Absolute Pressure- The sum of gauge pressure and atmospheric pressure.

Accumulator- A pressure vessel containing water and/or steam, used for storing the heat of steam to be used at a later time at a decreased pressure.

Acid Cleaning- The method of washing the interior surfaces of steam generating systems by filling the unit with diluted acid followed by an determent to defend against corrosion, and afterward draining, washing and neutralizing the acid by a another wash of alkaline water.

Acidity- Amount of free carbon dioxide, mineral acids and salts such as sulfates of iron and aluminum, that undergo hydrolyzation giving hydrogen ions in water; and is reported as mill equivalents per liter of acid, or ppm acidity as calcium carbonate, or pH, the measure of hydrogen ions concentration.

Air- The mixture of oxygen, nitrogen, and other gases, that have varying amounts of water vapor, and forms the earth’s atmosphere.

Air atomizing oil burner- A burner used in firing oil where the oil is reduced (atomized) by restricted air, and forced into and through one or more currents by breaking the oil into the form of a fine spray.

Air deficiency- Mixture of air and fuel, that’s deficient in its air to supply the oxygen needed for full oxidation of the fuel.

Air free- A substance which air has been removed from.

Air fuel ratio- Ratio of weight and volume, of air to fuel.

Air infiltration- Air leak in a setting or duct.

Air vent- Opening at the top, highest drum of a boilers and pressure vessels to vent air.

Alkalinity- Is determined by analizing the water in the boiler water. Boiler water with a pH of 7 is considered alkaline.

Allowable working pressure- The pressure used in the construction of a boiler for the intendment of calculating minimum passable thickness or natural characteristics of the different parts of the boiler. See design pressure.

Ambient air- The air in the earths atmoshphere (outdoor air), that  surrounds the equipment.

Ambient temperature- Temperature of the air surrounding the equipment.

Aquastat- A device used in hydronic heating systems for controlling water temperature. To prevent the boiler from firing too often, aquastats have a high limit and a low limit.

Atomize- The breaking up of liquid into a fine mist.

ASME Code- The Code that is written by The American Society of Mechanical Engineers, that controls construction, repairs and the operation of steam boilers and associated equipment.

Aspirating burner- A burner in which the fuel in a vaporous or cautiously split form is burned in suspension, the air for combustion being furnished by bringing into contact with the fuel, air drawn through one or more openings by the lower static pressure created by the velocity of the fuel stream.

Atmospheric air- Air under the prevailing atmospheric conditions.

Atmospheric pressure- Pressure from the weight of air pressing down on earth.

Atomization- Method through which an amount of liquid is transformed into a fine mist or spray.

Atomizer- A device that converts a stream of liquid into a fine spray.

Baffle- A wall, barrier or panel used to change the direction of flow of liquid or gas.

Barometric pressure- The weight of the overlying air pressing down on the earth. It is also known as atmospheric pressure.

Barrel- Cylinder portion of a firetube boiler shell surrounding the tubes.

Base load- Is the term applied to that portion of a station or boiler load that is practically constant for long periods.

Beaded tube end- Rounded exposed end of a rolled tube when the tube metal is formed over against the sheet in which the tube is rolled and helps hold on a hose.

Blind nipple- A nipple, or a short piece of pipe or tube, closed at one end.

Boiler blowdown- Boiler blowdown is water intentionally wasted from a boiler to avoid concentration of impurities during continuing evaporation of steam. The water is blown out of the boiler with some force by steam pressure within the boiler. Occurs when water is removed from a steam boiler while the boiler is operating.

Boiler Blowdown safety valve- Boiler blowdown safety valve gets rid of excess pressure building in a boiler. A boiler safety measure.