Aim of the study:
Present the results of studies of the water hammer phenomenon in the pipes made from different materials. Showing the effect of changing the type of material of the pipe on the speed of the pressure wave during the transient flow in the pipes.

Material and methods:
Pipes made of galvanized steel and high-density polyethylene were tested. Measurements were made using strain gauges with high accuracy of measurements.

Results and conclusions:
The results of the pressure wave velocity range from 205 to 247 m/s for the polyethylene pipe and from 426 to 1351 m/s for the steel pipe. Therefore, the change in the type of the pipe material has a significant effect on the speed of the pressure wave during the water hammer. The value of this speed is influenced not only by the properties of the material itself or the liquid, but also its length and position relative to each other. It is evident that the value of speed in the polyethylene pipe does not change significantly in relation to the situation when the pipe is uniformly material. The situation is radically different in the case of a steel pipe, where the speed of the pressure wave changes along with the length of the pipe and its position relative to the tank. The smallest value of the speed in the elastic pipe is achieved when it is on the valve side and is only 13.15 m long, while the largest is reached when the 13.24 m steel pipe is located on the side of the tank.