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NORA Oilheat Technicians Manual

making pipe connections, use pipe dope sparingly. Excess dope may clog the small opening of the pressure control, thus preventing it from operating properly. When mounting the pressure control and the pressure gauge to the same boiler fitting, follow the method shown in Figure 12-18, previous page. Be certain to mount them in such a manner that their faces are perpendicular to the siphon loop circumference. The reason for this is that the siphon loop tends to expand, thus causing a forward and backward motion that could cause the mercury switch in the pressure control to operate improperly if the faces of these instruments were mounted parallel to the circumference of the loop. Figure 12-19 is a wiring diagram showing the pressure control. Like all other high limit controls, it is wired into the hot line in series with the primary control. Low-water cutoff The low-water cutoff prevents a burner from operating if the water level is too low in the boiler. This device is required on all steam boilers whether used for space heating or in a process application and may also be required on hot water systems. If a hot water boiler is installed above the radiation, or even at the same level, a lowwater cutoff should be used to protect the boiler in the event of a loss of water. Figure 12-20 shows a cutaway view of an external low-water cutoff. It is a float operated device. There is also an internal low-water cutoff with the float located inside the boiler. Figure 12-19: Pressure control wiring Pressure Control 12-16 Limit Controls and Thermostats Low Water Cutoff Low Voltage Thermostat Low Voltage Aquastat Burner Motor Ignition Transformer Chapter 12 Limit Controls/Thermostats


NORA Oilheat Technicians Manual
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