Steam Control Valves - Calculate Flow Factor Kv
Designing steam control valves and their Kv values.
The procedure below can be used for proper design of steam process control valves and their correct flow factors - Kv.
1. Determine Pressure Coefficient - Pcoef
Start with the absolute pressure before the control valve and the actual pressure drop available over the valve and determine the pressure coefficient - Pcoef - from the table below.
Pcoef = pressure drop / specific volume
Note! The pressure drop can not exceed critical pressure drop which is approximately 42% of the inlet pressure.
For full table - rotate the screen!
Pcoeff | ||||||||||||||||
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Absolute Pressure - Pin - (bar) Load Calculator! | Specific Volume - v - (m3/kg) Load Calculator! | Pressure drop (bar) Load Calculator! | ||||||||||||||
0.5 | 1 | 1.5 | 2 | 2.5 | 3 | 3.5 | 4 | 4.5 | 5 | 5.5 | 6 | 6.5 | 7 | 7.5 | ||
1 | 1.69 | 0.30 | ||||||||||||||
2 | 0.89 | 0.56 | 1.12 | |||||||||||||
3 | 0.61 | 0.82 | 1.64 | 2.46 | ||||||||||||
4 | 0.45 | 1.11 | 2.22 | 3.33 | 4.44 | |||||||||||
5 | 0.38 | 1.32 | 2.63 | 3.95 | 5.26 | 6.58 | ||||||||||
6 | 0.32 | 1.56 | 3.13 | 4.69 | 6.25 | 7.81 | 9.38 | |||||||||
7 | 0.27 | 1.85 | 3.70 | 5.56 | 7.41 | 9.26 | 11.1 | 13.0 | ||||||||
8 | 0.24 | 2.08 | 4.17 | 6.25 | 8.33 | 10.42 | 12.5 | 14.6 | 16.7 | |||||||
9 | 0.21 | 2.38 | 4.76 | 7.14 | 9.52 | 11.90 | 14.3 | 16.7 | 19.1 | 21.4 | ||||||
10 | 0.19 | 2.63 | 5.26 | 7.89 | 10.53 | 13.16 | 15.8 | 18.4 | 21.1 | 23.7 | 26.3 | |||||
11 | 0.18 | 2.78 | 5.56 | 8.33 | 11.11 | 13.89 | 16.7 | 19.4 | 22.2 | 25.0 | 27.8 | 30.6 | ||||
12 | 0.16 | 3.13 | 6.25 | 9.38 | 12.50 | 15.63 | 18.7 | 21.9 | 25.0 | 28.1 | 31.3 | 34.4 | 37.5 | |||
13 | 0.15 | 3.33 | 6.67 | 10.00 | 13.33 | 16.67 | 20.0 | 23.3 | 26.7 | 30.0 | 33.3 | 36.7 | 40.0 | 43.3 | ||
14 | 0.14 | 3.57 | 7.14 | 10.71 | 14.29 | 17.86 | 21.4 | 25.0 | 28.6 | 32.1 | 35.7 | 39.3 | 42.9 | 46.4 | 50.0 | |
15 | 0.13 | 3.85 | 7.69 | 11.54 | 15.38 | 19.23 | 23.1 | 26.9 | 30.8 | 34.6 | 38.5 | 42.3 | 46.2 | 50.0 | 53.9 | 57.7 |
Example - Pressure Coefficient
In a steam system with 9 bar gauge pressure the absolute pressure is 10 bar. If a pressure drop of 3.5 bar is acceptable and suitable for the steam consumer, the pressure coefficient Pcoef should be 18.4.
2. Determine Flow Factor - Kv
Select the pressure coefficient - Pcoef - column closest possible to the actual pressure coefficient calculated in step 1.
Follow the column down until reaching the appropriate actual flow value. Interpolate between values if necessary.
Go left in the table to find the actual flow factor Kv.
