Hazen-Williams Pipe Friction Loss
Calculate pressure drop (psi) in water pipes using the Hazen-Williams equation. Essential for sizing pumps and verifying fire suppression system pressure.
Results
What is it?
The Hazen-Williams equation is the most widely used empirical formula for calculating pressure loss due to friction in water distribution and fire suppression systems. It uses a roughness coefficient "C" to characterize pipe material and age. Unlike the Darcy-Weisbach equation, it is specific to water and avoids the need for friction factor charts.
How to use
Enter the flow rate, pipe diameter, total pipe length (add ~10�15% for equivalent fitting lengths if unknown), and select the pipe material. The C factor is pre-set for common pipe types. Results show total pressure drop in psi and per-100-ft loss for comparison against tabulated values.
Example scenario
A fire sprinkler designer routes 50 GPM through 2-inch galvanized steel pipe (C=120) over 100 feet. The friction loss is approximately 1.9 psi. Adding a 40 ft equivalent length for elbows and tees gives 140 ft total ? 2.7 psi drop � critical for verifying the minimum pressure at the last sprinkler head.
Pro tip
For domestic plumbing, keep friction loss below 4 ft/100ft (1.73 psi/100ft) to avoid noise and erosion. In HVAC hydronic systems, a design friction rate of 1.5�3 ft/100ft is typical. Remember the Hazen-Williams equation is only valid for turbulent flow with water � do not use it for viscous fluids or gases.