DIRECT CONNECTED COMPRESSOR – A compressor in which the prime mover is attached direct to the compressor without any interposed transmission such as chain, belt etc.

DISPLACEMENT OF COMPRESSOR – The volume displaced by the net area of the compressor piston. This is the capacity of an air compressor, usually expressed in cum per minute.

DOUBLE ACTING COMPRESSOR – A reciprocating compressor in which compression occurs on either side of the piston during every stroke.

DAMPERS – are nothing but a piston in a cylinder filled with oil or gas. The damper restrains undesirable bounce of the sprung vehicle mass and restrains the wheel assembly from loosing ground contact by being excited at its natural frequency.

DASH BOARD – Part of body containing driving and control instruments, switches etc.

DEAD AXLE – Axle that does not rotate or deliver power but merely forms a base upon which wheels may be mounted.

DEDION – Rear axle set up in which driving wheels are attached to the frame by a central pivot. Differential unit is bolted to frame and is connected to the driving wheels by drive axles.

DEPENDENT SUSPENSION – Wheel connected through an axle member so that movement of one wheel moves the other wheel.

DIAGONAL SPLIT BRAKE SYSTEM – A brake system design that will allow application of brakes on one front wheel and a diagonally opposite rear wheel, when part of brake system fails.

DIAPHRAGM CLUTCH – Uses a diaphragm or conical spring instead of coil springs to produce adequate pressure required for keeping the clutch in the engaged position.

DIFFERENTIAL – A mechanism between axles that permit one wheel to turn at a different speed than the other while transmitting power from the drive shaft to the wheel axles, when the vehicle is negotiating a turn.

DIFFERENTIAL CASE – A steel unit to which the ring gear is attached. Differential case drives spider gears and forms an inner boring surface for axle and gears.

DIFFERENTIAL LOCK – The differential lock grips one or both of the side gears to the differential case. This prevents their rotation on the pins. This enables a larger torque to be transmitted to the gripping wheel than that to the slipping wheel.

DIRECT ACTING SHOCK ABSORBER – Type of shock absorber which shortens or lengthens in action. Also called telescopic shock absorber.

DIRECT DRIVE – Such as high gear when crankshaft and drive shaft revolve at same speed.

DIRECTIONAL STABILITY (steering) – Ability of vehicle to move forward in straight line with minimum of driver control. Vehicle with good directional stability will not be unduly affected by side wind, road irregularities etc.

DISC BRAKE – When the brake pedal is depressed, pads lined with friction material are forced towards one another. In doing so, they come in contact with the disc (attached to the wheel) which normally rotates between them. This provides braking effort.

DISC WHEEL – Wheel constructed of stamped sheet.

DIVE – The front wheel of the vehicle lowering during braking.

DOLLY BLOCKS – Blocks of metal, variously shaped and contoured, used to straighten body panels and fenders. The dolly block is held on one side of the panel while the other side is struck with a special hammer.

DOUBLE LEADING SHOE – A drum brake having two leading shoes and no trailing shoes. Each shoe has its own actuating mechanism and pivot.

DOUBLE PISTON CALIPER – A hydraulic brake calliper with two pistons and provision for applying hydraulic pressure equally to both pistons. The calliper body is fixed solidly.

DOWN SHIFT – Shifting to lower gear.

DOUBLE LEADING BRAKE – A drum brake assembly with both front shoes self energized during forward wheel rotation.

DOUBLE REDUCTION AXLE – In the double reduction or triple reduction type final drive, the required speed reduction is obtained in two or more steps. This enables higher torque to be available at the road wheels. In heavy duty and off highway vehicles, multiple reduction is used.

DOUBLE TRAILING BRAKE – A drum brake assembly with both shoes self energized during rearward wheel rotation only.

DRAG – To accelerate a vehicle from standing start, over course one fourth mile in length. Also used by some drivers when referring to challenging another driver to an acceleration race.

DRAG LINK – A steel rod connecting pitman arm to one of steering knuckles. On some installations, drag link connects pitman arm to a centre idler arm.

DRAGSTER – Car especially built for drag racing.

DRAG WHEEL – Special steering wheel used on some dragsters. Often consists of cross bar spoke and portion of rim on each end.

DRIP MOULDING – is a U shaped channel, added to the side rails of the roof panel. It catches water on the roof and direct it to the back of the car during raining.

DRIVE LINE or DRIVE TRAIN – Propeller shaft, universal joints etc. connecting transmission output shaft to axle pinion gear shaft.

DRIVE PINION – A gear in the differential connected to the drive shaft.

DRIVE or PROPELLER SHAFT SAFETY STRAP – A metal strap or straps, surrounding drive shaft to prevent shaft from falling to ground in the event of a universal joint or shaft failure.

