User Guide
4 © Copyright 2008 TAC All Rights Reserved. F-24386-2
VALVE SIZING AND SELECTION
Water
Two-position
Two-position control valves are normally selected “line size” to keep pressure drop at a
minimum. If it is desirable to reduce the valve below line size, then 10% of “available
pressure” (that is, the pump pressure differential available between supply and return mains
with design flow at the valve location) is normally used to select the valve.
Proportional
Proportional control valves are usually selected to take a pressure drop equal to at least 50%
of the “available pressure.” As “available pressure” is often difficult to calculate, the normal
procedure is to select the valve using a pressure drop at least equal to the drop in the coil
or other load being controlled (except where small booster pumps are used) with a minimum
recommended pressure drop of 5 psi (34 kPa). When the design temperature drop is less
than 60°F (33°C) for conventional heating systems, higher pressure drops across the valve
are needed for good results (Table-3).
*Recommended minimum pressure drop = 5 psi (34 kPa).
Secondary Circuits with Small Booster Pumps: 50% of available pressure difference
(equal to the drop through load, or 50% of booster pump head).
Water Table
See Table-4 for water capacity of VB-9223 series valves.
C
v
Equation
Where:
C
v
= Coefficient of flow
GPM = U.S. gallons per minute (60°F, 15.6°C)
ΔP = Differential pressure in psi (pressure drop)
Table-3 Conventional Heating System.
Design Temperature
Load Drop °F (°C)
Recommended Pressure Drop*
(% of Available Pressure)
Multiplier on
Load Drop
60 (33) or More 50% 1 x Load Drop
40 (22) 66% 2 x Load Drop
20 (11) 75% 3 x Load Drop
Table-4 Water Capacity in Gallons Per Minute for VB-9223 Series.
Valve Body
Part Number
C
v
Rating
Differential Pressure (
ΔP in psi)
123456789101520253035
VB-9223-0-5-12 56 56 79 97 112 125 137 148 158 168 177 217 250 280 307 331
VB-9223-0-4-12 65 65 92 113 130 145 159 172 184 195 206 252 291 325 356 385
VB-9223-0-4-13
VB-9223-0-5-13
85 85 120 147 170 190 208 225 240 255 269 329 380 425 466 503
VB-9223-0-5-14 145 145 205 251 290 324 355 384 410 435 459 562 648 725 794 858
VB-9223-0-5-15 235 235 332 407 470 525 576 622 665 705 743 910 1051 1175 1287 1390
VB-9223-0-5-16 350 350 495 606 700 783 857 926 990 1050 1107 1356 1565 1750 1917 2071
C
v
=
GPM
ΔP=
GPM
C
v
()
GPM = C
v
ΔP
2
ΔP