ABSOLUTE HUMIDITY – Actual quantity of water vapour in the air, usually expressed as so many grains of moisture in a cubic foot of air.

ABSOLUTE PRESSURE – Pressure measured from the true zero or point of no pressure.

ADIABATIC COMPRESSION – Compression of air without receiving or giving up heat.

AFTER COOLER – A type of surface heat exchanger in which compressed air is cooled after compression.

AIR – A gas consisting of mechanical mixture of 23.2% (by weight) of oxygen 75.5% nitrogen and 1.3% argon, 21 % (by volume) of oxygen, 78.06% nitrogen and 0.94% argon.

AIR COMPRESSOR – A machine (driven by any prime mover), which compresses air into a receiver to be used at a greater or shorter distance.

AIR COOLED COMPRESSOR – A compressor whose cylinder has cast integral numerous thin fins to form excess cooling surface exposed to a draught of cool air which forms the medium to carry off some of the heat of compression.

AIR ENGINE – A very small reciprocating engine driven by compressed air.

AIR EXHAUSTER – A suction fan, a vacuum pump.

AIR METER – An apparatus used to measure the rate of flow of air or gas.

AIR RECEIVER – A vessel into which compressed air is discharged, to be stored until required.

ANEMOMETER – An instrument for measuring the velocity of flow of a gas, either by mechanical or electrical methods.

ATMOSPHERIC PRESSURE – The force exerted by the weight of the atmosphere on every point with which it is in contact.

AXIAL COMPRESSOR – A multistage, high efficiency compressor comprising alternate rows of moving and fixed blades attached to a rotor and its casing respectively. The flow of fluid is essentially parallel to the axis of the compressor.

ACCELERATOR – A pedal connected to the carburettor throttle valve of a motor vehicle or to the fuel injection control where oil engines are used.

ACKERMAN PRINCIPLE – Steering geometry in which the outer ends of the steering arms are bend slightly inward so that when the vehicle is making a turn, inside wheel will turn more sharply than the outer wheel. This principle produces toe out on turns.

ACKERMAN STEERING – Arrangement whereby a line extended from the track arms, when the wheels are set straight ahead, should meet on the chassis centre line at 2/3 of the wheel base from the front, allowing inner stub axle to move through a greater angle than the outer.

AERODYNAMIC DRAG – Is the air resistance to the motion of the vehicle. This consists of profile drag, induced drag, skin friction drag, interference drag, and cooling and ventilation drag.

AERODYNAMIC LIFT – Is the vertical component of the resultant force caused by the pressure distribution on the vehicle body.

AIR BLEEDER – A device used to remove air from a hydraulic system. Types include a needle valve, capillary tubing to the reservoir, and a bleed plug.

AIR BRAKE – A braking system which uses compressed air to supply the effort required to apply brakes.

AIRFOIL – Device, similar to a stubby wing.

AIR RESISTANCE – The motion of an automobile is associated with the displacement of air particles, which requires some power of the engine. Air resistance depends on the size and shape of the vehicle body, speed of the vehicle and wind velocity.

AIR SPRING – Container and plunger are separated by air under pressure. When container and plunger attempt to squeeze together, air compresses and produces a spring effect. Air spring has been used in some suspension systems.

ALL WEATHER TYRE – A tyre designed to provide good traction on dry, wet and dirt and snow covered roadways.

ANTI DAZZLE MIRROR – One having a photoelectric control circuit which changes it from a fully reflecting condition to partial reflection from a glass air interface when actuated by the head lamp beam of a following vehicle.

ANTILOCK BRAKE SYSTEM (ABS) – If the brakes are applied so hard that the wheels tend to stop turning and thus a skid starts to develop, the antilock brake system comes into operation and partly releases the brakes. This makes the wheels continue to rotate. However, intermittent braking continues. But it is held below the point where the skid would start.

ANTIMIST PANEL – A panel fitted to the rear window enclosing a volume of still air between itself and the outer glass.

ANTIROLL BAR – Torsion bar mounted transversely in the chassis in such a way so as to counteract the effect of opposite spring deflections.

ARCH – The curve of a leaf spring. If the centre is lower than the ends, it is called positive arch, if the centre is higher than the ends, it is called negative arch.

ARCING (brakes) – Grinding new brake linings to the same diameter (arc) as that of the brake drum surface.

ASPECT RATIO – The ratio of the width to the length. On tyres, it is the fully inflated height divided by the cross section.

AUTOMOBILE – is a self propelled vehicle. The power required to propel the vehicle is supplied by the engine (also called prime mover). Scooters, motor cycles, cars, buses, trucks etc., are different types of automotive vehicles.

AUTOMATIC LEVEL CONTROL – A suspension system which compensates for variations in load in the rear of the car, positioning the rear at a pre-designed level regardless of load.

AUTOMATIC TRANSMISSION – A power transmission system for road vehicles, in which the approximately optimum engine speed is maintained through mechanical or hydraulic speed changing devices which are automatically selected and operated by reference to the road speed of the vehicle.

