On disassembling a centrifugal pump for overhaul, the third engineer reports holes drilled axially in the back side of a single suction closed impeller. The reason for the these holes is which of the following?

Correct Answer: Option A — To reduce the axial thrust forces on the impeller

Balance holes drilled axially through the impeller shroud allow high-pressure discharge fluid to communicate with the suction side. This equalizes pressure across the impeller, significantly reducing axial thrust loads on the pump bearings and shaft, thereby extending the service life of the rotating assembly and internal pump components.