material suspension located on the container and at least one rigid sieve the rotor at least predominantly passes over the sieve surface which is provided with round sieve openings as high a throughput as possible and as low an energy consumption as possible are to be achieved by limiting the cross section of the sieve openings exclusively defined by circle segments application_number US 201213446402 A description the most common form of a pulper in which the invention may be applied is the upright cylindrical pulper which is open on top according to fig1 wherein screen 3 and rotor 4 are located in the floor area during operation paper stock f and water w are supplied into vat 2 the ready pumpable fibrous stock suspension 1 is drawn off through screen 3 as accepts a pulpers of this type have been known for a long time the same also applies to pulpers according to fig2 as already mentioned a horizontally positioned vat 2 of this type may be utilized underneath a paper machine for broke pulping another application is the secondary pulper for example according to de a 23 45 735 whose screen plate is equipped with screen openings are constructed according to the present invention all embodiments of the present invention have in common that the greatest portion of the.