A pre-hydrolysis pressure vessel system includes; a material inlet for receiving biomass material to be treated in the pre-hydrolysis pressure vessel system and a material outlet for expelling treated biomass material out from the pre-hydrolysis pressure vessel system; a transport screw arrangement including a transport screw provided inside an enclosing housing of the transport screw arrangement, said transport screw being configured for transporting biomass material through the enclosing housing towards the material outlet of the pre-hydrolysis pressure vessel system. The enclosing housing includes a cleaning arrangement that includes: at least one elongated fluid channel positioned in connection with an inner wall of the enclosing housing and wherein said at least one elongated fluid channel comprises a number of fluid outlets, and at least one cleaning fluid inlet which is provided through the enclosing housing in fluid connection with the at least one fluid channel.