Equivalent Length (Piping) 1

[StructIntern]

I am not a Mechanical guy. However, I was wondering if someone can explain the concept of equivalent length in piping for an outsider. Thanks.

 

[pennpiper]

StructIntern,
You did not give us anything as background to go on so I am just taking a shot in the dark.

a. Straight pipe will cause a flowing fluid or gas to have a pressure drop per lineal measure (feet or meter) due to friction.

b. A fitting such as an elbow (of the same material, size and wall schedule as the pipe) will have a pressure drop greater than the pipe due to the shape. This pressure drop is expressed in "Equivalent Lengths of pipe"

c. A valve will also have a pressure drop greater than the pipe due to the configuration of the valve internals. This pressure drop is also expressed in "Equivalent Lengths of pipe"

d. Google "Pressure drop in piping systems" and spend some time studying what you find there.

 

[vpl]

To add on to pennpiper's post:

The reason to express the pressure drop in "equivalent feet of pipe" is so that the piping system designer can ensure that all components will work together and you can get the fluid moved from Point A to Point B.



Patricia Lougheed

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[ione]

Give a read to this

http://www.cheresources.com/eqlength.shtml

and also to this thread (particular care to respectful member Katmar’s comments).

http://www.eng-tips.com/viewthread.cfm?qid=173164

 

[MiketheEngineer]

Even this old strucutral remembers that - BECAUSE we had this old codger of a Prof that BEAT it into our thin shelled brains way back when!!

 

[Cniper]

Further to your other replies, an Engineer can estimate in a long run of pipeline (ie distribution networks) by adding 10% to the measured length, due to the long lengths and minimal fittings. However for pipework which in small lengths could have numerous fittings and therefore a range of 50 - 100% additions should be added. The above will get an estimated effectiove length (EEL), to get a True Effective Length (TEL) one would then go to relevant tables for K and zeta values for each type of fitting which can be time consuming if doing manually. CIBSE Volume C has a table and diagrams for fittings etc, it depends how accurate you want to be to that end manufacturers will have the more accurate data.
in addition careful thought must be applied as tables etc tend to oversize pipework, useage must be researched as infrequenbt use can lead to Legionella as hot and cold water systems are the main causes as air conditioning systems have this issue controlled due to maintenance regimes.

 

[chicopee]

What I don't see from the above responders are the REASONS to determine the piping total length(that includes equivalent length).
I'll leave those reasons for the OP to determine.

 

[BigInch]

Reason ...
Equivalent lengths makes it easier to determine system pressure changes in those cases where, for instance, viscosity changes as temperatures rise. You could simply redo one calculation using an equivalent length of the system, rather than determine a new viscosity, recalculate pressure drops in each flow element and sum all the individual drops.

 

[btrueblood]

Or you can be contrary and model everything as an assumed 12" pipe diameter, and compute an "equivalent orfice size". Really messes with piping designer's heads...

 

[btrueblood]

doh - 12" pipe length, not diameter. I always blow the punchline.

 

[BigInch]

Kind of messing with your own head there, no?

 

[btrueblood]

Always, Big.