A screw compressor comprising: a housing for receiving a supply of working matter, the housing comprising: a rotor case have a suction pocket and a slide recess; a discharge case having a discharge pocket axially aligned with the slide recess; and a slide case having a piston cylinder axially aligned with the discharge pocket; a pair of intermeshing screw rotors (18, 20) disposed within the rotor case between the suction pocket and the slide recess for compressing the working matter and discharging the working matter into the discharge pocket; a slide valve assembly disposed adjacent the pair of intermeshing screw rotors (18, 20) and axially movable within the slide recess, discharge pocket and piston cylinder to regulate the capacity of the screw compressor; the slide valve assembly comprising: a slide valve axially movable within the slide recess and the discharge pocket; a piston head axially movable within the piston cylinder; and a piston rod connecting the slide valve with the piston head; and a pulsation damper carried by the discharge case to dampen pressure pulsations of working matter discharged from the screw rotors (18, 20) to the discharge pocket and passing into the piston cylinder; characterised in that: the pulsation damper comprises: a flange for separating the discharge pocket from the piston cylinder; a bore for receiving the piston rod; and a damping channel (46A, 46B) extending through the flange. a housing for receiving a supply of working matter, the housing comprising: a rotor case have a suction pocket and a slide recess; a discharge case having a discharge pocket axially aligned with the slide recess; and a slide case having a piston cylinder axially aligned with the discharge pocket; a rotor case have a suction pocket and a slide recess; a discharge case having a discharge pocket axially aligned with the slide recess; and a slide case having a piston cylinder axially aligned with the discharge pocket; a pair of intermeshing screw rotors (18, 20) disposed within the rotor case between the suction pocket and the slide recess for compressing the working matter and discharging the working matter into the discharge pocket; a slide valve assembly disposed adjacent the pair of intermeshing screw rotors (18, 20) and axially movable within the slide recess, discharge pocket and piston cylinder to regulate the capacity of the screw compressor; the slide valve assembly comprising: a slide valve axially movable within the slide recess and the discharge pocket; a piston head axially movable within the piston cylinder; and a piston rod connecting the slide valve with the piston head; and a slide valve axially movable within the slide recess and the discharge pocket; a piston head axially movable within the piston cylinder; and a piston rod connecting the slide valve with the piston head; and a pulsation damper carried by the discharge case to dampen pressure pulsations of working matter discharged from the screw rotors (18, 20) to the discharge pocket and passing into the piston cylinder; characterised in that: the pulsation damper comprises: a flange for separating the discharge pocket from the piston cylinder; a bore for receiving the piston rod; and a damping channel (46A, 46B) extending through the flange. the pulsation damper comprises: a flange for separating the discharge pocket from the piston cylinder; a bore for receiving the piston rod; and a damping channel (46A, 46B) extending through the flange. a flange for separating the discharge pocket from the piston cylinder; a bore for receiving the piston rod; and a damping channel (46A, 46B) extending through the flange.