Hydraulically operated mandrels

An expandable tubular mandrel for use in driving or withdrawing tubular piles, said mandrel including a pair of lengthwise sections, a head connected to and joining the upper ends of said sections, said sections below said head movable between retracted, pile-entering and expanded pile-gripping relationships, and hydraulically operated means to effect said relationships, said means including a series of piston-cylinder units spaced lengthwise of the mandrel and means incorporating said units therein with their axes extending lengthwise thereof in a manner such that expanding and contracting forces are applied to the sections when the units are operated to vary their overall lengths, to effect mandrel expansion when the overall length of at least one unit is changed in one direction and mandrel contraction when the overall length of at least one unit is changed in the opposite direction, means operable to deliver pressurized hydraulic fluid to and from said units to thus effect their operation, and said incorporating means includes connecting means for each unit, one for the cylinder and one for the piston rod thereof, one connecting means connected to at least one mandrel section and the other to both of said sections and operable to exert at least one of said forces thereon with the overall lengths of the units changed in one and the same direction.