DRIVE SHAFT – An assembly of one or two universal joints connected to a hollow tube and used to transmit torque and motion. A shaft in the power train that extends from the transmission to the differential and transmits power from one to the other. Also called PROPELLER SHAFT.

DROP CENTRE RIM – Centre section of rim being lower than two outer edges. This allows bead of tyre to be pushed into lower area on one side while the other side is pulled over and off the flange.

DROPPED AXLE – Front axle altered so as to lower the frame of the vehicle. Consists of bending axle downward at outer ends (solid front axle).

DRUM BRAKE – A brake unit using curved brake shoes which press against the inner circumference of a metal drum to produce braking action.

DUALS – Two sets of exhaust pipes and mufflers one for each bank of cylinders.

DUAL BRAKE SYSTEM – Tandem or dual master cylinder to provide a brake system that has two separate hydraulic systems, one operating the front brakes, the other operating the rear brakes.

DUAL SERVO BRAKES – A drum brake assembly with both front and rear shoes, self energized during forward and rearward wheel rotations.

DUMMY AXLE – provided in some vehicles increases the load carrying capacity of the vehicle. Wheels on the dummy axle can rotate freely.

DUNY BUGGY – Off road vehicle set up to run on sand.

DEGREE OF ATOMIZATION – is indicated by the smallness of the size of the particles in the spray and also by the smallness of the variation in the size of the particles.

DELAY PERIOD – Time interval between the start of injection and beginning of combustion as indicated by a rise in the pressure crank angle curve, from the curve which represents compression and expansion of air while motoring. Also called IGNITION DELAY.

DELIVERY VALVE – A spring loaded valve mounted at the top of the fuel injection pump barrel. This helps to cut off fuel spray from the nozzle tip abruptly and without dribble.

DEPTH FILTER – Fuel filter which has dozens of layers of porous material arranged in sequence and this arrangement compels the contaminant particles to follow tortuous path into the media.

DIESEL CYCLE – An engine cycle of events in which air alone is compressed and fuel oil is injected at the end of the compression stroke. The heat produced by compressing the air ignites the fuel oil, eliminating the need for spark plugs or a spark ignition system.

DIESEL ENGINE – An engine that operates on the diesel cycle and burns diesel oil by the heat of compression of air.

DIESEL INDEX – A rating of fuel according to its ignition qualities. The higher the diesel index number, the better is the ignition quality of fuel.

DIESEL KNOCK – Sudden, steep pressure rise due to instantaneous uncontrolled combustion of the fuel that has got accumulated during delay period. The pressure wave hitting piston and cylinder walls produce knocking sound.

DIRECT INJECTION ENGINES – have a single open combustion chamber into which the entire quantity of fuel is injected directly.

DISPERSION OF SPRAY – The divergency of the fuel spray which helps distribution of fuel droplets in air as uniform as possible.

DRIBBLING – Unatomized fuel running from the fuel nozzle.

DUAL FUEL ENGINE – An engine that uses an air gas mixture which is being ignited by a small quantity of fuel oil injected at the end of the compression process.

DURATION OF FUEL INJECTION – The crank angle during which fuel is injected into the engine cylinder. Usually as load increases this duration has to be increased.

DEGASSIFIER – A material employed for removing gases from metals and alloys.

DEOXIDIZER – A material used to remove oxygen or oxides from metals and alloys.

DESULPHURIZER – A material used to remove sulphur from molten metals and alloys.

DIE CASTING – Pouring molten metal under pressure into metal moulds.

DIRECTIONAL SOLIDIFICATION – It refers to the solidification which proceeds along a cast member in the direction of the hotter metal.

DIRT – Any extraneous material entering a mould cavity and usually forming a blemish on the casting surface.

DRAFT – Taper allowed on the vertical faces of a pattern to permit removal of it from the sand mould without excessive rapping or tearing of the mould walls.

DRAG – The lower or bottom section of a mould or pattern.

DRY SAND MOULD – A mould made of prepared moulding sand dried thoroughly before being filled with metal.

DEGASIFIER – A material employed for removing gases from metals and alloys.

DELTA IRON – An allotropic (polymorphic) form of iron, stable above 1390°C, crystallizing in the body centered cubic lattice.

DENDRITE – A crystal that has tree like branching pattern, being most evident in cast metals slowly cooled through the solidification range. Dendrite generally grows inward from the surface of a mould.

DEOXIDIZER – A substance that is used to remove either free or combined oxygen from molten metals, for example, ferrosilicon in steel making.

