SEMI FIXED COMPRESSOR – A unit larger than the portable type where skids are used in place of being mounted on a truck, the adaptation being for service where frequent moving is not necessary.
SEPARATOR – Device through which the compressed air after being cooled in the after cooler, is sent so as to separate the moisture from the air by centrifugal force.
SINGLE ACTING COMPRESSOR – A reciprocating compressor in which compression takes place on one side of the piston during alternate strokes.
SINGLE STAGE COMPRESSOR – A compressor in which the compression cycle takes place in a single cylinder.
SLIPPAGE EFFICIENCY – The ratio of volume of air actually measured to the apparent volume accounted for by the indicator diagram.
SPECIFIC HEAT OF AIR – Amount of heat that is to be supplied to raise the temperature of 1 kg of air through 1 degree C.
SPECIFIC HEAT OF AIR AT CONSTANT PRESSURE – Total specific heat of air which is made up of (1) the internal work of raising the temperature of air, and (2) the external work of pushing away the atmosphere to make room for its expansion.
SEMI FIXED COMPRESSOR – A unit larger than the portable type where skids are used in place of being mounted on a truck, the adaptation being for service where frequent moving is not necessary.
SEPARATOR – Device through which the compressed air after being cooled in the after cooler, is sent so as to separate the moisture from the air by centrifugal force.
SINGLE ACTING COMPRESSOR – A reciprocating compressor in which compression takes place on one side of the piston during alternate strokes.
SINGLE STAGE COMPRESSOR – A compressor in which the compression cycle takes place in a single cylinder.
SLIPPAGE EFFICIENCY – The ratio of volume of air actually measured to the apparent volume accounted for by the indicator diagram.
SPECIFIC HEAT OF AIR – Amount of heat that is to be supplied to raise the temperature of 1 kg of air through 1 degree C.
SPECIFIC HEAT OF AIR AT CONSTANT PRESSURE – Total specific heat of air which is made up of (1) the internal work of raising the temperature of air, and (2) the external work of pushing away the atmosphere to make room for its expansion.
SAFETY RIM – A type of wheel rim having a hump on the inner edge of the ledge on which the tyre bead rides. The hump helps hold the tyre on the rim in case of blow out.
SCRUB RADIALS – The distance on the road surface under the front tyre between an extension of the pivot axis and the centre of weight.
SCUFF – The tyre slide on the road surface during operation.
SCUFF TRAVEL – The amount of side travel of the tyre as the wheel moves from maximum jounce to maximum rebound.
SEAT ADJUSTER – A device to permit forward and backward (and sometimes upward and downward) movement of the front seat.
SECONDARY SHOE – A brake shoe that is operated by a primary shoe to apply brake.
SELF ADJUSTING BRAKE DESIGNS – Brakes that automatically compensate for wear of the brake linings.
SELF ALIGNING TORQUE – The natural tendency of the tyre to return to the neutral position after being turned.
SEMIMETALLIC BRAKE LINING – A brake lining combining both metallic and organic materials for improved braking performance.
SENSTRONIC BRAKE – CONTROL (SBC) – is basically a brake by wire system which eliminates the need for mechanical linkage between the brake pedal and brake master cylinder.
SEQUENTIAL GEAR BOX – is an electromechanical device that replaces the conventional gear shift mechanism and is bolted to the tunnel section or the floor of the car. It converts the conventional floor shifter to an electronically activated sequential shift system that is electronically controlled by microprocessors.
SERIES – The designation of a tyre aspect ratio.
SERVICE BRAKE SYSTEM– The main braking system of the vehicle which controls braking effect proportional to the drivers demand.
SHACKLE – Swinging support by which one end of a leaf spring is attached to the vehicle frame.
SHIM – A slotted strip of metal used as a spacer to adjust front end alignment on many cars and to make small correction in the position of the body sheet metal and other parts.
SHIMMY – Rapid oscillations, in wheel shimmy, for example, the front wheel tries to turn in and out alternately and rapidly (a violent front wheel shake). This causes the front end of the car to oscillate or shimmy.
SHOCK ABSORBER – The assembly on the vehicle that checks excessively rapid spring movement and oscillations. A device placed at each vehicle wheel to regulate spring rebound and compression.
SHOE – The part of a brake that supports the lining.
SHORT LONG ARM SUSPENSION – A suspension system in which a long and a short control arms are used to support the wheel.
SINGLE LEADING SHOE – A drum brake having two shoes; one is leading another is trailing. Leading shoe tends to wedge itself into the brake drum and provides more braking action than the trailing shoe.
SINGLE REDUCTION AXLE – In the single reduction type final drive, the required speed reduction (say up to 7 to 1) is obtained in one step.
SIPES – Slits in the tyre tread to produce more blade surface for traction.
