For minor losses, I read that the pressure drop is equal to the dynamic pressure * loss coefficient. However, in calculating dynamic pressure, it uses a single velocity. How do you determine this velocity when it will vary at the point of change in pipe diameter or direction? I have read somewhere that it would be a mean velocity between the two sides of the change, but how can this be determined? It seems that in these pipe systems, the head loss must be calculated for the system to determine velocities before a mean velocity at these points can be calculated. Is an iterative process the only way to achieve this or am I missing something?