Abstract: For selective operation in a Diesel mode and a pressure air mode a Diesel type pile hammer is additionally equipped with a pressure air accumulator, which is connected to the working space of the cylinder by a servo valve.

Abstract: A method and apparatus for forming rings that is particularly suited for forming plow rings from elongated lengths of stock having irregular cross sectional shape. A length of stock (12) is positioned against a mandrel (20), the end of the stock being pre-bent from a previous bending operation, with the free end of the stock extending beyond the mandrel. A movable bending element (24) is brought into contact with the stock opposite the point of contact with the mandrel, and advanced around the mandrel partially bending the stock. A clamp (82) clamps the partially bent stock against the mandrel and a cutter (98) then cuts the stock, leaving a partial bend in the newly formed free end of the stock, the cut portion of stock being clamped to the mandrel. The length of stock is moved away from the mandrel so that the bending of the cut portion around the mandrel can be completed.