Apparatus for treating a medical liquid, and method for checking the leaktightness of the apparatus

A treatment machine to which a disposable cassette is couplable for the treatment of a medical liquid, said disposable cassette having a hard material of construction, and including liquid conducting passages which are covered by a flexible film that is couplable to a coupling surface of the treatment machine via a flexible mat, with air between the flexible film and the flexible mat being removable in order to provide a vacuum therebetween, said treatment machine comrising:

• a coupling surface and a flexible mat arranged on the coupling surface,
• a measurement chamber arranged in the coupling surface, and
• a sensor arranged in the measurement chamber, the sensor being configured to detect a deflection of a region of the flexible mat disposed. above the measurement chamber, the deflection resulting from a differential pressure between (i) a pressure in an area between the flexible mat and the flexible film, and (ii) a pressure in the measurement chamber.

A disposable cassette couplable to a machine for the treatment of a medical liquid, said machine having a coupling surface and a flexible mat arranged on the coupling surface, a measurement chamber arranced in the coupling surface, and a sensor arranged in the measurement chamber, the sensor being configured to detect a deflection of a region of the flexible mat disposed above the measurement chamber, the deflection resulting from a differential pressure between the disposable cassette and the treatment machine, said disposable cassette comprising:

• a thin-walled three-dimensional part having a hard material of construction, and
• liquid conducting passages covered by a flexible film that is couplable to the coupling surface of the treatment machine via the flexible mat,
• with the disposable cassette being configured such that air between the flexible film and the flexible mat is removable in order to provide a vacuum-based coupling of the disposable cassette.