The results of experimental studies of deformed state of a long-stroke low-speed stage of a piston compressor unit made it possible to verify the calculation method for the given design stage, taking into account the influence of changing gas state parameters in the working chamber and wall temperature. The developed experimental testbed and research methodology are described. The model of the deformed state of the cylinder is implemented using the ANSYS Workbench Mechanical software package (ANSYS WM software package). The obtained data on deformations made it possible to supplement the existing method of calculating the working processes of low-speed long stroke piston stages with the function of changing the gap in the cylinder-piston seal. This issue is very relevant for processes in low-speed units, since the phenomenon of stress relaxation in cylinder walls is significantly different from the processes occurring in high-speed piston stages.