Gravity/atmospheric pressure not enough to feed paint

NiveusCorax

Young Tutorling
I have a cheap no-name single action gravity-fed pistol airbrush. Documentation says it came with 0.3 needle. I have replaced the original needle, nozzle and nozzle cap with a 0.2 setup. But in 0.2 setup, the airbrush doesn't even spray water or IPA, even at 40 PSI... unless I cover the paint cup with my hand. I figure that by covering the cup with a hand/palm, I'm creating a pressure in the cup that is slightly higher than atmospheric pressure (I live at sea level, I'm not trying to paint on the top of the mountain or anything).

What else did I try:
1. Instead of using a hand/palm:
1.1 cover paint with a cling film
1.2 covering paint cup with a masking tape
1.3 covering paint cup with a paint cup cover with its hole plugged
None of this worked, unless I press on the membrane.
2. Shake the airbrush (side to side or up and down) a bit.
This does work, but only while I shake the airbrush
3. Using a 40ml paint cup filled pretty much all the way with water or IPA.
This works, but would be a massive waste of paint as I normally don’t spray large enough surfaces to need 40ml.

I have confirmed:
1. Nozzle is not clogged (I have checked it under the microscope). And it can’t be clogged since I haven’t sprayed anything except for water and IPA through it.
2. The original 0.3 needle that came with the airbrush is the same diameter as the replacement 0.2 needle (measured with digital calipers), so packing screw should be creating a proper seal.

When replacing a needle, I have also replaced the nozzle and the nozzle cap. So I went fully from a 0.3 setup to 0.2 setup.

Note. I do have couple of other (dual-action) airbrushes with 0.4, 0.3 and 0.15 needle setups. What I wanted to do with this cheap one is to do experiments, since I will not be too bothered if I trash it completely in the process.

So, the question is, does anyone has any ideas why going from 0.3 to 0.2 setup would stop airbrush from spraying paint? And what to do to fix the issue?
 
Is it the right setup to use with the brush?
Does it blow air ok?
What happens when You back flush with water in the cup, does the cup bubble?
You could also try sealing the threads with chapstick to see if that makes a difference
 
If you are not even spraying water, there is insufficient suction being created by the airflow around the nozzle tip to draw the fluid forward. Either there is not enough protrusion of the nozzle through the nozzle cap, a miss matched sizing between the two, or just poor fitting components. I have had many a inexpensive brush that came with various sized components that would work with one or two of the other sizes, but rarely have I had good luck with all three.
 
Hello,

When you try to spray water or IPA, do you see bubbles in the cup? Covering the cup should not increase the pressure unless there is a blowback.
Make sure you are using the correct combo of parts. Every setup requires de correct nozzle, needle and air cap to work. Needles are usually the same diameter. What changes is the taper. A 0.5 needle will be much blunter than a .3 and a .2 will be very pointy. The air cap needs to match the nozzle. If there is no space (or too big a gap) around the nozzle, air can not draw the paint. Ideally, the nozzle should protrude ever so slightly on the air cap. If it is flush or behind, it will probably not work properly.

Thanks,
Ismael
 
Is it the right setup to use with the brush?
What do you mean by that? Seeing how many of airbrushes come with sets of different size needle sets, I assumed that as long as I replace the entire set (that is the needle, the nozzle and the nozzle cap) - it should work?
Does it blow air ok?
Yes it does.
What happens when You back flush with water in the cup, does the cup bubble?
Yes, blocking the front does cause the liquid to bubble in the cup. No, it does not bubble, if I'm not covering the front.
You could also try sealing the threads with chapstick to see if that makes a difference
Both the nozzle and the nozzle cap come with a gasket/o-ring. I did apply some chapstick on the threads of the nozzle and the nozzle cap. Unfortunately, it made no difference.
 
Hello,

When you try to spray water or IPA, do you see bubbles in the cup?
No, there are no bubble in the cup when I press the trigger. I do get bubble in the cup only if I cover the front with makeup sponge or something else.
Covering the cup should not increase the pressure unless there is a blowback.
Make sure you are using the correct combo of parts.
I have fitted new needle, new nozzle and new nozzle cap, that are all marked as 0.2
Every setup requires de correct nozzle, needle and air cap to work. Needles are usually the same diameter. What changes is the taper. A 0.5 needle will be much blunter than a .3 and a .2 will be very pointy. The air cap needs to match the nozzle. If there is no space (or too big a gap) around the nozzle, air can not draw the paint. Ideally, the nozzle should protrude ever so slightly on the air cap. If it is flush or behind, it will probably not work properly.