DEVELOPER – (1) In photography, a processing solution that reduces the exposed grains of an emulsion to metallic silver, thus making the image visible. (2) In zero radiography a dry powder used to make the electrostatic image visible. (3) In penetrant inspection, a material used to draw the penetrant back to the surface, thus revealing locations of cracks or fissures.

DEVIZES SAND – Coarse greenish yellow moulding sand, suitable for dry sand work in the foundry for medium and heavy castings, but not for fine work, owing to its large grain size.

DIAMAGNETIC SUBSTANCES – Actually set up fields that oppose applied fields.

DIAMOND – Allotropic form (crystalline form) of carbon (the hardest known mineral) which when very strongly heated, changes to graphite.

Used as a cutting tool, and a grinding tool and to dress grinding wheels.

DROSS – The scum that forms on the surface of molten metal’s, largely because of oxidation but sometimes because of the rising of impurities to the surface.

DRY SAND MIXTURE (Mould) – Specially prepared and for making the moulds that are to be dried before using. This demands sand that when dried or baked will give strength, porosity and permeability.

DUCTILE IRON – A high strength type of cast iron that will bend without fracturing.

DURALUMIN – Aluminium alloy containing copper, manganese and magnesium, which can be cast, forged or stamped, and is widely used for sheets, tubes, forgings, rivets, nuts, bolts and similar parts.

DYE PENETRANT – Penetrant with a dye added to make it more readily visible under normal lighting conditions.

DETERGENTS – Added to lubricating oils to improve the tendency of the oil to wash or cleanse the surface where oxidation products form, thereby resulting in a marked reduction in ring sticking, particularly in heavy duty service, and a marked improvement in cleanliness of pistons.

DETERGENT OIL – An oil which keeps particles and contaminants in suspension and has ability to neutralize acids resulting from combustion process.

DIRECT BEARING LUBRICATION – An oil injection system which feeds undiluted oil to two stroke cycle engine main bearings and rod big end bearings.

DRY SUMP-LUBRICATION – In this system, oil is gravity fed to supply side of oil pump from the remote oil tank. After the oil has been pumped through four stroke cycle engine, it is returned to the oil tank by return side of oil pump.

DETONATION – An uncontrolled instantaneous second explosion in a spark ignition engine, after the spark occurs, with excessively rapid burning of a portion of the compressed air fuel mixture (end charge almost exploding) resulting in a spark knock, or pinging noise.

DIESEL INDEX – A rating of fuel according to its ignition qualities. The higher the diesel index number, the better the ignition quality of the fuel.

DIMETHYLETHER – is a synthetic product with a high cetane number, producing little soot and reduced nitrogen oxide when combusted in diesel engines.

DISTILLATION – Heating a liquid, and then catching and condensing the vapours given off by the heating process.

DRAFT – The differential pressure in a furnace to ensure the flow of gases out of the furnace and flow of air into the furnace.

DUST – Fine grain particles light enough to be suspended in air.

DEFLECTION ANGLE – Total fluid turning angle i.e., difference between the fluid angle at inlet and the fluid angle at outlet.

DEGREE OF REACTION (compressor) – The ratio of the static temperature rise in the rotor to that in the whole stage.

DEGREE OF REACTION (turbine) – Ratio of enthalpy drop in rotor blades to enthalpy drop in the stage.

DIAPHRAGM – The component fixed to the cylinder or casing and contains the nozzles and serves to confine the fluid flow to the nozzle passages.

DIFFUSER – Unit connected to the outlet of the centrifugal compressor, which provides a gradually increasing area to convert velocity energy into pressure energy.

DIFFUSION – Process in which the energy of a moving stream of fluid is transformed in such manner, then an increase in pressure occurs.

DISC or WHEEL – The component to which the moving blades are attached directly and it is keyed or shrunk on the shaft.

DISC FRICTION – When a disc rotates in free air, a certain amount of pumping action would take place, imparting motion to the surrounding air, and this relative motion between the disc and air causes friction, called disc friction.

DOUBLE SIDED IMPELLER – Impeller of a centrifugal compressor in which suction takes place from both sides. Here, two similar impellers are placed back to back.

DYNAMIC HEAD – The difference between the total head pressure and the static pressure.

DECARBONIZATION – The loss of carbon from the surface of a ferrous alloy as a result of heating it in the presence of a medium such as oxygen that reacts with the carbon.

DEAD CENTER – Point at which the piston reaches its uppermost or lowermost position in the cylinder. At these positions, at the end of the stroke, the crank and connecting rod are in a straight line.

DECARBONIZE – To remove carbon build up on piston, combustion chamber and other parts.

DECOMPRESSOR – is the device that opens the engine intake or exhaust valve and retains it in the opened position. The compression effect is thus reduced and helps easy rotation of the crankshaft at the time of starting.

