how to determine the selection of the pump head

The lift is needed to lift the value of process plants, often called the calculated head.
If in the data table value directly gives the head, generally requires that the selected pump rated head required for the installation of 1.05 to 1.1 times the lift.
If the data table only shows the inlet pressure and outlet pressure Ps Pd, the device needed to lift = (outlet pressure Pd - inlet pressure Ps) ÷ medium weight ρ
For the viscosity> 20mm 2 / s or the media containing solid particles, you need to transport water when converted into the head, and then determine the rating of the pump head.