In real fluid flow, energy is lost due to pipe friction and turbulence. These losses, called head losses, are divided into:
Major losses – friction along the pipe length.
Minor losses – caused by bends, fittings, valves, and entrances.
The most common method for calculating major losses is the Darcy–Weisbach equation, while the Hazen–Williams equation is also widely used.
In short pipe systems with many fittings, minor losses can sometimes exceed major losses. Engineers typically estimate these losses using standard coefficients or equivalent pipe lengths during hydraulic design. (Wikipedia)