In order to to make the purchasing of valves simple sets of standard valve sizings are available. Finding the correct size may be achieved by use of valve sizing equations.
Calculation must be at the extremes of low and pressure drop and it is standard practice to oversize to the next size up.Following is a list of the more common coefficients
BS4740 Valve Sizing Coefficient Av
Q= Av. √ (ΔP / Ρ) Q = Flow ( usually max rate through valve (m3 / s)
ΔP = Corresponding Pressure drop acrtoss valve (N / m2)
Ρ = Density of liquid (Kg / m3
Av Valve Sizing Coefficient [m2
Due to its units the valve sizing coefficient is often called the Area Coefficient ΔP = Corresponding Pressure drop acrtoss valve (N / m2)
Ρ = Density of liquid (Kg / m3
Av Valve Sizing Coefficient [m2
American Valve Sizing Coefficient Cv
Q= Cv. √ (ΔP / SG) Q = Flow ( usually max rate through valve (US Gallons / min)
ΔP = Corresponding Pressure drop acrtoss valve (lbft / in2)
SG = Specific (realtive) gravity of the liquid relative to water at 20'C
This is the most common coefficient quoted although difficulty in working with the units means it is easier to work in anouther and convert to it ΔP = Corresponding Pressure drop acrtoss valve (lbft / in2)
SG = Specific (realtive) gravity of the liquid relative to water at 20'C
European Valve Sizing Coefficient Kv
Q= Kv. √ (ΔP / Ρrel) Q = Flow ( usually max rate through valve (m3 / Hr)
ΔP = Corresponding Pressure drop across valve (Kgf / cm2)
Ρrel = Relative Density of liquid
ΔP = Corresponding Pressure drop across valve (Kgf / cm2)
Ρrel = Relative Density of liquid