Patent ID: 7475473

Claim:
A device for operating a fastening tool for joining at least two plate-shaped workpieces of similar or different materials, comprising: a hydraulic cylinder having a cylindrical cavity, a main piston having a piston rod integrally connected to a punch for performing the joining operation, the main piston dividing the cavity of said cylinder into a piston rod remote work chamber and a piston rod adjacent work chamber such that the main piston has one side pressurized by pressure prevailing in said piston rod remote work chamber and has an axially opposite side pressurized by pressure prevailing in said piston rod adjacent work chamber, a clamp piston having a piston rod integrally connected to a clamp for exerting a clamping force upon the workpieces, said clamp piston along with its piston rod coaxially extending about the piston rod of said main piston and being displaceable with respect thereto, and each of said work chambers having a fluid pressure port selectively to be pressurized or depressurized, the improvement comprising: the clamp piston being disposed in said piston rod adjacent work chamber of said hydraulic cylinder and said piston rod adjacent work chamber has sections disposed on axially opposite sides of said clamp piston and communicating with each other by fluid flow passages such that the axially opposite sides of said clamp piston both are pressurized by pressure prevailing in said piston rod adjacent work chamber.