ENGINEERING DICTIONARY

ABMA - American Boiler Manufacturers Association. ABRASION - The wearing away of a surface by rubbing, as with sandpaper on wood. ABRASION RESISTANCE - The ability of a material to resist surface wear. ABRASIVE EROSION - Erosive wear caused by the relative motion of solid particles which are entrained in a fluid, moving nearly parallel to a solid surface. ABSOLUTE HUMIDITY - Amount of moisture in the air, indicated in kg/kg of dry air. ABSOLUTE PRESSURE - Total pressure measured from an absolute vacuum. It equals the sum of the gauge pressure and the atmospheric pressure corresponding to the barometer. ABSOLUTE PRESSURE - Air at standard conditions (70°F air at sea level with a barometric pressure of 29.92 in Hg) exerts a pressure of 14.696 psi. This is the pressure in a system when the pressure gauge reads zero. So the absolute pressure of a system is the gauge pressure in pounds per square inch added to the atmospheric pressure of 14.696 psi (use 14.7 psi in environmental system work) and the symbol is "psia". ABSOLUTE TEMPERATURE SCALE - A scale of temperature measurement in which zero degrees is absolute zero. ABSOLUTE VELOCITY - The vector sum of the velocity of a fluid parcel relative to the earth and the velocity of the parcel due to the earth's rotation; the east-west component is the only one affected. ABSOLUTE ZERO - A hypothetical temperature at which there is total absence of heat. Since heat is a result of energy caused by molecular motion, there is no motion of molecules with respect to each other at absolute zero. It is theoretically the coldest possible temperature. ABSOLUTE ZERO TEMPERATURE - Temperature measured from absolute zero (-459.67°F, or -273.16°C). ABSORBENT - A material which, due to an affinity for certain substances, extracts one or more such substances from a liquid or gaseous medium with which it contacts and which changes physically or chemically, or both, during the process. Calcium chloride is an example of a solid absorbent, while solutions of lithium chloride, lithium bromide, and ethylene glycols are liquid absorbents. ABSORBER - That part of the low side of an absorption system, used for absorbing vapor refrigerant. ABSORPTION - A process whereby a material extracts one or more substances present in an atmosphere or mixture of gases or liquids accompanied by the material's physical and/or chemical changes. ABSORPTION REFRIGERATION SYSTEM - One in which the refrigerant, as it is absorbed in another liquid, maintains the pressure difference needed for successful operation of the system. ABSORPTION REFRIGERATOR - Refrigerator that creates low temperatures by using the cooling effect formed when a refrigerant is absorbed by chemical substance. ABSORPTION SYSTEM - A refrigeration system in which the refrigerant gas evolved in the evaporator is taken up in an absorber and released in a generator upon the application of heat. ABSORPTION TOWER - A tower or column, which effects contact between a rising gas and a falling liquid, so that part of the gas may be taken up by the liquid. ACCELERATION - The rate of change of velocity, as a function of time. Expressed in m/s. ACCELERATION DUE TO GRAVITY - The rate of increase in velocity of a body falling freely in a vacuum. Its value varies with latitude and elevation. The International Standard is 32.174 ft. per second per second. ACCELERATION PERIOD - In cavitation and liquid impingement erosion, the stage following the incubation period, during which the erosion rate increases from near zero to a maximum value. ACCELERATION - The time rate of change of velocity; i.e., the derivative of velocity; with respect to time. ACCEPTABLE WELD - A weld that meets all of the requirements and the acceptance criteria prescribed by the welding specifications. ACCESSIBLE HERMETIC - An assembly of motor and compressor, inside a single bolted housing unit. ACCUMULATOR - Storage tank which receives liquid refrigerant from evaporator and prevents it from flowing into suction line before vaporizing. ACETONE - A filler added to acetylene cylinders, capable of absorbing 25 times its own volume of acetylene. ACID - Literally hitter, but chemically the state of a water solution containing a high concentration of hydrogen ions. ACID ATTACK - Caused by an incomplete flushing after an acid cleaning process of boilers or similar equipment. ACID CLEANING - The process of cleaning the interior surfaces of steam generating units by filling the unit with dilute acid accompanied by an inhibitor to prevent corrosion and by subsequently draining, washing, and neutralizing the acid by a further wash of alkaline water. ACID CONDITION IN SYSTEM - Condition in which refrigerant or