AP20 Sprung a Leak.. :(

[Gwhite]

The college team I help coach has twenty six AP20's we bought several years ago. We haven't had any serious issues with them until today. A student removed the cylinder to check the pressure, and when she put a new cylinder on, there was a fairly loud hissing sound, and a definite breeze coming from inside the trigger guard. I haven't had a chance to study the parts diagram yet, but I'm guessing the regulator blew a seal.

Does anyone have any experience with this particular failure? I can send it back to Walther USA for repair, but I have no idea how good, expensive or fast their service is. I have a very complete spare parts kit, and I could also try to fix it myself. Unless the repair is pretty trivial, I'm leaning towards devoting my time to repair work I can't easily farm out.

Thanks for any comments/info.

[m1963]

We have not had this problem, yet. Perhaps replace o-ring 101, first? (See attached.) If you come up with a solution, please be sure to post it.

[Gwhite]

That's an excellent idea! I converted them all to have the tank horizontal when we first got them, and it's possible some dirt got in there, or the O-ring got damaged in the process. The breeze I feel is in about the right location if that is blown.

The parts list has it as a 2.9 x 1.8 mm, which is not a standard size. We have an AP20 spare parts kit, and the kit includes at least one. The parts list for that has a bit more info. It's described as PU (Polyurethane, presumably), and "93Shore", which is also harder than most regular O-rings. Definitely a non-standard part. The shelf life of polyurethane O-rings in nominally only 5 years, and the pistols are approaching that, so I suppose it may have just given out.

I'll let folks know how things work out, one way or another.

[spektr]

I could be wrong, BUT, my FWB P44 did the same thing when I took the tank off while the gun was cocked. When I put it back on, it leaked, I shot it, it still leaked. I took the tank off, cycled it about 20 times and whatever didnt like what I did lined up the right way again and all was well..... Its worth a try.

[Gwhite]

I tried firing it several times (with the tank on) in case the firing valve was leaking. The leak seem to be forward of that location, and the gas isn't coming out of the barrel.

I check the spare parts kit, and we have two spare #101 O-rings AND a complete regulator assembly. I'll try the O-ring first, and if that doesn't work, I'll install the spare regulator. If the regulator has gone bad, I can send that off for repair.

[brent375hh]

When I see metric O-rings in odd sizes, I do the conversion to often find that they are not proprietary, but US standard sizes available at McMaster, Grainger etc.

[m1963]

The FKM o-ring, in this particular size, exists. I could not find it in the US. I would not want to order it at the prices listed....shipped from the, EU, though.

[Gwhite]

I've done a lot of that sort of conversion over the years. The Czech Tau-7 pistols were designed with oddball metric O-rings, mostly 2.2 mm cross-section, where DIN standard is either 2.0 or 2.4 mm. Some applications you can go up or down a size without issue, and sometimes an English O-ring will work better.

The biggest annoyance is that Hammerli/Walther decided to use polyurethane where it isn't needed. The shelf life is a third that of nitrile O-rings The material is "non-standard" (for a static seal with air), the hardness is non-standard, and the size is non-standard. Other than that, they are fine...

Fortunately, I have spares, and I think the AP20 is popular enough that parts will be available for a good long time. For an introductory air pistol, it's an excellent design, especially the wide adjustability of the grip and the ability to convert it to left-handed easily.

[Gwhite]

The FKM o-ring, in this particular size, exists. I could not find it in the US. I would not want to order it at the prices listed....shipped from the, EU, though.

Wow! 35 Euros for ONE tiny O-ring? Ouch...

I'm sure Walther will want $5 to $10 for factory replacements, which suddenly seems like a bargain.

[m1963]

Isn't that crazy?

The Hammerli AP20 is one of the most basic/simple designs, though. I just wish the Ft. Smith, Arkansas Walther/Hammerli folks were easier to contact.....

[Gwhite]

We bought all of our AP-20's through Neal Stepp. Even purchasing over 2 dozen, he couldn't get them to give us any price break. Fortunately, Neal's regular price was lower than anyone else was asking. Neal seems to have better luck communicating with them than most, but he's indicated it's a struggle on more than one occasion.

[brent375hh]

Search O-rings in a dash number 006.
2.9mm ID with a cross section of 1.78mm, tolerance of .08mm.
McMaster has them with 90 durometer in 3 different formulas.

[Gwhite]

Thanks! I'm not sure why I didn't find those earlier. The McMaster search engine used to list "English" O-rings in mm so you could easily find a close match, but apparently they "fixed" that... They actually list dash 006 as coming in two different sizes, but one of them is a non-round backup ring.

The closest match to the factory part (in polyurethane) is: https://www.mcmaster.com/9558K512/ at 5 for $11.14

The standard Nitrile part (which I think should work just as well and last longer) is: https://www.mcmaster.com/5308T115/ at $2.69 for 100

We've got a two day match this weekend, but I may be able to sneak off to the workroom & see what's up.

[robjob]

"FKM" aka kalrez orings are made of a special high temp, chemical resistant material. Crazy expensive. Totally unnecessary for this application

[Gwhite]

I had a chance to sneak into the shop during our match today and investigate. The leak is from the inside of the regulator (Diagram Item 8: "Pressure Reducer", # 2798182), not the seal between the regulator and the frame. However, it's not a total loss. O-rings will seal better & better as the pressure increases IF they seal well at low pressure. In this case, I think there is a tiny bit of dirt or a scratch inside that makes it not quite seal well at low pressure. If you screw the cylinder on SLOWLY and stop as soon as it starts hissing, it will bleed out the entire cylinder. However, if you screw the cylinder on quickly, or even give it a quick twist when it starts leaking, there is a distinct POP from inside as the seal seats, and then you are fine.

Unfortunately, the "Pressure Reducer" appears not to be designed to be serviced, at least not easily. It is only shown as a complete assembly in the parts diagram, with no internal parts listed.

I tried blowing a drop of oil through it to see if that would help, but no luck. We'll try to use it for a while, and if it gets worse, we'll send it off for repair (if possible), or order a replacement assembly. As I mentioned, we have a spare in our parts kit, but if they can't be repaired and are prone to failures like this, we'll want to keep one at the ready. The bad news is that a new one costs ~ $130 or so. If they won't repair them, I'll tear the dead one apart & see what I find.