Ive been TM for 9.5 years now, before that I had several top portables most of them with vacs in parallel. Then I got one with smaller vacs but it was set up in series. The one in 'series' although with smaller vacs, produced much more suck and left the carpets noticeably drier.
Parallel set ups it is claimed produce more 'air flow', whilst series set ups produce more 'water lift'.
Well I have heard many arguments and discussions but the way I have always seen it, air flow, air velocity, whatever, isn't it surely about how much and how fast you can get the water out of the carpet, in other words - water lift.
Airflow is all very well but its about how much water it is carrying.
Of course with a big TM the amount of air flow/water lift is going to be many times that of a porty so is the difference is not that critical, you are still going to get the water out.
Dave.