L/D = Length/Diameter ratio (equivalent pipe length)So if you have a 1" gate valve with and L/D = 8that 1" gate valve is equal to having 8" of straight 1" pipe when doing pressure drop calculations and other flow calcs. I have a page out of a late 60s early 70s Crane TP 410 that lists the L/D values for various types of valves.However by 1976 these values changed. But I've never seen any justification or explanation of the changes. Does anybody know the history of these changes?Here are some examples of changes:Wedge gate:60s version = 1376 Version = 8Swing Check:60s version = 13576 Version = 508" and larger Butterfly:60s version = 4076 Version = 8" ~ 45, 10-14" ~ 35, 16-24" ~ 25 The Crange Technical Paper 410 "Flow of Fluids" is based on testing done by the Crane valve company on their valves.They may well have decided the old values were overly conservative, hence the decrease in equivalent diameters. It may be that better computing and measuring equipment allowed them to refine their results.

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