Q. When selecting a motor for a vertical turbine pump, we need to know the down thrust from the pump so that the capability of the motor thrust bearing can be checked. How can the pump down thrust be calculated?

A. Below is a simplified version of this calculation, which was taken from a Hydraulic Institute Standard, ANSI/HI 2.3 Rotodynamic (Vertical) Pumps for Design and Application. This equation is for impellers with no back wearing ring and at BEP only.

US customary units:

Thrust at BEP in lb

Where:

H = Single stage head at BEP in ft

ρ = Density of pumped liquid in lb/ft3

g = Acceleration due to gravity in ft/s2

C = Coefficient from figure 2.3.3.2.2 below

Adf = Area of impeller front wearing ring minus shaft area in in.2

B = Number of bowls

W = Weight of all the impellers and total shaft in lb

Metric units:

Thrust at BEP in N =

Where:

H = Single stage head at BEP in m

ρ = Density of pumped liquid in kg/m3

g = Acceleration due to gravity in m/s2

C = Coefficient from figure 2.3.3.2.2 below

Adf = Area of impeller front wearing ring minus shaft area in mm2

B = Number of bowls

W = Weight of all the impellers and total shaft in N