AB controls

Bocks Suv

In front of the trigger there's a small imbedded knob. What does it do?

If this s a Paasche VL, it's a trigger pre-set knob. It allows you to set the trigger to a pre-determined paint flow setting to, in effect, make the brush behave like a single-action brush. Depress the trigger without drawing back and the paint will flow at the pre-set rate. You can, of course, still draw back on the trigger for a heavier paint flow.

Bocks Suv

I see lots of articles about ABs, but I have a basic question about my double action, internal mix Paasche.<snip> Also, I've noticed that inside the body of the AB there's a long needle with a locking collar to hold it in position. Does the position of the needle ever need to be changed, or is it just to hold it in position and accessed just for cleaning? <snip>-GT

The 'locking collar' is a needle chuck. The needle needs to removed periodically for cleaning. Loosen the chuck, withdraw the needle, clean and CAREFULLY replace. Don't damage the pointed tip when replacing the needle - it's very important to the proper functioning of the airbrush. See this llink for lots of information about AB's: https://sites.google.com/site/donsairbrushtips/home