Forum adverts like this one are shown to any user who is not logged in. Join us by filling out a tiny 3 field form and you will get your own, free, dakka user account which gives a good range of benefits to you: No adverts like this in the forums anymore. Times and dates in your local timezone. Full tracking of what you have read so you can skip to your first unread post, easily see what has changed since you last logged in, and easily see what is new at a glance. Email notifications for threads you want to watch closely. Being a part of the oldest wargaming community on the net. If you are already a member then feel free to login now.

So a few years ago I bought a FoxHunter KMS AS18. This is the cheapest of the cheap when it comes to starter airbrushes and I'm keen to trade up, but I want to be sure that I actually know how to maintain, clean, repair and generally actually use my existing airbrush before I buy something less expendable.

Recently, I thought I'd cracked it. I was getting good flow control. My cleaning regime was delivering consistent results and I was punching out some mighty fine minis using the airbrush to do basecoating and zenithal highlighting.

Then I started to get blowback - i.e. air running up into my paint reservoir. Now, I'd encountered this before. It happened when I pulled back to release paint into the airstream and was a clear sign of a blocked nozzle. But this time it's happening when I depress the button for air but before I pull back for paint. In fact, when I pull back for paint, I'm getting good(ish) flow and the air goes the way it's supposed to. I've taken the whole thing apart and cleaned it to within an inch of its life and it's still happening. I do have a slightly bent needle tip and the nozzle does have a tiny ding to its tip and I was inclined to replace both if I didn't just buy a new airbrush. But I know for a fact that neither of those things is causing the blowback.

Can anyone shed light on what's causing this and how I can fix it? I want to sort this out and get my airbrushing mojo back before I go drop some dough on a new toy.

I can provide pics of any angle of my airbrush if you have questions.

R.

Couple of things it could be, all of which can lead to air getting into your reservoir - in order of most likely first:

Poor seal at the nozzle cap - the bit that keeps the air behind the nozzle; try wrapping a bit of PTFE tape there and see if it stops the blow back.

Missing O-ring from somewhere. Check seals and rings.

Clog in the air channel - are you cleaning with an ultrasonic cleaner? If not, try it, it is possible paint is somewhere you're not expecting it.

Split cup. I've got an airbrush where the brazing of the cup to the barrel has gone, leaving a small hole. Not worth the effort repairing - it'd need all the plating removing, brazing and then replating. It bubbles in the cup, but also leaked (more after cleaning).

What winterdyne said...

My first guess is the seal at the nozzlecap since you have blowback when you just press for air. Had that happen to me and took me a long time to find out through trial and error, mostly error

Poor seal at the nozzle cap - the bit that keeps the air behind the nozzle

Wouldn't that just cause air to leak from the nozzle cap rather than back-up through the reservoir? If I remove the nozzle cap entirely, air flows out very smoothly from the air channel.

Clog in the air channel - are you cleaning with an ultrasonic cleaner?

Again, wouldn't that cause a disruption to the air-flow rather than forcing it back up through the reservoir? I was looking at getting an ultrasonic cleaner, but as I could buy a new airbrush for less, it seemed a bit pointless.

Split cup

Whut?

Assuming you're referring to the well or reservoir, this cheapo airbrush has a separate reservoir, connected with a screw neck. I've removed it and run the airbrush putting water directly into the well and I still get air backing up. So it's not the reservoir.

R.


Automatically Appended Next Post:
@granander - I'be had a closer look at the nozzle cap. Although I don't understand the physics of the problem at all, I can now see that the O Ring behind the nozzle cap is a bit skew-wiff. I'll have a play and see if I can fix it.

 precinctomega wrote:

Poor seal at the nozzle cap - the bit that keeps the air behind the nozzle

Wouldn't that just cause air to leak from the nozzle cap rather than back-up through the reservoir? If I remove the nozzle cap entirely, air flows out very smoothly from the air channel.

I find with the cheap airbrushes, the o-ring behind the nozzle cap gets knackered really fast. I now just use PTFE there and have far fewer problems; if it misbehaves I just wind another thread on there.

You may also find your spray direction goes off-centre - you may at first attribute this to your bent needle, but the nozzle cap needs to be aligned pretty precisely to sit over the nozzle.

Talizvar - That's really helpful and explains where the blowback may be coming from perfectly. I've actually cannibalized a new needle and nozzle from an old, unused airbrush I've had kicking around. The O-ring on the nozzle cap looks fine, but I've given it a tweaking. There was a teeny-tiny split in the tip of the nozzle which I didn't think would make a difference but, looking at the diagram it's possible that it was the source of the blowback.

winterdyne - I really appreciate the advice. If I still can't get the nozzle cap to sit right, I'll try some PTFE. It looks perfectly straight, but knowing that it could be on less than perfectly may be all I need to get it just right.

Thanks to all!

Regards,

R.

Nope. Nozzle cap straight. PTFE tape applied. Worse than ever.

You mentioned that you were thinking of upgrading. Might I recommend that this is a fine opportunity to do just that?

The truth is that while you can get reasonable results with a cheap airbrush, you are just as likely to have frustrating problems like this with them. Cheap is cheap. A good airbrush is a finely machined tool. A cheap airbrush replaces fine machining with rubber o-rings that will invariably break-down, get lost or otherwise create issues. When you have a problem with a good airbrush it's much easier to diagnose (and usually comes down to needing to clean it better).

My own recommendation is an Iwata Eclipse, but there are many airbrushes out there that will do well for you.

The problem could be hardened paint in the paint nozzle. A small flake of dry paint can and has caused me problems,
I had the same issue and I used a pin to clean out the paint
nozzle. I had a little speck of paint in there that caused me
a lot of problems. I cleaned the airbrush as I normally do with
no results. Once I cleaned the nozzle out everything worked properly. Good luck with this issue.