Machine for sealing parallelepipedal boxes having a variable height

A machine for sealing parallelpipedal boxes of different heights comprising

• a rest plane for the boxes,
• conveyor means to advance the boxes along said rest plane from an inlet section of said conveyor means,
• a tape-applying head mounted for vertical displacement above said rest plane and for thrust by its own weight toward a position of maximum depression,
• lifting means to lift said tape-applying head from the position of maximum depression,
• sensitive means carried by said tape-applying head and engageable by a front wall of each of the boxes coming from said inlet section of said conveyor means to control the instanteous actuation of said lifting means to vertically displace said tape-applying head to a distance above said rest plane which is higher than the height of the box engaging said sensitive means,
• said lifting means including
• at least one fluid-operated ram having a control chamber,
• valve means controlled by said sensitive means to connect alternately to a pressurized fluid source and to an outlet,
• a cutoff valve inserted between said control chamber of said fluid-operated ram and said controlled valve means,
• said cutoff valve automatically cutting communication between said controlled valve means and said control chamber of said ram whereas the pressure within said control chamber of said ram drops below a preselected magnitude.