On
the chance that you are not already familiar with the basic principle
of an internal mix airbrush, I made a sketch to illustrate it.
This represents the head assembly of a typical internal mix
brush. The needle is centered in the nozzle or tip, and is surrounded
by paint. Moving the needle forward or back changes the size
of
the opening at the front and the amount of paint that is sprayed.
Surrounding the tip is the regulator which is made so that
pressurized air can exit in a circular opening around the tip.
The air escaping creates a vacuum that draws paint out of the
tip
and down the needle to break free at the point and form a spray pattern.The thing that makes this work is called the Bernoulli principal or Venturi effect. If you're curious, do a Google on either of these words and you will find all kinds of information.
In a single action brush, the needle is moved by turning a threaded shaft. In a double action it is moved by pulling back the trigger. In either type, air is controlled on or off by pressing the trigger.
The sketch is crude. The actual devices are very precise.
Here
is an cutaway image
that I borrowed from Badger of the Model 100.The front part is different than the 155, but from the needle bearing on back, it is pretty much the same except for the lack of a cut-out in the handle. Notice the "O" ring in the air valve assembly. It does not like lacquer thinner. Also notice that the needle bearing prevents paint from leaking into the rear portion of the brush. As long as the needle bearing is in good shape, the rear portion should never need cleaning. Notice the spring screw just in front of the needle chuck. This can be adjusted to change the force needed to pull back the trigger.
I
don't have a cutaway view of the Model 155, but here
is a parts breakdown. Notice that, in
addition
to the fact that paint enters from the bottom instead of the top, the
nozzle portion is different. There is no Teflon head
washer,
and the part labeled TIP is free floating. It is held in
place by
being captured between the head and the main body of the brush. The
only parts of the brush that come in
contact with paint are the tip, the needle, and the main body.
The head and regulator, parts 51-071 and 41-034, should never
need cleaning.
Here is a nice image of the
tip that I borrowed from Dick Blick.This same tip is used in models 175, 200NH, and 360. Note, if the tip doesn't seat right, air can leak into the paint path and cause bubbles in the paint cup. Tighten the head and regulator finger tight, but don't overdo it.
If you have an internal mix airbrush, it probably resembles one of these two types. An exception is the Testors Aztek which is a unique design.
Notice that the needle of the 155 has a knob on the back end. This makes it impossible to remove from the front of the brush, but very convenient to remove from the back.
When I bought the brush, I also bought some air brush lube and applied it to all the moving parts. After some time, I noticed that the trigger action was a bit stiff. I found that the lube had gotten sort of gummy. So I cleaned everything and put a tiny bit of sewing machine oil on all the metal parts that rub together. I didn't lube the needle because I decided that lubing Teflon was kind of redundant. The trigger movement has felt fine ever since.