Centrifugal Pump

Defination
A machine for moving a liquid, such as water, by accelerating it radially outward in an impeller to a surrounding volute casing.

A Centrifugal pump have a high-speed rotating impeller whose blades throw the water outwards.

Energy usage

The energy usage in a pumping installation is determined by the flow required, the height lifted and the length and friction characteristics of the pipeline. The power required to drive a pump (P_i), is defined simply using SI units by

where:

P_i is the input power required (W)

ρ is the fluid density (kg/m³)

g is the standard acceleration of gravity (9.80665 m/s²)

H is the energy Head added to the flow (m)

Q is the flow rate (m³/s)

η is the efficiency of the pump plant as a decimal

Pump Efficiency

Pump efficiency, η (%) is a measure of the efficiency with wich the pump transfers useful work to the fluid.

η = P_in/P_out   (2)

where 

η = efficiency (%)

P_in = power input

P_out = power output  

 Different types of pump head

• Total Static Head -  Total head when the pump is not running
• Total Dynamic Head (Total System Head) - Total head when the pump is running
• Static Suction Head - Head on the suction side, with pump off, if the head is higher than the pump impeller
• Static Suction Lift - Head on the suction side, with pump off, if the head is lower than the pump impeller
• Static Discharge Head - Head on discharge side of pump with the pump off
• Dynamic Suction Head/Lift - Head on suction side of pump with pump on
• Dynamic Discharge Head - Head on discharge side of pump with pump on

Problems of centrifugal pumps

• Cavitation—the NPSH of the system is too low for the selected pump
• Wear of the Impeller—can be worsened by suspended solids
• Corrosion inside the pump- caused by the fluid properties
• Overheating due to low flow
• Leakage along rotating shaft
• Lack of prime—centrifugal pumps must be filled (with the fluid to be pumped) in order to operate
• Surge