SADDLE – A casting, fabricated chair, or member used for the purpose of support.
SAFE WORKING PRESSURE – See “Design Pressure.”
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.
SAFETY SHUT-OFF VALVE – A manually opened, electrically latched, electrically operated safety shut-off valve designed to automatically shut off fuel when de-energized.
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.
SOFTENING – The act of reducing scale forming calcium and magnesium impurities from water.
SOFT WATER – Water which contains little or no calcium or magnesium salts, or water from which scale forming impurities have been removed or reduced.
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 – A 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.
TERTIARY AIR – Air for combustion supplied to the furnace to supplement the primary and secondary air.
THEORETICAL AIR – The quantity of air required for perfect combustion.
THEORETICAL DRAFT – The draft which would be available at the base of a stack if there were no friction or acceleration losses in the stack.
THEORETICAL FLAME TEMPERATURE – See “Adiabatic Flame Temperature.”
THERM – A unit of heat applied especially to gas. One therm = 100,000 Btu.
THERMAL EFFICIENCY – The efficiency of a boiler, based on the ratio of heat
absorbed to total heat input. This does not include heat loss from the boiler shell.
THERMAL SHOCK – A cycle of temperature swings that result in failure of metal due to expansion and contraction.
THERMOCOUPLE – A temperature measuring instrument.
TILE – A preformed refractory, usually applied to shapes other than standard brick.
TOTAL AIR – The total quantity of air supplied to the fuel and products of combustion. Percent total air is the ratio of total air to theoretical air, expressed as percent.
TOTAL PRESSURE – The sum of the static and velocity pressures.
TOTAL SOLIDS CONCENTRATION – The weight of dissolved and suspended impurities in a unit weight of boiler water, usually expressed in ppm.
TRAP – A receptacle for the collection of undesirable material.
TREATED WATER – Water which has been chemically treated to make it suitable for boiler feed.
TRIM – Ancillary boiler components, like water level controls, pressure controls, and temperature controls.
TUBE – A hollow cylinder for conveying fluids.
TUBE HOLE – A hole in a drum, heater, or tube sheet to accommodate a tube.
TURBULENT BURNER – A burner in which fuel and air are mixed and discharged into the furnace in such a manner as to produce turbulent flow from the burner.
TURNDOWN RATIO – Ratio of maximum to minimum fuel or steam input or boiler output.