Thanks,
Ismael
Yes, the nozzle is protruding slightly outside the nozzle/air cap.
 
If you are not even spraying water, there is insufficient suction being created by the airflow around the nozzle tip to draw the fluid forward. Either there is not enough protrusion of the nozzle through the nozzle cap, a miss matched sizing between the two, or just poor fitting components. I have had many a inexpensive brush that came with various sized components that would work with one or two of the other sizes, but rarely have I had good luck with all three.
So what you are saying is that parts might be poorly engineered/machined and it will simply not going to work? Time to give up?
 
When you look from the front: Is the nozzle centered in the air cap? Any chance you can post pictures? Is there a MAC valve in the airbrush?
 
What do you mean by that? Seeing how many of airbrushes come with sets of different size needle sets, I assumed that as long as I replace the entire set (that is the needle, the nozzle and the nozzle cap) - it should work?
What I mean is, Did the .2mm set come with the brush or was it purchased afterwards?

Can You take photos of the brush and also the new .2mm set up fitted to the brush. It may help us figure this out :)
 
When you look from the front: Is the nozzle centered in the air cap? Any chance you can post pictures? Is there a MAC valve in the airbrush?
Actually, it doesn't look centered. I broke out my macro lens, here are the images.
Also, I tried 0.2 needle, 0.2 nozzle and 0.3 air cap. 0.2 nozzle is not centered inside 0.3 air cap, but it does spray.
 

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So what you are saying is that parts might be poorly engineered/machined and it will simply not going to work? Time to give up?
Based on the photo's you posted - I would have to say, probably. The nozzle should be centered in the nozzle cap opening. The nozzle should also protrude from the nozzle cap at least a little. While I do have quite a few inexpensive brushes in my collection, this is the sort of risk one runs buying them. Some work well, but some from the same source may be more hassle than not.

If you can adjust the nozzle post to help center the nozzle a bit more, you may make the brush serviceable.
 
Based on the photo's you posted - I would have to say, probably. The nozzle should be centered in the nozzle cap opening. The nozzle should also protrude from the nozzle cap at least a little. While I do have quite a few inexpensive brushes in my collection, this is the sort of risk one runs buying them. Some work well, but some from the same source may be more hassle than not.

If you can adjust the nozzle post to help center the nozzle a bit more, you may make the brush serviceable.
Yeah, once I looked at the nozzle though the macro lens, I can see the problem myself. But hat is OK. This airbrush came in a set with a battery operated compressor. So it was more or of a bonus than a deliberate purchase.

In any case, the original 0.3 setup works fine, so I can still use it for things like varnishing, etc.

Thank you all for your help.
 
Yeah, once I looked at the nozzle though the macro lens, I can see the problem myself. But hat is OK. This airbrush came in a set with a battery operated compressor. So it was more or of a bonus than a deliberate purchase.

In any case, the original 0.3 setup works fine, so I can still use it for things like varnishing, etc.

Thank you all for your help.
yeah, that is what I was saying earlier - I have some that came with 2 or 3 different nozzles, needles, and parts - usually two of the setups work OK, and one is just junk...
 
Just curious, if I may ask: Why are you trying to use a 0.2mm setup in a pistol grip airbrush?
I was going to ask the same question.
The smallest is a Rich GP2 with 0.4 mm setup. The Creos PS 290 and the Sparmax GP 850 both have 0.5 mm. I use them for primer, clearcoat and filling in larger areas. What kind of experiments where you planning to do?
 
Just curious, if I may ask: Why are you trying to use a 0.2mm setup in a pistol grip airbrush?
That would be a long and boring story. To make it short - I got "addicted" to miniature painting. Have moved from never having done it before to owning a collection of paints, brushes, tools and now 4 airbrushes in a very short span of time. So I'm clearly suffering from GAS (Gear Acquisition Syndrome).
The 0.2 setup was originally intended to be used with my HM-331 airbrush. Unfortunately, the replacement set I acquired does not exactly fit that particular airbrush (nozzle threads are just a bit off). IT does fit the pistol grip one. And you know what happened next :)
 
I was going to ask the same question.
The smallest is a Rich GP2 with 0.4 mm setup. The Creos PS 290 and the Sparmax GP 850 both have 0.5 mm. I use them for primer, clearcoat and filling in larger areas. What kind of experiments where you planning to do?

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As should be clear from my previous reply - I have no idea what I'm doing. I don't know... I wanted to see how small a dot I can get, maybe see that happens if I try to spray non acrylic paints, say oil paints thinned with mineral spirits, or whatever other crazy idea i might get in my head.
 
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