State the pump affinity laws and their applications.

Pump affinity laws relate pump performance at different speeds or impeller diameters: (1) Flow: Q₂/Q₁ = (N₂/N₁) or (D₂/D₁), (2) Head: H₂/H₁ = (N₂/N₁)² or (D₂/D₁)², (3) Power: P₂/P₁ = (N₂/N₁)³ or (D₂/D₁)³. Applications include: predicting performance when using VFD speed control, estimating effect of impeller trimming, scaling from test data to actual conditions. Important limitation: these laws are approximate and assume geometrically similar flow conditions; significant deviations occur at extreme speed changes or major impeller trim.