SKID – A tyre sliding on the road surface.
SKID CONTROL – A device that operates to prevent wheel lock up during braking and thus skidding.
SLIDING MESH GEAR BOX – The gear box consists of three shafts and a set of gears, gear selector mechanism and gear shift lever. Different gears are engaged by sliding the appropriate gears.
SLIP ANGLE – The angle between the tyre and the actual directional movement.
SLIP JOINT – In the power train, a variable length connection that permits the drive shaft (propeller shaft) to change its effective length.
SOCIETY OF AUTOMOTIVE ENGINEERS (SAE) – A professional engineering society responsible for setting many vehicle standards used in the world today.
SPIN BALANCER – A car tyre balancer which turns the raised tyre at a road speed where imbalance can be detected by wheel shake.
SPINDLE (steering system) – A part of the steering knuckle assembly on which the front wheels are mounted.
SPONGY PEDAL – A brake pedal that feels soft or spongy.
SPRING FREQUENCY – Springs are also compared in frequency. Springs which return quickly to their original shape or oscillate rapidly after being deflected are said to have higher frequency than those that return or oscillate slowly.
SPRING RATE – The flexibility of a spring depends on the property called spring rate. It is defined as the weight in kg required to deflect it one cm. A soft spring has a lower rate than a stiff or inflexible spring.
SPRING SHACKLE – Provides a means for the leaf spring assembly to compensate for changes in its length.
SPRING SUSPENSION – The operating components of a spring suspension system, which absorbs the force of road shocks by flexing and twisting.
SPRUNG WEIGHT – That part of the vehicle which is supported on springs (the frame and body for example).
SQUIRM – The twist of the tyre tread in the foot print.
STABILIZER SHAFT – An interconnecting torsion bar between left and right lower suspension arms on a vehicle which reduces body roll on turns and adds stability.
STAR WHEEL – An adjustable link between the primary and secondary brake shoes.
STEER ANGLE – The angle the wheels are turned to from straight ahead.
STEERING AND IGNITION LOCK – A locking device that locks the ignition switch in the off position, and also locks the steering wheel so that it cannot be turned.
STEERING ARM – The arm attached to the steering knuckle to turn the knuckle, and wheel, for steering.
STEERING AXIS – The centre line of the ball joints in a front suspension system extended to the road surface.
STEERING AXIS INCLINATION – The inward tilt of the steering axis or front wheel pivot from the vertical.
STEERING COLUMN – The housing that supports the steering shaft.
STEERING GEAR – That part of the steering system, located at the lower end of the steering shaft that carries the rotary motion of the steering wheel to the vehicle wheels for steering.
STEERING KICKBACK – Sharp rapid movements of steering wheel as the front wheels encounter obstructions in road, the shocks of these encounters kickback to the steering wheel.
STEERING KNUCKLE – The front wheel spindle or stub axle which is supported by the king pin, so that it and the wheel can be turned for steering. Part of the front suspension system.
STEERING LINKAGE – Linkage that connects the steering gears to the front wheels.
STEERING RATIO – The number of degrees the steering wheel is turned divided by the number of degrees the vehicle wheels are turned.
STEERING SHAFT – Shaft extending from steering gear to the steering wheel.
STEERING STOPS – limit the angular deflections of the front wheels. They avoid rubbing of tyres against the frame or against the fenders which would cause undue wear and tear of the tyres.
STEERING SYSTEM – The mechanism that enables the driver to turn the wheel axles (usually the front) and thus turn the wheels away from the straight ahead position so that the vehicle can be guided.
STEERING WHEEL – The wheel at the top of the steering shaft in the drivers compartment which is used to guide or steer, the vehicle.
STONE SHIELD – is bolted to the radiator support and the fenders. It fits beneath the bumper of the car. It prevents striking of small flying stones on to the radiator grille and radiator and thus avoids their damage.
STOP LIGHT SWITCH – A switch applied by the master cylinder pressure that turns on brake lights.
STOPPING DISTANCE – is the distance in which a vehicle will be brought to rest from steady speed, when the brake is applied.
STREAMLINING – The shaping of an object that moves through a medium (such as air or water) or past which the medium moves, so that less energy is lost by parting and reuniting of the medium as the object moves through it.
STUMBLE – The term related to vehicle driveability, the tendency of an engine to falter and then catch, resulting in a noticeable stumble effect felt by the driver.
SUSPENSION – The suspension system supports the vehicle body and at the same time isolates the vehicle and its occupants from shocks and vibrations generated by the road surface. It also maintains steering control and stability at all times.
SUSPENSION ARM – In the front suspension, one of the arms is pivoted at one end to the frame and at the other to the wheel (steering knuckle) support.
SUSPENSION COMPLIANCE – Rearward and upward movement of the suspension when the tyre meets an obstacle on the road surface.