AXLE – A cross bar supporting a vehicle on which one or more wheels turn.

AXLE (full floating) – Axle used to drive rear wheels. It does not hold the wheels on nor support them.

AXLE (semi quarter or one quarter floating) – Axle used to drive wheels, hold them on and support them.

AXLE THREE QUARTER FLOATING – Axle used to drive rear wheels as well as hold them on and support them.

AXLE FLANGE – A flat surface on the outboard end of the axle shaft to allow wheel attachment.

AXLE GEAR – A gear in the differential carrier that drives the driving wheels.

AXLE RATIO – Relationship or ratio between the numbers of times the propeller shaft or drive shaft must revolve to turn the axle shafts one turn.

AXLE SHAFT – The shaft used to transmit power from the differential to the wheels.

ACCUMULATOR – A device used for storing liquid under pressure (sometime used to smooth fluid flow).

ADVANCE (injection timing) – To set the timing of the injection pump or injectors for an earlier injection.

AFTER BURNING – The burning of fuel that is left in the combustion space when the fuel injection stops.

AFTER COOLER – A device used on turbocharged engines to cool the air which has undergone compression, before its entry into the engine cylinder.

AIR CELL – A small auxiliary combustion chamber used in certain types of compression ignition engines, for promoting turbulence and improving combustion.

AIR FUEL RATIO – At full load operation, the air fuel ratio is at least 35 to 50 percent greater than the stoichiometric value. Air fuel ratio in a normal diesel engine varies from around 100: 1 at idle speed to about 30: 1 at full load.

AIR INJECTION SYSTEM – The system which injects the required quantity of fuel into the combustion space with the aid of compressed air.

AIRLESS INJECTION – Injection of liquid fuel into the cylinder of an oil engine by a high pressure fuel pump, so dispensing with the compressed air necessary in the early diesel engines. Also called SOLID INJECTION or MECHANICAL INJECTION.

AIR STARTING VALVE – A valve which admits compressed air to the air starter for starting purposes.

AIR VENT – Arrangement that helps to remove air from the fuel injection system.

ANTECHAMBER – A small auxiliary combustion chamber, used in some compression ignition engines, in which partial combustion of fuel takes place and this is used to force the burning mixture into the cylinder, so promoting more perfect combustion.

ATOMIZATION – The breaking up of fuel jet into fine particles as it is sprayed into the combustion chamber.

ATOMIZER – A device which disperses liquid fuel into fine particles (pulverized spray).

AERATOR – A device for fluffing (or decreasing the density of) and cooling the sand by the admixture of air.

AIR GATE – A vertical channel for the removal of gases from the mould; checking of the filling of the mould cavity with metal and feeding up the casting with metal during solidification.

AIR HOLE – Hole in a casting caused by air or gas trapped in the metal during solidification.

AIRLESS BLAST CLEANING – A process whereby the abrasive material is applied to the object being cleaned by centrifugal force generated by a rotating vane type wheel.

ANTIPIPING (material) – Usually refers to an insulating material placed on the top of a sprue or riser that keeps the metal in liquid or semi liquid form for a long period of time and minimizes the formation of the usual conical pipe or shrink in the top of a sprue or riser.

ARBOR – A metal barrel, frame, or plate to support or carry part of a mould or core.

ATMOSPHERIC RISER – Blind riser which employs atmospheric pressure to aid feeding.

ABRASIVE – A natural or artificial material such as sand stone, emery, aluminium oxide or silicon carbide.

ACID – A chemical term to define a material which gives an acid reaction.

ADDITIVES – Chemicals added to oil or fuel to increase its effectiveness and obtain desirable qualities.

ADHESIVES – Materials or compositions that enable two surfaces to join together. An adhesive is not necessarily a glue, which is considered to be a sticky substance, since many adhesives are not sticky.

AGGREGATE – Small particles such as powders that are used for powder metallurgy, that are loosely combined to form a whole, also sand and rock as used in concrete.

ALLOTROPIC METALS – Metals which exist in one lattice form over a range of temperature, but at a certain temperature the lattice form changes to another type which is stable over another temperature range.

ALLOY – A substance having metallic properties and is composed of two or more chemical elements, of which at least one is a metal.

ALLOYING ELEMENTS – Elements either metallic or non-metallic added intentionally to the base metal, to make a marked change in the properties of the base metal and to secure certain desirable properties.

ALLOY STEEL – Steel containing significant quantities of alloying elements (other than carbon and the commonly accepted amounts of manganese, silicon, sulphur and phosphorus) added to effect changes in mechanical and physical properties.

ALNICOS – Alnicos materials are composed mainly of aluminium, nickel, cobalt and iron. Some include additions of copper and titanium. They are high-coercive force, high magnetic energy alloys.

ALOXITE – Artificial abrasive material used in the manufacture of grinding wheels. Essentially it consists of alumina, or aluminium oxide, the chemical symbol for which is Al2O3·

ALPHA IRON – The body centered cubic form of pure iron, stable below 1025°C.

