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TechnotePage 6 of 8IntroductionThe valve is an automatic regulator valve that with a referenceto the differential pressure automatically adjusts tothe kv value necessary to maintain the required flow. Thekv value of the valve automatically compensates for anychanges of the differential pressure, so that the flow willnever exceed the pre-set flow.These valves are available in types that have been calibratedin the factory to the rated flow, and in types the indexedflow of which can be pre-adjusted by the user before orafter the installation of the valve in the system, or from theoutside as the system is working.The valve can be used on the basis of the calculated flowwithout regard to the distribution of pressure in the system.Figure 2.5 illustrates the difference between the static andthe dynamic application in the form of flow variation as afunction of the differential pressure across the valves at agiven pre-adjustment.As will be seen from the chart, the flow through the staticvalve will increase as the differential pressure increases,and decrease as the differential pressure falls, whereas thedynamic balancing valve will maintain a constant flow (withinthe regulation range) independently of the differentialpressure within the dynamic balancing valve.Further, please note that the indexed flow (100 %) througha static balancing valve will not be achieved unless the differentialpressure across the valve is equal to the indexeddifferential pressure Δp.When are Flow Measurement Devices equired?Static Systems:During the adjustment it should be possible to measure theflow through each terminal (coil in air-condition, not radiatorsin heating systems), distributing line, main distributingline and supply line.The measurements will typically be carried out as an indirectmeasurement, i.e. measurement of the differential pressureconverted into a flow value in relation to the k v valueof the measured device. The measurements are carried outacross each circuit-balancing valve with the k v value relativeto the valve setting and the associated flow chart.The accuracy of the measured flow is not likely to be betterthan +/- 25 % dependent on the hand wheel position. Thisinaccuracy should be taken into consideration in connectionwith the verification of the flow. Still, it is of no particularimportance to the relative comparison between theflow through the individual terminals and distributing linesduring the balancing procedure.Dynamic Systems:Dynamic valves will typically balance the system at an accuracyof +/- 5 % of the rated flow.So, as direct measurements involve a degree of accuracy of+/- 25 %, it will be inappropriate to verify the flow throughthe individual terminals.Instead, measurement/verification of the flow in the supplyline is recommended.For verification of the flow in the supply line it is recommendedthat a fixed orifice device is used with a specified accuracywhich is +/- 5% above that of the measured flow.Where are Balancing Valves required?Figures 2.6 and 2.7 show a section of the same system, inwhich figure 2.6 has been designed as a static system, andfigure 2.7 as a dynamic system. The section contains onesupply line for 3 main distributing lines, each of which has3 distributing lines with 3 terminals each (totally 27 terminals).UK Intro AUG 11www.frese.eu
TechnotePage 7 of 8Introduction1Figure 2.6 Water distribution system, static balancingFigure 2.7 Water distribution system, dynamic balancingIn the static system each terminal has to be balanced in9 groups of 3 terminals each. Hereafter the 9 terminalsections have to be balanced in 3 groups of 3 distributinglines each. After that the 3 main distributing lines have tobe balanced. And finally the distributing line is adjusted toensure the total design flow.This balancing procedure requires one balancing valve perterminal, one balancing valve per distributing line, one balancingvalve per main distributing line and one balancingvalve in the supply line.In the dynamic system the individual terminals can be adjustedindependently of each other. This simply requires onebalancing valve per terminal.UK Intro AUG 11www.frese.eu
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Page 3: IndexHEATING & COOLING APPLICATIONS
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Reference ProjectForum Marmara Shop
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