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5.4.2 Calculating a nominal size
Determine the required Cv value by using the formula shown below and then the
corresponding nominal size based on the Cv value.
To calculate a Cv value (for selecting nominal size when valve-inlet pressure is 2.5 kPa up
to 200 kPa):
If P
>P
/2,
2
1
Q
Cv
=
P
I nlet pressure
1
：
R educed pressure
P
2
：
∆P ： Ｐ
1
C v value for a specific nominal size
Cv ：
Nominal Size
For selecting a nominal size in the case of inlet pressure is in a range 200 kPa up to 400 kPa,
refer to Table 1.
(
273
) t
G
+
Δ Δ Δ Δ
P
P (
P
)
+
1
2
. 2
94
(kPa ･ A )
(kPa ･ A )
(kPa)
2
－ Ｐ
15A
Cv value
1.5
6
If P
/2,
≤P
2
1
Cv
=
M ax. gas flow rate (Nm
Q ：
G as temperature
t ：
S pecific gravity (relative to air)
G ：
20A
25A
2.0
3.0
Q
(
273
) t
G
+
. 2
55
P
1
3
/h)
( ℃ )
■ E P D T - 1 7 9 c ■
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