Equivalent pipe length method issues

[LeadByExample]

Hi all,

This topic may have been answered somewhere else, if so the search doesn't seem to retrieve it.

Anyway, here is my quandary (I have spent many hours on line to find this without prevail).

I am looking for information regarding the equivalent pipe length method for plastic in mm (i.e. 15mm, 22mm, etc. NOT inches) and for all types of plastic fittings (elbows, tees, etc.).

However the most elusive information of the equivalent pipe length method appears to be the unequal fittings (reductions and expansions) and how it is applied.

I have found a little bit of information about unequal fittings, unfortunately invariably it is in inches and it is not explained how it is applied, either. Let me give some simple examples (figures not representative).

Lets assume a straight pipe of one meter with a diameter 22mm connecting to a one meter straight pipe with a diameter of 10mm with a reduction fitting. Now if we assume the fitting adds one meter of pipe.

However, which diameter? Or in other words, do you have 'two' meters of 22mm and one 10mm or one meter of 22mm and 'two' meters of 10mm?

This of course also applies to unequal Tee fittings. For example an unequal Tee fitting connects 22mm through the branch to another 22mm and through the run to a 15mm (all one meter long). Now assume one meter is added through the 22-22mm and 1.5 meter for the 22-15mm run.

Do I assume 3.5 meters of 22mm before the Tee fitting and one meter for the branched 22mm and one meter of 15mm. Or is it one meter of 22 before the Tee fitting 'two' meters for the branched 22mm and 'two and a half' for the 15mm pipe?

Any helpful information, would be greatly appreciated.

 

[Onetap]

You'd apply the EL factor for a tee and add another factor for a reducer or enlarger, which is based on the proportion of the areas. You generally wouldn't have a reducer or enlarger on its own, without a tee causing a corresponding change in the flow rate.

The most detailed description I've seen is in the CIBSE guide, 'Flow of fluids in pipes and ducts', but it uses lots of Greek letters and tends towards being incomprehensible. You could probably get a copy in a reference library.

It doesn't need to be an exact figure, you usually can't choose an excat pipe or pump size that suits your requirement, but have to elect one the next size up. Everyone sticks on a margin, since oversizing is acceptable, but undersizing can be financially embarrassing. Any errors in the reducer/enlarger are likely to be small compared to the rest of the circuit. The pipe manufacturers' tables are adequate for most things.

 

[LeadByExample]

Onetap, thanks for your reply, your answer sheds a little light, however there are still some questions.

Where are these values for PEX pipe in non imperial sizes (i.e. in mm)? And how are the EL applied (see original post), before or after?

I understand it doesn't have to be an exact figure, however I would like my margin to be based on relatively accurate values.

I also understand a reduction by itself is unusual, it was just an example to show there can be a significant difference in what you take as your base diameter (two meters of 22mm or 10mm).