Explain the Operating Point - Pumping System

Intersection of the characteristic curve and the system curve. This is the head and flow rate data for the pump "operation". The operating point data (h and Q) are used for the Affinity Laws. For example, if one operating point (h₁ and Q₁) are know, these values may be used to determine operating points along the same system curve but for a smaller or larger impeller diameter or rpm. 

The relationship between h and Q² is a constant (h/Q²) for all plot points along the system curve. The hf equations include v² and v^1.85, which are related to Q² by the continuity equation. Also, based on the Affinity Laws, 

h₂/h₁ = (n₂/n₁)² = (Q₂/Q₁)²   OR,   h_f1/ h_f2 = (Q₁/ Q₂)²  

Using the constant (h/Q²) for a system curve, operating point values of h or Q can be used to determine the h or Q values at a different operating point on a different characteristic curve (due to changes in rpm or impeller dia.).