DIPSTICK – The metal stick that passes into the oil sump. Used to determine quantity of oil in the engine sump.

DIRECT COOLED PISTON – A piston which is cooled by the internal circulation of a liquid.

DISPLACEMENT – In an engine, the total volume of fresh charge an engine is theoretically capable of drawing into all cylinders during one operating cycle. The space swept through by the piston in all cylinders in moving from one end of a stroke to the other.

DOHC ENGINE – An engine having two camshafts over each line of cylinders, one operating intake valves, and the other operating exhaust valves. Double overhead camshaft engine.

DRY SLEEVE – A cylinder sleeve (liner) where the sleeve is supported in the cylinder block metal over its entire length. The coolant does not touch the sleeve itself.

DYNAMOMETER – A device for absorbing and measuring the power output, or brake horse power, of an engine. May be an engine dynamometer, which measures power output at the flywheel, or a chassis dynamometer, which measures the power output at the driven wheels.

DEAD CENTER – Point at which the piston reaches its uppermost or lowermost position in the cylinder. At these positions, at the end of the stroke, the crank and connecting rod are in a straight line.

DECARBONIZE – To remove carbon build up on piston, combustion chamber and other parts.

DECOMPRESSOR – is the device that opens the engine intake or exhaust valve and retains it in the opened position. The compression effect is thus reduced and helps easy rotation of the crankshaft at the time of starting.

DIPSTICK – The metal stick that passes into the oil sump. Used to determine quantity of oil in the engine sump.

DIRECT COOLED PISTON – A piston which is cooled by the internal circulation of a liquid.

DISPLACEMENT – In an engine, the total volume of fresh charge an engine is theoretically capable of drawing into all cylinders during one operating cycle. The space swept through by the piston in all cylinders in moving from one end of a stroke to the other.

DOHC ENGINE – An engine having two camshafts over each line of cylinders, one operating intake valves, and the other operating exhaust valves. Double overhead camshaft engine.

DRY SLEEVE – A cylinder sleeve (liner) where the sleeve is supported in the cylinder block metal over its entire length. The coolant does not touch the sleeve itself.

DYNAMOMETER – A device for absorbing and measuring the power output, or brake horse power, of an engine. May be an engine dynamometer, which measures power output at the flywheel, or a chassis dynamometer, which measures the power output at the driven wheels.

DEPTH GAUGE – Gauge used for the purpose of measuring the distance between two surfaces, to find or check the depth of a counterbored hole, a recess etc.

DIAL GAUGE – Instrument indicating the movement of a projecting plunger by the movement of a hand or pointer over a graduated dial.

DIAL SHEET GAUGE – Gauge fitted with a dial or clock for measuring or comparing the thickness of sheet metal plates.

DIVIDERS – These are essentially scribers for marking arcs, and circles, hence their points are hard and sharp. They are used for dividing distances into a number of equal parts. Also used for transferring dimensions from a rule to the work.

DRILL GAUGE – Tool for measuring the size of drills.

DRILL GRINDING GAUGE – A tool for checking the angle and length of the cutting lips on a twist drill while grinding it. Also it may be called a drill point gauge or a drill angle gauge.

DEAD CENTER – The center fitted to the tailstock of a lathe and so named because it does not rotate. Also the exact or precise center of an object.

DEMAGNETIZER – Device for removing permanent magnetism from steel tools and parts.

DIE HEAD – Device to enable small or medium sized work to be screwed in capstan or turret lathes. The die head consists of a cylindrical body with a shank to enable it to be clamped in the turret.

DIE SCREW – Tool used when threading cylindrical pieces beyond the capacity of a die plate.

DISTANCE BLOCK – Accurately ground steel block used to hold a component at a set distance from another surface, or to operate a trip mechanism tool when the tool carrier or worktable reaches the desired position.

DIVIDING HEAD – Indexing or dividing head is an attachment used on the milling machine table, for accurately dividing the circumferences of components for grooving or fluting, gear cutting, cutting of splines, squares or hexagons.

DOG – A tool or accessory which can be clamped on a workpiece to drive it while held between centers, as a lathe dog. Also, the name given to a projecting part on a machine tool which strikes and moves another part, such as the reversing dogs on a grinding machine or planer.

DRIFT PIN – A round tapered steel pin used to align rivet holes so that the rivet will pass through the holes easily.

DRILL ADAPTER – An attachment used to fit square shank drills and Morse taper sockets.

DRILL CHUCK – A self centering tool holding device, for driving drills and other such cutting tools in a drilling machine.

