Bronkhorst Mass Flow - Manual (Page 24)

BRONKHORST HIGH-TECH B.V.
4.7 K
v
-value calculation
This calculation method can be used to determine the K
v
-value of the main orifice of a control valve.
4.7.1 For gases
Determine desired ∆p across valve.
∆ p must be at least 20% of supply pressure, or in closed loop systems, of total pressure difference in loop.
If ∆p is 20-50% of supply pressure, use formula:
K
T
p p v
vn n =
⋅
⋅
Φ
∆ 514
2
ρ
under critical
If ∆P is 50-100% of supply pressure, use formula:
K
p
T
v
vn
n
=
⋅
⋅
Φ
257
1
ρ overcritical
Units:
Φ
vn
= flow [m
n
3 /h]
p
1
= supply pressure [bara]
p
2
= downstream pressure [bara]
∆ p = pressure difference (p
1
- p
2
) [bard]
T = temperature [K]
ρ
n
= density [kg/m
n
3 ]
The orifice diameter can be determined by: d= 7.6 K
v
[mm]
4.7.2 For liquids
K
p
v v
=
⋅
Φ
∆
ρ
1000
Units:
Φ
v
= volume flow [m 3 /h]
ρ = density at 20°C and 1 atm [kg/m 3 ]
∆ p = delta p [bard]
The orifice bore diameter can be determined by:
d K
v
= 7.6 [mm]
*
page 24 9.17.001