The water hammer problem is considered as one of the most important questions of unsteady flows in pipelines therefore, it is still a subject of research for many scientists. This phenomenon may be steadied on two levels: practical and theoretical. The paper presents results of an experimental and theoretical study of the transients flow in pressurized pipe. Experimental tests have been conducted on the test bench of transient flow, operating in the Hydraulics Laboratory of the Department of Civil and Environmental Engineering University of Gdansk. The study consisted the pressure measurements at characteristic points of tested pipe during the pressure wave propagation. Measurements were carried out with a pipe made of high density polyethylene and galvanized steel. Based on the measurements and calculations have been also compared characteristic parameters of the pressure wave. The article also shows the numerical results for classical method of characteristics. Comparing the results of measurements and numerical simulations it is clear that the results obtained through the solving classic system of equations is significantly different from the measurement results. It appears that the damping of pressure wave in pipe goes in a substantially different way, and is influenced by the many factors, including material of the pipe. The propagation of the pressure wave goes in a particularly complex way in the case of pipelines whit different material characteristics.