ALUMEL – A nickel base alloy containing about 2.5% Mn, 2% AI, and

1 % Si, used chiefly as a component of pyrometric thermocouples.

ALUMINIUM – Greyish white metal, very light in weight, and having in its pure form low mechanical strength, frequently alloyed with other elements to improve its physical characteristics.

ALUMINIUM ALLOY – Aluminium which is alloyed with other metals to give it strength and desirable properties.

ALUMINIUM BRONZE – Alloy containing 90% copper and 10% aluminium, extensively used for die casting.

ANTIFREEZE – A chemical added to the coolant in order to lower its freezing point.

ANTIFRICTION BEARINGS – Ball, roller and needle bearings exhibit very low friction and are suitable for very high speeds, and high loading.

ANTIMONY – Brittle, bluish white metallic element designated Sb. Melting point 630°C. Used as a constituent in some alloys, for instance, bearings and storage battery plates.

ARGON – An inert gas used in certain welding and heat treatment processes.

ARSENIC – A brittle, greyish metallic element designated As. Melting point 814°C. Used as a constituent in some alloys, and in the manufacture of lead shot.

ASBESTOS – A fibrous organic mineral that is non-combustible, non-conducting and acid resistant.

ATOM – The smallest particle of an element.

AUSTENITE – A solid solution of iron and carbon and sometimes other elements in which gamma iron, characterized by a face centered crystal structure, is the solvent. This is stable only within a particular range of composition and temperature, and is non-magnetic.

AUSTENITIC CAST IRON – Cast iron containing such a proportion of alloying constituents (nickel, chromium, copper or manganese) that the structure in the cast state is completely austenitic at ordinary temperatures.

ABSOLUTE VISCOSITY – Force per unit area required to move a surface at unit velocity, when it is separated by a fluid of unit thickness from a stationary surface.

ADDITIVES – Chemical compounds used to alter the characteristics of lubricating oils.

ANGLE OF REPOSE – The minimum inclination which a plane can have consistent with the body on it sliding down the plane by the force of gravity. It is the same as the friction angle.

ANTI CORROSION ADDITIVES – Chemical compounds added to lubricating oil to reduce or prevent the chemical reaction of acids (formed by the oxidation of oil) which destroy some bearing materials, such as lead in lead copper bearings, used for crankshafts and connecting rods of engines.

ANTI OXIDATION ADDITIVES – Chemical compounds added to decrease oxidation of the oil. These have a greater affinity for oxygen than does the oil.

API HEAVY DUTY TYPE OIL – Motor oil having oxidation stability, bearing corrosion preventive properties, and detergent-dispersant characteristics necessary to make it generally suitable for use in both high speed diesel and gasoline engines under heavy duty service conditions.

API PREMIUM TYPE OIL – Motor oil having the oxidation stability and bearing corrosion preventive properties necessary to make it generally suitable for use in internal combustion engines where operating conditions are more severe than regular duty.

API REGULAR TYPE OIL – Motor oil generally suitable for use in internal combustion engines under moderate operating conditions.

ACCELERATOR – Device for rapid control of the speed of an engine, for quick opening and closing of the throttle which regulates the quantity of air fuel mixture into the engine cylinder.

ACHESON GRAPHITE – That made from coke in an electric furnace.

ACTIVATED CARBON – A highly absorbent form of carbon used to remove odours and toxic substances from gaseous emissions or to remove dissolved organic matter from wastewater.

ADDITIVE – A substance added to fuel or oil or grease which improves the properties of the same.

ADIABATIC FLAME TEMPERATURE – The maximum possible temperature attained by the products of reaction, when the reaction goes to completion and all the heat released is used to heat up the products.

AERATION TEST BURNER – Apparatus by which the combustion characteristics of commercial gases can be correlated and calibrated.

AEROSOL – A particle of solid or liquid matter that can remain suspended in the air because of its small size. Particulates under 1 micron in diameter are called aerosols.

AFTER BOIL – Boiling of the fuel in the carburettor or coolant in the engine immediately after the engine is stopped.

AFTER BURNING – In an internal combustion engine, the persistence of the combustion process beyond the period proper to the working cycle, i.e., into the expansion period.

AFTER BURNER – In an automobile engine, a type of exhaust manifold that burns the hydrocarbon and carbon monoxide remaining in the exhaust gas.

AIR ASPIRATOR SYSTEM – An air injection system using a valve opened and closed by pulses in the exhaust system.

AIR FUEL MIXTURE – Air and fuel travelling to the combustion chamber after being mixed by the carburettor.

AIR FUEL RATIO – Ratio (by weight) between air and fuel that makes up engine fuel mixture.

AIR INJECTION SYSTEM – A system which injects air into the exhaust manifold or thermal reactor so that the combustion of the carbon monoxide and unburned hydrocarbons in the exhaust can be completed.

AIR MASS METERING – In some fuel injection systems, fuel metering is controlled primarily by engine speed and the amount of air actually entering the engine.

AIR POLLUTION – Contamination of earth’s atmosphere by various natural and manmade pollutants such as smoke, gases, dust etc.