DRILL DRIFT – A wedge shaped piece of steel that is used to remove tapered shank tools, such as drills from spindles, sockets and sleeves.

DRILL HOLDER – An attachment used for holding drills in the turret of a capstan lathe.

DRILLING JIG – Device, usually of hardened steel plate, for holding a piece of work in a definite position, provided with guide bushes through which drills can pass so as to locate holes in exact positions in the work.

DRILL SLEEVE – A steel part tapered inside and outside which fits onto the tapered shank of a cutting tool, such as a drill or reamer, to adapt it to the size of the hole in the drill press spindle.

DRILL VISE – A work holding device in which the work is set and held while drilling and other operations are performed.

DRILL SOCKET – An adapter for holding taper shank drilling tools which have a taper shank larger than the taper hole in the drilling machine. One end is tapered outside to fit the drilling machine spindle hole while the opposite end has a larger taper hole to receive the cutting tool shank.

DEDENDUM – The depth of a gear tooth space below the pitch line or circle. Also, the radial distance between the pitch circle and the root circle, which also includes the clearance.

DIAPHRAGM – A flexible dividing partition separating two compartments.

DOUBLE FLARE – A flared end of the tubing having two wall thicknesses.

DOWEL – A pin, usually of circular shape like a cylinder, used to pin or fasten something in position temporarily or permanently.

DRIFT PIN – A round tapered steel pin used to align rivet holes so that the rivet will pass through the holes easily.

DIESEL ENGINE – An internal combustion engine having fuel injected into the combustion chamber near the end of the compression stroke. The fuel is ignited by the heat of compression only.

DIODE – A device that allows current to pass but only in one direction.

DISC GRINDER – Grinding machine embodying one or more abrasive discs mounted horizontally on a vertical spindle, the work reposing on the surface of a flat rotating carrier or table.

DRAWCUT SHAPER – Type of machine with a traverse tool movement. In this, the work is fixed to the table which reciprocates under the tool, the tool moving across the table for the purpose of obtaining the feed.

DRILL GRINDER – Machine employed for the accurate grinding of the cutting points and lips of twist drills.

DRILL PRESS – A fixed machine to drive a tool in rotary motion.

DRILLING MACHINE – Machine tool used for the production of holes with a drill, fall under two classes—bench drilling machine and the pillar drilling or upright drilling machine.

DROP STAMP – Machine for producing drop stampings and forgings, may be free falling type or controlled falling type.

DRY CELL (dry battery) – A battery that uses no liquid electrolyte.

DUPLEX MILLER – Manufacturing type milling machine sometimes called a duplex head miller, has two head stocks supporting two opposed spindles. This enables two face mills or two horizontal cutters, to work simultaneously on opposite sides of the workpiece.

DYNAMOMETER – A device for absorbing the power output of an engine and measuring torque or horse power, so that it can be computed into brake horsepower.

DEAD ZONE – In a shop floor, when two overhead bridge cranes serve adjacent bays, part of floor area (about 15 to 20%) inaccessible for any of the hooks, as close as they may be. This is dead zone.

DERRICK – A framework over a drill hole (e.g., on oil well) for supporting the boring mechanism for hoisting.

DIESEL ELECTRIC DRIVE – System consisting of a diesel generator set and electric motors on all motions.

DOUBLE BOTTOM RIG – Two trailers joined to a tractor.

DOUBLE FACED PALLET – A pallet with two decks that form the top and bottom surfaces.

DOUBLE STRING TIE – A method of tying heavy packages.

DOUBLE WALL CORRUGATED FIBREBOARD – Fibreboard consisting of three flat facings and two corrugated pieces arranged in alternate layers.

DOUBLE WRAP – Two or more sheets of paper used to wrap breakable articles.

DRIVEWAY INSTALLATION – A loading ramp that raises or lowers the truck so that the floor of the truck is level with the dock.

DRUM – In hoisting unit, a device for spooling the rope in one layer or in more than one layer.

DUNNAGE – Lumber or other material used to brace a shipment in transport.

DAMAGING STRESS – The minimum stress which, if exceeded in the material, would render the part unfit for service before the end of its normal expected life.

DAMPING CAPACITY – The ability to absorb vibration. More accurately defined as the amount of work dissipated into heat by a unit volume of material during a completely reverse cycle of unit stress.

DENDRITE – A crystal formed during solidification of a metal or alloy characterized by a structure like that of a fir tree.

DENSITY – The ratio of the mass of a body to its volume.

DUCTILE or MALLEABLE METAL – A metal that may be worked to a different size or shape without breaking or shattering.

DUCTILITY – The property of a material to deform permanently or to exhibit plasticity, elongation or bending or twisting without rupture (breaking or cracking) while under tension.