Steam Flow (kg/h) Load Calculator! | ||||||||||
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Kv | Pressure Coefficient - Pcoeff | |||||||||
1 | 1.25 | 1.56 | 1.95 | 2.44 | 3.05 | 3.81 | 4.77 | 5.96 | 7.45 | |
0.01 | 0 | 0 | 0 | 0 | 0 | 1 | 1 | 1 | 1 | 1 |
0.02 | 0 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 |
0.02 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 2 | 2 | 2 |
0.03 | 1 | 1 | 1 | 1 | 2 | 2 | 2 | 2 | 3 | 3 |
0.05 | 2 | 2 | 2 | 2 | 3 | 3 | 3 | 4 | 4 | 4 |
0.08 | 2 | 3 | 3 | 3 | 4 | 4 | 5 | 5 | 6 | 7 |
0.11 | 4 | 4 | 5 | 5 | 6 | 6 | 7 | 8 | 9 | 10 |
0.17 | 5 | 6 | 7 | 8 | 8 | 9 | 11 | 12 | 13 | 15 |
0.26 | 8 | 9 | 10 | 11 | 13 | 14 | 16 | 18 | 20 | 22 |
0.38 | 12 | 14 | 15 | 17 | 19 | 21 | 24 | 27 | 30 | 33 |
0.58 | 18 | 20 | 23 | 26 | 29 | 32 | 36 | 40 | 45 | 50 |
0.86 | 27 | 31 | 34 | 38 | 43 | 48 | 54 | 60 | 67 | 75 |
1.3 | 41 | 46 | 51 | 57 | 64 | 72 | 80 | 90 | 100 | 112 |
2.0 | 62 | 69 | 77 | 86 | 96 | 108 | 120 | 135 | 151 | 168 |
2.9 | 93 | 103 | 116 | 129 | 145 | 162 | 181 | 202 | 226 | 253 |
4.4 | 139 | 155 | 174 | 194 | 217 | 242 | 271 | 303 | 339 | 379 |
6.6 | 208 | 233 | 260 | 291 | 325 | 364 | 407 | 455 | 508 | 568 |
9.9 | 312 | 349 | 390 | 436 | 488 | 546 | 610 | 682 | 763 | 853 |
14.8 | 468 | 524 | 586 | 655 | 732 | 818 | 915 | 1023 | 1144 | 1279 |
22.2 | 703 | 786 | 878 | 982 | 1098 | 1228 | 1373 | 1535 | 1716 | 1918 |
33.3 | 1054 | 1179 | 1318 | 1473 | 1647 | 1841 | 2059 | 2302 | 2574 | 2877 |
49.9 | 1581 | 1768 | 1976 | 2210 | 2471 | 2762 | 3088 | 3453 | 3860 | 4316 |
74.8 | 2372 | 2652 | 2965 | 3315 | 3706 | 4143 | 4632 | 5179 | 5790 | 6474 |
112 | 3558 | 3978 | 4447 | 4972 | 5559 | 6215 | 6948 | 7769 | 8686 | 9711 |
168 | 5336 | 5966 | 6671 | 7458 | 8338 | 9322 | 10423 | 11653 | 13028 | 14566 |
253 | 8005 | 8949 | 10006 | 11187 | 12507 | 13983 | 15634 | 17479 | 19543 | 21849 |
379 | 12007 | 13424 | 15009 | 16780 | 18761 | 20975 | 23451 | 26219 | 29314 | 32774 |
568 | 18010 | 20136 | 22513 | 25170 | 28141 | 31463 | 35177 | 39329 | 43971 | 49161 |
852 | 27016 | 30204 | 33769 | 37755 | 42212 | 47194 | 52765 | 58993 | 65956 | 73741 |
1278 | 40523 | 45307 | 50654 | 56633 | 63318 | 70791 | 79147 | 88489 | 98934 | 110612 |
For full table - rotate the screen!
