SPA CO2 guns - valve seal failure

[nervoustrigger]

Hey guys, this seal...



on my Plinkster (CR600W) failed after only about 10 cartridges.  It's a washer (as opposed to an O-ring), probably polyurethane based on the color.  The same seal on my CP1-M has been through probably 50 cartridges and I haven't read about this being a common problem so I suppose it was a fluke.  Hunting around for a replacement, I found an oversized washer in an assorted seal kit, so I used a hollow punch to size it to fit into the recess.  It worked for about another 10 cartridges before failing but I have no idea as to the material and the kit was over 10 years old so it may have been degraded.

When I went in for the second time, I decided to use a -009 O-ring.  A 90 durometer Buna-N is what I had handy.
There's an undercut in the brass ring into which it snaps positively.  Taking the calipers to it, the O-ring sits about 0.020" lower than the tip of the piercing pin.  I know the end of the cartridge will stretch somewhat before the pin punches through but I wasn't sure it would seal so I made a 0.015" shim washer to go under it.  It is working fine so far, however I think the shim was unnecessary because I can no longer pierce a cartridge with hand strength.  I have to insert something into the cap and make about a half turn before I hear the cartridge break and pressurize the valve.

Knowing 90D polyurethane should be somewhat more durable in this application, I went ahead and ordered some.  I'm gonna ride out the Buna-N and then use the poly whenever I have to go in again.  So in the meanwhile, if any of you guys would like me to drop you one in the mail, send me a PM with your address.

[Wayne52]

I've made my own with 3/8" hard delrin rods on a drill press for my HiPAC's, I'm still using them.  At the time Alex was on a long vacation and his seals weren't available at the time, well I won't need anymore from him anyway because I'll just make my own.  When I did order the delrin rods I made sure it would handle the pressures that I was going to be working with.

[nervoustrigger]

Hi Wayne, thanks for the feedback.  Delrin is a good durable material for a Crosman valve where the cartridge is pierced by a pin that is driven in by the hammer strike.  Or, as in your example, the sealing face of a Hipac PCP conversion kit.  However it wouldn't work for the type of piercing pin on the SPA valve; one that pierces by tightening the end cap to press the cartridge against a hollow cone.

[fivestar45]

Did you take any measurements of that seal? I'm wondering if the common seal that Crosman uses in several of their guns that have a manual piercing pin will work. Crosmans part # 38-128
If you have the dimensions of what you need I can check them against the Crosman part.

[nervoustrigger]

Well, it measured 0.078" - 0.080" thick so I'm guessing  it was a 2mm nominal thickness, but I don't know if it was suffering from some degree of compression set.

I didn't measure the OD but gauging by how the -009 O-ring (0.348") snapped nicely into the undercut, I'm guessing it was a 9mm OD.

The ID isn't a critical dimension...as long as it's a least 0.100" (2.5mm), it will fit around the piercing cone.

[cobalt327]

A quick check shows:
38-128 13mm OD x 4.25mm ID x 3.5mm thick
G397-012 9mm OD x 4mm ID x 1.5mm thick. But if the 90 duro -009 works well, that's by far the cheaper solution.

Good luck.

 

[nervoustrigger]

Mark, thanks for supplying those seal dimensions.  The second one would almost work but I suspect it is too thin, so yeah a -009 looks like the best option so far. 

In the way I'm using it with a 0.015" thin shim underneath it, I'm relying on the pressure to push the O-ring out radially to seal against the side walls.  I was a little reticent about that but it's working great and I was glad to get it disassembled, repaired, and back up and running within an hour.

[fivestar45]

O K..I have one in my hand. O D is .508" it tapers to the edges but in the center where the pin goes through it's .138" thick and has a .170" hole in the center. In looking at the Plink's parts layout it looks like you have a seal retainer that unscrews. If you back that out you might have a better ideas of the dimension of what will fit.

[nervoustrigger]

Okay yeah that agrees closely with Mark's measurements.  So that's a no go for the SPA valve.  Thanks for checking!

[nervoustrigger]

Just a quick update to say I've run about 30 cartridges through it since replacing the seal with the 90 durometer -009 O-ring and 0.015" shim and it has been holding up nicely. 

[saxpride]

My valve seal looks like plaque eating a dog's teeth. Need a new seal!!
My Plinkster was bought in Mid 2018, sad to see bits and pieces of it deteriorate so quickly. Any other things I should look to fix soon?
If you have any orings available nervoustrigger I'd be happy to take one to replace this mess.

[nervoustrigger]

No problem, just let me know by PM where to mail them.

As far as other maintenance stuff, the only other wear item i would recommend watching is the breech O-ring...the one inside the barrel that seals against the bolt.

[Wayne52]

Jason have you tried PTFE ?  That might work too.

