air pressure Vs. airbrush

scrambler8 wrote:

Needle size will affect the flow/force of the air. The same thing happens with the garden hose when you place a finger over the end or in building sprinkler pipes, which get smaller in diameter as they get further away from the riser. Or, restrictor plates that are used in air delivery systems. Your mention of the air flow channels within an airbrush have the same effect. A smaller needle requires a smaller hole and will have a different effect. I have two Harder & Steenbecks, one with a .15 mm nozzle and one with a .4 mm nozzle. There is a noticable difference in their operation - at the same pressure setting.

Um, how is this so when air does not pass through the needle nozzle combo? Only paint passes through the needle and nozzle, air flows around it. What am I not understanding here?

I guess it depends on airbrush model and one's definition of "blow a lot harder"  I was taking the the phrase to mean something about the pressure you feel on your hand if you pointed the airbrush at it.

With my Paasche H #1 vs #5, I haven't noticed any real big difference.  Certainly the width of the airstream is wider with the #5 than the #1, but I don't recall feeling particulary that it was any more or less pressure.  Comparing my Badger 200NH, which uses only one tip for fine, medium, and heavy work, to my Paasche H, they seem to be in the same world as far as how the air comes out.  I'm sure that if I started doing side-by-side comparisons, I might well be able to notice the difference, but during my normal painting usage, I haven't noticed any big difference.

Andy

Needle size will affect the flow/force of the air. The same thing happens with the garden hose when you place a finger over the end or in building sprinkler pipes, which get smaller in diameter as they get further away from the riser. Or, restrictor plates that are used in air delivery systems. Your mention of the air flow channels within an airbrush have the same effect. A smaller needle requires a smaller hole and will have a different effect.

I have two Harder & Steenbecks, one with a .15 mm nozzle and one with a .4 mm nozzle. There is a noticable difference in their operation - at the same pressure setting.

I wouldn't think that needle size would have any bearing on the air flow.  Even without mentioning which models of airbrushes you have, they are different airbrushes, with different triggers and internal air channels, so I would be suprised if the air came out of each identically.  On the other hand, if the difference is a really big difference, maybe there is something messed up in your Iwata's trigger such that it doesn't fully open the air valve or possibly some other internal blockage.