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Monday, 14 January 2019

PUMP POWER CALCULATION

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
Ph​​
:
Hydraulic power of the pump (kW).
Ps​​
:
Shaft power of the pump (kW).
Pm
:
Required power to the Motor (kW).
Q
:
Volumetric flow of fluid through the pump (m3/h).
ρ
:
Density of the fluid being pumped (kg/m3).
g
:
Gravity (9.81 m/s2).
h
:
Head produced by the pump (m).
dP
:
Differential pressure across the pump (kPa)
ηp​​
:
Pump efficiency (%).
ηm​​
:
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 - m3/h
ρ - kg/m3
g - m/s2
h - m
Ph = Qρgh/3.6 x 10^6
P - kW
Q - m3/hr
dP - kPa
Ph = QdP/3,600​​
P - kW
Q - L/min
dP - kPa
Ph= QdP/60,000​​
P - kW
Q - L/s
dP - kPa
Ph = 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 = Ph/ηp
P= Shaft power
Ph = Hydraulic power of pump (dicussed above)
η= 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".

Pm = Ps/ηm
P= Motor power
Ps  = Shaft power
η= 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)

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