860,534. Refrigerating. PHILIPS GLOEILAMPENFABRIEKEN N.V. March 1, M57 [March 6, 1956], No. 6903/57. Class 29 [Also in Groups XXVI and XXVII] A refrigerating plant comprising a compressor and expansion apparatus and regenerative heat exchangers between the expansion apparatus and compressor in both the high and low pressure parts of the circuit, thermal energy being supplied to the gas in one of the regenerators and withdrawn from the gas in the other, has at least one additional regenerator provided together with means for connecting the additional regenerator or regenerators in the circuit in place of one or both of the existing regenerators which are connected with at least one chamber having a pressure which lies between the high and low pressure parts of the circuit so that at all times at least three regenerators are involved in the change-over process. The invention is described with reference to closed circuit system comprising a turbine type compressor 1 and turbine 2 connected to a common shaft 3 which is also coupled to a motor 4. The inlet and outlet pipes 7, 5, 10 and 8 of the compressor and turbine are each connected to a cock 11, 12, 13 and 14. The pipe 5 includes a water cooler 6 and the pipe 8 a heat exchanger 9. The cocks 11, 12, 13 and 14 are arranged so that the pipes 7, 5, 10, 8 may be connected to each of three pipes 15, 16, 17; 18, 19, 20; 21, 22, 23 and 24, 25, 26 respectively. The pipes 15, 18, 23, 26 are connected to a regenerator 35; the pipes 16, 19, 22, 25 to the regenerator 36 and the pipes 17, 20, 21, 24 to the regenerator 37. The pipes 24, 25, 26, are connected by pipes 38, 39 40 to a cock 41 which selectively connects the pipes to a three-way cock 45 connected in turn to storage vessels 48, 50. With the cocks in the position shown a gas, e.g. hydrogen, compressed in the compressor 1 is led through the pipes 5, 20 and cock 12 to the regenerator 37. If the system is used as a refrigerator, thermal energy would be withdrawn from the gas in the regenerator 37. From the regenerator 37 the gas passes through the pipes 21, 10 and cock 13 to the turbine 2. The turbine exhaust gas flows through a heat exchanger 9 where it withdraws heat from a medium to be cooled to a cock 14 connected to a regenerator 35 in which it is heated before passing through pipes 15, 7 and cock 11 to the compressor 1. During this period the regenerator 36 is connected through the pipes 25, 39, 43 and cock 41 to the cock 45 connected to the gas storage vessel 48, the pressure in which lies between the pressures in the pipes 5 and 7 so that the pressure in the regenerator 36 is decreased. After a time, the cock 45 is actuated to connect the regenerator 36 to the gas storage vessel 50, the pressure in which is lower than that in the gas storage vessel 48 but still lies between the pressures in the pipes 5 and 7, so that the pressure in the regenerator 36 is further decreased. After some time, the regenerator 35 becomes too cold. The cocks 11, 14 are then operated to connect the regenerator 36 to the low part of the pipe system. The regenerator 35, which it replaces, is then connected through pipes 26, 40, 43 and cocks 41, 45 to the low pressure vessel 50. As a result, the pressure in the regenerator 35 is increased. The cock 45 is then set to its second position to connect the regenerator 35 to the high pressure vessel 48 so that its pressure is further increased. Later the regenerator 37 becomes too hot, the cocks 12, 13 are then operated to connect the regenerator 35 to the high pressure part of the pipe system. The regenerator 37 is then connected successively to the pressure vessels 48, 50 to decrease its pressure. Later the regenerator 36 becomes too cold and is replaced in the low pressure part of the system by the regenerator 37 by operation of the cocks 11, 14. The regenerator 36 is then connected successively to the pressure vessels 50, 48 to increase its pressure. This process is repeated with each regenerator until the condition shown is obtained when one change-over cycle is completed. The higher the number of pressure vessels, the smaller the losses due to pressure exchange. The compressor and turbine may be replaced by a reciprocating compressor and a reciprocating expansion engine. In a modification, Fig. 8 (not shown), the pressure vessels 48, 50 are dispensed with, and the cock 45 is replaced by another cock adapted to connect the pipe 43 to various stages of the compressor or turbine. In a further modification, Fig. 11 (not shown), four regenerators are provided, two of which are connected to the pipe system at any one time, the remaining two being connected together through a control cock. A regenerator may be coupled at the same time, to the pressure stage of a compressor and of a turbine, in which case, multiway cocks must be provided between each regenerator and the stages of the compressor and turbine.