Yoshitake GPK-2001, Руководство по установке и эксплуатации

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■ EPDT-098a ■
-10-
4.5 Nominal size selection calculation formula
An appropriate nominal size can be calculated by obtaining Cv value for the operating
conditions in question, as shown below.
•
Calculation formula for Cv value
● Rated Cv value table (External sensing)
Nominal size 15A 20A 25A 32A 40A 50A 65A 80A 100A
Cv value 5.0 7.2 10.9 14.3 18.8 32 54 70 108
* Please contact us on Cv value of internal sensing method.
[Example]
The flow rate of the pressure reducing valve is calculated under the following conditions:
Nominal size 15A, saturated steam, Inlet pressure of 0.6 MPa = 0.7 [MPa A], Reduced
pressure of 0.4 MPa = 0.5 [MPa A], you can find that Cv value of 15A is 5.0 from the chart.
The following formula is established.
* Use a safety factor of 80 to 90% for nominal size selection in view of friction losses in
piping.
W: Max. steam flow rate [kg/h]
P
1
: Inlet pressure [MPa ･ A]
P
2
: Reduced pressure [MPa ･ A]
ΔP: P
1
- P
2
[MPa]
k: 1+0.0013× {superheated steam
temp.[°C] - saturated
steam temp. [
°C]}
2
P
P
1
2

) P P(P 138
Wk
Cv
2 1
+ 
=
2
P
P
1
2

1
120P
Wk
Cv
=
2
) 7 . 0 (
) 5 . 0 (
1
2
=
 =
P
P
k
P P P Cv
W
) ( 138
2 1
+ 
=
1
) 5 . 0 7 . 0 ( 2 . 0 0 . 5 138
+   
=
h k g / 338
=