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PostPosted: Tue May 09, 2017 10:32 am 
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Joined: Tue Feb 18, 2014 3:10 pm
Posts: 184
I just resealed five cylinders for my early Steyr CO2 pistol (CO2 Match, LP-1p, LP-1) with the following SAE (US Spec) polyurethane o-rings...

#020 - Tube to valve assembly seal
#005 - Internal valve stem seal

Polyurethane (cream or green color, doesn't matter) is recommended for longevity as they won't absorb CO2 gas, particularly the 005 o-ring that soaks in the liquid CO2. You can use a BUNA-90, 020 o-ring, or the factory 2mm x 20mm for the larger seal. But you will need to replace it more often.

Mine cylinders are now good for another 25 years. Have fun with yours...


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PostPosted: Tue May 09, 2017 10:52 am 
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Joined: Sat Sep 04, 2004 6:04 pm
Posts: 1416
Location: Massachusetts
Good to know. Thanks!

Did you get the polyurethane O-rings from McMaster Carr? I see that they carry those sizes.

Also, did you get the durometer 90 rings, or just 70? 70 may be OK for CO2, but PCP would probably be better off with 90.


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PostPosted: Tue May 09, 2017 11:07 am 
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Joined: Tue Feb 18, 2014 3:10 pm
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Gwhite wrote:
Good to know. Thanks!

Did you get the polyurethane O-rings from McMaster Carr? I see that they carry those sizes.

Also, did you get the durometer 90 rings, or just 70? 70 may be OK for CO2, but PCP would probably be better off with 90.


McMaster Carr carries these for quantity purchase, but I bought just the number I needed locally here in Dallas. These are quite expensive o-rings.

Duro 70 will probably be best for CO2, especially for the 020, as it will seat more easily (staticlly-mounted) against the tube. But I bought the 90's and they work fine.


Last edited by DFWdude on Tue May 09, 2017 12:04 pm, edited 1 time in total.

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PostPosted: Tue May 09, 2017 11:13 am 
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Joined: Tue Feb 18, 2014 3:10 pm
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BTW, the 005 o-rings will fit over the valve stem loosely. Don't be upset to see this, because this is what you want. Remove the old seal and you will see it falls off, too. The Steyr design is simple, and efficient, with the valve stem simply capturing the o-ring between the metal sealing surfaces. The loose o-ring permits the CO2 to exit once the seal is cracked. And you can just imagine the o-ring floating back and forth on the stem within the liquid CO2 once on the gun.

You can try a smaller ID o-ring, but it will seal against the stem shaft, and prove impossible to crack the seal open, either with the bleeder tool, or when mounted on the pistol. Trust me on this as I tried it. All I got was a full cylinder of CO2 and no way to drain it. And I'm not about to describe how I did it, either.


Last edited by DFWdude on Tue May 09, 2017 4:19 pm, edited 2 times in total.

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PostPosted: Tue May 09, 2017 11:18 am 
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Joined: Thu May 22, 2008 2:21 pm
Posts: 35
Location: Virginia
If they are static o-rings, 70 durometer is likely good enough. The o-ring store sells 70 and 90 durometer polyurethane o-rings in cast or polyether urethane (EU): http://www.theoringstore.com/index.php? ... &cPath=367

I've found that if an order is already in place for McMaster-Carr, larger quantities can be added for similar o-rings at about the same price. The o-ring store used to ship for less, but I think they realized that business model was not sustainable.


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PostPosted: Wed May 24, 2017 1:22 pm 
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Joined: Tue Feb 18, 2014 3:10 pm
Posts: 184
Update...

I have found the urethane 020 for the static cylinder to plug interface will work on MOST Steyr cylinders, but not ALL, resulting in a slow leak. On my two matched, original cylinders, the urethane 020 worked fine on one cylinder, but not the other one. Go figure. So I had to use a metric 2mm x 20mm BN90 seal on that. A 2mm x 21mm BN90 works even better. The 2mm metric size is slightly fatter in crossection than the 020. It won't last as long as the urethane, but it seals better.

I have also found luck with 2.4mm x 18.6mm, or 2.4 x 19.3mm o-rings. Stretching these over the 21.5mm seat on the brass fitting thin them out a bit.

Altogether I resealed 5 cylinders ( 2 Long and 2 short steel, and one short aluminum) and found the slow leak only on the one cylinder noted above.

Bottom line, you can use either metric or SAE, but I recommend the metric (in urethane) if you can get it, BN90 if not, for a sure seal. The urethane 020 you take your chances.

In all cases, for the smaller valve stem seal, I strongly recommend you get the 005 in Urethane ONLY, because than seal is not static, and is not contained. (Any buna rubber seal will absorb CO2 and balloon within its large space)


Last edited by DFWdude on Sun Jun 18, 2017 7:48 am, edited 1 time in total.

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PostPosted: Sun Jun 18, 2017 7:42 am 
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Joined: Tue Feb 18, 2014 3:10 pm
Posts: 184
Oh, and about that CO2 burst disk...

Among my 5 CO2 cylinders, two of them continue to leak down a few grams from full, then stop.

All this time, I thought the silver burst disc with the funny half-round notch was a static (no moving parts), one-time burst disc, like you see on 20lb CO2 (or air) supply cylinders. Turns out this is a more complex, conventional valve with a seal and spring. The visible silver "disc" with the notch is actually a sliding lock that retains a hefty spring underneath. Encapsulating the spring is a machined brass fitting with a teeny-tiny, green, polyurethane disc on the bottom that seals against an elegantly machined, brass nipple.

Not only does the polyurethane disc wear over time, but I suspect the spring has also taken a set... after 25+ years, that might be expected.

Since this tiny polyurethane disc (3mm dia x .5mm thick) is a bespoke part not likely to be found in new (non-dry-rotted) condition at any of the suppliers... and because I decided not to volunteer myself to any "safety" lectures (I understand completely, thank you)... I simply turned up some replacements in delrin on my lathe. Very tricky to get the dimensions correct in such a small size. But after several tries, the pop-off valve now has a new seal, and no more leaks.


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