Hazen-Williams Friction Loss Equation - calculating Head Loss in Water Pipes
Friction head loss (ftH2O per 100 ft pipe) in water pipes can be estimated with the empirical Hazen-Williams equation.
The Darcy-Weisbach equation with the Moody diagram is considered to be the most accurate model for estimating frictional head loss for a steady pipe flow. Since the Darcy-Weisbach equation requires iterative calculation an alternative empirical head loss calculation like the Hazen-Williams equation may be preferred:
h100ft = 0.2083 (100 / c)1.852 q1.852 / d4.8655 (1)
where
h100ft = friction head loss in feet of water per 100 feet of pipe (fth20 /100 ft pipe)
c = Hazen-Williams roughness constant
q = volume flow (gal/min)
d = inside diameter of pipe (inches)
Note that the Hazen-Williams formula is empirical and lacks a theoretical basis. Be aware that the roughness constants are based on "normal" conditions with approximately 1 m/s (3 ft/sec) .
Example - Friction Head Loss in Water Pipe
200 gal/min of water flows in a 3 inch PEH pipe DR 15 with inside diameter 3.048 inches. The roughness coefficient for PEH pipe is 140 and the length of the pipe is 30 ft. The head loss for 100 ft pipe can be calculated as
h100ft = 0.2083 (100 / 140)1.852 (200 gal/min)1.852 / (3.048 in)4.8655
= 9 ft H2O / 100 ft pipe
The head loss for 30 ft pipe can be calculated
h30ft = h100ft (30 ft) / (100 ft)
= 9 (30 ft) / (100 ft)
= 2.7 ft H2O
Related Mobile App from The Engineering ToolBox 
- free apps for offline use on mobile devices.
Online Hazens-Williams Calculator
Imperial Units
The calculators below can used to calculate the specific head loss (head loss per 1 00 ft (m) pipe) and the actual head loss for the actual length of pipe. Default values are from the example above.
SI Units
The Hazen-Williams equation is not the only empirical formula available. Manning's formula is commonly used to calculate gravity driven flows in open channels.
The flow velocity can be calculated as
v = 0.408709 q / d2(2)
where
v = flow velocity (ft/s)
Limitations
The Hazen-Williams equation is assumed to be relatively accurate for water flow in piping systems when
- the Reynolds Numbers is above 105 ( turbulent flow )
- the water temperature is in the range 40 - 75 oF (5 - 25 oC) and the kinematic viscosity is approximately 1.1 cSt
For hotter water with lower kinematic viscosity (example 0.55 cSt at 130 oF (54.4 oC)) the error will be significant.
Since the Hazen-Williams method is only valid for water flow - the Darcy Weisbach method should be used for other liquids or gases.
- 1 ft (foot) = 0.3048 m
- 1 in (inch) = 25.4 mm
- 1 gal (US)/min =6.30888x10 -5 m3 /s = 0.227 m3 /h = 0.0631 dm3 (liter)/s = 2.228x10-3 ft3 /s = 0.1337 ft3 /min = 0.8327 Imperial gal (UK)/min
Related Topics
-
Fluid Flow and Pressure Loss in Pipes and Tubes
Fluid flow and pressure loss in pipe lines. Water and sewer systems. Steel pipes, pvc pipes, copper tubes and more. -
Fluid Mechanics
The study of fluids - liquids and gases. Involving velocity, pressure, density and temperature as functions of space and time.
Related Documents
-
Copper Tubes - Pressure Loss vs. Water Flow
Water flow and pressure loss (psi/ft) due to friction in copper tubes ASTM B88 Types K, L and M. -
Darcy-Weisbach Equation - Major Pressure and Head Loss due to Friction
The Darcy-Weisbach equation can be used to calculate the major pressure and head loss due to friction in ducts, pipes or tubes. -
Equivalent Length Method - Minor Pressure Loss in Piping Systems
Calculate minor pressure loss in piping systems with the Equivalent Pipe Length Method. -
Fluid Flow Friction Loss - Hazen-Williams Coefficients
Hazen-Williams friction loss coefficients for commonly used piping materials. -
Friction Loss in Steel, Copper and Plastic Pipes
Friction head loss (ft/100 ft) vs. water flow in steel, copper and PVC plastic pipes. -
Hazen-Williams Pressure Loss Equation
The Hazen-Williams equation can be used to calculate the pressure drop (psi) or friction loss in pipes or tubes. -
Hot Water Systems - Equivalent Length vs. Fittings Resistance
Equivalent length of fittings like bends, returns, tees and valves in hot water heating systems - equivalent length in feet and meter. -
Lined Pipes - Pressure Loss vs. Water Flow
Pressure drop diagrams for PTFE, PP, PFA and PVDF lined pipes. -
Manning's Formula and Gravity Flow
Calculate cross-sectional average velocity flow in open channels. -
Piping Equations
Calculate cross-sectional areas, weight of empty pipes, weight of pipes filled with water, inside and outside surface areas. -
Plastic Pipes - Friction Head Loss vs. Water Flow
Friction head loss (ft/100 ft) vs. water flow in plastic pipes like PVC, PP, PE or PEH. -
Pressure Loss in Pipes connected in Series or Parallel
Calculate pressure loss in pipes connected in series or parallel. -
PVC Pipes - Equivalent Length and Pressure Loss in Fittings
Minor loss in PVC and CPVC fittings expressed as equivalent length of straight pipe. -
PVC Pipes Schedule 40 - Friction Loss vs. Water Flow
Water flow in thermoplastic PVC and CPVC pipes Schedule 40 - friction loss (ft/100 ft, psi/100 ft) and flow velocities at dimensions ranging 1/2 to 16 inches. -
PVC Pipes Schedule 40 - Friction Loss vs. Water Flow Diagrams
Friction loss (psi/100 ft) and velocity for water flow in plastic PVC pipe schedule 40. -
Steel Pipes - Maximum Water Flow Capacities vs. Size
Maximum water flow capacities in steel pipes - pipe dimensions ranging 2 - 24 inches. -
Steel Pipes Schedule 40 - Friction Loss vs. Water Flow Diagram
Friction loss and velocity diagrams - in imperial (psi/100 ft, ft/s) and SI (Pa/100m, m/s) units. -
Steel Pipes Schedule 40 - Pressure Loss
Water flow and pressure loss in schedule 40 steel pipes - Imperial and SI units - gallons per minute, liters per second and cubic meters per hour. -
Steel Pipes Schedule 80 - Friction Loss vs. Water Flow Diagram
Water flow in steel pipes schedule 80 - pressure drop and velocity diagrams in SI and Imperial units. -
Water Distribution Pipes - Materials
Materials used in water distribution pipes. -
Water Flow in Tubes - Reynolds Number
Reynolds number for clean cold water flow. -
Water Supply Systems - Online Design Application
Free online tool for designing water supply systems in buildings.