SUSPENSION GEOMETRY – The angular action of the suspension as it goes from its static position to the extremes of travel (compared to vertical lines).
SYNCHROMESH – A device in the transmission that synchronizes gears about to be meshed so that there will not be any gear clash. Also called SYCHRONIZER.
SAC VOLUME – is the dead volume between the nozzle seat and the end of the spray holes, in a multi hole injector.
SEMI DIESEL – A diesel which utilizes injection of fuel, but also uses electric spark ignition.
SMOKE – is nothing but the carbon particles suspended in the exhaust gases.
It may be blue smoke, black smoke and white smoke.
SODIUM COOLED VALVE – A valve designed to allow the stem and head to be made hollow and partially filled with metallic sodium for better cooling.
SOLID INJECTION SYSTEM – The system which injects only the metered quantity of fuel by means of a pumping device. Also called AIRLESS INJECTION SYSTEM.
SQUISH – Radial inward flow of air from the annular space above the piston; into the combustion chamber cavity during the compression stroke of the piston.
SQUISH AREA – The area confined to the cylinder head and flat surface of the piston when on compression stroke, which causes squish.
SQUISH HEIGHT – refers to the clearance between the piston top and cylinder head, at TDC. This is reduced to a minimum consistent with manufacturing capabilities and operational aspects.
SUCTION SWIRL – Rotary motion imparted to the air during suction by admitting air into the engine cylinder in a tangential direction.
SUPER CHARGING – Process of admitting into the engine cylinder, a charge larger in quantity (i.e., weight) than what the cylinder would contain due to regular suction stroke i.e., by natural aspiration.
SURFACE FILTER – Fuel filter similar to a sieve, consists of a number of discrete holes and pores, through a single layer of material.
SWIRL – Rotation of mass of air as it enters the engine cylinder. This is one form of turbulence.
SWIRL COMBUSTION CHAMBER – Part of the combustion space, spherical or cylindrical in shape, located in the cylinder head, in which vigorous swirl is created and into which fuel is injected and combustion starts and spreads into the space above the piston.
SWIRL RATIO – is the ratio of (air) swirl speed in the combustion chamber to engine speed.
SAG – Defect which appears as an increase or decrease in metal section due to sinking of sand in the cope (decreased section) or sagging in the core (increased section).
SAND BLAST – Sand driven by a blast of compressed air (or steam). Used to clean castings, to cut, polish or decorate glass and other hard substances.
SCAB – A blemish on the casting caused by eruption of gas from the mould face.
SEAM – Surface defect on a casting similar to a cold shut, but not as severe.
SEMICENTRIFUGAL CASTING – is one in which the mould, usually a stacking of several flat sand or die moulds, is rotated about a vertical axis.
SHOT – Abrasive blast cleaning material.
SHRINKAGE ALLOWANCES – are provided to take care of the contraction in dimensions of the solidified casting as it cools from its freezing temperature to room temperature.
SHRINK HOLE – A hole or cavity in a casting resulting from contraction and insufficient feed metal, and formed during the period the metal changed from the liquid to the solid state.
SHELL MOULDING – Process in which clay free silica sand coated with a thermosetting resin or mixed with the resin is placed on a heated metal pattern for a short period of time to form a partially hardened shell. The unaffected sand mixture is removed for further use. The pattern and the shell are then heated further to harden or polymerize the resin sand mix, and the shell is removed from the pattern.
SKIMMING GATE – Part of the mould that retains non-metallic inclusions or impurities and delivers sound metal further into the runners.
SLEEK – Term meaning to make smooth. It is applied to the trowelling of a sand surface.
SLUSH CASTING – Casting made by pouring an alloy into a metal mould, allowing it to remain sufficiently long to form a thin solid shell, and then pouring out the remaining metal.
SNAG – Removal of fins and rough places on a casting by means of grinding.
SNAP FLASK – Moulding box, hinged on one side so that it may be opened to allow the finished mould to be removed.
SPRIGS – Small pegs of wood or metal used to strengthen weak portions of a mould or to assist in the mending up of a damaged mould.
SPRUE – The vertical portion of the gating system where the molten metal first enters the mould.
STACK MOULDING – Moulding method in which the half mould forms the cope and drag. They are placed on top of the other and moulds stacked one over the other are poured through a common sprue.
STRICKLE – Piece of wood by means of which surplus sand is removed from a moulding box or other surface. They may also be used to shape sand surfaces into any required shape.
SURVIVABILITY – The ability of a moulding mixture to retain its initial properties for a specified length of time.
SAND (moulding) – Substance used in foundries for making the moulds.
SCRAP – Materials or metals that have lost their usefulness and are collected for reprocessing.
SEALANT – A sealing agent that has some adhesive qualities, it is used to prevent leakage.
