1 and a second wire 2 between which forms a dewatering space 9 into which the fibre pulp suspension 3 is applied on both sides of the dewatering space 9 against the outer surface of the wires 1 and 2 are pressure pulse elements 10 via which water is discharged from the fibre pulp suspension 3 in the dewatering space 9 in the manner schematically shown by arrows 11 and 12 it is essential to the pressure pulse elements 10 used in the apparatus of the invention that the pressure pulse element 10 generates at least two pressure pulses that amplify each other one of them being directed to the dewatering space 9 between the wires 1 and 2 and the other being directed away from the dewatering space 9 the pressure pulse elements 10 may be for example drainage foils as shown in fig4 a or rolls as shown in fig4 b wherein the rolls may be rotating or non rotating further one skilled in the art will appreciate that various combinations of such pressure pulse elements 10 may implemented on either side of the dewatering space 9 i e the pressure pulse element 10 or portion thereof generating the positive pressure pulse on one side of the dewatering space 9 may be different from the pressure pulse element 10 or portion thereof generating the coinciding negative pressure pulse along the dewatering.