Patent ID: 7661336

Claim:
A hydraulic screw tensioning device for tightening and loosening highly stressed screws or bolts, comprising: a cylinder ( 5 - 7 ) adapted to be supported on a machine part ( 1 ) that is adapted to be clamped by a threaded bolt ( 2 ) and a nut ( 3 ), said nut ( 3 ) being threaded onto a threaded end ( 4 ) of said threaded bolt ( 2 ); a change sleeve ( 21 ) having a threaded proximate portion ( 22 ), wherein said threaded proximate portion is adapted to be also threaded onto the threaded end ( 4 ) of said threaded bolt ( 2 ), extending through the nut ( 3 ); a first annular piston ( 31 ) guided in a sealed manner in an element of said cylinder ( 5 - 7 ), wherein said first annular piston ( 31 ) is fitted onto said change sleeve ( 21 ) by a push fit; an annular surface on said first annular piston ( 31 ), wherein said annular surface extends perpendicular to an axis of said cylinder ( 5 - 7 ) and is adapted to be pressurized; a collar ( 23 ) that is monolithic with said change sleeve ( 21 ) at its distal end, opposite to and remote from the threaded portion ( 22 ), wherein an inclined surface ( 32 ), axially remote from said perpendicular surface of said first annular piston ( 31 ), is supported on an inclined surface ( 24 ) of said collar ( 23 ), and wherein said inclined surface ( 24 ) merges into an outer surface of said change sleeve ( 21 ) via a rounded-off groove ( 25 ); at least one second annular piston ( 35 ) guided in a sealed manner in an element of said cylinder ( 5 - 7 ), wherein said at least one second annular piston ( 35 ) is fitted onto said change sleeve ( 21 ) and is supported against said first annular piston ( 31 ) by a push fit; respective, facing inclined axial annular surfaces ( 36 , 39 ; 11 , 13 ) on said at least one second annular piston ( 35 , 38 ) and on said element of said cylinder ( 5 - 7 ) or on annular shoulders ( 10 , 12 ) of said cylinder ( 5 - 8 ), wherein said axial annular surfaces are inclined in the same direction and are located on a pressure-remote side of said at least one second annular piston facing away from pressure, said facing inclined axial annular surfaces defining a limit for a maximum stroke of said at least one second annular piston; and respective, facing annular surfaces on said at least one second annular piston ( 35 , 38 ) and on said annular shoulders ( 10 , 12 ) of said cylinder ( 5 - 7 ), axially remote from said facing inclined axial annular surfaces ( 36 , 39 ; 11 , 13 ), wherein said annular surfaces extend perpendicular to an axis of said cylinder ( 5 - 7 ) and are adapted to be pressurized.