Friction loss is the loss of energy or “head” that occurs in pipe flow due to viscous effects generated by the surface of the pipe. Friction Loss is considered as a “major loss”.
“Head” is a very convenient term in the pumping business. Pressure is not as convenient a term because the amount of pressure that the pump will deliver is dependent upon the weight (specific gravity) of the liquid being pumped and as you know, the specific gravity changes with the fluid temperature and concentration.
Each litre of liquid has weight so we can easily calculate the kilograms per minute being pumped. Head or height is measure in meters so if we multiply these two together we get kilogram meters per minute which converts directly to work at the rate of 610 kgM/min = 1 kilowatt.
Please note that we always measure from the center-line of the pump impeller to the highest liquid level.