The invention generally relates to a process for the preparation of water absorbent polymer particles comprising the process steps of (i) preparing an aqueous monomer solution comprising at least one partially neutralized monoethylenically unsaturated monomer bearing carboxylic acid groups (a1) and at least one crosslinker (a3) (ii) optionally adding fine particles of a water absorbent polymer to the aqueous monomer solution (iii) adding a polymerization initiator or a at least one component of a polymerization initiator system to the aqueous monomer solution (iv) optionally decreasing the oxygen content of the aqueous monomer solution (v) charging the aqueous monomer solution into a polymerization reactor (vi) polymerizing the monomers in the aqueous monomer solution in the polymerization reactor (vii) discharging the polymer gel out of the polymerization reactor and optionally comminuting the polymer gel (viii) drying the polymer gel (ix) grinding the dried polymer gel thereby obtaining water absorbent polymer particles (x) sizing the grinded water absorbent polymer particles by a sizing device com prising a screen and (xi) optionally treating the surface of the grinded and sized water absorbent polymer particles wherein in process step (x) the screen oscillates at a first frequency and wherein the screen oscillates at a further frequency which is less than the first frequency or inclines an angle with a horizontal plane in the range of from 5 to 25° or both of the above.
