Abstract: For the production of coaxial corrugations in the walls of thin-walled tubes with very tight tolerances, the invention provides a device having jaws adapted to be moved equally in opposite directions and which press against the ends of the tube so as to have a corrugation formed therein so as to feed the tube wall axially towards the corrugation in the process of being generated. The jaws are moved by means of a central lead screw with screw threads of opposite hand.

Abstract: A method for the automatic control of absorption refrigeration plant or a heat pump, by control of the supply of refrigerant to the evaporator of the plant as dependent on the temperature and the pressure of the vapor issuing from the evaporator in such a way that there is a slight degree of overheating of the vapor. At the same time the boiler power is varied in accordance with the temperature of the refrigerant vapor emerging from the boiler. The cooling for the expelled refrigerant vapor is provided by the rich solution from an absorber in a dephlegmatizer having two stages and the solution cooling circuit includes an intermediate cooler for enhancing the rectifying process when marginal conditions are unfavorable.