Abstract: A horizontally oriented tubular housing is provided at one open end in its circumferential wall with a cut-out at the upper side of the housing, which cut-out resembles a segment of the tubular housing. A ram is reciprocable in the housing axially thereof and a door is mounted at the open end and pivotable about arms located at opposite lateral sides of the housing, to and from a closure position overlying the open end. The door has a plate-shaped first portion a surface of which faces the open end when the door is in closure position and which carries on this surface rigid therewith another portion resembling a segment of the tubular housing so dimensioned as to fit into and close the cut-out of the circumferential wall of the tubular housing when the door is in its closure position.