SEMICONDUCTORS – A few substances containing metallic elements have considerably less electrical conductivity. These contain a few electrons to give them conductivity intermediate between metals and insulators.
SEMISTEEL – Cast iron to which a small proportion of mild steel or wrought iron scrap is added during the melting of the pig iron so that the product will have a lower carbon content than the average iron, from 2.5-3.2% and which is tougher.
SILICA – Silicon dioxide, SiO2 occurring in nature as quartz, opal etc.
SILICON – Non-metallic element which can be added to steel, cast iron and non-ferrous alloys. It acts as a DEOXIDIZER, and also tends to form graphite by throwing the carbon out of solution and thereby increases the impact resistance of the steel, and, up to a silicon content of 1.75%, the elastic limit is increased also.
SILICON ALUMINIUM – An alloy of 50% silicon, and 50% aluminium used for making silicon additions to aluminium alloys.
SILICON BRASS – A series of alloys containing 0.5-0.6% silicon, 1-19% zinc and a substantial amount of copper.
SILICON BRONZE – Alloy containing about 90-95% of copper, to which is added silicon and manganese, equivalent in strength to medium carbon steel with resistance to corrosion and fatigue.
SILICON CARBIDE – A refractory and abrasive material made by sand, coke, and saw dust in an electric arc furnace.
SILICON CARBIDE BRIQUETS – Silicon carbide in BRIQUET form used as an inoculants and deoxidizer in cupola melted gray iron.
SILICON COPPER – An alloy of silicon and copper, used as a deoxidizer and hardener in copper base alloys.
SILMANAL – It is the name given to a rather expensive alloy of silver, manganese, and aluminium that has unusual magnetic properties for special applications.
SILVER – A white, ductile metal that is an excellent conductor of heat and electricity.
SILVERY IRON – A type of pig iron containing 8-14% silicon, 1.5% carbon max, 0.06% sulphur max and 0.15% phosphorous max.
SLAG – The more or less completely fused and vitrified matter separated during the reduction of a metal from its ore.
SLURRY – A watery mixture of insoluble material such as mud, lime or plaster of Paris.
SMOG – The irritating haze resulting from the sun’s effect on certain pollutants in the air, notably those from automobile exhaust. Also a mixture of fog and smoke.
SMOKE – Solid or liquid particles under 1 micron in diameter. Particles suspended in air after incomplete combustion of materials containing carbon. The matter in the exhaust emission which obscures the transmission of light.
SODIUM SILICATE – Na2SiO3-Also called water gas.
SOLDERING ALLOY – Fusible alloy used to join together two metallic surfaces with the aid of heat. Soft solder is an alloy of lead and tin, in which the proportions of the two constituents may vary from almost pure lead to almost pure tin.
SOLDERING FLUID – Liquid flux used when soldering.
SOLID SOLUTIONS – Solid solutions are alloys containing alloying elements that are relatively soluble in the base metal in the solid state.
SOLUBLE OIL – Specially prepared oil whose water emulsion is used as a cutting or grinding fluid.
SOLUTE – A substance that is dissolved in a solution and is present in minor amounts.
SOLVENT – A substance that is capable of dissolving another substance and is the major constituent in a solution.
SORBITE – Structure consisting of evenly distributed carbide of iron particles in a mass of ferrite, formed when fully hardened steel is tempered at between 550 and 650°C.
SPELTER – Hard solder used during brazing containing 60% copper, 20% tin and 20% zinc.
SPHEROIDITE – It is the structure in steel, in which cementite takes the form of rounded particles, or spheroids, instead of plates.
STAINLESS STEEL – Steel which resists corrosion by the atmosphere and the attack of acids and which does not scale when subjected to high temperature. Alloy steels containing iron, at least 11 % chromium, nickel, molybdenum and 0.1-1 % carbon.
STEATITE – Steatite is the name given to a fired ceramic product which contains 80 per cent or more talc bonded with ceramic fluxes to a nonporous structure.
STEEL – An alloy of iron and less than 2% carbon plus some impurities and small amounts of alloying elements is known as plain carbon steel. The alloy steels contain substantial amounts of alloying elements such as chromium or nickel besides carbon.
STELLITE – Non-ferrous alloy containing 35-80% cobalt, 10-40% chromium, 0-25% tungsten and 0-10% molybdenum.
SYNTHETIC MATERIALS – A complex chemical compound which is artificially formed by the combination of two or more compounds or elements.
SCHIELE’S PIVOT – A pivot bearing on a shaft, designed to give uniform wear in the direction of the axis with uniform pressure, the coefficient of friction being assumed to be constant.
SCRAPER RING – A piston ring that assists in compression and wipes off the excess oil from the cylinder walls.
SEAL – A material, shaped around a shaft, used to close off the operating compartment of the shaft, preventing oil leakage.
