... Every airbrush leaks, even Microns...
This is simply not a true statement
.
The head system on the H&S uses an O-ring on the air cap, as well as a teflon seal at the base of the nozzle. The seal at the base of the nozzle is dependent on the air cap being screwed on far enough to create a seal against the inside of the brush body. On the other hand, for an o-ring to make a seal under low pressure circumstances (say, less than 200psi) requires some squish on the ring itself. In this picture of the H&S head assembly the arrows on the air cap, as well as the nozzle indicate where seals are made when the head is installed correctly. As HiraMahi has already indicated that both his .2 and .4 set up's have produced bubbles in the color cup, one can draw the conclusion that the seal at the base of the nozzle has not been established with the air cap installed.
The soft jaw insert on the pliers included in the Iwata tool kit make for an excellent aid in giving a head like that of the H&S just that tiny bit more of a snug up to create the two seals needed within the head system.
To further dispel the notion that ALL airbrush heads leak, well, I currently have these 8 import brushes on my desk. The most expensive one was $42.00US. They all use a "Micron" style head system, and not one of them leaked at the head to brush body junction when I received each of them. An area I test on each and every brush I own. (Edit: Oooops, I forgot, one of them did have an air leak at the head to body junction, which was cured by snugging the head up with the nylon jawed pliers prior to use.)
They didn't leak, because even though inexpensive, they did also add an o-ring seal to the head assembly to make up for a lack in tight tolerance that would be found on a real Micron head assembly. Curious note of mention - The Micron head will screw right on these imports, but will not completely seal - even when using the imports o-ring on the Micron head. The head threads need to be waxed...
2 out of the 8 did leak air at the air cap junction. The 6 that did not leak at that junction came with wax already applied to the threads of the air cap - a nice touch I thought. As far as I can tell, I am guessing that while the brushes all look the same, there may be at least three different actual manufacturers represented in this group.
My Iwata Micron CM-BV2 did not leak air at the head to brush junction, even though there is no wax, and no other method of seal. They depend on tight tolerance in this junction to create a seal between the two assemblies, and they fit together beautifully. It did leak at the air cap junction, which I solved with wax.
Now, with that all being said, I do also have a good number of brushes that leak at the head junction. I have heard some makers "design" in some amount of air loss in this area, and that it is harmless. But, it makes me wonder how one can count on consistency if loosing an undetermined amount of air pressure before atomizing paint. I always look to cure this condition prior to calling any of my brushes ready to use.