oil in a system, is mixed with vapor and fluids that are acidic in nature. ACID EMBRITTLEMENT - A form of hydrogen embrittlement that may be induced in some metals by an acid. ACID GAS - A gas that that forms an acid when mixed with water. In petroleum processing, the most common acid gases are hydrogen sulfide and carbon dioxide. ACID RAIN - Atmospheric precipitation with an pH below 5.6 to 5.7. ACID SOAK - A method of acid cleaning, in which the acid is pumped into the boiler and rests there for a period of time. ACIDIC - The reaction of a substance with water resulting in an increase in concentration of hydrogen ions in solution (see acid). ACIDIFIED - The addition of an acid (usually nitric or sulfuric) to a sample to lower the pH below 2.0. The purpose of the acidification is to "fix" a sample so it will not change until it is analyzed. ACIDITY - Represents the amount of free carbon dioxide, mineral acids, and salts (especially sulfates of iron and aluminum) which hydrolyze to give hydrogen ions in the water. The acidity is reported as millie equivalents per liter of acid, or ppm acidity as calcium carbonate, or pH, the measure of hydrogen ion concentration. ACOUSTIC - A term pertaining to sound, or the science of sound. ACROSS THE LINE - A method of motor starting, which connects the motor directly to the supply line on starting or running. ACTION - Refers to the action of a controller. It defines what is done to regulate the final control element to effect control. ACTIVATED ALUMINA - Chemical which is a form of aluminum oxide. It is used as a drier or desiccant. ACTIVATED CARBON - Is a specially processed carbon, used as a filter drier. Commonly used to clean air. ACTIVATED SLUDGE - An aerobic biological process for conversion of soluble organic matter to solid biomass, removable by gravity or filtration. ACTIVE STORAGE PILE - A method of stockpiling coal, sometimes called live storage. The pile is located outside the plant but adjacent to it, and usually contains four or five days of operating supply. The pile is not compacted, as it is not stored long enough to be exposed to the hazard of spontaneous combustion. ACTUATOR - The portion of a regulating valve, which converts mechanical, fluid, thermal, or electrical energy; into mechanical motion to open or close the valve seats or other such devices. ADIABATIC - Occurring with no addition or loss of heat from the system under consideration. ADIABATIC CHANGE - A change in the volume, pressure, or temperature of a gas, occurring without a gain of heat or loss of heat. ADIABATIC COMPRESSION - Compressing a gas without removing or adding heat. ADIABATIC COOLING - A method in which paramagnetic salts are pre-cooled, and then demagnetized, thereby producing further cooling. ADIABATIC EFFICIENCY -The ratio of actual work output of a heat engine to the ideal output. ADIABATIC EXPANSION - The expansion of a gas, vapor, or liquid stream from a higher pressure to a lower pressure, with no change in enthalpy. ADIABATIC PROCESS - A thermo-dynamic process in which no heat is extracted from or added to the system of the process. ADIABATIC SATURATION PROCESS - A process to determine absolute or relative humidity. ADJUSTABLE DIFFERENTIAL - A means of changing the difference between the control cut-in and cutout points. ADJUSTABLE RESISTOR - A resistor whose value can be mechanically changed, usually by the use of a sliding contact. ADSORBENT - A material which has the ability to cause molecules of gases, liquids or solids to adhere to its internal surfaces without changing the adsorbent physically or chemically. In water treatment, a synthetic resin possessing the ability to attract and to hold charged particles. ADSORPTION - The adhesion of the molecules of gases, dissolved substances, or liquids in more or less concentrated form, to the surface of solids or liquids with which they are in contact. Commercial adsorbent materials have enormous internal surfaces. ADSORPTION INHIBITORS - They are materials which caused them to be adsorbed on to the metal surface due to their polar properties. ADVECTION - The transfer of heat by horizontal movement of air. AERATION - Exposing to the action of air, like blowing air through water before discharging to a river. AERATION CELL - (see oxygen cell) AEROBIC - A condition in which "free" or dissolved oxygen is present in water. AERODYNAMIC NOISE - Also called generated noise, self-generated noise; is noise of aerodynamic origin in a moving fluid arising from flow instabilities. In duct systems, aerodynamic noise is caused by airflow through elbows, dampers, branch wyes, pressure reduction devices, silencers and other duct components. AGGLOMERATE - The clustering