Selection Guide

Schneider Electric 839 North Perryville Rd. Rockford, IL 61107 1-888-444-1311 www.schneider-electric.com
F-27649-2 September 2013
© 2013 Schneider Electric. All rights reserved.
VB-7200 Two-Way Globe Valve Bodies
Venta
8
Valve Sizing and Selection
Sizing for 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 and Floating
Proportional and floating 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.
Do Not Exceed the MAXIMUM Recommended
Pressure Drop Of the Valve
Conventional Heating System
Design
Temperature
Load Drop
°F (°C)
Recommended
Pressure Drop
(% of Available
Pressure)
Multiplier on
Load Drop
60 (33) or more 50% 1x Load Drop
40 (22) 66% 2x Load Drop
20 (11) 75% 3x Load Drop
Actuator must be rated to provide close off pressure.
Cv (Flow Coefficient) Determination
The valves’ water capacity is based on the following
formula:
Other forms of this formula are:
These formulas can be used to calculate one of the
three quantities if the other two are known.
Flow coefficients (Cv’s) for valve bodies are given on
pages 2 to 6.
Metric (SI) Units
Kvs is defined as the flow in m3/h with DP = 100 kPa
(1.0 Bar) with the valve completely open.
Flow is calculated using the following formula:
Pressure drop is calculated using the following form
of the above formula:
These formulas can be used to calculate one of the
three quantities if the other two are known.
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