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Hi, everyone!

So I've finally bought an airbrush. I'll use it first for priming, basecoating, zenithal highlighting.
It's an Harder & Steenbeck Evolution SIlverline (2 in 1), so quite a good one.
To start testing the basics without having to cleanup and so on, I've decided to simply use some distilled water, and see how the double action works, how much is too much pressure, ...Since won't use the airbrush for fine details, I've mounted the 0.4 needle.
Fist impression was disastrous! Just pulling down the lever caused heavy bubbling in the cup. Pulled the lever back and the water started spray out intermittently. This is usually due to nozzle clogging, but man, it's a new device!
So I've read the instruction troubleshooting and noticed that it could be due to a not tightly fixed air head. FIxed it (I didn't fix it too tight at first to avoid too much stress for the gasket) and it was actually waaaaaaay better!
Water started to came out continuously and the bubbling in the cup -almost- ceased.

The question is about this -almost-.
When I play with the lever, some small bubbles appear in the cup. It's not like the bubbling you have doing a back flush; just some small bubbles that came up. Happens also by just pressing down the lever (so only air came out).
Is it normal? Due to the fact that the water is, like, "100% thinned paint"?

Many thanks!

Doesn't sound like "quite a good one". There's an air leak somewhere, gaskets are a pain to deal with once theres an isaue due to the tiny tolerances involved on most airbrushes with them I've used.

Can you just exchange it for a new one? You should surely be able to expect it to just work.

Well, let' say that it's a good one on paper, at least...
I can replace it; I've bought it on Amazon and it just arrived a couple of days ago.
I'd just like to confirm that there is actually something defective and it isn't only due to the fact that I'm doing a dumb test.

Other important issue (that I have to confirm is still there after fixing the air head) is that if I have the airbrush at 45° (maybe even horizontal) and I don't press anything, slowly a drop of water will came out from the nozzle. Looks like the needle isn't blocking completely the nozzle hole. I've tried pushing the needle (and holding with the nut) a little harder in the nozzle, but still have this issue.
I didn't test the 0.2 needle with this issue.
Sounds bad bad bad bad?

I'll do some more tests this evening.

Well, yesterday evening the test went way better. No bubbling/small bubbles in the cup, no oozing from the nozzle.
I have no idea what happened...
Maybe I've dismounted/remounted a couple of pieces after the last session to better dry them, but I'm not really sure.
I've also tested the .2 needle+nozzle and everything was ok with it, too.
Maybe the gasket was a little too "new"? Maybe I've made some mistakes arranging the parts in the first tests? (althought I've dismounted/remounted it several times)
Have to think/test for a couple more days to decide if it is actually my fault or the airbrush fault.

Looks like all the problems are related to the air head. Both the bubbles and the drops oozing from the nozzle are due to air leaks from the air head, mainly air head/nozzle coupling, if I got the airbrush mechanics right. (in fact, the needle has nothing to do with the oozing, like I tought first. Actually, one can remove it and still no liquid will leak out)
Still, I've contacted H&S support, just to be sure everything is right. Waiting for a response...

Bubbles in the cup usually indicates a problem with the medium or the assembly, not the airbrush. It means air is trying to escape from the tip and doesn't have a route to escape the brush, causing a leark. This could be because the brush is clogged, the head assembly is loose, the seal is bad, etc.

I've banged my head on just about every airbrush problem known to man. Don's Airbrush Tips is a good resource for this kind of problem. There's a series of steps to think through when trying to find the problem, and he does a good job explaining them.

OP - you might want to start by trying beeswax around the nozzle. It sounds like the seal is imperfect, which is something that can be fixed easily.

Thanks for the link. I'll read it carefully.

As said, the airbrush is brand new, and no paint run through it yet. So it can't be due to clogging.
...well, it actually can be due to clogging, like some grainy dust or similar. But a simple clean procedure and some air blowing (and I did a lot) will fix it.
Can be due to seal imperfections, but again, if this is the case I'll return it for a new one instead of trying to fix it. And that's what I'm trying to figure out.

My impression after further tests and reading about airbrush mechanics is that the "problem" is the coupling of air head and nozzle. There is no gasket or sealing involved in this. It is just that, if the air head is a little loose, the nozzle is not "pressing" on the front end of the air head, so there's some space between the two and the air will go back to the cup. Same for the water leaking; if there is some little space between the nozzle tip and the air head tip, the water (or paint) uses this path to come out autonomously.

Now, a good thing could be to have the gasket in the back of the nozzle a little thicker, so it stars pressing against the airbrush body (and on the air head on the other side) before reaching the screw limit with the air head.
Anyway, if the head is fixed firmly, looks like the problem actually disappears.

(hope all this chitchat is understandable)

I've read several pages from Don's site techsoldaten linked. Great site!
Interesting thing, there are dozen of airbrushes' reviews. There is also an H&S Evolution Solo review. Not exactly my model, but 90% compatible.
I found these line comforting:
"As usual, I began by shooting plain water. And, I got bubbles in the cup and pulsing in the spray. I thought, oh no, now what. What I found was that I hadn't tightened the head enough to get a good seal between the nozzle and the body. You have to tighten enough to compress the rubber o-ring on the head. A little tweak and it sprayed fine."
So, he conducted the same test I did with same first impression. And same solution.
If this happened to Don, too, and the review conclusion says it is a fine brush, I'm quite relieved

Probably not especially helpful, but I had that exact same airbrush and never encountered any of the problems you've described. Actually, I never had any problems with it at all.

It could be really useful if you can try to unscrew the air head a little and see if you notice the bubbling problem. In other words, how firmly do you have to fix the air head to avoid the bubbling? Like, you have to just "hit" the body, or you have to force a little, too?
I'll be really grateful!