ALCOHOL – Volatile liquid fuel consisting wholly or partly, of alcohol, able to withstand high compression ratios without detonation.

ANTHRACITE COALS – Slow burning coals which yield very little ash, moisture and less than 10 per cent volatiles, generally used in closed stoves.

ANILINE POINT – The lowest temperature at which an oil is completely miscible with an equal volume of aniline.

ANTIBACKFIRE VALVE – Valve used in air injection reaction exhaust emission control system to prevent backfiring during the period immediately following sudden declaration.

ANTIKNOCK – In engine fuels, that property which opposes knocking i.e., auto ignition.

ANTIKNOCK COMPOUND – An additive put into gasoline to suppress knocking or detonation e.g., Tetra ethyl lead.

ANTIPERCOLATOR – Device for venting vapours from main discharge

tube, or well, of a carburettor.

APIEZON OILS – The residue of almost zero vapour pressure left by vacuum

distillation of petroleum products.

API GRAVITY – The American Petroleum Institute (API) has established

the formula for calculating the specific gravity of a fuel or oil as Degree

API= ((141.5/specific gravity at 60/60 degree F)–131.5). The symbol

60/60 degree F is interpreted as the ratio of the weight of a given volume

of oil at 60 degree F to the weight of the same volume of water at 60

degree F.

ASH – An inorganic non-combustible residue obtained by combustion of

an oil or fuel in the presence of air.

ASH AND SLAG – Impurities that do not burn and usually troublesome

elements in coal fired boilers.

ASH FREE BASIS – When fuels are delivered on an ash free basis, it means

that the percentage of the ash has been deducted and the other

constituents have their percentages recalculated on 100 per cent total

without the ash.

ATMOSPHERIC GAS BURNER SYSTEM – A natural draught burner

injector, in which the momentum of a gas stream projected from an

orifice into the injector throat inspirates from the atmosphere a part of

the air required for combustion.

ATOMIZATION – The spraying of a liquid through a nozzle so that the

liquid is broken into a very fine mist.

ATOMIZER – A nozzle through which oil fuel is sprayed into the combustion

chamber of an oil engine or boiler furnace. It breaks up the fuel into a

fine mist so as to ensure good dispersion and combustion.

A

UTOIGNITION – The self-ignition or spontaneous combustion of a fuel

when introduced into the heated charge in the cylinder of a compression

ignition engine.

AUTOMATIC CHOKE – A carburettor choke device (valve) that

automatically positions itself in accordance with the carburettor needs

or engine temperature.

ADIABATIC PROCESS – Thermodynamic process in which no heat is transferred to or from the system during the process. A reversible adiabatic process is called ISENTROPIC PROCESS.

AIRFOIL – A streamlined form bounded principally by two flattened curves and whose length and width are very large in comparison with thickness. The airfoil may be a symmetrical airfoil or a non-symmetrical airfoil.

AIRFOIL DRAG FORCE – Force acting on the airfoil in the direction of motion, represents frictional forces.

AIRFOIL LIFT FORCE – Force acting on the airfoil in the direction perpendicular to the direction of motion. Basic force causing the aeroplane to maintain its lift.

AIR RATE – Kilograms per second of airflow required per net horse power developed. Also called FLOW RATE.

ANGLE OF ATTACK – The angle of inclination of the non-symmetrical airfoil with the direction of the undisturbed flow.

ANGLE OF DEVIATION – The difference between the fluid angle at outlet and the blade angle at outlet. This may be positive or negative. Sometimes called DEVIATION.

ANGLE OF INCDIENCE – The difference between the fluid angle at inlet and the blade angle at inlet. This may be positive or negative. Sometimes called INCIDENCE.

ANNULAR TYPE COMBUSTION CHAMBER – The combustion chamber which is made up of four concentric surfaces surrounding the axis of the rotor, forming three chambers on either side of the rotor, the middle casing acts as a flame tube and the inner and outer casings act as air casings, with a series of burners at the front end.

ASPECT RATIO OF BLADE – Ratio of blade height to blade chord.

AXIAL FLOW COMPRESSOR – A type of compressor in which the fluid flow is almost parallel to the axis of the compressor and the flow is decelerating or diffusing and pressure rises are obtained by causing the fluid to pass through a number of expanding spaces with consequent reduction in velocity.

AGING – The process of holding metals at room temperature or at a predetermined temperature for the purpose of increasing their hardness or strength by precipitation. Aging is also used to increase dimensional stability in metals such as castings.

AGE HARDENING – Change in the physical properties, e.g., hardness and strength that occurs in certain light metals after heat treatment.

ALLOYING OF METAL – The addition of varying proportions of other elements to a basic metal in order to produce an alloy having specific properties.

ANODIC TREATMENT – Formation of a protective layer of oxide on the surface of aluminium and its alloys by electrolytic action, in order to resist corrosion.

ANNEALING – A heat treatment in which metals are heated and then cooled very slowly for the purpose of decreasing hardness. Annealing is used to improve machinability and to remove stresses from weldments, forgings and castings. Also used to remove stresses resulting from cold working and to refine and make uniform the microscopic internal structures of metals.