SEIZING – The phenomenon in which the metal surfaces adhere and then tear owing to relative motion, caused by the attraction between molecules on opposite sides of the common surface between two elements of a bearing.
SERVICE RATING – For lubricating oils used in engines, a designation that indicates the type of service for which the oil is best suited.
SHIM (bearing) – A strip of copper or similar material used under a bearing cap, for example, to increase bearing clearance.
SKIMMING – Using a machine to remove oil or scum from the surface of the water.
SLUDGE – Accumulation in oil pan, containing water, dirt and oil, sludge is very viscous and tends to prevent lubrication.
SPLASH FEED OIL SYSTEM – A type of engine lubricating system that depends on the splashing of oil for lubrication of moving parts. The engine is enclosed, and the crankcase contains oil into which the cranks dip and splash as they rotate, throwing the oil over the various bearings.
STATICAL FRICTION – Friction at starting from rest, and this is greater than the friction of motion and depends on the hardness of the bodies and the length of time during which they have been in contact.
SUMP – A system for storing oil, either in the crankcase (wet sump) or in a separate tank (dry sump).
SYNTHETIC OIL – Oil made from material other than petroleum.
SYPHON LUBRICATOR – The unit in which the oil stored in a cup above a journal, is delivered slowly to the bearing through a wick which acts as a syphon.
SAFETY CONTROLS – Devices that guard against (1) overpressure leading to explosions from the water side or steam side, (2) overheating of metal parts, possibly also leading to explosion in a fired boiler, (3) fire side explosions (furnace explosions) due to uncontrolled combustible mixtures on the firing side.
SECONDARY AIR – Air introduced into a furnace above and around the flames as may be necessary to promote combustion. This air is in addition to the primary air which enters either as a mixture with fuel or as blast underneath a stoker.
SHREDDER– A machine used to break up waste materials into smaller pieces by cutting or tearing.
SCRUBBER – A device that uses a liquid spray to remove aerosol and gaseous pollutants from an air stream.
SLACK – A coal of fine size, often screenings, and maximum size is not likely to exceed 62.5 mm.
SLAG TAP FURNACE – A furnace for burning pulverized fuel in which the ash puddles in the bottom of the furnace in a molten state and is removed periodically or continuously, depending on the design of the system, while still in the molten condition.
SMOG – A term coined from smoke and fog. This is applied to the fog like layer that hangs over many areas under certain atmospheric conditions. Smog is compounded from smoke, moisture and numerous chemicals which are produced by combustion and from numerous natural and industrial processes.
SPECIFIC GRAVITY – A measure of the weight per unit volume of a liquid as compared with the weight of an equal volume of water.
SURFACE IGNITION – Ignition of air fuel mixture in the combustion chamber produced by hot metal surfaces or heated particles of carbon.
SYNTHETIC FUELS – Fuels such as ethanol and butanol derived from coal, and hydrogen from water.
SECONDARY AIR – Air quantity which is about five times the minimum air for combustion, that flows around the annular space of the combustion chamber and cools the products of combustion.
SECONDARY ZONE – Portion of the combustion chamber wherein about 30% of air is added at the right points in the combustion process so as to complete the combustion of fuel.
SHAFT, ROTOR, SPINDLE – The rotating assembly of the turbine which carries the blades.
SHROUD – A band placed around the periphery of the blade tips in order to stiffen the blades and prevent spillage of the fluid over the blade tips. Shrouds may be continuous or in segments integral with one or more blades.
SINGLE SHAFT GAS TURBINE – Turbine unit in which all compressors and turbines in the plant are mounted on one shaft and are coupled in series arrangement.
SLIP – The failure of the whirl velocity of air at the outlet of the centrifugal impeller becoming equal to the impeller tip speed.
SLIP FACTOR – Ratio of whirl velocity of air at the outlet of the compressor (centrifugal type) to the impeller tip speed. This factor limits the work capacity of the compressor even under isentropic conditions.
SOLIDITY OF A BLADE – The ratio of blade chord to pitch, and ranges from 1.0 to 2.0.
SONIC VELOCITY – Speed of sound in a gas. This is the velocity at which a pressure wave is propagated throughout the gas and this velocity depends upon the pressure and density of the gas.
SPECIFIC POWER – Net horse power developed per kg per second of air flow.
STAGGER ANGLE – The angle made by the axial direction and the chord line, a parameter describing the setting of a row of blades of given form and spacing.
STAGE OF A TURBINE – Unit which consists of the fixed nozzle row (or fixed blade row) and the moving row of blades which receives the gases.
STAGNATION ENTHALPY – Enthalpy of a moving gas when brought to rest isentropically. Also called TOTAL HEAD.
