These are the head losses of the liquid due to friction with the pipe. These losses increase with the roughness, length of the pipe and the flow rate through it. And they are reduced if the pipe diameter increases. Obstacles such as reductions, extensions, valves or elbows (singular losses) also contribute to increase the head losses.
It is established that the head losses due to 90º bends are equivalent to 5 linear metres of pipe and those due to valves to 10 metres.
According to the above, it is recommended not to exceed a head loss of 4%. In particular, in order to favour the work of the pump, it is recommended to install pipes of a larger diameter on the suction side.