wvmarle:
Why would you get air in the pumps? With dissimilar liquids (especially including foodstuffs) you normally have to dedicate a pump/hose/etc set to one liquid anyway.Try out various such flow meters.
Or if the liquids are small volume, use a peristaltic pump.
That will be one device design for various liquids.
So many same devices must be make for many pumps.
I will look into peristatic pump and how use it to do precise measuring