co2
these pick show before and after being exposed to liquid co2 for 24hrs

[Benelli B76]

The colour in polyurethane seals is irrelevant, it is just a dye, I worked is a urethane factory for 20 years, we used red, blue or green to suit the customer. Plain urethane can be white or toffee colour and either TDI, NDI, or MDI mix. It is the best all round material to use but sometimes too hard to easily seal in certain applications (high Shore hardness) which can be measured with a Durometer if you buy one.

Baz

[flogger]

Go on line and put in. an 0 ring material selection guide 19/05/2016-Martins Rubber.Tells about all types including neoprene.

[jirushi]

Thank you gents.

@Ped, those photos are super interesting.
I have just changed some cap o-rings to urethane lol.

There is still the question why I sometimes find silicon o-rings in for instance old, factory original Sharp CO2 guns, and o-ring kits.
Would be interesting to know. I guess the answer is: it works, but it can damage quickly, so urethane is better.

Will a nitril o-ring, say nbr90, leak CO2 after a while, when it is for instance used as a valve body o-ring? After is has deformed under the influence of atmospheric pressure.

Lastly, another area of interest is valve seals. Here are different materials I have in my spares box.
The red polyurethane one, made by Lawrie, seems to be the best, in the fact that my CO2 guns with Lawrie's valve seals have never developed a leak so far (touch wood). With the orange TR Robb seal, which is quite soft, my QB78 started to leak from the valve after about 1 year.
I also regularly encounter translucent, colourless valve seals.

[draitzer]

I use nitrile O-rings in old Crosmans for the static seals (valve assembly, valve OD, bolt seal) with no problem over years of use. For tube caps and valves, urethane seems better. The highly-regarded Crosman expert Tim MacMurry insists that 90 duro urethane is the only acceptable answer for everything.

Some folks like Delrin for valves but it can be hard to get an initial seal without a gentle hammer-tap; one friend likes UHMW polyethylene for these.

Don R.

[--ped--]

for crosman seals i use nbr70 in most cases on the co2 guns except for cap seals then i offer pu90 as an option but can supply pu90 as well for valve seals
pumpers nbr70 and hnbr but my sheridan solder valves i use a 90 grade seal along with pu90
for stem seals i have 3 choices pu90 ptfe or a sheet material used in fork truck access screens

[jirushi]

Thank you very much Don R. Good to know that Tim uses 90 duro urethane.
I find it much harder to find online (on Dutch o-ring stores) than nitrile.
Will have to look further.

Luckily I have just received lots of o-ring kits from Ped containing excellent urethane seals.

Delrin valves don't work for me. I have two for Crosman 180, from Baker Airguns in the US. They just don't work at all LOL.