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# 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.

### Hazen-Williams Formula in Imperial Units

The Hazen-Williams equation for calculating head loss in pipes and tubes due to friction can be expressed as:

P d = 4.52  q 1.85 / (c 1.85 d h 4.8655 )                                 (1)

where

P d = pressure drop (psi/ft pipe)

c = design coefficient determined for the type of pipe or tube - the higher the factor, the smoother the pipe or tube

q = flow rate (gpm)

d h = inside hydraulic diameter (inches)

Note! The Hazen-Williams equation estimates an accurate head loss due to friction for fluids with a kinematic viscosity of approximately 1.1 cSt. More about fluids and kinematic viscosity .

The results is acceptable for cold water at 60 o F (15.6 o C) with kinematic viscosity 1.13 cSt. For hot water with lower kinematic viscosity (0.55 cSt at 130 o F (54.4 o C)) the error will be significant.

Since the Hazen Williams method is only valid for water flowing at ordinary temperatures between 40 to 75 o F (4 - 14 o C) , the Darcy Weisbach equation should be used for other liquids or gases.

### Online Hazens-Williams Calculator - Imperial Units

The calculator below can used to calculate head loss in imperial units:

### The Design Factor - c

The design factor is determined for the type of pipe or tube used:

• The c-value for cast iron and wrought iron pipes or tubes ranges from 80 to 150, with average value 130 and design value 100 .
• The c-value for copper, glass or brass pipes or tubes ranges from 120 to 150 , with average value 140 and design value 140 .
• The c-value for cement lined steel or iron pipes has average value of 150 and design value 140 .
• The c-value for epoxy and vinyl ester pipes can be set to 150 .

### Hazen-Williams Formula in Metric Units

h = 10.67  q 1.85 / (c 1.85 d h 4.8655 )                                       (2)

where

h = head loss per unit pipe (m h2o /m pipe)

c = design coefficient determined for the type of pipe or tube - the higher the factor, the smoother the pipe or tube

q = flow rate (m 3 /s)

d h = inside hydraulic diameter (m)

Pressure drop in Pa can be calculated from the head loss by multiplying the head loss with the specific weight of water:

p = h γ

where

p = pressure loss (N/m 2 , Pa)

γ = specific weight (N/m 3 )

Specific weight of water at 4 o C is 9810 N/m 3 .

## Related Topics

• ### Fluid Flow and Pressure Loss

Pipe lines - fluid flow and pressure loss - water, sewer, steel pipes, pvc pipes, copper tubes and more.

## 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.
• ### Fluid Flow - Hydraulic Diameter

Calculate hydraulic diameter for pipes and ducts.
• ### Fluid Flow Friction Loss - Hazen-Williams Coefficients

Hazen-Williams friction loss coefficients for commonly used piping materials.
• ### 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.
• ### Liquids - Kinematic Viscosities

Kinematic viscosities of some common liquids like motor oil, diesel fuel, peanut oil and many more.
• ### Pressfit Pipes - Pressure Loss vs. Water Flow Diagram

Water flow pressure loss diagram.
• ### Pressfit Piping - Friction Loss vs. Water Flow

Water flow friction loss in pressfit piping.
• ### Pressure Units - Online Converter

Convert between pressure units like Pa,  bar, atmosphere, pound square feet, psi and more.
• ### Viscosity - Absolute (Dynamic) vs. Kinematic

Vicosity is a fluid's resistance to flow and can be valued as dynamic (absolute) or kinematic.

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## Citation

• The Engineering ToolBox (2004). Hazen-Williams Pressure Loss Equation. [online] Available at: https://www.engineeringtoolbox.com/william-hazens-equation-d_645.html [Accessed Day Month Year].

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12.8.9