bias in Crane 410 fitting losses
bias in Crane 410 fitting losses
(OP)
Hi all, I'm new to this site. I'm trying to find out if the resistance coefficients for valve and fittings in the Crane 410 paper are biased high or low relative to "reality." I have always figured that they are biased high to ensure that the calculation overestimates the pressure drops, but is this really true? I'm interested in doing a maximum flow calc (to determine if the system losses will prevent pump runout without throttling valves).
Thanks in advance
Gregg
Thanks in advance
Gregg





RE: bias in Crane 410 fitting losses
Good luck,
Latexman
RE: bias in Crane 410 fitting losses
thread378-173164: Crane 410 fittings
RE: bias in Crane 410 fitting losses
Thanks
Gregg
RE: bias in Crane 410 fitting losses
Some things have changed in the meantime, e.g. most fittings have thinner walls and are probably smaller than is 'traditional', thanks to advances in casting and analysis, and economic pressures to reduce material waste and safety factors.
I.e., pressure drops may be a little larger than Crane predicts.
Mike Halloran
Pembroke Pines, FL, USA
RE: bias in Crane 410 fitting losses
From the windmills of my mind I recall that the numbers for comparable valves form all the major players were within all in very small range. This comparison was deemed essential so that a figure/figure component could be interchanged without any extra thought.
RE: bias in Crane 410 fitting losses
RE: bias in Crane 410 fitting losses
RE: bias in Crane 410 fitting losses
I had the same question. When you're doing a pipeline project, the uncertainty is typically around 10-20% so does it matter if a gate valve is 8 ft or 18 ft?
I think the real application is in plants where people are sizing pumps/compressors with much smaller safety factors than folks use outside the plant fence.
David
RE: bias in Crane 410 fitting losses
The process requires a flow of "X" - the process engineer adds a couple of percent margin just in case the calcs are a bit out, the pipeling people add their margin, the "boss" want a bit of marigin so he can get an increased output further down the track, the pump guy adds a bit of margin to the pump - just in case etc etc.
So does the difference between an equivalent head loss of 10 or 12ft loss across a valve / bend / T really matter.
RE: bias in Crane 410 fitting losses
The original post asked if the Crane coefficients were intentionally biased "high" to ensure that design calculations overpredict the losses, since this is usually the conservative approach. Over the years, several people have told me that this is the case. Based on the responses above, I no longer believe that to be true - instead, the Crane values are probably pretty good estimates. It is therefore up to the user to decide how much conservatism to apply in the calculation.
Thanks to the people who responded.
RE: bias in Crane 410 fitting losses
http://virtualpipeline.spaces.msn.com