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6 © Copyright 2006 TAC All Rights Reserved. F-24388-1
Table-6 Steam Capacity in Pounds Per Hour for VB-7253 Series.
C
v
Equation
Where:
C
v
= Coefficient of flow
Q = Lbs. per hour of steam
ΔP = Differential pressure in psi (pressure drop)
P2 = Outlet pressure in psia (absolute) (P2 = Inlet pressure + 14.7 – ΔP)
K = 1 + (0.0007 x °F superheat) (K = 1 for saturated steam)
Cavitation Limitations
on Valve Pressure
Drop
A valve selected with too high a pressure drop can cause erosion of discs and/or wire
drawing of the seat. In addition, cavitation can cause noise, damage to the valve trim (and
possibly the body), and choke the flow through the valve.
Do not exceed the maximum differential pressure (pressure drop) for the valve selected.
The following formula can be used on higher temperature water systems, where cavitation
could be a problem, to estimate the maximum allowable pressure drop across the valve:
Pm = 0.5 (P
1
– Pv)
Where:
Pm = Maximum allowable pressure drop (psi)
P
1
= Absolute inlet pressure (psia)
Pv = Absolute vapor pressure (psia) (refer to Table-6 or Table-7)
Note: Add 14.7 psi to gauge supply pressure to obtain absolute pressure value.
Valve Body
Part Number
C
v
Rating
Differential Pressure (ΔP in psi)
a
a
Values are for saturated steam (K = 1). Left column under each inlet pressure is for two-position control, and right column is for proportional control.
2 psig Inlet 5 psig Inlet 10 psig Inlet 15 psig Inlet 20 psig Inlet 25 psig Inlet
0.2 1.6 0.5 4 1 8 1.5 12 2 14 2.5 16
VB-7253-0-4-1 0.4 2.2 5.9 3.7 9.5 5.8 14 7.8 18 9.7 20 12 23
VB-7253-0-4-2 1.3 7.1 19 12 31 19 45 25 57 32 66 38 76
VB-7253-0-4-3 2.2 12322052327643965311264129
VB-7253-0-4-4 4.4 24 65 41 105 64 153 86 192 107 225 127 257
VB-7253-0-4-5 5.5 30 81 51 131 80 191 107 240 133 281 159 321
VB-7253-0-4-6 7.5 41 111 70 178 110 260 146 328 182 383 217 438
VB-7253-0-4-7 10 55 147 93 238 146 347 195 437 243 511 289 584
VB-7253-0-4-8 12 65 177 112 285 175 416 234 525 291 613 347 701
VB-7253-0-4-9 20 109 295 186 475 292 694 390 874 485 1021 579 1168
VB-7253-0-4-10 28 163 442 279 713 438 1040 585 1312 728 1532 868 1753
VB-7253-0-4-11 40 218 590 372 951 584 1387 780 1749 970 2043 1157 2337
Valve Body
Part Number
C
v
Rating
Differential Pressure (ΔP in psi)
a
30 psig Inlet 35 psig Inlet 40 psig Inlet 50 psig Inlet 75 psig Inlet 100 psig Inlet
3183.5204 22 5 277.5371048
VB-7253-0-4-1 0.4 132615291732213830533968
VB-7253-0-4-2 1.3 44 86 50 95 56 105 67 124 97 172 126 221
VB-7253-0-4-3 2.2 74 145 84 161 94 177 114 211 164 291 214 373
VB-7253-0-4-4 4.4 148 289 168 322 188 354 228 421 328 583 427 747
VB-7253-0-4-5 5.5 185 362 210 402 235 443 285 526 410 729 534 934
VB-7253-0-4-6 7.5 252 493 286 548 320 603 389 718 559 994 728 1273
VB-7253-0-4-7 10 336 658 381 731 427 805 518 957 745 1325 971 1697
VB-7253-0-4-8 12 403 789 458 877 598 1127 726 1340 1043 1855 1359 2376
VB-7253-0-4-9 20 671 1315 763 1462 854 1609 1037 1914 1490 2649 1941 3395
VB-7253-0-4-10 28 939 1841 1068 2047 1282 2414 1555 2871 2235 3974 2912 5092
VB-7253-0-4-11 40 1342 2631 1526 2924 1709 3219 2073 3829 2980 5299 3883 6790
C
v
=
QK
Q=
K
ΔP • P2
3
ΔP • P2
3C
v