ANODIZING – To subject a metal to electrolytic action, as takes place at the anode of a cell, in order to coat it with a protective or decorative film, used for nonferrous metals.

AUSTEMPERING – A heat treating process consisting of quenching a ferrous alloy at a temperature above the transformation range in a medium such as molten lead, the temperature of the quenching medium is maintained below that of pearlite and above that of martensite formation to produce a tough, hard microstructure.

AUSTENITIZING – The process of forming austenite (a solid solution of iron and carbon and sometimes other elements).

AFTER COOLER – A device used on turbocharged engines to cool air which has undergone compression.

ATDC – After TDC, after top dead centre.

AIR CLEANER – A device mounted on the intake manifold for filtering out unwanted solid impurities such as dirt and dust from air that is being drawn into the engine cylinder through the inlet manifold.

AIR COOLED ENGINE – An engine that is cooled by passage of air around the cylinder, not by passage of a liquid through water jackets.

AIR STANDARD CYCLE – A standard cycle of reference by which the performance of the different internal combustion engines may be compared, and their relative efficiencies calculated.

AKROYD ENGINE – The first compression ignition engine, patented by Akroyd Staurt in 1890.

ALUMINIUM CYLINDER BLOCK – An engine cylinder block cast from aluminium or aluminium alloy, and which usually has cast iron sleeves installed for use as cylinder bores.

ANTIFREEZE – A chemical, added to the coolant (usually ethylene glycol) to lower its freezing point and thereby prevent the coolant from freezing in cold weather.

ANTI ICING SYSTEM – A carburettor unit designed to prevent formation of ice on a surface or in a passage.

ARTICULATED CONNECTING ROD – The auxiliary connecting rods of a radial engine, which work on pins carried by the master rod instead of on the main crank-pin. Also called LINK RODS.

ACME THREAD GAUGE – A gauge used for checking and testing the 29° angle and the width at the end of a thread cutting tool while grinding it. It is also used for setting the tool square with the axis of the workpiece.

ANGLE PLATES – Some work has to be set at a particular angle to the surface of the table, and this is often effected by bolting it to an adjustable angle plate.

ARDOMETER – A type of total radiation pyrometer.

ANGLE PLATE – Right angled metal plate used to secure parts during machining or when taking measurements.

ANVIL – Heavy block on which to hammer and shape metals.

APRON – The function of a lathe apron is to carry the mechanism for sliding and surfacing motions and screw cutting.

ACCURATE – Without error within tolerances allowed, precise, correct, conforming exactly to standard.

ACHME THREAD – A screw thread having an included angle of 29° and largely used for feed screws on machine tools.

ACUTE ANGLE – An angle which is less than a right angle i.e. 90°

ADDENDUM – The portion of the tooth of a gear that extends from the pitch line to the outside.

ALIGN – To bring two or more components of a unit into correct positions with respect to one another.

ALLOWANCE – The intentional or desired difference between the maximum limits of mating parts to provide a certain class of fit.

ANGLE – The amount of opening or divergence between two straight lines that meet at a vertex or that intersect each other.

ANGLE OF THREAD – The included angle between the sides forming the groove of the screw thread

ANNULUS – A figure bounded by concentric circles or cylinders (e.g., a washer, ring, sleeve etc.).

ARC – A circular section of the circumference of a circle bounded by two equal radii.

ASSEMBLY – A unit that contains the parts that make up a mechanism or a machine.

AXIS – The line real or imaginary, which passes through the center of a body and about which the body would rotate if set revolving.

ACCELERATING PUMP – A small cylinder and piston fitted to some types of SI engine carburettor, and connected to the throttle so as to provide a momentarily enriched mixture when the engine is accelerated.

ACCUMULATOR – A device used for storing liquid under pressure (sometimes used to smooth out pressure surges in a hydraulic system).

ACTUATOR – A device which uses fluid power to produce mechanical force and motion.

AFTER COOLER – A device used on the turbocharged engines to cool the air which has undergone compression.

AIR COMPRESSOR – A device used to increase air pressure.

AIR COOLED ENGINE – An engine that is cooled by the passage of air around the cylinders, not by passage of a liquid through water jackets.

AIR CONDITIONER – A device used to control the temperature, humidity, cleanliness and movement of air inside a room or a car.

AIR HAMMER – Power hammer, used for roughening out heavy forgings in foundry work.

ALTERNATOR – A electrical generator that produces alternating current (flow of current is considered to change in direction with each half cycle).

ARBOR PRESS – A hand operated machine capable of applying high pressure for the purpose of pressing parts together or removing parts.

AUTOMATIC LATHE – Specialized development from capstan and turret lathes, with a full automatic cycle of turning, boring and drilling of the workpiece, the function of the operator consists of loading or taking finished work from the machine.

AUTOMATIC SCREW MACHINE – Fully automatic single spindle or multiple spindle bar stock turret lathe.

