Book - School of Science and Technology

246 Piping design for indirect heating systemsBalancingvalveDifferentialgaugeLoad(a)(b)RegulatingvalveFigure 9.9 Special circuit balancing valve: (a) combined regulating value and flow meltering device(Hatterstey), (b) separate regulating and orifice measuring value arrangementRegulating valvesReference has been made here, in several earlier paragraphs, to the virtual impossibility ofachieving an exact balance between various branch circuits by selection of pipe sizesalone. In order to overcome this problem, branches are provided with regulating valveswhich may be adjusted to take up over-pressure. Traditionally, gate valves were used forthis purpose but they, in common with most other commercially available angle radiatorvalves, were virtually useless for this application since the relation between control ofwater flow and spindle rotation was far too critical. Valves having a good regulationperformance are now available and it is accepted practice to provide major branches withbalancing valves of the type shown in Figure 9.9. These have connections to which asensitive manometer or other test instrument may be fitted to provide data for comparisonwith curves or tables provided by the manufacturer to show pressure loss and water flowcharacteristics.An alternative to manually adjusted regulating valves is the constant flow regulator.These are claimed to provide a constant flow rate over a considerable range of operatingconditions. Generally, these devices comprise an inner cartridge with precision machinedholes through which water passes. The cartridge is positioned against a spring within thebody of the regulator and as the pressure differential increases the cartridge moves tocompress the spring causing the holes open to flow to become blocked, thereby reducingand regulating the rate of flow. Cartridges are interchangeable to suit different systemoperating conditions. Such devices are only required at terminals, thereby reducing thetotal number of regulating devices in the system.Use of constant flow regulators should avoid the need for system balancing duringcommissioning, but double handling is required since the devices have to be removed fromthe system during flushing, otherwise the holes may become blocked with debris. Someconcern is often expressed over the inevitable development of dirt within a system in usefouling the holes and affecting the ability of the device to regulate to the required flowrate.Since, however, it is not practicable to integrate flow measurement with a flow regulatorof this type, independent measuring devices are required to check that flow rates areset up and maintained at the correct levels.