Hydrocyclone separator

A hydrocyclone separator for size classifying solid material in liquid suspension, comprising:

• a head part having an inlet conduit configured to lead a suspension including the solid material into the head part, and having an overflow discharge tube arranged axially in the head part,
• a tapered separation part, and
• an apex discharge part for underflow discharge,
• the tapered separation part being arranged between the head part and the apex discharge part with a wide opening end face aligned and arranged to the head part and a narrower opening end face aligned and arranged to the apex discharge part,
• wherein the apex discharge part has a first opening aligned and attached with the narrower opening end face of the tapered separation part, and has a second opening for underflow discharge in a surface opposite to the first opening, the first opening being larger than the second opening, and an inner surface of the apex discharge part has a curvature extending from the first opening to the second opening, wherein the tapered separation part and the apex discharge part has a common symmetry axis, and
• wherein the apex discharge part at the second opening ends in a curvature in a tangential angle, β, within the range of 0°<β<40° from a reference plane defined transverse to the common symmetry axis.