If materials can
be deposited of the air flow (sediment), you have to use a constant velocity
of air in all pipelines.
The partial acceptable opinion, that the velocity of air in exhaust systems
should increase on its way to the filter, is hard to justify. Due to the higher
velocity, the main pipe close to the filter would not be blocked up.
But then there would be a too small velocity accepted in distant places (or a too high velocity close to the filter). If the velocity of air is too small, you should increase it in the complete system by increasing the r.p.m. of the fan.