STAGNATION TEMPERATURE – The hypothetical temperature which would result if all the kinetic energy of a flowing gas were to be converted into heat under conditions of no gain or loss of heat i.e., adiabatic conditions. Also called TOTAL HEAD TEMPERATURE. This is the sum of static temperature and dynamic temperature.
STALLING – The phenomenon of reduction in the lift force (acting on an air foil) at higher angles of incidence. Also called LIMIT OF STABILITY.
STATIC HEAD EFFICIENCY – Ratio of the temperature equivalent of the work output and leaving energy to the isentropic temperature drop from the total head inlet to the static outlet pressure.
STEADY FLOW – Flow of fluid in which the quantities such as velocity, pressure, temperature etc., may change from point to point but they do not vary with time at any particular point.
STRAIGHT COMPOUNDED UNIT – The system in which the low pressure compressor is driven by the low pressure turbine and the high pressure compressor by the high pressure turbine. Power is taken from the low pressure turbine shaft.
SUBSONIC DIFFUSER – A diffuser having a diverging cross-section in the direction of flow.
SUPERSONIC DIFFUSER – A diffuser having a converging cross-section in the direction of flow.
SYMMETRIC STAGE AXIAL FLOW COMPRESSOR – An axial flow compressor which has symmetric blade arrangement so that the pressure rise in the moving row and the pressure rise in the fixed row are equal.
SHERADIZING – Heat treatment process in which zinc dust is used for producing a rust proof surface on ferrous metals. It derives its title from the name of the inventor SHERARD OSBORN COWPER COLES.
SILICONIZING – Process in which iron and steel parts are impregnated with silicon for improving the surface resistance to corrosion, heat and wear.
SOAKING – A prolonged heating of a metal at a predetermined temperature to create a uniform temperature throughout its mass.
SOLUTION HEAT TREATMENT – A process in which an alloy is heated to a predetermined temperature far a length of time that is suitable to allow a certain constituent to enter into solid solution. The alloy is then cooled quickly to hold the constituent in solution, causing the metal to be in an unstable supersaturated condition. This condition is often followed by age hardening.
STRAIN HARDENING – An increase in hardness and strength of a metal that has been deformed by cold working or at temperatures lower than the recrystallization range.
SUBZERO HEAT TREATMENT – Method of heat treatment of steel, introducing a cooling period or periods at a temperature well below freezing point, the object being to ensure complete transformation of austenite to martensite.
SCORED – Scratched or grooved, as a cylinder wall may be scored by abrasive particles moved up and down by the piston rings.
SCRAPER – A device in engine service, to scrape carbon etc., from engine block, piston etc.
SCRAPER RING – On a piston, a type of oil control ring designed to scrape excess oil from cylinder wall and cause it to flow down into the crankcase.
SCREEN – A fine mesh screen in the fuel or lubricating systems that prevents large particles (dirt and particles of dust) from entering the system.
SCUFFING – A type of wear of moving parts characterized by transfer of material from one to other part and results in pits and grooves.
SEALER – A thick, tacky compound usually spread with a brush, which may be used as a gasket or sealant, to seal small openings or surface irregularities.
SEAT – The surface on which another part rests, such as a valve seat. Also, applied to the process of a part wearing into fit, for example piston rings seat after a few kilometers of driving.
SEMIFLOATING PISTON PIN – is clamped in the piston pin bosses and free to rotate in the connecting rod small end or clamped in the connecting rod small end and free to rotate in the piston pin bosses.
SEVERE RINGS – Piston rings which exert relatively high pressure against the cylinder walls, sometimes by the use of an expander spring behind the ring. Such rings can be used in an engine having excessive cylinder wear.
SHROUD – A hood placed around an engine cooling fan to improve fan (cooling) action.
SIAMESED CRANKSHAFT – Crankshaft configuration where two rods are mounted on the same crankpin (journal). One rod is forked and the other rod is mounted on inside of the fork.
SIDE BY SIDE CRANKSHAFT – Crankshaft configuration where connecting rods are mounted next to each other on the same crankpin (journal).
SINGLE PIECE CONNECTING ROD – has small end, rod or shank and big end as one unit. This is used in most of the small two stroke engines meant for two wheelers.
SPRING (valve) – A coiled wire that varies its length by flexing, and twisting.
SPRING FREE LENGTH – The length of the spring when measured without any load on it.
SPRING MECHANICAL PRELOAD – The length or pressure of a spring, measured while it is in the installed condition.
SPRING RATE – The amount of force necessary to compress a spring a specific distance, kilograms per centimetre, to indicate the stiffness or softness of a spring.
SPRING RETAINER – In the valve train, the piece of metal that holds the springs in place and is itself locked in place by the valve spring retainer locks.
SPRING RETAINER LOCK – The locking device on the valve stem that locks the spring retainer in place.
