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PA83 (Chemical)
22 Jan 09 13:04
Can anyone help....

How do convert cv to cg ?

I know that cv = constant x kg

Cv [US Gallons/min/psi] = 0,03445 KG [m³/h/bar] (related to natural gas, density = 0,83 kg/m³) ( by manufacture)


Note: But the service that valve is for H2. Is valid the same relation or the constant is different ??.

Thanks.  
BigInch (Petroleum)
22 Jan 09 20:22
Cv is GPM/(psi^0.5)
Divide by the specific gravity of your gas to adjust for gases other than air.

**********************
"Pumping accounts for 20% of the world's energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies) http://virtualpipeline.spaces.live.com/

PA83 (Chemical)
23 Jan 09 6:45
The gass is H2 (200 bara e 35ºC)
(densidade = 14,55 kg/m3 ;  Z=1,084; cp/cv =1,45)

cv ou kv ?? please is urgent

considering :
Cv [US Gallons/min/psi] = 0,03445 KG [m³/h/bar] (related to natural gas, density = 0,83 kg/m³) ( by manufacture)

 
psafety (Specifier/Regulator)
23 Jan 09 11:45
Cg=Cv*C1

C1=39.76*(Xt)^0.5
 
PA83 (Chemical)
23 Jan 09 11:49
Xt ???

 
psafety (Specifier/Regulator)
23 Jan 09 12:13

"Xt ???"

I should have clairified.  This formula is from Fisher Control Valve. Xt is another coefficient they assumed we needed.
PA83 (Chemical)
23 Jan 09 13:08
"Xt is another coefficient they assumed we needed..."  


How??

 
CJKruger (Petroleum)
23 Jan 09 23:08
psafety, do you have the reference for C1 = 39.76*(Xt)^0.5, and do you know if it is an exact relationship or approximate ?

 
TD2K (Chemical)
24 Jan 09 1:11
PA83, are you talking about converting between Cv and Cg where Cg is the Fisher valve coefficient for gases?

As said, Cg = C1 * Cv.

I'll typically look up the C1 as it varies depending on the type of control valve, conventional style globe valves are usually around 30 but it can be quite a bit lower

If you can clarify what you want it would help, the hydrogen conditions by itself doesn't have anything to do with the Cv or Cg.
psafety (Specifier/Regulator)
26 Jan 09 12:02
CJKruger,

I clipped this from the bottom of one of Fisher's coefficient's pages.  It is in each of their control valve pdf files.

=========================================================
Conversion of Sizing Coefficients
Following are conversions for use with other common sizing equations.
Kv = (0.865)Cv
C1= 39.76(XT)^0.5
Cg = CvC1
Km = FL^2
Cs = 1/20(Cg). Cs is only applicable for inlet pressures up to 70 bar(a)

==========================================================

psafety
 
BigInch (Petroleum)
26 Jan 09 12:17
Let's give him the whole book,
http://www.documentation.emersonprocess.com/groups/public/documents/book/cvh99.pdf

**********************
"Pumping accounts for 20% of the world's energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies) http://virtualpipeline.spaces.live.com/

JLSeagull (Electrical)
26 Jan 09 12:47
Fisher published tables with the obsolete gas sizing coefficient long before ISA and IEC established the current control valve sizing formuli.  Consider avoiding obsolete vendor constants such as Cg since these International organizations publish concensus standards using Cv or Kv.

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