Abstract: A driving and extracting apparatus has a hammer frame within which a reaction mass is freely movable. The reaction mass is caused to reciprocate within the hammer frame by the selective application of drive pressure to opposite drive cylinders at a frequency corresponding to the natural frequency of the mass. A pneumatic spring at each end of the reaction mass prevents contact between the reaction mass and the ends of the hammer frame. Sensors in the hammer frame detect the position of the reaction mass and adjust the pneumatic springs accordingly.