DYNAMIC CREEP – Creep that occurs under the conditions of fluctuating load or fluctuating temperature.

CALENDERING – A process that involves rolling of the product into sheets to achieve the desired surface finishes and thickness.

CASTING – Process of producing a metal object by pouring molten metal into a mould.

COINING (embossing) – Shaping a piece of a metal in a mould or die often creating raised figures or numbers.

COLD DRAWING – Reducing the cross section of a metal bar or rod by drawing it through a die, at a temperature below the recrystallisation range, usually room temperature.

COLD ROLLING – Reducing the cross-section of a metal bar in a rolling mill below the recrystallisation temperature, usually room temperature.

COLD SAWING – Any sawing process in which the chips are not heated to the softened state.

COLD WORKING – Deforming a metal plastically at a temperature below its lowest recrystallisation temperature. Strain hardening occurs as a result of this permanent deformation.

CONFINED FLOW – Confined flow is the basis of drop forging and hot pressing. In this, the metal is ultimately confined in all directions, being forced to behave as pasty fluid in filling every portion of the confining cavity.

CENTERLESS GRINDING – Method of grinding metallic parts in which the piece to be ground (circular piece) is supported on a work rest, and passed between a grinding wheel running at a high speed and a controlling wheel running at a slow speed.

CENTRIFUGING – Casting of molten metals by using centrifugal force instead of gravity. The mould (or moulds) is rotated about a centre where molten metal is poured and allowed to follow sprues outward and get into the mould cavity.

CENTRIFUGAL CASTINGS – Castings of cylindrical design are made by the introduction of molten metal into revolving permanent moulds, known as centrifugal casting machines, where the centrifugal force is employed to bring pressure in filling of the mould.

CLADDING – The joining of one metal (usually sheet or plate) to another by using heat and pressure or by an explosive force. With this method, a thin sheet of more expensive metal or one less likely to corrode may be applied to a less expensive metal or one more likely to corrode.

CLIMB MILLING – Milling process in which the work is fed in the same direction as the path of the teeth on the cutter, below the arbor.

COUNTER SINKING – It is the opening out of the ends of a hole to form a conical hollow for receiving the head of a countersunk screw, rivet or bolt.

CRIMPING – Producing flutes or corrugations. Often used to gather metal as for stovepipe joints.

CROWNING – Shaping of the rim of a belt pulley so that the diameter at the centre of the face is greater than at the edges so as to keep the belt on the crown of the pulley.

CUPPING – Process in which a flat blank is converted into a cup like form.

CUT OFF – An operation that shears a stamping from a strip or bar.

DEFORMATION – Alteration of the form or shape as a result of the plastic behaviour of a metal under stress.

DIECASTING – Casting metal into a metallic mould by using pressure instead of gravity or centrifugal force.

DIFFUSION – The process of atoms or other particles intermingling within a solution. In solids, it is a slow movement of atoms from areas of high concentration towards areas of low concentration. The process may be (a) migration of interstitial atoms such as carbon, (b) movement of vacancies or (c) direct exchange of atoms to neighbouring sites.

DINKING – Cutting of non-metallic articles from the sheet, usually involving such operations as blanking and piercing.

DRAW FILING – Finishing operation in filing during which the file is moved in the direction of the greater length of the work, being held like a spoke shave.

DRAWING – Process, in press work, which involves reducing the diameter or cross-sectional dimensions of a cup, shell, tube, bar or wire.

DRILLING – Power or hand operated method for the production of holes in metal or other solid materials with a drill.

DROP FORGING – Drop forging is the operation in which a metal part is formed by repeated hammer blows on a bar or billet placed between a pair of dies containing the impression of the finished shape desired.

DEAD WEIGHT GOVERNOR – The governor in which the radius of the ball path is controlled by levers and weights, the latter being usually attached to the control sleeve.

DEDENDUM – The radial distance from the pitch circle to the bottom of the tooth space.

DIAMETRAL PITCH – Number of teeth per inch diameter.

DISC CAM – An irregular disc rotating about a fixed axis and imparting reciprocating or oscillating motion to a follower in a plane at right angles to the cam axis.

DYNAMICS OF MACHINES – Treatment with the forces acting on the parts of a machine and the motions resulting from these forces.

DYNAMOMETER – A device for measuring the forces or couples which tend to change the state of rest or of uniform motion of a body.

DEGREE DAY – A unit, based upon temperature difference and time, used in specifying the nominal heating load in winter.

DEFROSTING – Removal of accumulated ice from the cooling unit.

DEFROSTING CYCLE – A cycle which permits cooling unit to defrost during off period.

