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25 | schneider-electric.com Selection Guide
January, 2019 tc © 2019 Schneider Electric. All rights reserved. All trademarks are owned by Schneider Electric Industries SAS or its affiliated companies.
Document Number: F-27086-14
Flow Characterization: Proportional/Floating Control
The Vx-2x13-xxx-9-xx series ball valve assemblies provide equal percentage flow, which is achieved with a flow characterizing
insert (Figure-11). The parabolic shape of the orifice allows a gradual change in flow, so that equal movements of the valve stem,
at any point of the flow range, change the existing flow an equal percentage, regardless of the flow rate. As shown in the graph in
Figure-12, a ball valve equipped with the flow insert mirrors the flow characteristic of the coil, resulting in linear heat transfer.
Ball
Flow Characterizing Insert
Opening
100
90
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0
100908070605040302010
0
Linear Heat Trans
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Percent of Ball Opening
Percent of Maximum Flow
Figure 9. Flow Characterizing Insert. Figure 10. Equal Percentage Flow Control.
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-17. 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
Secondary Circuits with Small Booster Pumps: 50% of available pressure difference (equal to the drop through load, or 50% of
the booster pump head).
3-Way Mixing Valves
3-way mixing valves used in variable flow applications (Figure 10) should be sized using the preceding guidelines. 3-way mixing
valves used in constant flow applications, such as boiler bypass, should be sized to use 20% of “available pressure,” or equal to
25% of the pressure drop through the load at full flow.
VB-2000 Series Ball Valves
with SmartX Actuators
8. VBB/VBS and VB-2000 Series
Ball Valve Assemblies
8. VBB/VBS and VB-2000 Series
Ball Valve Assemblies