I give up. O Ring material for Steyr CO2 LP5

[RodJ]

Lots of helpful information and advice received from my post about opening up a Steyr LP5, so thanks to all.

Does anyone know off hand what the proper o-ring material is??? Or what materials will work?

HNBR seemed correct, so ordered from Amazon an o-rings assortment of HNBR rings (and they were green, so looked correct) and slipped one on the male nipple where the CO2 supply tank / cylinder screws on the pistol. Long and short, they are swelling up and getting torn apart after removing and then reinstalling the tank. This is true regardless of which tank I use (I have several). I even tried a slightly smaller ring. Arg!

I’m getting lots of help and some purchases from Pilkguns but Jennifer is probably tired of taking my calls and I’d like to just go pick some up locally.

Thanks!

[Gwhite]

I posted earlier that what you need is polyurethane. O-ring color coding isn't standardized, so green means nothing about the material.

https://newdealseals.com/en/o-rings/pol ... -pu-seals/

The trick is finding metric polyurethane O-rings. They are out there, but aren't as readily available as many other materials. Your best bet may still be getting a real Steyr part.

[RodJ]

Thank you GWhite — and I apologize for missing / forgetting that. I measured the old ring at ID/OD at (IIRC) 7/32” and 9/32”. That’d be close to 5.5mm and 7mm. Does that sound close?

Any suggestion on hardness (durometer)?

Another TT forum save!

This is why I sent a PayPal donation to Pilkguns to help pay for the forum.

[Gwhite]

I converted a couple CO2 Steyrs to PCP several years ago. I thought the CO2 version used the same sized cylinder spigot O-ring as the PCP, in which case it's 1.5 mm x 4 mm (ID). However, my rememberer isn't what it used to be...

Steyr may use polyurethane on their PCP's anyway. In addition to not absorbing CO2 as fast, it's also very tough & abrasion resistant. Here's an outfit that sells replacement O-rings for LP2, LP10 & LP50, and they are specifically polyurethane:

https://spares.bagnallandkirkwood.co.uk ... -ref-44-5/

As for durometer, a D90 O-ring will also absorb less CO2 than a softer one.

[RodJ]

Thank you! Wish I could return the assistance.

[SPPcoach]

Thank you! Wish I could return the assistance.

GWhite has helped me and my athletes many times. Thanks.

[spektr]

The simple answer is this...... If you have exposure at pressure to CO2, use Polyurethane.
If you have only intermittent exposure to Co2, such as the bolt to chamber O ring. Use Buna.
Buna is softer and seals the chambers better than polyurethane. It isnt rocket science.
Polyuethane will probably be green, in the past that was an identification requirement, but it is not a current standard to do so.

[RodJ]

Thanks spektr.

I guess it’s not rocket science… unless you’re Morton Thiokol and it’s the space shuttle. Gulp! I got wrapped up in chemical compatibility and seemed HNBR was the correct route.

Onward through the fog!

Stay safe.
Rod

[David M]

I have used Automotive Airconditioning O rings with CO2 (HNBR Compound)

https://wolfchestershop.com.au/assorted ... g-o-rings/

[Gwhite]

Thanks spektr.

I guess it’s not rocket science… unless you’re Morton Thiokol and it’s the space shuttle. Gulp! I got wrapped up in chemical compatibility and seemed HNBR was the correct route.

Onward through the fog!

Stay safe.
Rod

The issue isn't chemical compatibility (does the environment rot out my O-rings?), it's resistance to "explosive decompression". From:

https://vansealcorp.com/material-specifications/

"Polyester Urethane (Urethane)
Polyurethane is the toughest, most extrusion-resistant and most abrasion-resistant of all elastomeric sealing materials. Polyurethane is also very resistant to explosive decompression and has excellent properties over a wide temperature range. Polyurethane O-rings are used in a wide variety of products, including quick-disconnect hydraulic fittings, hydraulic cylinders and valves, pneumatic tools, CO2 firearms, or for any application requiring extreme abrasion or extrusion resistance. Used on skate board wheels, molded gears, o-rings, etc."

[RodJ]

GWhite
Oddly one of the things that happened to the HNBR rings I bought is that they swelled up, guessing from absorbing Co2. Really weird. Anyway, urethane rings are on the way. I do really thank you for the multiple assists.

Everyone else who replied and offered advice, too.

Rod

[Gwhite]

The swelling is from the absorbed CO2 expanding. Basically, your O-ring got the "bends" like divers do when they come up too fast.

Tau-7 CO2 pistols use Nitrile O-rings & get away with it, but there's a trick. The O-ring that seals the CO2 cartridge in the pistol is mounted to the cap, and not the pistol. When you have to change cylinders, they give you TWO caps. You take off the first one, the O-ring swells, but you install the next cartridge with the OTHER cap. That gives the CO2 time to leak out of the O-ring in the first cap. If you try to immediately re-use the cap with the swollen O-ring, it will usually get chewed up in the process.

Over time, the O-rings get shredded internally and have to be replaced, but it can take a while before they get so bad that they leak.

If Steyr put their O-rings on the cylinders, you might get away with the same trick, and many older CO2 pistols did this. I had a Walther CP-1 that was designed that way, but they still used polyurethane O-rings.

I also seem to recall that you can slow down the CO2 absorption a bit with grease, which you should use (sparingly) anyway.

[mister G]

I used a Canadian source when looking for replacement o-rings for my Domino /FAS 604.
Plenty of air gun parts sites on the 'net.
Do NOT use grease or any petroleum lubes because they will eat up your rings. A silicone lube is recommended.

[mister G]

Google "air gun parts canada" and you'll find several sources.