I recently managed to wreck the tip (part VLT-3: brass 'cone') on my old Paasche VL. In short, the needle got pushed through and split the thing. Anyway, I ordered a replacement set online, i.e. needle, tip, and air cap.
So far so good.
I decided to fit the new needle (VLN-3) and air cap (VLA-3), along with the new tip. With all those in place, the airbrush flatly refuses to spray much of anything (even water), except over a very small range of the needle's travel. Cue a long session of cleaning the brush. Still no joy. It appears that not enough suction was being generated to pull the liquid out of the cup.
Swapping various components in and out, it became clear that the culprit was the air cap. With the old air cap fitted, everything works more or less as before. This despite there being no discernable shape difference between old and new air caps. (For the record, the old one was stamped with the digit '3', whereas the new one has three engraved stripes around the circumference.)
Anyway, I'm happy now that everything works again. Just a bit of a head's up in case anyone comes across a similar problem. Clearly something changed between my 'old' Paasche, and the newer models that makes the parts not fully interchangable.
regards, Jason