This final assignment contains explanation and description of the blocking issues of the conducting abrasive tube in the mixing chamber, which is in the cutting head at AWJ. It also explains the following effect on the negative pressure in the mixing chamber. A selection procedure for different blockage cases is presented. All the cases are modelled with program called Solidworks and printed on a 3D printer. Assignment also concludes a structure of the measuring device, as well as the experiment, that measures the negative pressure in the mixing chamber of the cutting head. Experiments were performed for different kinds of blockages, with three different input water pressures into the cutting head. All the measurements were carried out in four different combinations, for two different water and focussing nozzles.