1. No experience in globe valves of size > 8" (post no 10). Web indicates availability of 12" - 14" - 16" globe control valves (e.g. Valtek), but their Cvs cannot be found. C R Branan's "Pocket Guide to Chemical engineering" (Gulf 1999), Control valve design - Table 1-6 - liquid flow, indicates Cv=12*d2
as a rough estimate in the absence of specific data, where d=valve diameter (inches). Nevertheless no limit of d size is mentioned. The coefficient is 32 (average) for butterfly valves, instead of 12 for globe valves.Note:
Suppose you install a 12" globe, understood Cv = 12*122
; ΔP due to flow restriction (16"/12") and enlargement is not included. Coefficient is 11.5 for single-seat top guided globe.
2. Not having experience on butterfly control valves in liquid service, they are used so and should be also considered. Probably pricing will be the decisive factor. An expert could clarify it now, apart from technical matters. I do not know whether a butterfly valve of lower size (e.g. 14" or 12") would be recommended.
"Behaviour" of two manual butterfy valves was once investigated on a branched gas flow (1980); control was satisfactory. No problem was heard after the implementation.A book from Instrument Society of America was used to estimate ΔP of butterfy valve in function of its opening angle.
Edited by kkala, 24 February 2013 - 06:56 AM.