User Guide

F-27194-5 © Copyright 2010 Schneider Electric All Rights Reserved. 7
gpm = Flow rate of water that will pass through fully open valve, measured in U.S. gallons
per minute (60 °F (15.6 °C) water).
ΔP = Differential pressure (pressure drop), measured in psi.
Steam Two-position
Two-position zone valves and direct radiation valves are normally sized using a minimum of
10% of inlet pressure (psig).
Proportional
Proportional control valves are normally sized using:
• For low pressure (15 psig or less), use ΔP of 80% of gauge inlet pressure.
• For steam pressures greater than 15 psig, use ΔP of 42% of absolute (gauge plus 14.7)
inlet pressure.
• When the C
v
required is between two valve sizes, select the larger size. Do not size
steam valves using a pressure drop greater than 42% of the absolute inlet pressure.
Steam Table
See Table-5 for steam capacity of VB-8223 series valves.
C
v
Equation for Steam
Where:
C
v
= Coefficient of flow.
Q = Flow rate of steam that will pass through fully open valve, measured as pounds per hour
of steam.
ΔP = Differential pressure (pressure drop), measured in psi.
P2 = Outlet pressure, measured in psia (absolute pressure). 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:
P
m
= 0.5 (P
1
– P
v
)
Where:
P
m
= Maximum allowable pressure drop
P
1
= Absolute inlet pressure (psia)
P
v
= Absolute vapor pressure (psia) (refer to Table-6)
Table-5 Steam Capacity in Pounds Per Hour for VB-8223 Series
Valve Body
Part Number
Cv
Rating
Differential Pressure (
ΔP in psi)
2 psig
Inlet
5 psig
Inlet
10 psig
Inlet
15 psig
Inlet
20 psig
Inlet
25 psig
Inlet
30 psig
Inlet
35 psig
Inlet
0.2 1.6 0.5 4 1 8 1.5 12 2 14 2.5 16 3 18 3.5 20
VB-8223-0-5-12 56 305 826 520 1331 818 1942 1093 2448 1359 2860 1620 3271 1879 3683 2136 4094
VB-8223-0-5-13 85 463 1253 790 2021 1241 2947 1658 3716 2062 4341 2459 4965 2852 5590 3242 6214
VB-8223-0-5-14 145 790 2138 1348 3447 2118 5027 2829 6339 3518 7405 4195 8470 4865 9536 5531 10601
VB-8223-0-5-15 240 1308 3539 2231 5706 3505 8322 4683 10493 5823 12257 6943 14021 8053 15784 9156 17548
VB-8223-0-5-16 370 2016 5456 3439 8796 5404 12830 7219 16177 8977 18896 10704 21615 12415 24334 14115 27053
C
v
QK•
3 PΔ P2•
----------------------------=
Q
3C
v
PΔ P2•
K
------------------------------------=