A turbine pump has a transition chamber (9), which separates a low-pressure section (1B) from a high-pressure section (1A) and into which an additional inlet port (5) opens. The chamber (9) is defined by a stator stage (10) consisting of a disc (11) with a peripheral edge (12), integral with said disc (11) and forming a spacer ring integrated into the stator stage, and with radial blades (17) joined with the disc (11) at both ends.