5.5 Nominal size selection calculation formula
The appropriate nominal size can be calculated by obtaining the Cv value for the operating conditions
in question, as shown below.
• Cv value calculation formula
P
>
1
P
2
2
Cv
P
<
1
P
2
2
Cv =
• Rated Cv value table (When Cv correction coefficient is C=1)
Nominal size
Rated Cv value
※ C orrection of rated Cv value
If the inlet pressure exceeds 0.7 MPa, and the pressure reducing ratio exceeds 10:1,
find the appropriate correction coefficient C using chart below, and multiply the rated
Cv value, and obtain the corrected Cv value.
1.0
0.9
(B)
0.8
0.7
0
0.02
0.04
P :Reduced pressure MPa
2
6. Installation
6.1 Example of piping
Pressure
gauge
Wk
=
∆
+
138
P(P
P
)
1
2
Wk
120P
1
15A
20A
25A
1
2.3
4
(A)
0.06
0.08
0.10
Drain separator
DS-1
Strainer
Stop
valve
Stop
valve
Stop
Sight glass
valve
1810
Blow
Trap
W: Max. steam flow rate [kg/h]
P
: Inlet pressure [MPa・A]
1
P
: Reduced pressure [MPa・A]
2
ΔP: P
−P
1
k: 1+0.0013 × {super-heated steam
32A
40A
50A
6.5
9
16
[Ex.]
Take a pressure reducing valve whose inlet
pressure is 0.8 MPa, reduced pressure is 0.05
MPa. Find the inlet and reduced pressure
intersection point (A) at the left chart, then
draw a horizontal line in the leftward
direction to point (B) which indicates a
correction coefficient of 0.85. For a nominal
size of 25A, the corrected Cv value would be
calculated as follows:
4(rated Cv value) × 0.85(correction
coefficient) = 3.4
3 port
solenoid valve
By-pass
stop valve
Reducer
Stop
GP-1200
valve
Pressure reducing valve
‑6‑
[MPa]
2
temp.[℃]−saturated steam
temp.[℃]}
65A
80A
100A
25
36
64
Air pressure
Non-return
valve
Standard unit
Relief
pipe
Pressure
gauge
Safety
valve
■EPDT-101■