| Term | Definition |
|---|
| Lagging | A light gauge steel covering used over a boiler, usually combined with insulation, to provide a low temperature outer surface.
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| Leakage | The uncontrolled quantity of fluid which enters or leaves through the enclosure of air or gas passages.
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| Liberation | See "Heat Release."
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| Limit Control | A switching device that completes or breaks an electrical circuit at predetermined pressures or temperatures. Also known as an interlock. See interlock.
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| Lining | The material used on the furnace side of a furnace wall. It is usually of high grade refractory tile or brick or plastic refractory material.
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| Load | The rate of output required; also the weight carried.
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| Load Factor | The ratio of the average load in a given period to the maximum load carried during that period.
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| Low Gas Pressure Control | A control to stop the burner if gas pressure is too low.
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| Low Oil Temperature Control | (a.k.a. Cold Oil Switch) A control to prevent burner operation if the temperature of the oil is too low.
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| Low Water Cutoff | Safety device that shuts off the boiler/burner in the event of low water, preventing pressure vessel failure.
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| Lug | Any projection, like an ear, used for supporting or grasping.
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