Crane Resistance Coefficient (K factor) for Pipe Elbows
Crane Resistance Coefficient (K factor) for Pipe Elbows
(OP)
In Crane TP410, on page A-29, there is a table for K values of 90 degree pipe bends as a function of r/d. I deal with many r/d values in between the increments in the table. For the purposes of putting K in spreadsheet formulas, is there a generally accepted curve fit for K as a function of r/d?
I realize I could make a lookup table and interpolate, but this would make the spreadsheet much more complicated. I am also aware that there is considerable variation in the data as seen in the graph on Crane page 2-13.
Garrett
I realize I could make a lookup table and interpolate, but this would make the spreadsheet much more complicated. I am also aware that there is considerable variation in the data as seen in the graph on Crane page 2-13.
Garrett





RE: Crane Resistance Coefficient (K factor) for Pipe Elbows
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You could fit a curve to his data and convert from Le to K
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RE: Crane Resistance Coefficient (K factor) for Pipe Elbows
Garrett
RE: Crane Resistance Coefficient (K factor) for Pipe Elbows
RE: Crane Resistance Coefficient (K factor) for Pipe Elbows
Since it's Crane's book, any "official" curve fit or underlying formula would come from them. They have a website (www.crane.com).
Patricia Lougheed
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RE: Crane Resistance Coefficient (K factor) for Pipe Elbows
Thank you
Leonard
RE: Crane Resistance Coefficient (K factor) for Pipe Elbows
Or perhaps you need a more accurate answer from your calcs than a conservative assumption would provide (?)
ValveEngineer
RE: Crane Resistance Coefficient (K factor) for Pipe Elbows
RE: Crane Resistance Coefficient (K factor) for Pipe Elbows
That is the type of function I was looking for. I wanted to avoid splitting the range in two, so I came up with:
K = a( atan(r/d) ) + b (r/d)-1 + c (r/d)0.5
where,
a = -19.1084132244392
b = 17.0419398956139
c = 17.487997553414
I did not find anything on the Crane web site http://www.cranevalve.com/.
The systems I am looking at have many bends, so I do not want to build in a conservative r/d as it will get multiplied many times. So far, the above formula is working ok.
Garrett
RE: Crane Resistance Coefficient (K factor) for Pipe Elbows
Your curve is better. However, note that you are not calculating the resistance coefficient K. You are calculating K/ft (or L/D, since K/ft = L/D) where ft is the fully turbulent flow friction factor. According to Crane, you need to multiply K/ft (or L/D) by ft to get K.
Good job!
RE: Crane Resistance Coefficient (K factor) for Pipe Elbows