Setting pressure B.C.'s for pump
 

I am modeling a device like a centrifugal pump for incompressible liquids. I do not know a-priori what the total inlet flow rate will be, as it will depend strongly on geometry and speed of rotor in the pump. I am not sure what type of boundary condition to use for the inlet and outlet, clearly velocity inlet can't be used.

I am thinking to use a pressure-inlet and a pressure-outlet for the boundary conditions. Based on your experience, is this the best choice?

Also, I do not understand the explanation for setting the "Gauge Total Pressure" in the Pressure-Inlet B.C. panel. If I assume that I am pumping from, say, a pool of water exposed to the atmosphere, with zero head level, and I am expelling into a another pool, with just a small static pressure relative to the intake pool, what should I set the inlet total pressure to? What about the static pressure at the pressure-outlet and the operating pressure?

Thanks