Brazed plate heat exchangers must meet various safety requirements, such as the permisseble burst pressure. To accurately determine the allowable pressure and minimize safety factors, we need to know as well as possible the changes, that occur on the heat exchanger during the pressure load. The changes are represented by the global deformation of the heat exchangers. For this purpos, we design a measuring line where we measure the change in volume, using a pressure difference meter and vertical measuring pipes. The system in design so that the heat exchanger is completely filled with water and immerst in the vessel which is full of water. On the outside we have installed vertical measuring pipes in which we measure the height of the water column in the pipe with the help of a pressure difference meter. In the second part, we calibrated the measuring pipes and evaluated the most important external infuences. During the calibration, actual diameter of the vertical measuring pipes turned out to be 2 % to 3,04 % larger than the theoretical one. The greatest external infuences is the expansion of vessel, in the case of a measuring pipes with a diameter of 4 mm at the maximum measured value, can be more than a third of the measuring range. The results show that the effect of water heating can be neglected if the preparation process in appropriate. However, the expansion of the hydraulic hoses when they are subjected to pressure must also be taken into account. With the help of measurements, we also defined an appropriate procedure for venting heat exchangers, in way that reduces the impact of air bubbles that may remain trapped in the heat exchanger to a negligible value. Finally, we performed measurements on samples, for which we determined the volume deformation depending on the compressive load.
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