Equivalent Length for HDPE Fittings
Equivalent Length for HDPE Fittings
(OP)
Does anyone have a source where I can get a table that provides the resistance coefficients (K) for HDPE pipe fittings?
Thanks
Thanks
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Equivalent Length for HDPE Fittings
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RE: Equivalent Length for HDPE Fittings
David Simpson, PE
MuleShoe Engineering
In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist
RE: Equivalent Length for HDPE Fittings
http://www.plasticpipe.org/pdf/chapter06.pdf
If that does not work, try ISCO.
http://www.isco-pipe.com/products-and-services/hdp...
RE: Equivalent Length for HDPE Fittings
The head loss through a fitting is caused mainly by changes in velocity and flow direction of the fluid. The roughness of the internal surface of the fitting has very little influence in normal commercial fittings and valves - regardless of whether they are fabricated from metal or plastic. This means that resistance coefficients (K values) for steel fittings can be safely used for plastic fittings of the same geometry. However, equivalent lengths given in terms of steel pipe will generally be on the low side when used for plastic fittings. This is because the head loss through the fitting is being expressed in terms of something that is not directly related to the fitting (ie. in terms of the attached pipe) and the equivalent length is not purely a function of the fitting.
This topic comes up so regularly that I wrote an article expanding on it (and related matters). If you would like more detail than I have given here please read the article.
bimr has linked to a useful document published by PPI, but I have 2 comments on their data in Table 2-2 on page 174. They have unfortunately used the symbol K' to represent the Equivalent Length. It would be very easy to read these values as resistance coefficients because that is what K usually represents - and this would lead to huge errors. My second comment is that their values for molded elbows seem rather high. I have converted resistance coefficients calculated using the Darby 3-K method for a variety of fittings to equivalent lengths in a range of materials in another article. My equivalent length values are quite a bit lower than the PPI values.
Katmar Software - AioFlo Pipe Hydraulics
http://katmarsoftware.com
"An undefined problem has an infinite number of solutions"
RE: Equivalent Length for HDPE Fittings
RE: Equivalent Length for HDPE Fittings
"Fluids flowing through a fitting or valve will experience a friction loss that can be directly expressed using a resistance coefficient, K’, which represents the loss in terms of an equivalent length of pipe of the same diameter. (20) As shown in the discussion that follows, this allows the loss through a fitting to be conveniently added into the system flow calculations. Table 2-2 presents K’ factors for various fittings.
Where a pipeline contains a large number of fittings in close proximity to each other, this simplified method of predicting flow loss may not be adequate due to the cumulative systems effect. Where this is a design consideration, the designer should consider an additional frictional loss allowance, or a more thorough treatment of the fluid mechanics.
The equivalent length of pipe to be used to estimate the friction loss due to fittings may be obtained by Eq. 2-9 where LEFF = Effective Pipeline length, ft; D is pipe bore diameter in ft.; and K’ is obtained from Table 2-2. (2-9) LEFF = K’D Fluids flowing through a fitting or valve will experience a friction loss that can be directly expressed using a resistance coefficient, K’, for the particular fitting.
(2-9) LEFF = K’D "
RE: Equivalent Length for HDPE Fittings
An advantage of working this way (i.e with the LEFF/D ratio) is that it allows us to work in whatever length units we like. If you express your pipe bore in ft you will get the equivalent length in ft, while if I express my bore in mm my equivalent length will be in mm and be just as valid as your value. It also allows us to use a single equivalent length (ratio) for all sizes of a particular fitting.
Katmar Software - AioFlo Pipe Hydraulics
http://katmarsoftware.com
"An undefined problem has an infinite number of solutions"