showed that the turbulence generating elements on the surface of the rotor should preferably be if not exactly similar to the ones described in u s pat no 5 000 842 at least relatively closely resembling them that is the turbulence generating elements shall most preferably be angular and in many cases plow like in order to both generate an intense turbulence in the fiber suspension and guide the movement of the suspension in the screening space to a desired direction as noticed from the above a new way of treating pulp in connection with screening has been developed in which way the consistency of the pulp in the screening space between the rotor and the screen drum remains essentially the same during the whole screening operation what has been presented in the above is to be understood as just some preferable examples of the invention from which the invention may differ in many relations within the scope of the appended claims thus it is completely possible that inside the rotor there are not only one or three but e g two or four or even more dilution liquid chambers the number of the chambers is completely dependent on the object of application of the rotor accordingly it is totally possible and in some cases even recommendable that the walls between the chambers are not completely impermeable but between them may be arranged some kind of e g throttled flow connection further it is possible to lead dilution liquid into all chambers via one and the same inlet tube and to regulate the flow of the liquid into the screening space by changing the size of the flow openings in the longitudinal direction of the rotor.