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PRESSURE LOSS FROM FITTINGS 2K METHOD

SUMMARY

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 2K method.

1. DEFINITIONS

D : Internal diameter of pipe (Inches)K : Resistance CoefficientK : Resistance Coefficient for fitting at Re = 1K : Resistance Coefficient for large fitting at Re = Re : Reynolds number

f

1

2. INTRODUCTION

The 2K method allows the user to characterise the pressure loss through

fittings in a pipe. As the name suggests, two K coefficients are used to

characterise the fitting, which when combined with the flow conditions

and pipe diameter may be used to calculate the K-value (excess head),

which is in turn used to calculate the head or pressure loss through the

fitting via the excess head method .

The 2K Method is more accurate than the Equivalent Length method, or

Excess Head (K-value) method as it applies an additional constant to

improve characterisation of the fitting pressure drop with variation of

the fluid Reynolds Number.

There is a further extension of the 2K method called the 3K method,

which adds a third K coefficient and is reported to be more accurate than

the 2K method, particularly for very large fittings.

For alternative methods of characterising pressure loss from fittings and

a discussion of which method is most appropriate please refer to the

summary of methods for estimating pressure loss from fittings .

3. CALCULATION OF K VALUE USING 2K VALUES

The 2K method is an extension of the Excess Head (K method) which

attempts to take into account variations in pressure drop through a

fitting caused by the size of the fitting and the fluid's Reynolds number

(particularly in lower Reynolds numbers).

3.1 Formula for Calculating Excess Head Coefficients or K Values from 2K Values

The formula for calculating the excess head from the 2K values, Reynolds

Number and pipe internal diameter is given below. Note that the pipe

internal diameter is in inches.

K = +K 1 +

From the K-value head loss through the fitting may be calculated.

h = K

ReK1

( D1)

L 2gV 2

Pipe BendsConcrete Pump Pipe and Bend PipeExperienced Pipe Bends Manufacturer

3.2 Values of K1 and K for Various Fitting Types

Below is a list K-values for common fittings.

1)800

Stub-in-tpye Branch 1000

Tee, Run Through

Screwed 200

Flanged/Welded 150 0.05

Stub-in-type Branch 100

Valves, Gate/Ball/Plug

Full Line Size, Beta = 1 300

Reduced Trim, Beta = 0.9 500 0.15

Reduced Trim, Beta = 0.8 1000 0.25

Valves

Globe, Standard 1500

Globe, Angle 1000

Diaphragm, dam type 1000

Butterfly 800 0.25

Check Valves

Lift 2000

Swing 1500

Tiliting-disk 1000

Fitting Type K1

4. EXAMPLE CALCULATION OF PRESSURE LOSS USING 2K-VALUES

This example demonstrates how to use the 2K 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.

4.1 System details

Pipe Size : DN100 (4")

Pipe Diameter : 102.3 mm

Pipe Length : 50 m

Fittings : 3 x 90 long radius (R/D = 1.5) elbows

Fluid Velocity : 3 m/s

Fluid Density : 1000 kg/m3

Reynolds Number : 306,900

Friction Factor : 0.018

Gravitational Acceleration : 9.81 m/s

4.2 Calculation

Using the table of fittings and 2K-values above we find that the excess

head or K-value for the 90 long radius elbow.

K = +K 1 +

K = + 0.2 1 +

K = 0.252

With this we can calculate the head loss for a single elbow.

h = K

ReK1

( D1)

306, 900800 (

102.3/25.41 )

L 2gV 2

32

h = 0.252

h = 0.116m

Using the equation for head loss in pipe, we can calculate the loss

through the straight piping :

h = f

h = 0.018

h = 4.03m

The total head loss for the system is the addition of the head loss from

the pipe and the fittings.

h = h + 3 h

h = 4.03 + 3 0.116

h = 4.378m

L 2 9.8132

L

P DL2gV 2

P 102.3/100050

2 9.8132

P

T P L

T

T

Article Created: October 17, 2012

ARTICLE TAGS

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.

However the 2K values must be converted to single K values for each

fitting type individually.

2K Method Elbow Fitting Flow Rate Fluid Flow Head

Pressure Drop Pressure Loss Valve

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