TECHNICAL DATA 5
Control Valves Sizing
How to calculate Kv
Flow coefficient Kv in the quantity of water in m3/hr which goes through the valve, when fully open, by pressure
drop of 1 kg/cm
2
Data:
.
quantity of fluid that the valve must supply to the systems (m
3
/hr)
.
valve inlet pressure (bar)
.
Design the pressure drop through the valve
.
Calculate the Kv necessary for the valves
Water
Kv = Q * 10 / dp
1/2
Q = flow (m
3
/hr)
dp = pressure drop (kPa)
Saturated steam
Kv = QC * 10
22.7 ( p2 * dp )
1/2
Q = flow (kg/hr)
C
= 1 + 0.0013 ( t-t
s
)
t = steam temperature in working conditions
t
s
= saturated steam temperature at pressure p2
p2 = outlet pressure (kPa)
dp = pressure drop (kPa)
Choose the valve with the Kv closest to the calculate one.
Water System
Two-way valve
For this application, pressure drop through the valve must be high in order to have a good control flow characteris-
tic and a properly working system.
1 Pressure drop of valves must be 30 to 50% of pressure drop of systems.
2. Pressure drop of valves must be equal to, or higher than pressure drop of battery or heat exchanger under
control, more precisely:
Temperature drop of heat exchanger
Design pressure drop of valves
30
o
C
equal to pressure drop of heat exchanger
20
o
C
twice to pressure drop of heat exchanger
10
o
C
three times as pressure drop of heat exchanger
The specification above are normal and conform to generally
acceptable industry standard. Cyrus is not responsible for
damages resulting from misapplication or misuse of its products.
