When sizing gas piping, why does the code sometimes require adding equivalent lengths for fittings such as elbows and tees?

Giải thích

Elbows, tees, and valves add resistance to gas flow, and some sizing methods account for that by adding an equivalent length of straight pipe for each fitting. This increases the effective length used to select pipe size, guarding against excessive pressure drop. Simpler table methods may build in an allowance instead, so follow the specific method's rules.