IMM wrote:

"parish" parish_AT_ntlworld.com wrote in message
...

Basic physics tells us that as
the bin fills up it will affect the
airflow through it and the same with
the filters

Do you know how a cyclone works? It gives full flow and the solids drop
down into a container.

I know, but when then contents of the bin reach up to perforated baffle,
where the air passes from the outer to the inner cyclone, it will impede
the airflow, i.e. slow it down. As I keep saying, it would require
instruments to measure the reduction in suction as it will be very
small, maybe only a few percent, but there will be a reduction.

Having said that, the "Max" line on the bin is roughly level with the
bottom of the baffle but when all the carpet fibres and hair binds
together to form a mat it tends to get dragged up to the baffle even
when, switched off, the bin is only half full.

The small filters can make a difference, but these
are changeable in literally seconds.