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slickstyles5 (Aerospace) (OP)
14 Oct 10 16:59

I am currently calculating pressure losses through my oil circuit and would like to know if anyone has typical absolute roughness values to use for hydraulic hoses? I am using Aeroquip hoses -16 (1 inch) size.

I read somewhere that 0.0001 feet is a conservative number to use?

Does anyone have technical info on this?


BigInch (Petroleum)
14 Oct 10 19:55
Think you've got too many zeros in there.  
Take one out.

"I am sure it can be done. I've seen it on the internet."  BigInch's favorite client.

"Being GREEN isn't easy." Kermitfrog

Helpful Member!  katmar (Chemical)
15 Oct 10 9:09
This sort of data has always been hard to find.  If you use the Gates flow calculator at
and then use your own pressure drop calculator to find their roughness value by trial and error you will see that they use your value of 0.0001" (or 0.0305 mm).

Generally the questions that come up about the roughness of "hose" are difficult to answer because the term "hose" can cover such a wide range of types, but if you are using a quality hydraulic hose then your value looks OK to me.

Katmar Software
Engineering & Risk Analysis Software

katmar (Chemical)
15 Oct 10 9:14
Sorry, I typed 0.0001" instead of 0.0001' in the post above. It should be 0.0001 ft - the value of 0.0305 mm was the correct conversion and the " was just my typo.

Katmar Software
Engineering & Risk Analysis Software

slickstyles5 (Aerospace) (OP)
15 Oct 10 10:21

Yes I had just found the Gates calculator this morning and it pretty much gives me the same results.

I will keep that for future reference!

Thank you so much!
Helpful Member!  ione (Mechanical)
15 Oct 10 10:48
I got approx 0.000045' (0.0137 mm) using Katmar's approach
katmar (Chemical)
15 Oct 10 12:08
ione, that is a bit distressing that you got a different answer!  Were you using the Gates calculator?  I tried 4 different combinations of flow and pipe size and I got virtually exactly 0.0001 ft every time.  I took the oil as SG=0.8 and viscosity = 3 cP.  Then I took 200 ft of pipe using from 5 USgpm in a 0.5 inch pipe up to 200 USgpm in a 3 inch pipe.  Using trial and error in my Darcy-Weisbach based software to match the Gates overall pressure drop I found the roughness to be 0.0001 ft every time.

Katmar Software
Engineering & Risk Analysis Software

ione (Mechanical)
15 Oct 10 12:44
My apologies, I entered wrong values for absolute viscosity in the examples I've run in my pressure drop calculator. What I got now is  0.000083' (0.0254 mm). I think that  the difference it's now just a matter of approximation.
katmar (Chemical)
15 Oct 10 12:51
Thanks ione, we are close enough now that if we were working with pencils off a Moody chart we would be getting the same answer. Sometimes spreadsheets make us believe we are achieving higher levels of accuracy than are real.

Katmar Software
Engineering & Risk Analysis Software

slickstyles5 (Aerospace) (OP)
15 Oct 10 17:04
I couldn't agree with you more! There's a fine line when it comes to these approximations, but I feel confident in my results at this point.

ps. I use Excel sheets to do my pressure drop calculations!!  

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