AUTOMATIC WELDING MACHINE – Machine designed to carry out high speed electric arc or resistance welding in mass production processes, combining rapid production with accurate control of temperature.

ADJUSTABLE RAMP – A loading platform that is power operated or mechanically operated.

APRON CONVEYOR – A conveyor for transporting packages or bulk materials, consisting of a series of metal or wood slats (also rubber, cotton, felt wire etc.) attached to an endless chain. Also called SLAT CONVEYOR.

ARRESTING GEAR – Means of sustaining the load which do not interfere with the hoisting gear but prevent it from coming down due to gravity e.g., ratchet and pawl arrangements and friction type.

AUTOMATIC GRAB – A crane grab in which the grasping and releasing of the load are effected without manual assistance.

ACICULAR STRUCTURE – A microstructure characterized by needle shaped constituents.

ALLOTROPY – Ability of a material to exist in several crystalline forms.

AMORPHOUS – Non-crystalline, a random orientation of the atomic structure.

ANISTROPY – A material that has specific physical properties in different directions. Rolled steel is strongest in the direction of rolling.

API GRAVITY – Gravity expressed in units of standard American Petroleum Institute (hydrometer).

AUSTENITE – A solid solution of cementite or iron carbide, Fe₃C in iron.

AGING OF A PERMANENT MAGNET – It is the process of normal or accelerated change, under continued normal or specified artificial conditions, in the strength of the magnetic field maintained.

ARC WELDING – Method of welding or uniting two metallic pieces in which the metal is melted by the heat of an electric arc.

ATOMIC HYDROGEN WELDING – Welding of metallic pieces in which heat is liberated by hydrogen atoms when combining into molecules, is used to fuse the metal.

AUTOMATIC ARC WELDING – Method of arc welding in which the arc moves along the joint to be welded, feeds the electrodes to the arc, and governs the arc length, by automatic means.

ABSOLUTE MOTION – Motion of a body in relation to some other body which is at rest.

ACCELERATION – Rate of change of velocity with respect to time, of a particle which is in motion. It is a vector quantity.

ADDENDUM – The radial distance from the pitch circle to the top of the tooth.

ANGULAR ACCELERATION – The time rate of change of angular velocity.

ANGULAR VELOCITY – The time rate of change of angular displacement of a point rotating about a fixed axis (expressed in radians per unit time) Angular velocity of a machine part is often expressed in revolutions per minute (RPM) and is denoted by n.

ANGULAR VELOCITY OF PRECISION – The rate of change in the direction of the plane of rotation of a rotating disc.

ARC OF CONTACT – The arc traced out along the pitch circle while one pair of teeth of gear wheels is in contact (divided into arc of approach and arc of recess).

ABSOLUTE HUMIDITY – The weight of the water vapour which is associated with unit quantity of air.

ABSORBER – A device for absorbing a refrigerant, a low side element in an absorption system.

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 – A plant in which ammonia is continuously evaporated from an aqueous solution under pressure, condensed, allowed to evaporate (so absorbing heat), and then reabsorbed.

ABSORPTIVITY – Ability of a material to absorb heat.

ACCUMULATOR – A steel shell partly filled with liquid refrigerant, the space above which is maintained by the compressor at a pressure corresponding to the required refrigerant temperature. The shell is placed in a suction line for separating liquid entrained in the suction gas.

ACTIVATED AMMONIA – Desiccant which operates by adsorption of water molecules. A form of aluminium oxide AlO2·

ACROLEIN – A warning agent having the formula CH2 CH CHO is often used with methyl chloride to call attention to the escape of refrigerant. The material has a compelling, pungent odour and causes irritation of the throat and eyes.

ACTUATORS – Secondary control mechanisms which function in response to the requirements of the primary group in actually controlling some part of the refrigeration system.

ADIABATIC COMPRESSION – Compression of a vapour or gas in such circumstances that there is insufficient time for any substantial exchange of heat between it and its surroundings.

ADIABATIC COOLING – Method in which paramagnetic salts are pre-cooled, and then demagnetized, thereby producing further cooling.

AERATION – A term generally employed with reference to air circulation or ventilation. In milk cooling, it refers to a method where the milk flow over refrigerated surfaces is exposed to the atmosphere.

AIR CIRCULATION – A method for natural or forced motion of air.

AIR CONDITIONING – The simultaneous control of all, or at least the first three of the following factors affecting the physical and chemical conditions of the atmosphere within a structure: Temperature, humidity, motion, distribution, dust, bacteria, or lesser degree human health or comfort.

AIR CONDITIONING UNIT – Equipment designed as a specific air treating combination, consisting of means for ventilation, air circulation, air cleaning and heat transfer with control means for maintaining temperature and humidity within prescribed limits.

AIR COOLED CONDENSERS – Condenser used to cool the refrigerant, the cooling effect depends on air drawn through tubes and fins for a good distribution of air.

AIR COOLER – The cold accumulator used in the Linde process of air liquefaction for the preliminary cooling of the air.

AIR DUCTS – Pipes or channels through which air is distributed throughout building or machinery for heating and ventilation.

