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NORA Oilheat Technicians Manual

ber that if the cut out point is changed and the differential is left the same the cut in point will also change. The same thing happens in reverse, if the cut in point is changed, the cut out point also changes. Figure 12-17 shows a mercury tube pressure switch with the cover off, indicating various parts and adjustment points. The pressure control must always be installed above the water level of the boiler, and a pigtail, or siphon, as shown in Figure 12-18, must be installed between the boiler and the control. The siphon loop prevents steam from damaging the control bellows. The pressure control should be installed in the fitting provided by the boiler manufacturer, or in the pressure control mounting of the low-water cutoff. When Chapter 12 Limit Controls/Thermostats Figure 12-17: Mercury tube pressure switch Differential Adjusting Screw Scale Plates Differential Setting Indicator Pressure Setting Indicator Differential Lever Pressure Adjusting Screw Travel Limit Slot Operating Installation of a Pressure Control Manual Reset Lever Mercury Switch Eccentric Adjustment Screw Figure 12-18: Pressure control, siphon loop Right Wrong Lever Diaphragm Assembly Leveling Indicator Chapter 12—Limit Controls and Thermostats 12-15


NORA Oilheat Technicians Manual
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