User Guide

F-24393-3 © Copyright 2010 Schneider Electric All Rights Reserved. 5
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 to Bypass Flow
Proportional mixing valves used to bypass flow (Figure-6) are piped on the outlet side of the
load to throttle the water flow through the load and therefore control heat output of the load.
These 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).
Proportional to Blend Water Flows
Proportional valves used to blend two water flows (Figure-7 and Figure-8) control the heat
output by varying the water temperature to the load at constant flow. These valves do not
require high pressure drops for good control results. They can be sized for a pressure drop
of 20% of the “available pressure” or equal to 25% of the pressure drop through the load at
full flow.
Water Table
See Table-4 for water capacity of VB-9313 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-9313 Series.
Valve Body
Part Number
C
v
Rating
Differential Pressure (ΔP in psi)
1 2 3 4 5 6 7 8 9 10 15 20 25 30 35
VB-9313-0-4-12 67 67 95 116 134 150 164 177 190 201 212 259 300 335 367 396
VB-9313-0-5-12 74 74 105 128 148 165 181 196 209 222 234 287 331 370 405 438
VB-9313-0-4-13 91 91 129 158 182 203 223 241 257 273 288 352 407 455 498 538
VB-9313-0-5-13 101 101 143 175 202 226 247 267 286 303 319 391 452 505 553 598
VB-9313-0-5-14 170 170 240 294 340 380 416 450 481 510 538 658 760 850 931 1006
VB-9313-0-5-15 290 290 410 502 580 648 710 767 820 870 917 1123 1297 1450 1588 1716
VB-9313-0-5-16 390 390 552 675 780 872 955 1032 1103 1170 1233 1510 1744 1950 2136 2307
C
v
=
GPM
ΔP=
GPM
C
v
()
GPM = C
v
ΔP
2
ΔP