Hazen-Williams Friction Loss Equation

Hazen-Williams friction loss calculator for water flow in pipes

 Solve for: Discharge, Q (ft3/s): Discharge and Velocity Pipe Diameter (Q known) Pipe Diameter (V known) Energy (Head) Loss (Q known) Energy (Head) Loss (V known) Pipe Length (Q known) Pipe Length (V known) Hazen-Williams Coefficient (Q known) Hazen-Williams Coefficient (V known) Velocity, V (ft/s): Select units: Pipe Diameter, D (ft): Use feet and seconds units Use meters and seconds units Pipe Length, L (ft): © 2014 LMNO Engineering, Hazen-Williams C: Research, and Software, Ltd. Head Loss, hf (ft): http://www.LMNOeng.com Energy Slope, S (ft/ft):

Units: ft=foot, m=meter, s=second.

Hazen-Williams Equation:  V = k C (D/4)0.63 S0.54   where   S = hf / L  and   Q = V π D2 / 4

k is a unit conversion factor:
k=1.318 for English units (feet and seconds).  k=0.85 for SI units (meters and seconds)
C=Hazen-Williams Coefficient. D=Pipe inside diameter.

Hazen-Williams Coefficient (C) varies from approximately C=60 for 40-year old cast iron pipe to C=150 for new plastic pipe. The higher the C, the smoother the pipe. Table of Hazen-Williams Coefficients.

The Hazen-Williams method is valid for water flowing at ordinary temperatures of 40 to 75 oF (4 to 25 oC) through pressurized pipes. The Hazen-Williams equation is typically used to analyze city water supply systems. For other liquids or gases, the Darcy-Weisbach method should be used.  Major loss (hf) is the energy (or head) loss (expressed in length units - think of it as energy per unit weight of fluid) due to friction between the moving fluid and the pipe wall. It is also known as friction loss. The Darcy-Weisbach method is generally considered more accurate than the Hazen-Williams method. However, the Hazen-Williams method is very popular, especially among civil engineers, since its friction coefficient (C) is not a function of velocity or pipe diameter. Hazen-Williams is simpler than Darcy-Weisbach for calculations where you are solving for flowrate (discharge), velocity, or diameter. More Discussion and References.

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Discussion and References for Closed Conduit Flow