together of a few or many particles into a larger solid mass. AGITATOR - A device used to cause motion in confined fluids. AIR - A substance containing by volume approximately 78 - 79% nitrogen; 20.95% oxygen, .94% argon, traces of carbon dioxide, helium, etc. AIR BLAST TRANSFORMER - A transformer cooled by forcing a circulation of air around its windings. AIR CAPACITOR - Is a capacitor, which uses air as the dielectric between the plates. AIR CHANGES - A method of expressing the amount of air leakage into or out of a building or room in terms of the number of building volumes or room volumes exchanged. AIR CLEANER - A devise used to remove air borne impurities. AIR COIL - Coil on some types of heat pumps used either as an evaporator or a condenser. AIR CONDITIONER - They are basically refrigeration devices cooling air and rooms rather then food compartments. AIR CONDITIONER, UNITARY - An evaporator, compressor, and condenser combination; designed in one or more assemblies, the separate parts designed to be assembled together. AIR CONDITIONING -The process of treating air to simultaneously control its temperature, humidity, cleanliness, and distribution to meet the requirements of the conditioned space. AIR CONDITIONING UNIT - An assembly of equipment for the treatment of air so as to control, simultaneously, its temperature, humidity, cleanliness and distribution to meet the requirements of a conditioned space. AIR CONDITIONING, COMFORT - The process of treating air so as to control simultaneously its temperature, humidity, cleanliness and distribution to meet the comfort requirements of the occupants of the conditioned space. AIR COOLER - A factory-encased assembly of elements whereby the temperature of air passing through the device is reduced. AIR DIFFUSER - A circular, square, or rectangular air distribution outlet, generally located in the ceiling and comprised of deflecting members discharging supply air in various directions and planes, and arranged to promote mixing of primary air with secondary room air. AIR DIFFUSION AERATORS - They are aerators into which air is pumped into the water through perforated pipes, plates, or any other method. AIR DUCT - A tube or conduit for conveying air from one place to another. AIR FLOTATION - A process of accelerating sedimentation, by introducing air into the water, this lowers the density of the water, and increases the differences in the densities of the water and the suspended particles. (DAF), Dissolved Air Flotation. AIR GAP -The space between magnetic poles, or between the rotating and stationary assemblies in a motor or generator. AIR HANDLER - The fan blower, heat transfer coil, filter, and housing parts, of a system. AIR INFILTRATION – The leakage of air into a room through cracks in doors, windows, and other openings. AIR PURGE - The removal of undesired matter by replacement with air. AIR SATURATED - Moist air in which the partial pressure of the water vapor is equal to the vapor pressure of water at the existing temperature. This occurs when dry air and saturated water vapor coexist at the same dry-bulb temperature. AIR SENSING THERMOSTAT - A thermostat unit, in which the sensing element is located in the refrigerated space. AIR STANDARD - Air having a temperature of (20°C), a relative humidity of 36 percent, and under a pressure of 14.70 PSIA. The gas industry usually considers (16°C) as the temperature of standard air. AIR VENT - Valve, either manual or automatic, to remove air from the highest point of a coil or piping assembly. AIR WASHER - A water spray system or device for cleaning, humidifying, or dehumidifying the air. AIR, AMBIENT - Generally the air surrounding the object. AIR, DRY - Air without contained water vapor. AIR, OUTDOOR - Air taken from outdoors and, therefore, not previously circulated through the system. AIR, RE-CIRCULATED - Return air passed through the conditioner before being again supplied to the conditioned space. AIR, REHEATING - In an air conditioning system, the final step in treatment, in the event the temperature is too low. AIR, RETURN - Air returned from conditioned or refrigerated space. AIRBORNE SOUND - Sound which reaches the point of interest by radiation through the air. AIR-COOLED CONDENSER - Heat of compression is transferred from condensing coils to surrounding air. This may be done either by convection or by a fan or blower. AIR-SENSING THERMOSTAT – A thermostat unit, in which the sensing element is located in the refrigerated space. ALCOHOL BRINE - A water and alcohol solution, which remains as a liquid below 0°C. ALGAE - A minute fresh water plant growth which forms a scum on the surfaces of re-circulated water apparatus, interfering with fluid