why do we find two different sets of pump affinity laws in literature and on the web:
One set is correct (according to my knowledge) and says that for constant shaft speed the following is true Q1/Q2=D1^3/D2^3, H1/H2=D1^2/D2^2 and P1/P2=D1^5/D2^5.
The other set of laws that is widespread on the net (almost exclusive) and even in literature says that Q1/Q2=D1/D2, H1/H2=D1^2/D2^2 and P1/P2=D1^3/D2^3.
What is true, and how is it possible that in engineering community agreement is not reached regarding the most fundamental laws of practical hydrodynamics.
The first set of equations refers to a comparison between different centrifugal pumps with geometrically similar impellers, operating with identical specific speeds. Model laws are only applicable at constant efficiency.

The second set refers to the same pump. These equalities are not as accurate as the laws relating to rpm denoted by n: