Fittings such as elbows, tees, valves and reducers represent a significant component of the pressure loss in most pipe systems. This article details the calculation of pressure losses through pipe fittings and some minor equipment using the K-value method, also known as the Resistance Coefficient, Velocity Head, Excess Head or Crane method.

The K-value, Resistance Coefficient, Velocity Head, Excess Head or Crane method allows the user to characterise the pressure loss through fittings in a a pipe. The K-value represents the multiple of velocity heads that will be lost by fluid passing through the fitting.

It is more accurate than the Equivalent Length method, as it can be characterised against varying flow conditions i. Reynold Number. However it is less accurate than other methods as it does not take into account the varying geometries of fittings at different sizes. These K-values also generally assume fully developed turbulent flow, and thus are inaccurate at low Reynolds Numbers. It is in some ways similar to the equivalent length method, and the two may be equated by the formula below:.

There are many tabulations of K-values, as well as methods for calculating K-values.

### Pipe Friction Loss Calculations

Below is table of typical K-values for various fitting types. This example demonstrates how to use the excess head method to calculate the head loss through simple pipe and fitting arrangement. The example uses water in system of standard weight carbon steel pipe.

Note that for this example we consider a flat system, with no elevation changes. With this we can calculate the head loss for a single elbow. Using the equation for head loss in pipe, we can calculate the loss through the straight piping :. The total head loss for the system is the addition of the head loss from the pipe and the fittings.

In the above example we first calculated the head loss for a single fitting and then multiplied by the number of fittings.

It is also correct to add or multiply the K-values of fittings and then covert to a pressure or head loss. This is useful when there are many fittings of several types. Email Name. Summary Fittings such as elbows, tees, valves and reducers represent a significant component of the pressure loss in most pipe systems.

Definitions : Internal diameter of pipe : pipe friction factor : Acceleration due to gravity : Head loss : Resistance Coefficient : Length as indicated : Average velocity.

Article Created: October 12, Excess Head.

Flow Rate. Fluid Flow. Pressure Drop.IPSor products where the actual OD matches the nominal size e. As a result some published tables using the Hazen-Williams equation with a standard temperature may show different results.

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Calculation Details Email Print. Always refer to and follow the pipe manufacturers recommended velocity limits. Email Address: Send. Agree Decline. We Value Your Feedback! Take Survey.A large amount of research has been carried out over many years to establish various formulae that can calculate head loss in a pipe.

Most of this work has been developed based on experimental data. Overall head loss in a pipe is affected by a number of factors which include the viscosity of the fluid, the size of the internal pipe diameter, the internal roughness of the inner surface of the pipe, the change in elevation between the ends of the pipe and the length of the pipe along which the fluid travels.

Valves and fittings on a pipe also contribute to the overall head loss that occurs, however these must be calculated separately to the pipe wall friction loss, using a method of modeling pipe fitting losses with k factors. The Darcy formula or the Darcy-Weisbach equation as it tends to be referred to, is now accepted as the most accurate pipe friction loss formula, and although more difficult to calculate and use than other friction loss formula, with the introduction of computers, it has now become the standard equation for hydraulic engineers.

Weisbach first proposed the relationship that we now know as the Darcy-Weisbach equation or the Darcy-Weisbach formula, for calculating friction loss in a pipe. The establishment of the friction factors was however still unresolved, and indeed was an issue that needed further work to develop a solution such as that produced by the Colebrook-White formula and the data presented in the Moody chart.

**Pipe Flow - Calculating Head Loss Example**

The Moody Chart finally provided a method of finding an accurate friction factor and this encouraged use of the Darcy-Weisbach equation, which quickly became the method of choice for hydraulic engineers. The introduction of the personnel computer from the 's onwards reduced the time required to calculate the friction factor and pipe head loss.

This itself has widened the use of the Darcy-Weisbach formula to the point that most other equations are no longer used. Before the advent of personal computers the Hazen-Williams formula was extremely popular with piping engineers because of its relatively simple calculation properties.

However the Hazen-Williams results rely upon the value of the friction factor, C hw, which is used in the formula, and the C value can vary significantly, from around 80 up to and higher, depending on the pipe material, pipe size and the fluid velocity. Also the Hazen-Williams equation only really gives good results when the fluid is Water and can produce large inaccuracies when this is not the case.

The empirical nature of the friction factor C hw means that the Hazen-Williams formula is not suitable for accurate prediction of head loss. The friction loss results are only valid for fluids with a kinematic viscosity of 1.

These C hw values provide some allowance for changes to the roughness of internal pipe surface, due to pitting of the pipe wall during long periods of use and the build up of other deposits. Sunday 12th April Pipe Friction Loss Calculations Flow of fluid through a pipe is resisted by viscous shear stresses within the fluid and the turbulence that occurs along the internal pipe wall, which is dependent on the roughness of the pipe material.

This resistance is termed pipe friction and is usually measured in feet or metres head of the fluid, which is why it is also refered to as the head loss due to pipe friction. Head Loss in a Pipe A large amount of research has been carried out over many years to establish various formulae that can calculate head loss in a pipe. Darcy Weisbach Formula The Darcy formula or the Darcy-Weisbach equation as it tends to be referred to, is now accepted as the most accurate pipe friction loss formula, and although more difficult to calculate and use than other friction loss formula, with the introduction of computers, it has now become the standard equation for hydraulic engineers.

The Moody Chart The Moody Chart finally provided a method of finding an accurate friction factor and this encouraged use of the Darcy-Weisbach equation, which quickly became the method of choice for hydraulic engineers. Hazen-Williams Formula Before the advent of personal computers the Hazen-Williams formula was extremely popular with piping engineers because of its relatively simple calculation properties. Common Friction Factor Values of C hw used for design purposes are: Asbestos Cement Brass tube Cast-Iron tube Concrete tube Copper tube Corrugated steel tube 60 Galvanized tubing Glass tube Lead piping Plastic pipe PVC pipe General smooth pipes Steel pipe Steel riveted pipes Tar coated cast iron tube Tin tubing Wood Stave These C hw values provide some allowance for changes to the roughness of internal pipe surface, due to pitting of the pipe wall during long periods of use and the build up of other deposits.

Pipe Flow Software. Pipe Flow Expert Software.This head loss calculator can compute any of the six elements of the Darcy Weisbach equation from pipe head loss, friction to fluid velocity. There is in depth information about the formula below the form. Instruction: Please complete any 5 of the fields below to discover the sixth component of the Darcy-Weisbach equation! How does this head loss calculator work? This is a useful tool for all those interested to calculate pipe head loss or any of the other five elements in the Darcy-Weisbach equation such as pipe friction, pipe characteristics or fluid velocity.

The form is very simple to use and comprises of 6 fields from which you need to complete 5 in order to retrieve the answer to the sixth variable.

Most fields have measurement units you can choose from for you convenience. The answer offered by the head loss calculator, offers both the English and metric units so you can be sure to quickly get an idea of the result. This is a formula used to analyze the factors that influence the flow of fluid through a pipe and the overall head loss. It takes account of the length and diameter of the pipe, the friction coefficient, fluid velocity and the acceleration caused by gravity.

The head loss due to pipe friction is defined as the resistance measured in feet or m head of the fluid. This is the standard equation used in hydraulic engineering and is mainly used for calculating pipe friction loss. Head Loss Calculator.

### Irrigation in the Pacific Northwest

The Darcy-Weisbach equation This is a formula used to analyze the factors that influence the flow of fluid through a pipe and the overall head loss.This Excel template calculates friction head loss or pressure drop for a pipe flow using Darcy Weisbach friction factor equation.

Parameters required for this template are allowable pipe diameter, pipe roughness, pipe length, pipe flow rate, fluid density, and fluid viscosity. Parameters calculated are pipe diameter, friction factor, cross-sectional area, average velocity, Reynolds number, transition region friction factor, frictional head loss, frictional pressure drop, and frictional pressure drop. Home Education.

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## Pipe Friction Loss Calculations

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You will not be able to recover this file! Yes No Close. SpreadsheetZone Creating DocumentThe 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:. Note that the Hazen-Williams formula is empirical and lacks a theoretical basis.

The head loss for ft pipe can be calculated as. 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. 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 Hazen-Williams equation is assumed to be relatively accurate for water flow in piping systems when. For hotter water with lower kinematic viscosity example 0. Since the Hazen-Williams method is only valid for water flow - the Darcy Weisbach method should be used for other liquids or gases. Add standard and customized parametric components - like flange beams, lumbers, piping, stairs and more - to your Sketchup model with the Engineering ToolBox - SketchUp Extension - enabled for use with the amazing, fun and free SketchUp Make and SketchUp Pro.

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Please read AddThis Privacy for more information. If you want to promote your products or services in the Engineering ToolBox - please use Google Adwords. 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. Tag Search en: hazen-williams equation. Privacy We don't collect information from our users.

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## How to Calculate Head Loss

Make Shortcut to Home Screen?Formula Home. Search Member. Wall drag and changes in height lead to pressure drops in pipe fluid flow. To calculate the pressure drop and flowrates in a section of uniform pipe running from Point A to Point B, enter the parameters below.

The pipe is assumed to be relatively straight no sharp bendssuch that changes in pressure are due mostly to elevation changes and wall friction. The default calculation is for a smooth horizontal pipe carrying water, with answers rounded to 3 significant figures. Pressure at A absolute :. Average fluid velocity in pipe, V :.

Pipe diameter, D :. Pipe length from A to B, L :. Elevation gain from A to B, D z :. Fluid density, r :. Fluid viscosity dynamicm :. Reynolds Number, R :. Friction Factor, f :. Pressure at B :. Changes to inviscidincompressible flow moving from Point A to Point B along a pipe are described by Bernoulli's equation. Bernoulli's equation states that the total head h along a streamline parameterized by x remains constant. No energy is lost in such a flow. For real viscous fluids, mechanical energy is converted into heat in the viscous boundary layer along the pipe walls and is lost from the flow.

Therefore one cannot use Bernoulli's principle of conserved head or energy to calculate flow parameters. Still, one can keep track of this lost head by introducing another term called viscous head into Bernoulli's equation to get. As the flow moves down the pipe, viscous head slowly accumulates taking available head away from the pressure, gravity, and velocity heads. Still, the total head h or energy remains constant. For pipe flow, we assume that the pipe diameter D stays constant.

By continuitywe then know that the fluid velocity V stays constant along the pipe. With D and V constant we can integrate the viscous head equation and solve for the pressure at Point B .

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