This YouTube video, "Class 18 | Friction Loss Calculation | Hazen Williams Formula | Hydraulic Calculations," by "Irfan CFPS" provides a tutorial on calculating friction loss in sprinkler systems using the Hazen-Williams formula. The video explains how to calculate the pressure loss of water flowing through a straight pipe due to friction and then extends this calculation to include pipe fittings, such as elbows. The video also provides a link to an online friction loss calculator based on the Hazen-Williams formula, which can be used to avoid manual calculations. The video concludes by previewing upcoming content on different sprinkler types.