Centrifugal Pumps

Pump power requirement

Flow rate, Q = gal/min lit/sec
Density, ρ = lb/ft³ kg/m³
Energy head added to the flow, H = feet meter
Efficiency of the pump, η = %
Pump power requirement, P = hp kW

Affinity laws for pumps, fans and hydraulic turbines

Law 1: When impeller diameter is constant

Impeller speed ratio, N₂ / N₁ =
Flow rate ratio, Q₂ / Q₁ =
Head ratio, H₂ / H₁ =
Power ratio, P₂ / P₁ =

Law 2: When impeller speed is constant

Impeller diameter ratio, D₂ / D₁ =
Flow rate ratio, Q₂ / Q₁ =
Head ratio, H₂ / H₁ =
Power ratio, P₂ / P₁ =

Troubleshooting

Cavitation - the net positive suction head (NPSH) of the system is too low for the selected pump

Overheating - due to low flow; air-lock

Lack of prime; self-priming