SQUARE ENGINE – An engine having the bore and stroke of equal measurements.
SQUISH – The action (radial inward air motion) in some combustion chambers in which the last part of the compressed charge is pushed, or squirted, out of a decreasing space between the piston and the cylinder head.
STIRLING ENGINE – A typical internal combustion engine in which the piston is moved by the changing pressure of a working gas that is alternately heated and cooled.
STROKE – In an engine, the distance that the piston moves from BDC to TDC or vice versa.
SUMP – A system for storing lubricating oil, either in the crankcase (wet sump) or in a separate tank (dry sump).
SUPER CHARGER – A device in the intake system of an engine which pressurizes the ingoing charge. This increases the mass of charge (air fuel mixture) burned and thus increases engine output. If the supercharger is driven by the engine exhaust gas turbine, it is called TURBOCHARGER.
SCLEROSCOPE – Instrument for measuring hardness.
SCREW GAUGE – Type of gauge for checking the accuracy of a screw thread.
SCREW PITCH GAUGE – A small tool with a number of blades, each having the same number of notches per inch as the thread it represents. It is used to find the pitch and number of threads per inch on a screw, tap or die.
SCREW THREAD MICROMETER – Type of micrometer with measuring points specially shaped to enable the measurement of pitch diameter and thickness of thread.
SCRIBER – Used for making lines on the work when marking off.
SINE BAR – Tool used for the accurate setting out of angles by arranging to convert angular measurements to linear ones.
SLIP GAUGE – Form of gauge made of hardened steel with two parallel faces worked to high precision and at a known distance apart.
SNAP GAUGE – A type of fixed gauge, plain or adjustable, arranged with inside measuring surfaces for checking diameters, lengths, thicknesses or widths of work-pieces.
SPRING CALIPERS – Inside or outside calipers for measuring work-pieces in which the tension against the nut is maintained by a circular spring at the end.
STEEL RULE – A thin flat measuring tool graduated in either fractional or decimal part of an inch or cm and made in many styles and lengths.
STRAIGHT EDGE – Strip of metal, usually steel, with one edge straight, used to determine the flatness of a surface.
SURFACE GAUGE – Tool used for marking out and setting up work in conjunction with a surface plate, used also for levelling work-pieces when fixing them to the worktables of machine tools e.g., planers, shapers, millers etc.
SCREW – A helix formed or cut on a cylindrical surface which may advance along the axis to the right or left. The helix may be single or multiple.
SCREW JACK – Device used for lifting a heavy load by means of a screw.
SCREW THREAD – A ridge of uniform section or shape in the form of a helix on the external or internal surface of a cylinder, or in the form of a conical spiral on the external or internal surface of a cone.
SELF CENTERING CHUCK – Design of chuck for holding hexagonal or cylindrical work, operating in such a way that the work is automatically centered.
SET SCREW – Usually a hardened steel screw having either no head or a square head and with various designs of points or ends to lock or tighten adjustable machine parts in position on a shaft.
SHOULDER SCREW – A screw having two or more diameters or shoulders and commonly used for supporting levers and other machine parts that have to operate freely. The screw body is slightly longer than the thickness of the piece pivoted on the screw so as to allow the piece to move freely when the screw is set up tightly against the bottom of the shoulder.
SLEEVE – A round piece of metal having a straight or tapered hole which fits over or into another piece to adapt parts to fit, as a taper sleeve for a lathe center.
SLIDE REST – A tool holding slide used on machine tools. It is usually adjustable for holding and guiding cutting tools. The compound slide or rest used on an engine lathe is an example. The compound slide permits the tool to be fed at any angle.
SLIDING TABLE (compound) – Device to enable holes to be drilled or bored very accurately with respect to each other.
SNAP FLASK – Strongly constructed wooden moulding box, split diagonally with hinges on one corner and locking latches on the opposite corner, so that the box may be removed from the mould prior to casting.
SOCKET HEAD – Screw threads having a hexagonal or other form of recessed socket in the head so that the screw can be turned with a wrench or key, as a hexagonal key.
SPLINES – Multiple keys cut in either a shaft or a hole of parts that are made to slide or move lengthwise on a shaft, as a sliding gear transmission.
SPLIT NUT – A nut which has been cut length wise so as to open for quick adjustment.
SPRING COLLETS – A type of draw in collet made of hardened steel and having three slots or saw cuts which permit the collet to be closed tightly against a tapered sleeve by the draw bar.
SQUARE THREAD – A form of screw thread in which the cross-section of the thread forms a square, making the width of the thread equal to the width of the space between the threads.
STAKE – Small anvil used for sheet metal work.
STEADY REST – A support attached to the ways of a lathe for turning long work pieces. Used to prevent slender work from springing away from the cutting tools or to permit machining operations to be performed on the end of the workpiece. Sometimes called a center rest or STEADY.
