The important parameters describing the performance of a hydraulic machine are P the power input, H the head produced across the machine and the efficiency,. For a given geometrical design of the machine, the performance is characterized by the variables:
H -the head increase across the machine, the fluid density,  - the angular velocity of the rotor, D - the diameter of the rotor, - the fluid viscosity and Q - the flow rate; and both P and  are expressed through these variables. How many non-dimensional parameters are involved herein? Gravitational acceleration g has also to be considered necessarily?