A piston/cylinder unit includes a closed cylinder filled with a fluid under pressure, a piston dividing the cylinder into a first working chamber and a second working chamber, and a piston rod extending through the second working chamber. A passage through the piston connects the first working chamber to the second working chamber, and a valve closing member is movable between an open position and a closed position wherein the member closes the passage. A solenoid includes a coil, a coil core, and an armature in the piston, the armature driving the valve closing member between the closed position and the open position in response to a magnetic field produced by a current applied to the coil, the cylinder forming a magnetic field guide tube. The coil is supplied with current by a power line in the piston rod, and may be grounded to the piston rod or the cylinder.