The Metabo manual has this -
"7.5 Rotary switch for setting the suction hose diameter (only ASR 35 M ACP, ASR 35 H ACP)
Adjust the rotary switch (5) to the hose diameter of the suction hose fitted.
The volume flow is being monitored if the switch (2) is in the "AR" or "IR" position.
If the volume flow falls below a set value, the filter cassettes (17) are automatically vibrated (without any reduction in suction power). If the value still remains too low, the volume flow control display lights up (in switch position "AR" an acoustic signal is also sounded) to indicate that the container must be emptied, or that the fleece filter bag (7) or the PE disposal bag (6) must be replaced.Ø 35 mm => 70 m3/h Ø 27 mm => 40 m3/h Ø 19 mm => 20 m3/h
Note: Note: If the suction hose diameter is 19 mm or less, and if the flow conditions in the suction hose are unfavourable, the volume flow control display (3) may occasionally light up and the acoustic signal may sound, even though the fleece filter bag does not yet need to be emptied. In this case, lay out the hose straight and clean it."
Note: If you need to turn the rotary switch (5) to a lower value because of a machine generating dust (e.g. small diameter of suction canal in the machine generating dust, compared to large suction hose diameter), there is no guarantee that dust will be conveyed adequately in the suction hose. The suction hose must be removed from the machine generating dust after every operating sequence, so it can be vacuumed clear."
No mention here of suction control?