SUMMARY
In order to move and increase the pressure of a fluid, power is consumed by a pump, fan or compressor. The power requirement of pump depends upon many factors, including pump and motor efficiency, differencial pressure, density of fluid, viscosity and fluid flow rate. In this article we are going to discuss the relationships to determine the pump power requirement.
DEFINITIONS
P_{h}

:

Hydraulic power of the pump (kW).

P_{s}

:

Shaft power of the pump (kW).

P_{m}_{}

:

Required power to the Motor (kW).

Q

:

Volumetric flow of fluid through the pump (m^{3}/h).

ρ

:

Density of the fluid being pumped (kg/m^{3}).

g

:

Gravity (9.81 m/s^{2}).

h

:

Head produced by the pump (m).

dP

:

Differential pressure across the pump (kPa)

η_{p}

:

Pump efficiency (%).

η_{m}

:

Motor efficiency (%).

HYDRAULIC POWER
Hydraulic power, also known as absorbent power, indicates the power imparted on the fluid which is to be pumped to increase the fluid's pressure and velocity. Hydraulic power can be calcuated using one of the formulae below:
Units

Formula

P  kW
Q  m^{3}/h
ρ  kg/m^{3}
g  m/s^{2}
h  m

P_{h}_{ }= Qρgh/3.6 x 10^6

P  kW
Q  m^{3}/hr
dP  kPa

P_{h} = QdP/3,600

P  kW
Q  L/min
dP  kPa

P_{h}= QdP/60,000

P  kW
Q  L/s
dP  kPa

P_{h} = QdP/1,000

SHAFT POWER
The power supplied by the motor to the pump shaft is called "Shaft power". It is defined as the sum of the hydraulic power and power loss due to inefficiencies in the transmission of power from the shaft to the fluid. The shaft power of pump is generally calculated as the ratio of hydraulic power of the pump to the pump efficiency.
Ps = P_{h}/η_{p}
Ps = Shaft power
P_{h} = Hydraulic power of pump (dicussed above)
η_{p }= Pump efficiency
MOTOR POWER
The power consumed by the pump motor inorder to turn the pump shaft is called as "motor power". The motor power is the sum of shaft power and power losses while converting electrical energy into kinetic energy. Mthematically motor power is calculated as "shaft power devided by motor efficiency".
P_{m}_{ }= P_{s}/η_{m}
P_{m }= Motor power
P_{s }= Shaft power
η_{m }= Motor efficiency
Some OTHER FACTORS WHICH INCREASE REQUIRED POWER
In addition to the motor we can use some other drive features which will increase the power requirement of pump to transfer a perticular fluid.
These are :
1) Belt drives
2) Gear drives
3) VSD's (Variable speed drives)