Water Distribution & Pipe Networks

• Series: the same flow through each pipe; head losses add.
• Parallel: the same head loss across each branch; flows add.
• Minor losses at fittings: h_m = K·V²/(2g).
• Pressure head: 1 psi = 2.31 ft of water.

Worked: a 12 in main

A 12 in ductile iron main, C = 120, carries 3.0 cfs (1,350 gpm) over 2,000 ft of level ground. h_f = 4.73 × 2,000 × 3.0^1.852/(120^1.852 × 1.0^4.87) = 10.2 ft, a pressure drop of 10.2/2.31 = 4.4 psi.

Thirty years on, tuberculation has dropped C to 100. The same flow now loses 14.3 ft, 6.2 psi — the reason old mains are cleaned and lined.