Application of similarity theory of pump
1. When the similar law is applied to the same vane pump running at different speeds, it can be obtained:
• Q1/Q2=n1/n2
• H1/H2=(n1/n2)2
• P1/P2=(n1/n2)3
• NPSH1/NPSH2=(n1/n2)2
Example：
Existing a pump, the model is SLW50-200B, we need change SLW50-200B from 50 Hz to 60 Hz.
(from 2960 rpm to 3552 rpm)
At 50 Hz, the impeller has an outer diameter of 165 mm and a head of 36 m.
H60Hz/H50Hz=(N60Hz/N50Hz)²=(3552/2960)2=(1.2)²=1.44
At 60 Hz, H60Hz = 36x1.44 = 51.84m.
To sum up, the head of this type of pump should reach 52m at 60Hz speed.
