Abstract: Direct-acting respirator arrangement capable of convenient sterilization in minimal time following each use, through structuring which permits integral removal of those component parts of the respirator that come into contact with the respiratory gas flow. There is provided a fixed structure incorporating a pump unit which is comprised of a variable volume chamber having a fixed wall part supported in the structure and a movable wall part operatively connected to a driven reciprocating movement element. The fixed wall part of the chamber is rigidly attached to a member through which at least the chamber feed and delivery lines extend. The member is provided with means enabling releasable connection to the structure. The movable wall part is provided with means for releasable connection to the reciprocating element.