[nervoustrigger]

Wayne, actually I'm still on the Buna-N O-ring on mine.  It's held up fine so far that I haven't needed to install a polyurethane. 

I think it would be really tricky to get a harder material to seal properly, especially across various brands of CO2 cartridges that require differing amounts of interference before the piercing cone penetrates the cartridge, plus the fact they have slightly different nose geometries.  Ribbonstone posted this pic recently for example:



Besides it's pretty convenient that a simple inexpensive O-ring works.  At this point the only thing I'm undecided on is whether the little 0.015" shim under the O-ring was necessary.  I'm gonna try omitting it if and when I have to replace the Buna-N O-ring.  Meanwhile I haven't heard any feedback from others as to whether they've needed it.  To those who've taken me up on the offer, I've been including a shim just in case.

[saxpride]

A big thank you to nervoustrigger for the o-rings. I received them quickly and put them in immediately.

Removed the old seal with a toothpick. Didn't take much for it to come out; it was hard as a rock.

New O-ring fit in perfect. Very snug fit. No need for the shim, which was included.

With the old seal, CO2 used to leak overnight. It would also leak if I didn't tighten the cap, so I had to crank it down.

With the new seal it holds CO2 for 48 hours at least. I stop tightening the cap once I hear the CO2 hiss. It's been several CO2 bottles and I'll continue to test it. But now I'm just happy my Plinkster works. If I can't test for greater than 48 hours it's because I'm shooting the thing.

Again, big thank you to nervoustrigger. I tried to find the o-ring online but it's a challenge to find the right one. Did you buy a set of them and happen to have one that fit? Just wondering how one can purchase one of these o-rings down the road. I was lucky to get some, maybe years down the road you'll run out hah!

Side Note: I checked the breech seal, still good. However the set screws for the barrel, one of them is too short and stopped working. So I have 2 set screws holding the barrel, not worried about it.
I shortened my hammer spring by cutting it until the spring is free-floating. I get 60-65 shots at 5.5 FPE with 7.9 gr CPHP. Great for this plinker.

Thanks GTA!!

[Wayne52]

I have one of the kit guns I bought from Mike@Mrodair it's the Master Blaster deal he had, mine is a .22 which I put the long barrel on with the stock.  I also opened the transfer port on it which helped for power and it's getting 11fpe.  It's definitely the quietest gun that I own.  During the summer I've gotten plenty of red squirrels in my back yard with it.



I have never had any problems with sealing at all.  I've actually just used a liberal amount of pellgun oil when putting cartridges in it.

[cobalt327]

Good job, nervoustrigger, and thanks for being generous with the parts and knowledge!

I should have gotten in on the Master Blaster from Mike at mrodair but I foolishly waited on the guys here at GTA to get a deal working with SPA. Lost out on everything by doing that. Live and learn. I did get a CP1M and a CP2 stock kit and Mike sold me a pair of breeches, one left and one right handed to fit the CP1M. Cost was $24.00 shipped. I got the barrel band and other bits and pieces from SPA while they were still selling to the public, so all I need is a .177 carbine barrel but those are made of unobtainium.

[Wayne52]

Mark my Airmax Dominator is still my top gun for hunting though, I shoot 40 regulated shots at a 3600psi fill @37fpe with my 23 grain cast pellets.  The accuracy is unreal, if I don't hit it it's not the guns fault.  I just tried seven shots with the master blaster with 19.5 grain cast and they were all hole in hole from that short 15 feet so I'm convinced these pellets work good in this gun too.

[cobalt327]

If I was going to get into PCP the Dominator would definitely be one to consider. I especially like the light weight and side lever breech.

[nervoustrigger]

Hi saxpride, that's great.  I'm glad it worked for you and thanks for confirming the shim was not needed.

And Mark, thanks too for the nod.

Regarding where to get them, I got a bag of 25 from Amazon for $5.  Here's a link...but let's just say the prices are highly variable.  $15 at the moment:


I've noticed this happens a lot with both O-rings and pellets (H&N and RWS in particular).  So if there's something I'm interested in but not in a hurry, I'll put it in the cart and then move it "Save for later".   Then I'll just take a peek at the price from time to time and buy when the price plummets.

Otherwise, check out theoringstore.com
https://www.theoringstore.com/index.php?main_page=product_info&cPath=367_459_458&products_id=16200
Prices are great and you can buy small quantities.  The problem I have is that I seldom need enough different sizes to make the shipping worthwhile. 

Lastly, don't hesitate to use a Buna-N if it's a pain to get your hands on polyurethane.  The one I used is holding up well and I expect it will for a long time to come.  Also I'll give you caution not to load up on polyurethane O-rings because this compound has a fairly short shelf life compared to most others.  I mean a pack of 10 would be a lifetime supply but most of us will probably be 10 years down the road before using 3 of them.