I think hungfarlow (hehehe, gotta find that name funny :) is right. Make sure you read the instructions on how to calibrate your airbrush properly. The A470 works as both a single and double action airbrush, and that cylinder near the back of it is used to calibrate the needle. To find out whether or not you have a paint clog, simply turn the know all the way to the left (I think it's left :) and you should see the needle tip protrude all the way out (about 2 mm). Press the trigger, and if stuff comes out, then something is wrong, as that should be the fully closed position.
Once again, review the instructions on calibrating the airbrush. It's a fairly decent one :)