Abstract: A screening apparatus for screening fibrous material in liquid suspension includes a housing having an inlet and accept fraction outlet and reject fraction outlet. The suspension is introduced under pressure via the inlet. A cylindrical screen is positioned centrally within the housing to define an involute reject passage within the housing and outboard of the screen with the rejected fraction passing under pressure from the reject passage outwardly of the housing via the rejected fraction outlet. The accepted fraction passes from the reject passage inwardly through the screen and is then passaged under pressure outwardly of the housing via the accepted fraction outlet. The suspension is under pressure in its travel through the apparatus and is pulsed en route by a plurality of elastically mounted diaphragms driven in compressing and decompressing strokes by means eccentrically mounted on a rotating mainshaft.