How does a cyclonic vacuum cleaner work?

Here's a rough guide to what everything does as the air flows through a typical multiple-cyclone vacuum cleaner. In this model:

1. Air enters through the brush bar at the bottom.

2. The air enters the first stage tangentially (perpendicular to the cylindrical dirt bin) and spins around the cyclone in the middle. The dirt particles swirl to the edge, fall downward, and collect at the bottom while the air is drawn up through holes in the cyclone itself.

3. The somewhat cleaner air passes into the second, upper stage.

4. Here, a similar process happens only with a number of smaller cyclones that remove much finer dirt particles.

5. The relatively clean air passes through a HEPA filter. Since most of the dirt has already been removed, this filter doesn't really impede the flow of air through the machine.

6. The air blows back into the room after passing through a second HEPA filter.

The motor unit (not shown on this drawing) and fan is located at the base of the machine in between the two back wheels.

Please note that this drawing is not an exact representation of what happens in a Dyson (or any other, similar machine): it's just designed to give you a very general idea of what's happening in a cyclonic cleaner. In a Dyson DC04, like the one photographed up above, the air flow is actually like this:

I've removed the cyclone and dustbin, moved it to the side, and turned it backwards so you can see clearly what's happening. The red line shows the airflow up to the point at which it enters the cyclone. The orange line shows the airflow after the air exits the cyclone. The air enters through the brush bar, passes up a pipe at the side of the machine to the top, where it enters the cyclone, spins around, passes through the upper HEPA filter, then leaves through a second pipe also near the top of the machine, before traveling back down another pipe to the fan and the lower HEPA filter and finally exiting just underneath the dirt bin.