Hazen-Williams Formula

This equation is used for the design of pipes under pressure.

Typical values of C are:

• Extremely smooth and straight pipes 140
• New, smooth cast iron pipes 130
• Average cast iron, new riveted steel pipes 110
• Vitrified sewer pipes 110
• Cast iron pipes, some years in service 100
• Case iron pipes, in bad condition 80

(Taken from: Schaum's outline series, Fluid Mechanics & Hydraulics 2nd Ed.)