Abstract: The invention discloses a single-impeller pump with a diffuser (1, 40, 50, 60, 80, 100, 120, 130) arranged in front of the impeller (14, 46, 57, 107) on the suction side of the impeller (14,46,57,107) which evolves in the longitudinal direction toward the pressure chamber (21,67,112) with channels (10, 72, 90, 109, 128, 139) arranged around the periphery of the funnel or wall (13, 42, 52, 69, 88, 102, 125, 135) which is present within the pump casing (11, 66, 85, 114, 127, 136) and is comprised between the suction opening (27), or an eventual ejector (44, 104), and the casing cover (12, 56, 64, 84, 110, 123, 133).