Hämmerli AP20 cylinder leak

[jpa]

Hi,
I recently bought a slightly used Hämmerli AP20. Now that I have had a chance to try it out, I notice that there is a significant air leak from between the body of the pistol and the cylinder when the cylinder is attached to the pistol. This gets better if I unscrew the cylinder a turn or so, to the point where I can complete a 60 shot course of fire if I'm lucky and don't take too much time.

Of course this is less than ideal. I was wondering if maybe there is a seal missing from within the cylinder fitting, down at the base. There is one O-ring that meets the parallel side of the pressure reducer on the pistol but that's all. Is there anyone else on this board who also uses this type of pistol, or who could advise as to what might me the problem?

I've uploaded a picture of the cylinder fitting area. Maybe there should be another seal down at the base?

Thanks!

[rmca]

It's normal for an air pistol to need replacing of the o-rings from time to time.

First, does the cylinder leak when it's unscrewed from the pistol?

If it has a gauge it's easier to see, if not leave it inside a closed plastic bag over night and see if it fills out.

Second, if the cylinder doesn't leak when off the pistol, it is probably the seal on the pistol that needs replacing. It should be a simple rubber o-ring.

I don't know of any gun that has a seal on the pistol and on the cylinder, so probably you aren't missing a part, but I may be wrong.

Hope this helps

[jpa]

Thanks very much for the reply.

My pistol is actually almost unused, not actually new but as good as. Or at least it should be ;)

The cylinder does not leak when unscrewed from the pistol. When it is screwed firmly on to the pistol, there is a noticeable leak - clearly audible, and I can actually feel it - from the join between the pistol and the cylinder. If I loosen the cylinder about half to one turn, the leak almost stops but I can still hear some air escaping. Like this, a 200 bar charge will escape in about half an hour.

There is no O-ring on the pistol; the only seal is the one O-ring just about visible in my photo of the cylinder, after the ledge, about half way down. I was wondering if there should be one right at the bottom too, where the valve is.

[Gwhite]

If the pistol has been sitting around unused, the O-ring may have stiffened up, the lubricant may have evaporated, or the seal may have gotten some dust on it. I would find some silicone O-ring lubricant, carefully pop off the O-ring (don't use anything hard or sharp that could nick the O-ring or the sealing surfaces), and then clean & re-lubricate the O-ring. You just want a really thin film of grease on it. Any more than that and it will just attract dirt.

[rmca]

You could try Gwhite suggestion, but I suspect that if the o-ring leaks that bad, it's probably past the salvation point.
Anyway, the good news is that they are probably the cheapest part to replace on the gun.
Carefully pry it out (avoid doing so with sharp objects), and then just get a couple of replacements that match exactly.
You can get them from Walther/Umarex directly, or from a shop that deals with compressed air. They are not hard to find.
Get a couple of extra ones for the future.

Unfortunately the exploded part drawing doesn't include the cylinder (it's shown as an assembly). Never the less here it is:
http://www.carl-walther.de/public/downl ... 4_30_d.pdf

Do lubricate, as Gwhite said, the new one before inserting it into the gun, making sure that you properly clean the place for it before installing.

Hope this helps

[jpa]

Thanks again for the replies.

I have already tried lubricating the O-ring with a smear of silicone grease, but I can't see a way to get the O-ring out, at least not without a sharp pin like hook of some sort, as it is so far down within the (very narrow) cylinder mounting.

The grease only added sound effects to the air leak, unfortunately :/

I have also emailed Walther about this but their website didn't have a direct email address for technical queries, so it might be a while before my message gets to the right person.

[jpa]

Well, I decided to be brave and phone Walther directly. I spoke to a very helpful person there who has promised to send me a replacement cylinder.

I didn't realise it before, but my cylinder also leaks when it is on the charging adapter, so the fault is definitely with the sealing of the cylinder.

The person I spoke to said that there is only one O-ring in the system, and it is fairly easy to get this seal out, but they have a machine at the factory for inserting the replacement. He also said that it would take more than ten years for the O-ring to dry out.