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# Hazen-Williams Pressure Loss Equation

### 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 oF (15.6 oC) with kinematic viscosity 1.13 cSt. For hot water with lower kinematic viscosity (0.55 cSt at 130 oF (54.4 oC)) the error will be significant.

Since the Hazen Williams method is only valid for water flowing at ordinary temperatures between 40 to 75 oF (4 - 14 oC) , 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 (m3 /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/m2, Pa)

γ = specific weight (N/m3 )

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

## 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.

## 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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