A brief note on liquid-pumping systems design

1 A brief note on liquid-pumping systems design 

For process plant design, it is convenient to calculate pumping performance in terms of head of liquid rather than by pressure. The head h) is the height of the vertical column of liquid which its pressure p) will sustain, and the two are related by 

Except for the influence of viscosity variation (which is not very important in many in-plant pumping systems), the head required to pump a given volumetric flowrate of liquid (0 through a piping system is independent of the fluid pumped, and in particular its density, as is the head generated by a centrifugal pump. Hence for such systems the head/flow characteristics are practically independent of the composition of the fluid pumped. 

The constant ki can be theoretically evaluated under ideal conditions by Euler s analysis, resulting in the conclusion that 

The power-versus-flowrate curve can be deduced from the head-versus-flowrate and efficiency-versus-flowrate curves for a given fluid density, using the equation above. It is found that the power curve tends to rise continuously as flowrate increases for a radially vaned impeller, while for a backward-sloped impeller the power rises less steeply (due to the head decrease) and may reach a maximum value and then decrease, which is described as a non-overloading characteristic. The curve shapes are summarized in Fig. 14.1. 

---