Steam Flow (kg/h) Load Calculator! | ||||||||||
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Kv | Pressure Coefficient - Pcoeff | |||||||||
9.31 | 11.6 | 14.5 | 18.2 | 22.7 | 28.4 | 35.5 | 44.4 | 55.5 | 69.4 | |
0.01 | 1 | 1 | 1 | 1 | 2 | 2 | 2 | 2 | 2 | 3 |
0.02 | 1 | 2 | 2 | 2 | 2 | 3 | 3 | 3 | 4 | 4 |
0.02 | 2 | 2 | 3 | 3 | 3 | 4 | 4 | 5 | 5 | 6 |
0.03 | 3 | 4 | 4 | 5 | 5 | 6 | 6 | 7 | 8 | 9 |
0.05 | 5 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 |
0.08 | 7 | 8 | 9 | 10 | 11 | 13 | 14 | 16 | 18 | 20 |
0.11 | 11 | 12 | 14 | 15 | 17 | 19 | 22 | 24 | 27 | 30 |
0.17 | 17 | 18 | 21 | 23 | 26 | 29 | 32 | 36 | 40 | 45 |
0.26 | 25 | 28 | 31 | 35 | 39 | 43 | 48 | 54 | 61 | 68 |
0.38 | 37 | 42 | 46 | 52 | 58 | 65 | 73 | 81 | 91 | 102 |
0.58 | 56 | 62 | 70 | 78 | 87 | 97 | 109 | 122 | 136 | 152 |
0.86 | 84 | 94 | 105 | 117 | 131 | 146 | 163 | 183 | 204 | 228 |
1.3 | 126 | 140 | 157 | 175 | 196 | 219 | 245 | 274 | 306 | 343 |
2.0 | 188 | 210 | 235 | 263 | 294 | 329 | 368 | 411 | 460 | 514 |
2.9 | 282 | 316 | 353 | 395 | 441 | 493 | 552 | 617 | 689 | 771 |
4.4 | 424 | 474 | 530 | 592 | 662 | 740 | 827 | 925 | 1034 | 1156 |
6.6 | 635 | 710 | 794 | 888 | 993 | 1110 | 1241 | 1388 | 1551 | 1734 |
9.9 | 953 | 1066 | 1191 | 1332 | 1489 | 1665 | 1862 | 2081 | 2327 | 2602 |
14.8 | 1430 | 1598 | 1787 | 1998 | 2234 | 2498 | 2792 | 3122 | 3491 | 3903 |
22.2 | 2145 | 2398 | 2681 | 2997 | 3351 | 3746 | 4189 | 4683 | 5236 | 5854 |
33.3 | 3217 | 3597 | 4021 | 4496 | 5026 | 5620 | 6283 | 7025 | 7854 | 8781 |
49.9 | 4825 | 5395 | 6032 | 6744 | 7540 | 8429 | 9424 | 10537 | 11781 | 13171 |
74.8 | 7238 | 8092 | 9047 | 10115 | 11309 | 12644 | 14137 | 15805 | 17671 | 19757 |
112 | 10857 | 12138 | 13571 | 15173 | 16964 | 18966 | 21205 | 23708 | 26506 | 29635 |
168 | 16285 | 18208 | 20357 | 22760 | 25446 | 28449 | 31808 | 35562 | 39759 | 44452 |
253 | 24428 | 27312 | 30535 | 34139 | 38169 | 42674 | 47711 | 53343 | 59639 | 66679 |
379 | 36642 | 40967 | 45803 | 51209 | 57254 | 64011 | 71567 | 80014 | 89459 | 100018 |
568 | 54963 | 61451 | 68704 | 76814 | 85880 | 96017 | 107350 | 120021 | 134188 | 150027 |
852 | 82445 | 92176 | 103056 | 115220 | 128820 | 144026 | 161025 | 180032 | 201282 | 225040 |
1278 | 123668 | 138265 | 154584 | 172831 | 193231 | 216038 | 241538 | 270048 | 301923 | 337560 |
Example - Determine Flow Factor
For a pressure coefficient Pcoef = 18.2 and steam flow = 592 kg/h - the flow factor Kv is 4.4.
The formula used for the flow factor - Kv
The tables above are based on the formula:
Kv = m / (31.7 (dP / v)1/2) (1)
where
m= steam flow (kg/h)
dP = pressure drop (bar)
v = specific volume of steam before control valve (m3/kg)
Steam Control Valve - Kv Calculator
Steam Kv calculator based on eq. 1:
m - steam flow (kg/h)
dp - pressure drop (bar)
v - specific volume of steam before valve (m3/kg)