Back-to-back centrifugal pump

A centrifugal pump, comprising:

• a pump inlet;
• a pump outlet;
• a pump shaft;
• a set of first stages, comprising first impellers, mounted on the pump shaft, and first outer diaphragms;
• a set of second stages, comprising second impellers, mounted on the pump shaft, and second outer diaphragms;
• and
• an intermediate crossover module arranged between the set of first stages and the set of second stages, the first impellers being arranged in a pressure-increasing sequence between the pump inlet and the intermediate crossover module, and the second impellers being arranged in a pressure-increasing sequence between a pump end opposite said pump inlet and said intermediate crossover module,
• wherein:
• said first outer diaphragms, said second outer diaphragms and said intermediate crossover module are stacked to form a pump casing,
• the intermediate crossover module forms at least one axial transfer channel between the set of first stages and the set of second stages, and a fluid connection between the set of second stages and the pump outlet,
• each one of said second outer diaphragms comprises at least one peripherally arranged through aperture, and
• said through apertures are aligned to form at least one passageway, which fluidly connects said at least one axial transfer channel with a most upstream one of said second impellers.