AIR INFILTRATION – The in-leakage of air through cracks and crevices and through doors, windows or other openings, caused by wind pressure or temperature difference.

AIR LIQUEFIER – A type of gas refrigerating machine based on the STIRLING CYCLE, the cycle of the hot air engine.

AIR WASHER – An enclosure in which air is forced through a spray of water in order to cleanse, humidify or dehumidify the air.

ALFOL – Technical name for thin corrugated aluminium foil in narrow strips, used for heat insulation, for which it is effective by reason of the numerous small air cells formed when packed.

AMBIENT SENSOR – A temperature sensor that provides an outside air temperature signal for an automatic temperature control type air conditioning system.

AMBIENT TEMPERATURE – In a domestic or commercial system having an air cooled condenser, it is the temperature of the air entering this condenser.

AMMONIA–NH3 – One of the earliest compounds used as a refrigerant.

AMMONIA MACHINE – An abbreviation for a compression refrigerating machine using ammonia as a refrigerant. Similarly, Freon, sulphur dioxide machine etc.

ANALYSER – Device used in the high side of an absorption system for increasing the concentration of vapour entering rectifier or condenser.

ANTIFREEZE LIQUID – A substance added to the refrigerant to prevent formation of ice crystals at the expansion valve.

ATMOSPHERIC CONDENSER – A condenser operated with water which is exposed to the atmosphere.

AUTOMATIC EXPANSION VALVE – A pressure actuated device which regulates the flow of refrigerant from the liquid line into the evaporator to maintain a constant evaporator pressure.

AUTOMATIC REFRIGERATION SYSTEM – One which regulates itself to maintain a definite set of conditions by means of automatic controls and valves usually responsive to temperature or pressure.

ACCELERATOR – Device for rapid control of speed, for quick opening and closing of the throttle. It is a foot or hand operated, spring returned, linked to the throttle valve in the carburettor. The minimum throttle opening is controlled by the setting of the throttle screw.

ACCELERATOR PUMP – In the carburettor, a small pump linked to the accelerator which momentarily injects a charge of fuel into the intake tract in addition to that supplied by the normal metering components, and thus enriches the mixture when the accelerator pedal is depressed.

ADVANCE – Setting the ignition timing so that spark occurs before the piston reaches top dead center.

AIR BLEED – An opening into a gasoline passage through which air can pass or bleed into the gasoline as it moves through the passage, to weaken the air fuel mixture.

AIR FUEL MIXTURE – Finely atomized mist of fuel and air necessary for combustion. This mixture consists of approximately 15 parts air to one part fuel (15: 1) at cruising speed.

AIR FUEL RATIO – The proportion of air to fuel in the working charge of an internal combustion engine, or in other combustible mixtures, expressed by weight for liquid fuels and by volume for gaseous fuels.

AIRGAP (spark plug) – Distance between centre and side electrodes, in a spark plug. Spark jumps across this gap.

AIR HORN – In the carburettor, the tubular passage through which the incoming air must pass.

AIR JET – A small jet in the air passage of a carburettor. This jet meters the amount of air fed to the diffuser in an air bleed type carburettor.

ANTIKNOCK SUBSTANCES – Substances added to petrol to lessen its tendency to detonate, or knock in an engine, i.e., Tetra ethyl lead.

ANTIKNOCK VALUE – The relative immunity of a volatile liquid fuel from detonation, or knocking, in a petrol engine, as compared with some standard fuel.

ANTIPERCOLATOR – Device for venting vapours from main discharge tube or well of a carburettor.

ANTI SIPHON SYSTEM – Use of a small passage designed into a carburettor to prevent fuel from siphoning from the float bowl into the engine.

ATOMIZED – Tiny particles of fuel mixed with air, making a fine mist.

AUTOMATIC CHOKE – A carburettor choke device (valve) that automatically positions itself in accordance with carburettor needs or engine temperature.

AUTOVAC – A vacuum operated mechanism for raising fuel from a tank situated below the level of the carburettor to a position from which it may be fed to the latter by gravity.

AIR PREHEATER – A device that makes the final heat recovery from boiler flue gases and uses the same to preheat the incoming furnace air for its reaction with fuel.

ANTI-INCRUSTATOR – A substance used to prevent the formation of scale on the internal surfaces of steam boilers.

ANTIPRIMING PIPE – A pipe placed in the steam space of a boiler, so as to collect the steam while excluding entrained water.

AUTOMATIC FEED WATER REGULATOR – Device that regulates feedwater supply to the boiler according to load, and so does away with hand operation of valves on feed lines. It is controlled by temperature; its action depends upon expansion and contraction of some metal part.

AUTOMATIC INJECTOR – One that is self starting after its operation has been stopped by the interruption of its water supply.

ACCELERATED FLOW – Type of flow that takes place in nozzles. The flow accelerates and pressure reduces.

ADMISSION – The point in the working cycles of a steam or IC engine at which the inlet valve allows entry of the working fluid into the cylinder.

