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VAPOR CONTROL VALVE HELP
Vapor control valve calculations are used with the permission of ISA,
the Instrumentation, Systems and Automation Society. The calculations are from
ANSI/ISA-75.01-1985 (R1995), Flow Equations for Sizing Control Valves. © Copyright
1995, ISA - The Instrumentation, Systems, and Automation Society. For information,
contact ISA Standards,
www.isa.org.
I used the vapor control valve sizing calculations in section 6 (pages 14 and 15).
These calculations will allow preliminary sizing but in general
the control valve vendor should take responsibility for sizing. Further
Cv and Xt values should be taken from the vendor's catalogue. The representative
values below can be used for preliminary sizing only.
REPRESENTATIVE VALUES OF VALVE CAPACITY FACTORS (Selected from
Table D-1 of ANSI/ISA-75.01-1985)
| Valve Type |
Trim Type |
Flow Direction |
Xt |
Fl |
Fd |
Cv/dČ |
| GLOBE Single Port |
Ported Plug |
Either |
0.75 |
0.9 |
1.0 |
9.5 |
| " |
Contoured Plug |
Open |
0.72 |
0.9 |
1.0 |
11 |
| " |
" |
Close |
0.55 |
0.8 |
1.0 |
11 |
| " |
Characterized Cage |
Open |
0.75 |
0.9 |
1.0 |
14 |
| " |
" |
Close |
0.70 |
0.85 |
1.0 |
16 |
| " |
Wing Guided |
Either |
0.75 |
0.9 |
1.0 |
11 |
| GLOBE Double Port |
Ported Plug |
Either |
0.75 |
0.9 |
0.7 |
12.5 |
| " |
Contoured Plug |
Either |
0.70 |
0.85 |
0.7 |
13 |
| " |
Wing Guided |
Either |
0.75 |
0.9 |
0.7 |
14 |
| GLOBE Rotary |
Eccentric Spherical Plug |
Open |
0.61 |
0.85 |
1.0 |
12 |
| " |
" |
Close |
0.40 |
0.68 |
1.0 |
13.5 |
| ANGLE |
Contoured Plug |
Open |
0.72 |
0.9 |
1.0 |
17 |
| " |
" |
Close |
0.65 |
0.8 |
1.0 |
20 |
| " |
Characterized Plug |
Open |
0.65 |
0.85 |
1.0 |
12 |
| " |
" |
Close |
0.60 |
0.8 |
1.0 |
12 |
| " |
Venturi |
Close |
0.20 |
0.5 |
1.0 |
22 |
| BALL |
Segmental |
Open |
0.25 |
0.6 |
1.0 |
25 |
| " |
Standard 80% Port |
Either |
0.15 |
0.55 |
1.0 |
30 |
| BUTTERFLY |
60° Aligned |
Either |
0.38 |
0.68 |
0.7 |
17.5 |
| " |
Fluted Vane |
Either |
0.41 |
0.7 |
0.7 |
25 |
| " |
90° Offset Seat |
Either |
0.35 |
0.60 |
0.7 |
29 |
Notes:
Flow direction tends to open or close the valve, i.e. push
the closure member away from or towards the seat.
In general an Fd value of 1.0 can be used for valves with a single
flow passage. An Fd value of 0.7 can be used for valves with two
flow passages, such as double-ported valves and butterfly valves.
In this table d may be taken as the nominal valve size, in inches.
References:
"ANSI/ISA-75.01-1985 (R1995), Flow Equations for Sizing Control Valves," ISA - The
Instrumentation, Systems, and Automation Society (1995).
Copyrighted 2001, 2003
Last updated 04May03
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