What durometer O-rings??

[Ronno6]

What hardness should the o-rings be in pumper airguns??
What material?

[AGEnthused2]

I haven’t rebuild any pumpers yet, so my opinion likely isn’t worth as much as an experienced airgunner/ pumper rebuilder.
If I were going to rebuild any of mine I would use 90 durometer orings, I use that hardness for my break barrel breech seals, they take the abuse well.

[Motorhead]

Buna/N  70 duro IMO

A 90 duro ring has very low elasticity and really does not want to shape shift unable to take up a tubes out of round specs or small surface imperfections.
Being a pump gun RESTS with no pressure bearing against the o-rings ( Which helps create better a seal ) a softer more compliant o-ring is better suited.

High wear as in the pump cup if an o-ring type, is better served with the higher duro ring for wear reasons alone.

JMO tho ....
Scott S

[BillK]

^ Agreed!^  90 duro is great for a non-moving O-ring.(Valve)  70 D is better for moving O-rings (pistons, bolts ect.)
Check out the http://www.theoringstore.com/
 for a good selection & good prices & shipping.

[Tom Tucker]

My experience is that going with 90 on the piston will generate a little more FPE as the pump count goes up, but it will not pump as smoothly.  There will be some stick-slide-stick-slide.  It helps to have a felt oil wiper behind it.

[Tack Driver 10]

Depends:

For max power at high pump pressure the 90s will perform better.

Personally I like the 70A duro cast polyurethane rings.
Seal well, easy to install and remove and very durable.

[eeler1]

Not sure we are all on the same page or not.  Material matters too.  But just on durometer and wear, a static (doesn't move, like sealing the outside of a compression chamber) seal is ok to use softer orings as it is easier to conform to the tube and groove.  Easy to install, not much stress on the oring.  Higher durometer is usually used on dynamic seals (moving like on a piston), because they don't wear out as quickly.  But harder to install as they don't stretch as much and are less forgiving to imperfections in the tube/groove.  So, what durometer oring in a pumper kinda depends on where it goes and how good you are at installing them and how well the gun is manufactured.

Co2 is a different animal, but you didn't ask about those.

[OTmachine]

I like energized Teflon o-rings, where you put a buna-nitrle o-ring under the Teflon ring to give it the required squash.