flow and heat transfer. Lower form of plant life, usually green and blue green algae appear in cooling water systems. They are responsible for copious amounts of stringy green slime masses. ALIVE - A term referring to a circuit in which a current is flowing. Also referred to as live. ALKALI - A substance having marked basic properties. Applying to hydroxides of potassium, sodium, lithium, and ammonium. They turn red litmus to blue. Includes hydroxides of the alkaline earth metals of barium, strontium, and calcium. ALKALINE - Having a pH greater than 7. ALKALINE BOIL-OUT - Employed to remove oil and grease deposits from heating surfaces. ALKALINITY - An expression of the total basic anions (hydroxyl groups) present in a solution. It also represents, particularly in water analysis, the bi-carbonate, carbonate, and occasionally, the borate, silicate, and phosphate salts which will react with water to produce the hydroxyl groups. ALLEN TYPE SCREW - A screw with a recessed hex shaped head. ALLOY - A substance having metal properties and being composed of two or more chemical elements of which at least one is a metal. ALLOY STEEL - Steel containing specific quantities of alloying elements (other than carbon) and commonly accepted amounts of manganese, copper, silicon, sulfur, and phosphorus). ALTERNATING CURRENT (AC) - Electric current in which the direction of the current alternates or reverses. In a 60 Hertz (cycle) current, the direction of current flow reverses in 1/120th of a second; most commonly used current. ALTERNATOR - A device which converts mechanical energy, into alternating current. ALTIMETER - An instrument used to measure the height above a reference point, such as ground or sea level. ALUM - Is an aluminum sulfate or filter alum. Acts in the range of 5.0 to 8.0 pH. ALUMINA - Aluminum oxide occasionally found as an impurity in water in very small amounts. AMBIENT AIR TEMPERATURE - Temperature of fluid (usually air) which surrounds object on all sides. AMBIENT CONDITIONS - The conditions of temperature, pressure, and humidity, existing around an instrument. AMBIENT NOISE -The normal sound in a room or other location. AMERICAN STANDARD PIPE THREAD - A type of screw or thread, commonly used on pipe fittings to assure a tight seal. AMERICAN WIRE GAUGE (AWG) - A system used in the United States for measuring the size of solid wires. AMINE - A chemical use in water treatment as a filming or neutralizing agent to protect the metal parts. AMMETER - An instrument for measuring the magnitude of electric current flow. AMMETER SHUNT - A low-resistance conductor, placed in parallel (shunt) with an ammeter movement, so that most of the current flows through the shunt, and only a small portion flows through the ammeter. This extends the useful range of the meter. AMMONIA - Chemical combination of nitrogen and hydrogen (NH3). Ammonia is a very efficient refrigerant and identified as R-117. AMORPHOUS - A solid not having a repetitive three-dimensional pattern of atoms. AMPACITY - A wire's ability to carry current safely, without undue heating. The term formerly used to describe this characteristic was current capacity of the wire. AMPERAGE - An electron or current flow of one coulomb per second, past a given point in a circuit. AMPERE - The unit used for measuring the quantity of an electrical current flow. One ampere represent a flow of one coulomb per second. AMPERE HOUR - A term used for rating battery capacity. As stated, an ampere for an hour; ex: 5 amperes for 20 hours = 100 amp hour on a 20 hr rating. AMPERE TURNS - A term used to measure magnetic force. It represents the product of amperes, times the number of turns of the coil, in an electromagnet. AMPLIFICATION - The process of obtaining an output signal greater than the input signal, through auxiliary power controlled by the input signal. The process of increasing the strength, current, power, or voltage, of the signal. AMPLITUDE - The maximum instantaneous value of alternating current or voltage. It can be in either a positive or negative direction. The greatest distance through which an oscillating body moves from the mid point. ANAEROBIC - A condition in which "free" or dissolved oxygen is not present in the water. ANALYSIS - The process of determining the composition of a substance, by chemical or physical methods. ANEMOMETER - An instrument for measuring the velocity of a fluid. ANGLE OF LAG OR LEAD - The phase angle difference, between two sinusoidal wave forms having the same frequency. ANGLE VALVE - A type of globe valve design, having pipe openings at right angles to each other. Usually one opening on the horizontal plane and one on the vertical plane. ANGSTROM UNITS - A unit of