Affinity Law of the Pump at various condition

⚙️ Affinity Laws of Pumps at Various Conditions

When Only Impeller Dia. Changes & Speed Remains The Same	When Only Speed Changes & Impeller Dia. Remains The Same	When Both Dia & Speed Change
Q2 = Q1 x (D2/D1)	Q2 = Q1 x (N2/N1)	Q2 = Q1 x (D2/D1) x (N2/N1)
H2 = H1 x (D2/D1) ²	H2 = H1 x (N2/N1) ²	H2 = H1 x { (D2/D1) x (N2/N1) }²
P2 = P1 x (D2/D1) ³	P2 = P1 x (N2/N1) ³	P2 = P1 x { (D2/D1) x(N2/N1)} ³

The Affinity Laws (also known as the Pump Laws) are fundamental relationships in fluid mechanics that describe how changes in impeller diameter and pump speed affect pump performance. These laws are widely used in pump design, selection, and troubleshooting to predict changes in capacity (Q), head (H), and power (P) when operating conditions are altered. 

🌡️ When Only Impeller Diameter Changes (Speed Constant)

If the pump speed remains constant and only the impeller diameter changes:

Explanation:  

- Increasing impeller diameter increases flow, head, and power consumption.  

- Reducing diameter decreases these values proportionally.  

⚡ When Only Speed Changes (Impeller Diameter Constant)

If the impeller diameter remains constant and only pump speed changes:  

Explanation:  

- Flow rate varies directly with speed.  

- Head varies with the square of speed.  

- Power varies with the cube of speed, meaning small speed increases can significantly raise energy consumption.  

🔧 When Both Diameter and Speed Change

If both impeller diameter and pump speed change simultaneously:  

Explanation:  

- This combined law accounts for simultaneous changes in both speed and impeller size.  

- Engineers use this relationship to predict pump performance when retrofitting or optimizing systems. 

📊 Parameters Defined

- Q1, H1, P1, D1, N1: Initial capacity, head, input power, impeller diameter, and speed.  

- Q2, H2, P2, D2, N2: Capacity, head, input power, impeller diameter, and speed after changes.  

✅ Conclusion

The Affinity Laws provide a powerful tool for predicting pump performance under varying conditions. By understanding how flow, head, and power scale with impeller diameter and speed, engineers can:  

- Optimize pump operation  

- Reduce energy consumption  

- Select appropriate equipment for system requirements  

- Troubleshoot performance issues  

These laws highlight the importance of careful adjustments—especially speed changes, since power consumption increases with the cube of speed.