Sizing - Pietro Fiorentini

Cg and Kg valve coefficient
LIQUIDS
Glossary
A. Subcritical conditions
(when ΔP < F 2 ΔPc)
Volume flow rate
Cv ΔP
Qf =
1.17 Gf
Weight flow rate
W = 855 Cv GfΔP
Note:
For values of ΔP ≥ ΔPk the
valve works under cavitation
conditions.
Deltaflux
Cv = valve flow rate coefficient: US gpm of water with
∆P = 1 psi
ΔP = valve pressure drop P1-P2: bar
ΔPc = maximum dimensioning differential pressure: bar
ΔPk = cavitation differential pressure: bar
Δt = overheating temperature delta t1 - ts: °C
F = valve recovery factor: non dimensional
G = gas relative density (air=1): non dimensional
Gf = liquid relative density at operating temperature
(water at 15°C=1)
Kc = valve incipient cavitation factor: non dimensional
Xg = weight percentage of gas or vapor in the mixture at
upstream pressure: %
P1 = valve upstream pressure: bar abs
P2 = valve downstream pressure: bar abs
Pc
Pk
Pv
T
t1
ts
Q
Qf
W
W1
W2
Vf
Vg1
Vg2
B. Critical conditions
(when ΔP ≥ F 2 ΔPc)
Volume flow rate
F Cv ΔPc
Qf =
1.17 Gf
Weight flow rate
W = 855 F Cv Gf Δ Pc
ΔPc = P1-Pc
Pc = Pv (0,96-0,28
Pv
Pk
ΔPk = Kc (P1-Pv)
= vena contracta critical pressure: bar abs
= thermodynamic critical point pressure: bar abs
= vapor pressure at operating temperature: bar abs
= upstream gas absolute temperature (273+°C): °K
= overheated steam upstream temperature: °C
= saturated steam temperature at upstream pressure: °C
= volume flow rate at 15 °C and 1.013 bar abs: Sm3/h
= volume flow rate: m3/h
= weight flow rate: Kg/h
= upstream mixture density: kg/m3
= downstream mixture density: kg/m3
= specific volume of liquid: m3/kg
= specific volume of gas or vapor at upstream pressure: m3/kg
= specific volume of gas or vapor at downstream pressure: m3/kg
)