What is an Ultimate Air Trap (UAT)?

Question

I am confused about what an Ultimate Air Trap is.
I understand somewhat that its task is to remove the air bubbles in the fuel feed to an engine. But how does it work?
How is it different from a normal RC Fuel tank? For example I am unable to see the difference between the following two. (The first is a normal fuel tank, the second one is a UAT.)

1. Fuel Tank

2. UAT

or this:

Internal Parts:

Other Questions:

1. Why is the tube to the rear end in the case of the fuel tank but only to the middle in the UAT? Also, is there a reason why is it hanging mid-air (not touching the wall)?
2. Is the white part in picture 4 a clunk or some kind of filter? I have read of Bubble trap in microfluidics is it a similar device?

Answer 1

As I see it, there are two differences.

One is that the main tank is gradually emptied during a flight, so the air pocket can be quite large. The UAT is small and fed from the tank, so it's always full.

The other is that an UAT is not just a tank, it's a pressure accumulator. Inside the tank is a 'duck bill shaped sack' that can change volume. Presumably this is designed to handle surges in demand, or brief pauses in supply from the main tank.

I don't see any mechanism for removing air that reaches the UAT. Maybe it's such a small amount that it's not a problem. Maybe that's why the clunk/filter thing is fixed near the middle of the tank. It never needs to suck up that last bit of fuel (because this tank is always full) and you want to keep it away from a small air bubble that might form near the top.