of the electric motor 7 the pump 9 which is formed for example by a centrifugal pump with an impellor is in this case mounted directly on the motor shaft 8 the pump 9 is accommodated in a pump casing 10 which comprises an inlet 11 and an outlet 12 the outlet 12 is connected to the discharge 5 b the pressure chamber device shown may be incorporated as a second pressure chamber in a high pressure circuit with a first pressure chamber for treating a substrate the electric motor 7 which is shown in more detail in fig2 and 3 comprises motor windings 20 which are insulated by an insulation material that is able to withstand a treatment medium that is specifically to be used comprising co 2 n 2 o lower alkanes such as ethane and propane or mixtures thereof the insulation material preferably consists of polyester tests have shown that this is an eminently satisfactory material other materials such as kapton or nomex are also possible furthermore the electric motor 7 comprises bearings 21 for the motor output shaft 8 the bearings 21 are of the lubrication free type i e no greases or oils are required for the bearings to function correctly the bearings 21 may comprise ceramic balls or a peek or bronze ball cage it is advantageous for the bearings 21 to comprise a self lubricating contact layer for.