Boiler house Level controls
2
3. Selection of the valve K v The DN40 valve body size is available with various seat sizes giving a choice of K v values. Use the graph to select a suitable K v as follows: a) The feedwater flowrate is the actual maximum steam generation rate of the boiler plus any blowdown rate where this is significant. In practice the use of the 'from and at' boiler rating will give a small safety margin. In the example this is 15 000 kg/h. b) The pressure drop across the valve is the feedpump pressure at the maximum flowrate, minus the boiler pressure, minus any valve and pipework losses. In the example the available pressure drop is 1.5 bar. c) Select the larger K v value, 16 in this example. If right on the line, or if in doubt, select a larger K v . 4. Selection of the actuator + valve adaptor The actuator has to be capable of shutting off against the maximum feedpump pressure to Class IV when the boiler is not under pressure. Select the actuator + valve adaptor from the table below: Actuator type PN9123E PN9223E
Valve K v selection graph Pressure drop across the fully open valve psi
1.45 2 3 4 5
10
20 30 50 100145
100 000 90 000 80 000 70 000 60 000 50 000
200 000
100 000 90 000 80 000 70 000 60 000 50 000
40 000
30 000
20 000
40 000
2.3 96
15 000
30 000
10 000 9 000 8 000 7 000 6 000 5 000 4 000
20 000
Maximum feedpump pressure bar g
Valve size K v value
10 000 9 000 8 000 7 000 6 000 5 000
25.0
11.0 (8)
40 (40)
16.0
11.0
(8)
40 (40)
3 000
DN40
10.0
11.0
(8)
40 (40)
6.3
11.0
(8)
40 (40)
2 000
4 000
Figures in brackets denotes the differential pressures for valves fitted with high temperature graphite stem sealing. These valves have a suffix 'H'. Valve stroke is 20 mm.
3 000
1 000
0.1
0.2 0.3 0.5
1 1.52 3 45
10
Pressure drop across the fully open valve bar
5. Electropneumatic positioner Specify EP6 positioner (4 - 20 mA input).
TI-S75-12 CTLS Issue 5
Page 2 of 4
Selection of Modulating Feedwater Valves Pneumatically Actuated
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