Hazen-Williams equation
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The Hazen-Williams formula can be used to calculate the pressure loss in a length of pipe due to friction dependent on the flow. This equation is commonly used for pressure drop calculations in American fire sprinkler systems, water distribution systems, and irrigation systems.
where:
Pd = pressure drop in pounds per square inch / foot
C = factor (friction loss coefficient) - the higher the C factor, the smoother the pipe. Typical C factors used in design, which take into account some increase in roughness as pipe ages are as follows:
- Asbestos-cement - 140
- Cast iron - 100
- Concrete - 100
- Copper - 150
- Steel - 120
- Galvanized steel - 120
- Polyethylene - 140
- Polyvinyl chloride (PVC) - 150
- Fibre-reinforced plastic (FRP) - 150
d = actual inside pipe diameter in inches
An alternate form of the Hazen Williams Equation is:
where:
V = Velocity (in feet per second)
C = as above
Rh = Hydraulic Radius (in feet)
S = Energy Gradient or Friction Slope (hf/L)
[edit] See also
[edit] References
- Turf Irrigation Manual, 5th Ed., by James A. Watkins, published by Telsco, 1987.
- Fluid Mechanics, 10th Ed., by E. John Finnemore and Joseph B Franzini, published by McGraw Hill, 2002.