wave length, equal in length to one ten billionth. ANHYDROUS CALCIUM SULFATE - A dry chemical, made of calcium, sulfur, and oxygen. ANION - A negatively charged ion such as the chloride ion (Cl-). ANION INTERCHANGE - The displacement of one negatively charged particle by another on an anion-exchange material. This principle is used with water treatment. ANNEAL - To soften by heating and allowing to cool slowly. ANNEALING - A process of heat treating metal, to get the desired properties of softness and ductility, (easy to form). ANODE - In electrolysis or electrochemical corrosion, a site where metal goes into solution as a cation leaving behind an equivalent of electrons to be transferred to the opposite electron, called the cathode. ANODIZING - The treatment of a metal surface whereby the metal is made anodic. ANSI - American National Standard Institute, which is an organization defining standards for computer language. ANSI-B.31.1 - Power Piping. ANSI-B.31.5 - Refrigeration Piping. ANTI KNOCK VALUE - A premature explosive combustion, as the detonation of the fuel air mixture in an internal combustion engine, produces a characteristic knock. The Anti Knock Value is the measure of its resistance to the condition which tends to produce this knock. ANTICIPATING CONTROL - One which, by artificial means, is activated sooner than it would be without such means, to produce a smaller differential of the controlled property. Heat and cool anticipators are commonly used in thermostats. ANTICIPATORS - A small heater element in two-position temperature controllers which deliberately cause false indications of temperature in the controller in an at tempt to minimize the override of the differential and smooth out the temperature variation in the controlled space. ANTI-CORROSIVE ADDITIVE - A lubricant additive to reduce corrosion. ANTI-FOAM ADDITIVE (FOAM INHIBITOR) An additive used to reduce or prevent foaming. ANTIFOAM AGENTS - The reduction of carry over by the addition of polymerized esters, alcohol’s, and amides. The antifoam agent is absorbed on the steam generating surface resulting in a hydrophobic condition, causing fewer but larger steam bubbles, which readily coalesce. These agents also weaken the wall of the bubble formed, causing them to quickly burst on the water surface. ANTIFOULANTS - Are materials which prevent fouling from depositing on heat transfer equipment. Materials that prevent deposits forming; include anti- oxidants, metal coordinators, and corrosion inhibitors. Compounds that prevent deposition are surfactants. They act as detergents or dispersants. ANTIFREEZE - Compounds of glycol’s or alcohol’s, that lower the freezing point of cooling water systems. ANTIOXIDANT - A substance which when added in small amounts to petroleum products, will delay or inhibit undesirable changes; such as the formation of gum, sludge, and acidity, which are brought about by oxidation. ANTI-OXIDANT - An additive for the purpose of reducing the rate of oxidation and subsequent deterioration of the material. ANTI-SCUFFING LUBRICANT - A lubricant that is formulated to avoid scuffing. ANTI-SEIZURE PROPERTY - The ability of the bearing material to resist seizure during momentary lubrication failure. ANTI-WEAR ADDITIVE - A lubricant additive to reduce wear. API - American Petroleum Institute. API GRAVITY (API DEGREE) - A measure of density used in the US petroleum industry. APPARENT (EMF) - The apparent voltage, as measured by the drop in pressure due to a current flowing through a resistance. APPARENT WATTS - The product of volts times amperes, in an alternating current circuit. AQUEOUS - Watery. A substance containing water. AQUIFER - A porous, subsurface geological structure carrying or holding water. ARC - A flash, caused by an electric current ionizing a gas or vapor. ARC BRAZING - A brazing process in which the heat required is obtained from an electric arc. ARC FURNACE - An electric furnace, in which heat is produced by an arc between two electrodes. ARC WELDING - A group of welding processes which produce coalescence of metals by heating them with an arc, with or without the application of pressure, and with or without the use of a filler metal. ARC WELDING - A process where coalescence is obtained by heating with an electric arc. ARCHIMEDES PRINCIPAL - States that an upward force acting on a body wholly or partly submerged in a fluid, is equal to the weight of the fluid displaced, and acts through the center of gravity of the fluid displaced, or the center of buoyancy. ARMATURE - the rotating part of an electric motor or generator. The moving part of a relay or vibrator. ARMATURE AIR GAP - The air space between the stationary and rotating parts of a