228. Pitting in the suction areas of a centrifugal pump bronze impeller is usually caused by __________.

Pitting in a centrifugal pump impeller's suction area is caused by cavitation. Cavitation occurs when vapor bubbles form in low-pressure areas and violently collapse, eroding the metal surface and creating pits. This localized damage, specifically in the suction area, distinguishes cavitation from abrasion, electrolysis, or general corrosion.