The TK284 has the smallest orifice of all my turbo brushes - it is pretty much impossible to stall with my central vac. It sorta seals to the ultra soft carpet, but the brush still turns and it is usable.
The TK270 has a larger opening - so I presume more air flows through. It too doesn't really seem to stall - it like it everywhere except the ultra soft - it is difficult on the backstroke, but near impossible on the forward stroke. even though it is sealed down, it still is spinning.
I have been a bit OCD about these

Like seriously OCD - I've read patents from Wessel Werk and Dupro, learned about different turbines (e.g. the above electrolux and the TK4 from dupro use a Mitchell Turbine - which is supposed to do better with high flow low head (i.e. more airflow, less pressue), while the wessel werk and TK2 use a Pelton Wheel turbine - which doesn't need as much flow, but extract the energy from the pressure.
I do see that you can get different modular orifices for the TK284, but I have no clue where to start looking for these. I'm pretty sure mine has the smallest (I see a circle 3 in roman numerals in it).
I have a waterlift gauge. Measuring the pressure in the pipes via another valve, I found
- no hose, about 130+ IOW (motor rated for 134)
- hose only (1 3/8", smooth bore): 30 IOW
- TK2: 44-50 IOW (depending on if it is in the air or on the carpet)
- TK4: 38-44 IOW
- TK270: 40-46
- TK284: 48-52
- suction only carpet brush: 30-50
Now, the permanent filter had seen some use. I cleaned it out and tried again - the numbers were about 3-4 IOW higher, but I didn't write them down.
(This is with an old Beam 294, with a Lamb 116119 motor: specs are here
http://dev.ametekfsm.com/Bulletins/116119-00.pdf )
Basically, more pressure in the pipe - approximately you can map the curves to airflow. BUT, the filter does restrict, so I'm sure the pressure readings would be higher above the filter, if I could measure it there.
Like I said, totally OCD