motor or generator, through which magnetic lines of force pass. ARMATURE BACK AMPERE TURNS - The magnetic field produced by current flowing in the armature winding, that opposes and reduces the number of magnetic lines of force, produced by the field magnets of a motor or generator. ARMATURE BAR - Copper bars used in place of wire windings, in large armatures, generators, or motors. ARMATURE CIRCUIT - The path that the current takes, in flowing through the windings from one brush to another. ARMATURE COIL - The loop or coil of copper wire, placed on the armature core, and forming part of the winding. ARMATURE CORE -The laminated iron part of the armature, formed from thin sheets or disks of steel, on which the windings are placed. ARMATURE CURRENT - The current flowing from the armature of a generator, to the armature of a motor. Not including the current taken by the shunt field. ARMATURE DEMAGNETIZATION - The reduction in the effective magnetic lines of force, produced by the armature current. ARMATURE REACTION - The effect, that the magnetic field produced by the current flowing in the armature, has on the magnetic field produced by the field coils. ARMATURE REGULATING RESISTORS - Are resistors, designed to regulate the speed or torque of a loaded motor, by placing a resistance in the armature or power circuit. ARMATURE RESISTANCE - The resistance of the wire used in the windings of the armature, measured between the rings or brushes, or from positive to negative terminals. ARMATURE SLOT -The groove or slot in the armature core, into which the coils or windings are placed. ARMATURE TESTER - Any device used for locating faults or defects in the armature winding. ARMATURE VARNISH - Is a liquid put on the field and armature windings, to improve the insulation of the cotton covering on the wires. ARMATURE WINDING - All of the copper wire placed on the armature, and through which the current flows. AROMATICS - A group of hydrocarbons of which benzene is the parent. They are called "aromatics" because many of their derivatives have sweet or aromatic odorous. ARTIFICIAL MAGNET - Is a manufactured magnet, which is distinguished from a natural occurring magnet. ASHRAE - The American Society of Heating, Refrigeration, and Air Conditioning Engineers. ASME - American Society of Mechanical Engineers. ASME APPENDIX SECTION I - Explains matter which is mandatory, unless specifically referred to in the rules of the code, including formulas. ASME BOILER CODE - The boiler code listing standards, specified by the American Society of Mechanical Engineers, for the construction of boilers. ASME PART PEB SECTION I - Requirements for electric boilers. ASME PART PFH SECTION I - Requirements for feed water heaters. ASME PART PFT SECTION I - Requirements for firetube boilers. ASME PART PG SECTION I - General requirements for all methods of construction. ASME PART PMB SECTION I - Requirements for miniature boilers. ASME PART PVG SECTION I - Requirements for organic fluid vaporizer generators. ASME PART PW SECTION I - Requirements for boilers fabricated by welding. ASME PART PWT SECTION I - Requirements for watertube boilers. ASME SECTION I - Power Boilers. ASME SECTION II - Material specifications. ASME SECTION III - Nuclear Power Plant Components. ASME SECTION IV - Heating boilers ASME SECTION IX ASME SECTION V - Nondestructive examination. ASME SECTION VI - Recommended rules for the care and operation of heating boilers. ASME SECTION VII - Recommended rules for the care and operation of power boilers. ASME SECTION VII APPENDIX - Consists of conversion factors for converting Imperial units to SI Units. ASME SECTION VII SUBSECTION C1 - Rules for routine operation of power boilers. ASME SECTION VII SUBSECTION C2 - Operating and maintaining boiler appliances. ASME SECTION VII SUBSECTION C3 - Rules for inspection. ASME SECTION VII SUBSECTION C4 - Prevention of direct causes of boiler failure. ASME SECTION VII SUBSECTION C5 - Is partial rules for the design of installations. ASME SECTION VII SUBSECTION C6 - Operation of boiler auxiliaries. ASME SECTION VII SUBSECTION C7 - Control of internal chemical conditions. ASME SECTION VIII - Pressure vessels. ASME SECTION X - Fiberglass reinforced plastic pressure vessels. ASME SECTION XI - Rules for in-service inspection of Nuclear Power Plant components. ASPECT RATIO - The ratio of the length to the width, of a rectangular air grille or duct. ASPIRATING PSYCHROMETER - A device which draws sample of air through it to measure humidity. ASPIRATION - Production of movement in a fluid by suction created by fluid velocity. ASTM - American Society for Testing and Materials. ASYNCHRONOUS - Not having the same frequency. Out of step, or