Water-Lifting Devices – Pumps - Practices of Irrigation and On-farm Water Management - page 445

In addition, water entering the screen of the suction pipe through the formation,
encounters resistance hence requires energy. This is called formation loss

Dynamic Discharge Head

It is the sum of static discharge head, friction head for discharge pipe, and the
velocity head of the discharging fluid.

12.4.2.5 Total Head

Total dynamic head ,orsimply' total head ' is the sum of dynamic suction head and
dynamic discharge head.
This is the total pressure, in meter, that the pump must overcome to perform its
work as designed. Numerically, it is the sum of the suction head, delivery head (if
any), velocity head, friction head for the suction and discharge pipe, and formation
loss (in terms of head) (if applicable). That is,

H T = DH + SH + VH + FH + FL (12.2)

DH = delivery head or discharge head (m)

SH = suction head or lift (m)

VH = velocity head (due to velocity of discharging water)

FH = friction losses in the suction pipe and delivery pipe (m)

FL = formation loss (m)

12.4.3 Pump Efficiency

The efficiency of a pump is a measure of its hydraulic and mechanical performance.
It is defined as the ratio of the useful power delivered by the pump (water horse-
power) to the power supplied to the pump shaft (brake horsepower). The efficiency
of the pump is expressed in percent and can be calculated using the following
equation:

WHP
BHP ×

E = 100% (12.3)

where

E pump efficiency

WHP

=

= Water horsepower

BHP = Brake horsepower

The efficiency range to be expected varies with the pump size, type, and design.
However, it is normally between 70 and 80%. A pump should be selected for a
given application so that it will operate close to its point of maximum efficiency.