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Pressure(head)Changes Caused By Pipe Size Change.

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Energy losses occur in pipe contractions, bends, enlargements, and valves and other pipe fittings. These losses can usually be neglected if the length of the pipeline is greater than 1500 times the pipe diameter. However, in short pipe- lines, because these losses may exceed the friction losses, minor losses must be considered.

Sudden Enlargements
The following equation is used for calculating the head loss, ft (m), across a sudden enlargement

hL=[1.1(V1-V2)1.92]/2g

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where
V1= velocity before enlargement, ft/s (m/s)

V2 =velocity after enlargement, ft/s (m/s)

g= 32.2 ft/s2 (9.81 m/s2)

It was derived by applying the Bernoulli equation and the momentum equation across an enlargement.

Gradual Enlargements

The equation for the head loss due to a gradual conical enlargement of a pipe takes the following

hL=[K(V1-V2)2]/2g

where K= loss coefficient, as given in engineering hand- books.

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Sudden Contraction
The following equation holds good for the head loss across a sudden contraction of a pipe

hL=[1/Cc-1)2V2/2g

where Cc= coefficient of contraction
and V= velocity in smaller diameter pipe, ft/s (m/s).
This equation gives best results when the head loss is greater than 1 ft (0.3 m).

Bend and Standard Fitting Losses
The head loss that occurs in pipe fittings such as valves and elbows and at bends is given by

hL=KV2/2g

To obtain losses in bends other than 90 degree the following formula may be used

k’=k?(deflection angle/90)

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Comments
  • Akande Olutayo Peter November 6, 2011 at 2:42 am

    it is okay

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