The present invention relates to a device for regulating the pumping capacity of constant-speed vertical-axis centrifuge pumps having an admission cross section with a weir, a suction orifice of a pump submerged in a reservoir that is open on top, an impeller axis, and a fluid inlet opening that emerges tangentially in the direction of the impeller rotation. The fluid inlet opening forms an opening in the weir and is located below the upper edge of the weir. The lower portion of a cylindrical reservoir wall is provided so that a rotational flow can be created in the reservoir. In the portion of the admission cross section that lies above the weir, and on the side of the fluid inlet opening that lies below the weir, there is a deflector plate, so that the fluid is deflected around the pump axis in the direction of rotation opposite to the above-mentioned rotational flow in the reservoir.