phase. ASYNCHRONOUS GENERATOR - An induction generator. ASYNCHRONOUS MOTOR - An induction motor, whose speed is not synchronous with the frequency of the supply line. ATMOSPHERE - Is the mixture of gases and water vapor surrounding the earth. ATMOSPHERIC ELECTRICITY - Is static electricity, produced between cloud fronts in the atmosphere. ATMOSPHERIC PRESSURE - Pressure exerted by the weight of the atmosphere; standard atmospheric pressure is 101.325 kPa or 1.01325 bars or 14.696 psia or 29.921 inches of mercury at sea level. ATOM - The smallest complete particle of an element, which can be obtained, yet which retains all physical and chemical properties of the element. ATOMIC NUMBER - The number of protons found in the nucleus of an atom, of an element. ATOMIC WEIGHT - The weight of an elementary atom, in relation to the weight of an atom of hydrogen. A hydrogen atom being taken as 1.00g. ATOMIZE - Process of changing a liquid to minute particles or a fine spray. ATTEMPERATING WATER IMPURITY - Refers to turbine deposits caused by impurities in the water used for attemperators. (Chemicals used with attemperating water should be of the volatile type). ATTEMPERATOR - An apparatus for reducing and controlling the temperature of a superheater vapor or a fluid. ATTENUATION - The sound reduction process in which sound energy is absorbed or diminished in intensity as the result of energy conversion from sound to motion or heat. ATTRITION - The rubbing of one particle against another in a resin bed; frictional wear that will affect the site of resin particles. AUTOMATIC - Self-acting. Operating by its own mechanism, when activated by some triggering signal. AUTOMATIC CONTROL - The process of using the differences, between the actual value, and desired value, of any variable, to take corrective action, without human intervention. AUTOMATIC CONTROLLER - A device that measures the value of a measured variable, and operates to correct or limit the deviation from a selected reference. Both measuring and control applications. AUTOMATIC DEFROST - System of removing ice and frost from evaporators automatically. AUTOMATIC EXPANSION VALVE (AEV) - A type of metering device that senses low-side pressure and modulates in order to maintain low-side pressure constant. AUTOMATIC EXTRACTION UNIT TURBINE - Bleeds off part of the main steam flow at one, two, or three points. Valved partitions between selected stages control the extracted steam pressure at the desired level. When extracted steam flowing through the unit does not produce enough shaft power to meet the demand, more steam flows through the turbine to exhaust. Located between steam supply and process steam headers. AUTOMATIC FROST CONTROL - Control which automatically cycles refrigerating system to remove frost formation on evaporator. AUTOMATIC GOVERNING SYSTEM - A system which correlates steam flow, pressure, shaft speed, and shaft output, for any one turbine unit. AUTOMATIC ICE CUBE MAKER - Refrigerating mechanism designed to automatically produce ice cubes in quantity. AUTOMATIC RESET (INTEGRATION) - Is a type of control, in which the controller output, changes at a rate proportional to the deviation or error. The output will continue to change as long as any deviation or error exists. AUTOMATIC STARTER - AUTOMATION - The employment of devices, which automatically control one or more functions. AUTOTRANSFORMER - A transformer in which both primary and secondary coils, have turns in common. The step up or step down of voltage, is accomplished by taps in common windings. AUXILIARY CONTACTS - A set of contacts that perform a secondary function, usually in relation to the operation of a set of primary contacts. Avogadro's HYPOTHESIS - States that equal volumes of different gases, at the same temperature and pressure, will contain equal numbers of molecules. Avogadro's  AVERAGING ELEMENT - A thermostat sensing element which will respond to the average duct temperature. AXIAL FAN - Consists of a propeller or disc type of wheel within a cylinder that discharges air parallel to the axis of the wheel. AXIAL FLOW COMPRESSOR - Uses rotor blades shaped like airfoils, to bite into the air, speed it up, and push it into the subsequent stationary blade passages. These passages are shaped to form diffusers, that slow up the incoming air, and make it pressurize itself by catching up with the air ahead of it. AZEOTROPE - Having constant maximum and minimum boiling points. AZEOTROPIC MIXTURE - Example of azeotropic mixture - refrigerant R-502 is mixture consisting of 48.8 percent refrigerant R-22 and 51.2% R-115. The refrigerants do not combine chemically, yet azeotropic mixture provides refrigerant characteristics desired.