How does the flow regulation of Eheim filters work?

[Sanniejop]

Hi,
Before buying a new filter I was wondering how the flow regulation works on those Eheim Professionel 3/4+ filters.
Is this just a mechanical adjustable flow restriction? Or is this an electrical controlled power setting of the filter pump motor?
I can not find this info on their website.

I hope that someone can tell me...
Thanks in advance

 

[Maf 2500]

The Professional 3 is definitely mechanical. I am pretty sure it is the same on 4+. The professional 5e, on the other hand, has electronic adjustment.