Device for achieving an axially pre-stressed joint

Claim 1

The combination comprising at least two parts having openings therein to receive a prestressed screw joint for connecting the parts, said screw joint consisting of an elongated screw member engaged in the openings in said parts and having a first portion axially securing said screw member in one of said parts in at least one direction and having a threaded second portion axially spaced from said first portion, a nut member engageable with said second portion for axial takeup against the other part, means defining a central axial bore in said screw member having an opening at the axial end thereof receiving said nut member and terminating in a bottom wall adjacent said first portion of said screw member, a piston rod mounted in said bore and means securing said piston to said screw member adjacent the opening end of said bore, said piston rod extending into said bore with the lower axial end face thereof spaced closely adjacent said bottom wall of said bore, and located closely adjacent the connection of said screw member in said one part, the major portion of the outer peripheral surface of said piston rod extending axially from a first plane transverse to its axis below its connection to said screw member to a second transverse plane adjacent its lower end face being radially spaced from said bore to provide an annular space therebetween and a means defining an axial channel in said piston rod for conveying a pressure medium into the space defined by the axial end face of said piston rod and the bottom wall of said bore thereby to effect axial expansion of said screw member, and sealing means between the lower end of said piston rod and the wall of said, the outer peripheral surface of said screw member confronting the surface defining the opening in said other part being spaced therefrom to permit free axial expansion of said screw member upon pressurization of said space.