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| Term | Definition |
|---|---|
| Saddle | A casting, fabricated chair, or member used for the purpose of support. |
| Safe Working Pressure | See "Design Pressure." |
| Safety Shut-Off Valve | A manually opened, electrically latched, electrically operated safety shut-off valve designed to automatically shut off fuel when de-energized. |
| Safety Valve | A spring loaded valve that automatically opens when pressure attains the valve setting. Used to prevent excessive pressure from building up in a boiler. |
| Sampling | The removal of a portion of a material for examination or analysis. |
| Saturated Air | Air which contains the maximum amount of water vapor that it can hold at its temperature and pressure. |
| Saturated Steam | Steam at the temperature and pressure at which evaporation occurs. |
| Saturated Temperature | The temperature at which evaporation occurs at a particular pressure. |
| Saturated Water | Water at its boiling point. |
| Scale | A hard coating or layer of materials on surfaces of boiler pressure parts. |
| Secondary Air | Air for combustion supplied to the furnace to supplement the primary air. |
| Secondary Treatment | Treatment of boiler feed water or internal treatment of boiler-water after primary treatment. |
| Sediment | (1) Matter in water which can be removed from suspension by gravity or mechanical means. (2) A non-combustible solid matter which settles out at bottom of a liquid; a small percentage is present in residual fuel oils. SEGREGATION - The tendency of refuse of varying compositions to deposit selectively in difference parts of the unit. |
| Self-Supporting Steel Stack | A steel stack of sufficient strength to require no lateral support. |
| Service Water | General purpose water which may or may not have been treated for a special purpose. |
| Shell | The cylindrical portion of a pressure vessel. |
| Sludge | A soft water-formed sedimentary deposit which normally can be removed by blowing down. |
| Slug | A large "dose" of chemical treatment applied internally to a steam boiler intermittently. Also used sometimes instead of "priming" to denote a discharge of water out through a boiler steam outlet in relatively large intermittent amounts. |
| Smoke | Small gas borne particles of carbon or soot, less than 1 micron in size, resulting from incomplete combustion of carbonaceous materials and of sufficient number to be observable. |
| Soft Water | Water which contains little or no calcium or magnesium salts, or water from which scale forming impurities have been removed or reduced. |
| Softening | The act of reducing scale forming calcium and magnesium impurities from water. |
| Solution | A liquid, such as boiler water, containing dissolved substances. |
| Soot | Unburned particles of carbon derived from hydrocarbons. |
| Soot Blower | A mechanical device for discharging steam or air to clean heat absorbing surfaces. |
| Spalling | The breaking off of the surface of refractory material as a result of internal stresses. |
| Specific Heat | The quantity of heat, expressed in Btu, required to raise the temperature of 1 lb of a substance 1°F. |
| Specific Humidity | The weight of water vapor in a gas water-vapor mixture per unit weight of dry gas. |
| Spray Angle | The angle included between the sides of the cone formed by liquid fuel discharged from mechanical, rotary atomizers and by some forms of steam or air atomizers. |
| Spray Nozzle | A nozzle from which a liquid fuel is discharged in the form of a spray. |
| Stack | A vertical conduit, which due to the difference in density between internal and external gases, creates a draft at its base. |
| Stack Draft | The magnitude of the draft measured at the inlet to the stack. |
| Stack Effect | That portion of a pressure differential resulting from difference in elevation of the points of measurement. |
| Stack Effluent | Gas and solid products discharged from stacks. |
| Stagnation | The condition of being free from movement or lacking circulation. |
| Standard Air | Dry air weighing 0.075 lb per cu ft at sea level (29.92" Barometric Pressure) and 70° F. |
| Standard Flue Gas | Gas weighing 0.078 lb per cu ft at sea level (29.92" Barometric Pressure) and 70° F. |
| Static Pressure | The measure of potential energy of a fluid. |
| Steam | The vapor phase of water, unmixed with other gases. |
| Steam Atomizing Oil Burner | A burner for firing oil which is atomized by steam. It may be of the inside or outside mixing type. |
| Steam Binding | A restriction in circulation due to a steam pocket or a rapid steam formation. |
| Steam Gauge | A gauge for indicating the pressure of steam. |
| Steam Generating Unit | A unit to which water, fuel, and air are supplied and in which steam is generated. It consists of a boiler furnace, and fuel burning equipment, and may include as component parts water walls, superheater, reheater, economizer, air heater, or any combination thereof. |
| Steam Purity | The degree of contamination. Contamination is expressed in ppm. |
| Steam Quality | The percent by weight of vapor in a steam and water mixture. |
| Steam Separator | A device for removing the entrained water from steam. |
| Strainer | A device, such as a filter, to retain solid particles allowing a liquid to pass. |
| Stratification | Non-homogeneity existing transversely in a gas stream. |
| Stud | projecting pin serving as a support or means of attachment. |
| Superheated Steam | Steam with its temperature raised above that of saturation. The temperature in excess of its saturation temperature is referred to as superheat. |
| Surface Blowoff | Removal of water, foam, etc. from the surface at the water level in a boiler. The equipment for such removal. |
| Surge | The sudden displacement or movement of water in a closed vessel or drum. |
| Suspended Solids | Undissolved solids in boiler water. |
| Swinging Load | A load that changes at relatively short intervals. |
