What O-Rings for Artemis P15/ Diana Skyhawk .22?

I hear it should be Buna-N 70 or 90.
OK, got that.

Now, what about the o-ring sizes for the Skyhawk/ P15....?    

They are 70’s and I can help but I have to go to work now. I will check back in the morning. See if you still need info.

The sizes in on the Artemis parts list are different than the sizes commonly used when buying o-rings in the US.
Artemis gives us the OUT-side diameter, and then the cross-section.
Sellers in the US give us the cross-section first, then the IN-side diameter.

In the table below you'll find the o-ring sizes and part numbers taken from the P15 parts diagram, and the numbers converted to US sizes for easier shopping. (No, I’m not perfect, so if you find a mistake, or have an addition, plz. correct me. Thanks!  )


                       USA Sizes                      vs.                   Artemis Sizes
     Cross Section X Inside Diameter        vs.     Outside Diameter X  Cross Section
Part No.      CS x ID (USA)                   vs.               CS X OD (Artemis)                                      18         “suppressor o-ring”  |  mentioned in the OEM parts diagram, both without size data
n/a:          1.5mm x 4mm         [two; for fill probe]       7mm x 1.5mm
33            1.5mm x 5mm                                            8mm x 1.5mm
38            1.5mm x 5mm                                            8mm x 1.5mm
30            1.5mm x 5.5mm                                         8.5mm x 1.5mm
48            1.5mm x 6mm                                            9mm x 1.5mm
23            1.5mm x 9mm                                            12mm x 1.5mm
                      Careful: The Skyhawk seems to have part no. 22 and no. 23 than in the P15 parts diagram!
53            2.0mm x 14mm                                          18mm x 2.0mm
34            2.0mm x 22.2mm                                       27mm x 2.4mm
                      I did not find this size at the O-Ring Store, but I found: 2.5mm x 22.0mm


Attachment:  P15 Parts Diagram 


Matthias

Is the fill port O-ring for the P12 like the one for the PP700?  Meaning an O-ring slipped over a screw that has a flat cut on the shank?  If so, just find one that is a snug fit to the screw shank.  The sizing is not critical otherwise.  The way it works is, when the fill hose pressure exceeds that of the reservoir, the O-ring expands and gets out of the way to allow air in.  When you bleed the line, the sudden pressure differential causes the O-ring to constrict and seal off against both the tapered underside of the screw head and the flat surface where the hole is drilled.  If the O-ring’s ID is a little too large, it won’t be able to do that properly.

Next time, give it a close inspection with magnification and see if there’s evidence of how or why it failed.  Some examples:
 
a.       Irregular glossy appearance – May have overheated.  O-rings when clean and dry have a matte finish.  If you see glossy, it probably melted.  Can happen when filling from a tank because the rapid pressure rise is accompanied by a rapid increase in temperature.  Won’t happen if filling from a hand pump.  Solution:  fill slower and/or use an O-ring material that tolerates high heat.
b.       Irregular shape – May have extruded into the gap.  Extrusion failures will usually show stretching in a specific location somewhere around its perimeter, or at least an irregular “this isn’t a circle anymore” appearance.  Solution: use a higher durometer, maybe even add a backer ring if feasible.
c.       Cracked or brittle – stretch it and see if it has become brittle or has tiny cracks in the surface.  Could be a sign it is getting exposed to a incompatible chemical (typ. lubricant).  In other cases, might just chalk it up to being a poor quality O-ring or one that was already quite old and past its shelf life.  Solution: remove the chemical or use a different O-ring material that is compatible with it.  (If you’re using only silicone grease or oil, you’re good.  However note some people have attributed gases emitted by compressors as being a contributing factor to seals deteriorating more rapidly).
 
Those are the 3 most relevant causes I can think of for a fill port O-ring.  Abrasion is the only other common cause that applies to airguns but that wouldn’t be relevant in this case.

This is definitely a weak design.  The o-ring blows out if you fill past 3650 psi, and you do not need to be very far past that pressure.

I have been avoiding replacing nine but I did it this morning.

A far better option would be a gauge and fill nipple like my P-rod, Bulldog, AirForce Texan, Seneca Carbine all have.

Regards,

Roachcreek

Photo’s of theBagall & Kirkwood fill port o-ring 10 pack and longer custom Lee545 shroud

It definitely seems like a somewhat cheesy design, but I've seen this same design used in other bullpups, including the Veteran.

Extrusion failure then.

Try a 90 durometer.  If you can find a fat O-ring (a -1xx size) that has a snug ID for the screw shank, that would be helpful too. 

If that fails, reduce the size of the gap...in this case, the gap is the portion of the screw shank that was shaved off.  It would be fairly trivial to take a flat head machine screw and file a smaller flat onto it.

When I was researching the P-15, that information  about overfilling came up.

I have had it happen twice, both times from over filling  past 3650 to just under 3700 psi on my JoeB gauge.

It has never failed if I fill to 3550-3600 psi.

I have been shooting 25.39’s at 690 FPS this morning inside, which is with the preload  screw flush, all the way in is in the low 890’s, which means I have over 200 FPS adjustment with preload alone. Also at flush it pushes  the CHP’S  @ 915 FPS.  Both the 25.39’s and 14.3’s are in one hole groups in the teens on my abbreviated range but when I need a scatter gun I shoot the 18’s and 33’s they group terrible.

Regards,

Roachcreek

FWIW, the original fill port O-ring (check valve O-ring is probably a better term now that I think about it) on my PP700 failed very early on.  The replacement has been going strong through many, many refills.   It’s only a 220 bar fill however and I usually stop short of that because the OEM reg doesn’t like it.  There were no sharp edges that I could attribute to its early demise.  Good idea to check for it though.

Is the fill port O-ring for the P12 like the one for the PP700?  Meaning an O-ring slipped over a screw that has a flat cut on the shank?  If so, just find one that is a snug fit to the screw shank.  The sizing is not critical otherwise.  The way it works is, when the fill hose pressure exceeds that of the reservoir, the O-ring expands and gets out of the way to allow air in.  When you bleed the line, the sudden pressure differential causes the O-ring to constrict and seal off against both the tapered underside of the screw head and the flat surface where the hole is drilled.  If the O-ring’s ID is a little too large, it won’t be able to do that properly.

Yes it is just like you described.  The screw in the P12 has a flat spot on two sides.  The edges are sharp so I could see how that might shorten the life of the O-ring a bit.