DEFROSTING EVAPORATOR – Unit in which frost accumulates on cooling coils when the compressor operates and melts after the compressor shuts off.

DEHUMIDIFY – To remove water vapour from the atmosphere, to remove water or liquid from stored goods.

DEHYDRATOR – A device used to remove moisture from the refrigerant.

DESICANT – Material used in a drier to trap moisture from the refrigerant. Also called drying agent.

DEWAR FLASK – A container which consists of alternate layers of radiation shields and spacer material in high vacuum.

DEW POINT – That temperature at which the air (space) becomes saturated with water vapour. When the air is cooled to the dew point, water vapour can condense into liquid form (provided its latent heat is removed).

DEW POINT THERMOSTAT – A thermostat used in such a way as to control humidity.

DICHLORODIFLUORO METHANE – The chemical compound known as Freon 12 or R -12.

DIELECTRIC – Thin insulating material separating two conductor plates in a capacitor.

DIFFERENTIAL – Difference of temperature or pressure between the on and off operation of the control.

DIRECT EXPANSION – A system in which the evaporator is located in the material or space refrigerated or in air circulating passages communicating with such space.

DIRECT EXPANSION EVAPORATOR – One that contains only enough liquid to continue boiling as heat is absorbed by it.

DISCHARGE SHUT OFF VALVE – A manual valve installed on the compressor, which controls the flow of the refrigerant from the cylinder head of a compressor to the discharge line.

DISPLACEMENT, ACTUAL – The volume of gas at compressor inlet conditions actually moved in a given time.

DISPLACEMENT, THEORETICAL – The total volume displaced by all the pistons of a compressor for every stroke during a definite interval, usually measured in cubic metre per minute.

DOMESTIC REFRIGERATOR – A refrigerator for home use.

DOUBLE ACTION PISTON COMPRESSOR – A type of compressor used in automotive A/C systems in which an axial swash plate pressed to the shaft is used to drive the pistons.

DOUBLE EFFECT EVAPORATOR – An arrangement of two evaporators such that the vapour from No. 1 is carried over into the tubes of No. 2. The drain from the first evaporator is led to the hot well and the drain from the second evaporator is led to the fresh water condenser and there cooled down to be used by the passengers.

DOUBLE THICKNESS FLARE – Indicates that the flare thickness of a tube end is made up of two thicknesses of tubing.

DRIER – Device designed to remove moisture from a refrigerant.

DRIERITE – Desiccant which operates by chemical action.

DRY BULB TEMPERATURE – The actual temperature of the air as measured by an ordinary thermometer.

DRY ICE – Frozen carbon dioxide, sold under the trade names, such as CARDICE and DRICOLD. This has the property of passing directly from the solid to the gaseous state without becoming a liquid.

DRY TYPE EVAPORATOR – An evaporator of the continuous tube type where refrigerant from a pressure reducing device is fed into one end and the suction line is connected to the outlet end.

DASHPOT (carburettor) – A device in the carburettor that prevents excessively sudden closing of the throttle.

DETONATION – A violent, instantaneous explosion of the final portion of the burning combustion gases caused by an excessive rise of pressure and temperature, also called AUTO IGNITION.

DIESELING – A condition in which a spark ignition engine continues to run after the ignition is shut off. Also called RUNNING ON.

DISTRIBUTOR (ignition) – Unit designed to make and break the ignition primary circuit and to distribute resultant high voltage to the proper spark plug in the cylinder at the correct time. Rarely used in motor cycles.

DISTRIBUTOR CAP (ignition) – Insulated cap containing a central terminal with series (one per cylinder) of terminals that are evenly spaced in circular pattern around the central terminal. Secondary high voltage travels to central terminal where it is then channelled to one of the outer terminals by the rotor.

DOWN DRAFT CARBURETTOR – Carburettor air horn is so arranged that the air passes downward through the carburettor on its way into the intake manifold.

DUAL BREAKER POINTS (ignition) – Distributor using two sets of breaker points to increase cam angle so that even at high speeds, spark with sufficient intensity will be produced.

DUAL CARBURETTOR – An engine on which two carburettors have been mounted.

DWELL ANGLE – The number of degrees on the breaker cam during which the breaker points are kept closed.

DWELL METER – A device used to measure the number of degrees that the ignition contact points remain closed.

DYNAMIC TIMING – A test of ignition timing made with the strobe light.

DOUBLE TUBE BOILER – Boiler having an auxiliary tube placed inside each main tube. Gases flow from one end to the other end through the auxiliary tube and from that end to the other end in the reverse direction through the annular space in the main tube.

DOWN COMER – A large vertical tube or pipe for circulating water from the water space of the steam drum to water wall headers.

