I have just done some airbrushing for the first time since about last September—Vallejo
Model Air Grey Primer. I opened the flap and unscrewed the top and using a stiff brush cleaned all the stuck primer. I was surprised at how difficult it it was to remove all of it (which is good for modelling). Having thoroughly shaken the bottle before, I shook it a second time. (It has a rattle object in it—an M4 nut). On shooting AB cleaner through my brush (a Harder and Steenbeck CR Plus, 0.4 mm) the flow fell to half during spraying. On cleaning it, I pushed as usual an interdental brush wet with cleaner into the nozzle and a worm of quite stiff primer came out. The AB had been thoroughly cleaned last time—cup cleaned, body brushed inside with cleaner (the tiny bottle brush being inspected in a bright light against a dark background and under a magnifying lens to detect hairs before every use of it), nozzle cleaned and inspected under a magnifying lens against a bright light, put into an ultrasonic cleaner, re-assembled in clean conditions.
Despite this rigorous cleaning every time, I get blockages quite often (say every 5th session), many showing evidence that thick paint was the culprit. Any paint that had hardened blow the neck of the bottle (which perhaps I did not detect) would probably have formed a flake (like I found on the cap when cleaning) rather than produced a worm which is what I found.
How often to you others get blockages? What causes them? Are they something that we must accept?