Ashereng suggested that I might get more detailed responses with process conditions so here goes...
Flowrate = 150 m3/hr
Suction P = tank head
Discharge P = 700 kPa
Temp. = 15 C
SG = 0.93
Viscosity = 350 cSt
Thanks to everyone for their answers.
I was wondering if anyone has any experience with using screw pump (speed to meter flow rate. In theory it should work (i.e. volume per rotation x RPM = volumetric flow), but there has to be something that I am missing otherwise EVERYONE would be doing it. Can this be done? If so, what kind...