DRAFT – The difference of pressure producing air flow through the boiler furnace, flue and chimney.

DUPLEX PUMP – A combination of two pumps arranged side by side and so connected that movement of each operates the steam valve of the other.

DECELERATED FLOW – Type of flow that takes place in the diffusers velocity decreases.

DEGREE OF REACTION – In an impulse reaction turbine, it is the ratio of the enthalpy drop that takes place in rotor blades to the total enthalpy drop that occurs in the stage.

DIAGRAM EFFICIENCY or BLADING EFFICIENCY – Ratio of the rate of doing work per kg of steam (diagram work) to the energy supplied to the rotor per kg of steam.

DIAGRAM FACTOR – Ratio of actual indicator diagram area to the hypothetical indicator diagram area.

DIAPHRAGMS – Partitions, which separate one wheel chamber from the next and in which nozzles are usually fitted in the case of pressure compounded impulse turbine.

DIFFUSER – The duct in which a fluid is decelerated causing a rise in pressure along the stream.

DISC FRICTION – Surface friction loss due to relative motion between the disc and steam particles when the disc is rotating in the viscous fluid i.e., steam.

DOUBLE ACTING ENGINE – A steam engine in which a power cycle is produced in each end of the cylinder during one revolution of the crankshaft.

DOUBLE DECK SPRAY POND – The pond having spray nozzles arranged at different elevations.

D SLIDE VALVE – A sliding valve which alternately admits steam to and releases the steam from each end of the steam engine cylinder.

DRY AIR PUMP – A pump designed to handle air and gases only, which will give a higher vacuum than possible with a wet air pump.

DALTON’S LAW OF PARTIAL PRESSURES – At a common temperature, a mixture of gases will exert on the sides of the vessel a total pressure equal to the sum of the pressures which each constituent would exert separately if it alone occupied the vessel.

DERIVED UNITS – are those derived from basic units, e.g., force, work, density etc.

DIMENSIONS – are the properties by which the physical quantity of an object may be described.

DRY BULB TEMPERATURE – The actual temperature of air, as opposed to wet bulb temperature.

DRY STEAM – Steam containing no moisture. It may be either saturated or superheated steam.

DRY SATURATED STEAM – Saturated steam, as generated from water, that contains no moisture in suspension.

DAMPER – Device which uses oil metered through orifices to control abrupt suspension movement during expansion and compression.

DAMPER ROD – Tube secured to the bottom of each fork slider to hold the slider onto the fork leg. Damper rod controls movement of front suspension by metering hydraulic fluid through orifices in the rod.

DIAPHRAGM SPRING – A slightly cone shaped metal disc which acts as a clutch pressure plate spring when flattened.

DIRECT DRIVE GEARBOX – Power is transmitted from clutch to input shaft (main shaft), to layshaft, to high gear pinion, which has output sprocket mounted on it.

DISC BRAKE – A brake consisting of a flat circular disc attached to the wheel. A hydraulic or mechanical caliper applies pressure to two brake pads and press them on the disc to slow or stop disc rotation.

DOUBLE PISTON CALIPER – A hydraulic brake caliper with two pistons and provisions for applying hydraulic pressure equally to both pistons. The caliper body is fixed solidly.

DOUBLE ROW CHAIN – A chain having two rows of rollers. Duplex (double row) chains are used for primary drives.

DRIVE PLATE – A clutch plate which is indexed into the clutch basket (outer hub) by tabs. Drive plate has friction material bonded to its surface. When clutch is engaged, drive plate transfers power to driven plate.

DRIVEN PLATE – A clutch plate which is indexed onto the clutch inner hub by tabs or splines around its inside diameter. Driven plate is usually a plain plate (no friction material) and drives gearbox input shaft through clutch inner hub.

DRIVE TRAIN – The drive system that transfers the power produced by the engine to the rear wheel, includes primary drive, clutch, transmission and fluid drive systems.

DRUM BRAKE – A brake consisting of two brake shoes mounted on a backing plate. One or two cams cause the shoes to expand against inside of the brake drum. Brake drum is part of hub or is bolted to hub.

DRY CLUTCH – A clutch assembly that does not run in an oil bath.

DECARBURIZING FLAME – A flame which removes carbon from the molten metal.

DEPOSITION EFFICIENCY (arc welding) – Ratio of the weight of deposited metal to the net weight of the filler metal consumed, exclusive of stubs i.e., left out electrode bits.

DEPTH OF FUSION – Distance that fusion extends into the base metal or previous pass from the surface melted during welding.

DIFFUSION WELDING – A solid state welding process that produces coalescence of the faying surfaces by the application of pressure at elevated temperature.