Losses in Pipe Fittings and Valves

In addition to losses due to friction in a pipeline system, there are also losses associated with flow through valves and fittings. These losses are called minor losses, but these losses must be considered if the piping system has a lot of such fittings. These losses are treated as equivalent frictional losses.

The minor loss may be treated either as a pressure drop Δp = -KρV2/2 or as a head loss Δh = -KV2/(2g).

The value of the loss coefficient ‘K’ is obtained through experimental data. Generally for valves and fittings, manufacturers provide loss coefficient ‘K’ value.

It may also be calculated from the equivalent length concept: K = fLe/D,

where Le is the equivalent pipe length that has the same frictional loss,
f is the Moody friction factor (Darcy-Weisbach friction factor) and
D is inner diameter of the pipe.

Below table gives loss coefficient (K) and Le/D values for some common fittings.

Loss coefficient ‘K’ values for common fitting types

S.No
Type of fitting
 Loss coefficient (K)
Le/D
145-degree elbow.0.3517
290-degree bend.0.7535
3Diaphram valve, open2.30115
4Diaphram valve, half open4.30215
5Diaphram valve, 1/2 open21.001050
6Gate valve, open0.179
7Gate valve, half open4.50225
8Globe valve, wide open6.40320
9Globe valve, half open9.50475
10Tee junction1.0050
11Union and coupling0.042
12Water meter7.00350

For sudden enlargements in the pipeline from smaller diameter (D1) to a larger diameter (D2), the value of loss coefficient ‘K’ can be obtained from the formula:

loss coefficient for sudden enlargement in pipe

For sudden contractions in the pipeline from a larger diameter (D2) to a smaller diameter  (D1),  the value of the loss coefficient ‘K’ can be obtained from the formula:

Loss coefficient for sudden contraction

The above equations should serve as guidelines. Corrections should be made for enlargements and contractions that are gradual. Use values of loss coefficient ‘K’ for fittings whenever provided by the manufacturer.

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All Comments

  • That is very nice

    sabry haiba hegazy Jan 18, 2017 6:54 pm Reply

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