Control valve sizing: Xt value

[im_danl]

Hello everyone!

I'm trying to do the design of a pipe system, and right now I'm struggling with the sizing of the control valve that my system it's going to use. (I've never done this before)

I've been trying to follow the sizing formulas used in the ISA 75.01 (Flow equations for Sizing Control Valves) and also getting some guidance from the Valve Sizing Handbooks from Baker Hughes and Emerson, but in general, the formulas are pretty much the same in all of those.

The problem that I'm facing right now it's a specific value called 'x_T' that denotes the 'terminal pressure drop ratio', basically the point of the pressure drop ratio at which the flow starts to be considered critical.

This value it's supposed to be supplied by the control valve's manufacturers in their product sheets or something like that, but I've searching through all the resource center from Baker Hughes and Emerson webpages and couldn't find a single x_T value, at least not for Globe Valves. Where do you guys find those? Is it a detailed value that you'll only get after doing a quotation or something like that? If so, how I'm supposed to size my valve before asking for a quotation?

That's pretty much what I'm struggling for with this formula, because every other variable it's related to my fluid properties and my process conditions, but that x_T it's a external value.

Thank you in advance for your help, Daniel.

 

[goutam_freelance]

The values of XT should be determined by air test by the manufacturer of CV. However, typical values are given in Table 2 of ISA 75.01.

One has to contact the manufacturer for their specific data.

 

[georgeverghese]

There are values for Xc ( which sound the same as the Xt you are looking for, given the definition of Xc ) in the chapter on Instrumentation-subsection on control valves, in the GPSA for globe, butterfly and ball type valves

 

[goutam_freelance]

Table 2 of ISA 75.01.

As per later edition(2012) of ISA75.01 the table No is Table D.2

 

[GBTorpenhow]

For Fisher valves their "Catalog 12" is pretty exhaustive, some vendors aren't as good at providing these in generalized cuts and you have to engage them for a quote/data sheet with a application/sales engineer.

 

[im_danl]

I understand, so basically in order to get specific values I'll probably have to make some contact with the manufacturers. I guess I'll stick with Table D.2 meanwhile, since I'm doing kind of a preliminary sizing.

Thank you for your answers!