AIR PUMP – A reciprocating or centrifugal pump used to remove air, and sometimes the condensate, from the condenser of a steam plant.

ANGLE OF ADVANCE – The angle in excess of 90 degree by which the eccentric throw of a steam engine valve gear is in advance of the crank.

ALLAN VALVE – A steam engine slide valve, in which a supplementary passage increases the steam supply to the port during admission to reduce wire drawing.

ATMOSPHERIC ENGINE – An early form of steam engine in which a partial vacuum created by steam condensation allowed atmospheric pressure to drive down the piston.

AXIAL DISCHARGE TURBINE – A steam turbine in which the absolute velocity of steam flow at exit is a minimum i.e., the steam discharges in the axial direction.

AXIAL FLOW TURBINE – Steam turbine in which the general direction of steam flow has been roughly parallel to the turbine axis.

ABSOLUTE TEMPERATURE – The temperature of a substance measured above absolute zero.

ABSOLUTE ZERO TEMPERATURE – Temperature at which all molecular motion ceases, according to the kinetic theory of gases. A point which has been determined on the thermodynamic scale (by theoretical considerations) beyond which a further decrease in temperature is inconceivable. This is equal to – 459.6° on the Fahrenheit scale and – 273.1° on the centigrade scale.

ABSOLUTE TEMPERATURE SCALES – Used for calculating changes in refrigerant vapour pressures.

ADIABATIC EXPANSION or COMPRESSION – Expansion or compression where the temperature rises during compression and falls during expansion without any loss of heat to the cylinder walls or absorption of heat from the walls.

ADIABATIC HEAT DROP – The heat energy released and theoretically capable of transformation into mechanical work during the adiabatic expansion of unit weight of steam or other vapour or gas.

ADIABATIC SYSTEM – is the system which is insulated from its surroundings. In this system no heat transfer takes place i.e., either into the system or out of the system. It can however exchange work with the surroundings.

AIR – A gas consisting principally of a mechanical mixture of 23.2 percent (by weight) of oxygen, 65.5 percent of nitrogen and 1.3 percent of argon.

AIR STANDARD EFFICIENCY – The thermal efficiency of an internal combustion engine working on the appropriate air standard cycle.

AMBIENT TEMPERATURE – Temperature (usually of the air) surrounding the operating equipment.

APPLIED THERMODYNAMICS – Also called engineering thermodynamics deals with special applications such as energy transfer as power generation, refrigeration and, compression and expansion of gases and fluids.

ATKINSON CYCLE – A working cycle for internal combustion engines, in which the expansion ratio exceeds the compression ratio, more efficient than the Otto Cycle, but mechanically impracticable.

ATMOSPHERIC LINE – A datum line drawn on an indicator diagram by allowing atmospheric pressure to act on the indicator piston or diaphragm.

ATMOSPHERIC PRESSURE – Force exerted by the weight of the atmosphere on every point with which it is in contact. It is generally taken as 1.03 kscm at sea level.

AVAGADRO’S LAW – Equal volumes of different gases at the same temperature and pressure contain the same number of molecules.

AVAILABLE ENERGY – That portion of a quantity of heat which could be transformed into work by means of a reversible engine.

ANTI DIVE SYSTEM – A system installed with some brakes that uses front fork damping and the front brake assembly to prevent excessive fork compression and to improve handling when brakes are applied.

AUTOMATIC TRANSMISSION – A transmission not using a manually operated clutch.

AXLE – A shaft used to support a part or parts across the frame or forks. e.g., front and rear axles.

ANTI DIVE SYSTEM – A system installed with some brakes that uses front fork damping and the front brake assembly to prevent excessive fork compression and to improve handling when brakes are applied.

AUTOMATIC TRANSMISSION – A transmission not using a manually operated clutch.

AXLE – A shaft used to support a part or parts across the frame or forks. e.g., front and rear axles.

ARC – A sustained electric discharge, where current flows through the gap between two electrodes.

ARC CUTTING – Process which melts the metals to cut with the heat of an arc between an electrode and the base metal.

ARC EYE – A burn on the exterior surface of the operators eye, due to its exposure to an open arc. Also called FLASH EYE.

ARC GAP – Distance between the tips of two electrodes, normally between an electrode and the workpiece. Also known as ARC LENGTH.

ARC PLASMA – A gas that has been heated to an at least partially ionized condition, enabling it to conduct an electric current.

ARC SPOT WELD – Spot welding made by an arc welding process.

ARC WELDING – A group of welding processes which produces coalescence of metals by heating them with an arc, with or without the application of pressure, and with or without the use of filler metal.

ATOMIC HYDROGEN WELDING – An arc welding process which produces coalescence of metals by heating them with an electric arc maintained between electrodes in an atmosphere of hydrogen. Shielding is provided by hydrogen.

AUTOGENOUS WELD – A fusion weld made without the addition of filler metal.

AUTOMATIC OXYGEN CUTTING – Cutting with an equipment without constant observation and adjustment of the controls by an operator.

AUTOMATIC WELDING – Welding which permits the operation without adjustment of controls by an operator.