Abstract: An apparatus for preheating hydraulic oil which is located at low temperatures in at least one air-cooled hydraulic oil cooler, wherein at least one hydraulic oil cooler is arranged outside an engine compartment, in particular of a large hydraulic excavator, characterized in that the oil, in particular hot oil, coming from a tank is fed to the inlet box of the hydraulic oil cooler and is passed on via connecting lines and an interposed pressure relief valve or a non-return valve to the outlet box of at least one hydraulic oil cooler, wherein the outlet box and the cold oil located therein can be heated and fed to the tank.

Abstract: An apparatus for expanding tube ends in a tube sheet of a heat exchanger tube bundle comprises a mandrel which can be inserted into the tube end and an expansion pressure generator connected to said mandrel. A source of filling liquid is also connected to the mandrel to the expansion pressure generator which has a port for the filling liquid selectively blocked by the plunger of the expansion pressure generator so that problems with check valves for the filling can be obviated.

Abstract: A tube end received in a bore of a tube sheet is expanded by introducing a mandrel into the tube end and utilizing fluid pressure to bias a pair of sealing rings outwardly to engagement with a tube end, thereby sealing off the clearance between the mandrel and the tube end. In addition to utilizing the fluid pressure to provide the sealing action, the invention admits the fluid pressure into the clearance and thereby expands the tube end.