STEP BLOCK – A block of steel or cast iron having a series of steps and used for supporting the ends of machine clamps when clamping work to the table.
STEPPED CONE PULLEY – A cone pulley having several diameters or steps for obtaining different speeds on machine tools.
STOPS – Devices attached to the movable table or ram or parts of a machine tool, such as a milling machine table, to limit the amount of travel.
STUD – A plain cylindrical piece having a threaded portion of suitable length at each end or a continuous thread over the entire length. One end is screwed into a machine or workpiece after which a second part is placed over the stud and held in place by a nut.
SWIVEL SLIDE – Device to enable the toolpost slide of a lathe to be set at an angle for taper turning or cutting V threads.
SWIVEL VICE – A bench or machine vice for holding workpiece which may be rotated on its base to the desired angle or position.
SCRAPER – Machine that removes earth slice by slice, transports and places it in an earth structure, or pushes it to a dump and then levels the same.
SCREW CONVEYORS – Installations serving to move materials over a trough by a rotating screw. Also called SPIRAL CONVEYORS.
SEAL – A small metal strip that is placed on a railroad car door when loading is completed.
SELF CLOSING GRAB – A crane grab which can pick up the load automatically but must be released with manual assistance.
SELF LEVELING – Bringing the lift to a stop so that its platform is level with the landing.
SEMI GANTRY CRANES – Hoisting installations in which one pair of legs travels over a track placed on a low foundation while the other pair receives support from an elevated track laid on a trestle or track girder attached to the building.
SHAKING CONVEYOR – Unit which consists of a deck in the form of a trough or pan suspended from, or supported by a stationary frame and the deck is induced to oscillate, causing the material to move along at a pace and in a mode governed by the character of the oscillations, e.g., oscillating conveyors and vibrating conveyors.
SINGLE FACED CORRUGATED FIBRE BOARD – Fibre board with a flat facing of corrugated material on one side.
SINGLE FACED PALLET – A pallet consisting of one deck.
SINGLE WALL CORRUGATED FIBRE BOARD – Fibre board with a flat facing of corrugated material on both sides.
SKID – Similar to pallets except it has no bottom surface.
SKIP HOIST – Conveyor which consists of a bucket moving between guides, with the power of a cable reeved round sheaves and drums which turn through electric drives. Used for vertical movement of coal.
SLIP SHEET – A single sheet of heavy, strong, corrugated fibre board or plastic. Unit load is pulled on it and the forks of the lift truck slide underneath.
SLOTTED STYLE BOX – A box with slots, made from a single piece of fibreboard.
SOFC – A container stacked on a flat car.
SOLID FIBRE BOARD – Two or more layers of fibre board glued together to make a single sheet.
SPAN – Horizontal distance between the axes of crane track rails.
SPEED GUARD – Device which prevents the hook loads from acceleration beyond a set limit. They are usually centrifugal brakes (e.g., centrifugal disc brake, centrifugal internal block brake), hydraulic units and eddy current brakes.
SPIRAL or SCREW CONVEYORS – Unit which employs an endless helicoids screw rotating in a trough. The movement of the screw gradually moves the material to a higher location.
STABILITY OF A CRANE – The ratio of the righting and tipping moments taken about a tipping axis.
STABILITY COEFFICIENT OF CRANE PROPER – The ratio of the moment produced by the dead weight of all crane components, with the allowance for a track gradient effect facilitating the chance of
overturning, taken about a tipping axis to the moment set up by a wind pressure exceeding the safe maximum operating value taken with respect to the same tipping axis.
STABILITY COEFFICIENT OF A CRANE UNDER A LOAD – Ratio of the moment set up by the dead weight of crane components with the allowance of additional forces (wind effect, inertia at starting and stopping the hoisting, slewing and travelling motions, effect of track ground gradient) taken about a tipping axis to the moment due to the working load about the same axis.
STOP OFF CAR – A car that stops at two or more destinations to finish loading or to partly unload.
STOWAGE – Arrangement of freight in the hold of the ship.
STRINGER – Timber that runs the length of a pallet.
SACRIFICIAL ANODE – A metal slug, usually magnesium and zinc, designed to concentrate galvanic corrosion upon itself and thus save a more important structure on which the anode is attached, such as a ship’s hull or a buried pipe line.
SCRATCH HARDNESS – The hardness of a metal determined by the width of a scratch made by a cutting point drawn across the surface under a given pressure.
SEGREGATION – Non-uniform distribution of alloying elements, impurities or micro phases.
SHEARING – A concentration of forces in which the bending moment is virtually zero and the metal tends to tear or to be cut along a transversal axis at the point of applied pressure.
SHEAR LOAD – A load that tends to force materials apart by application of side slip action.
SHEAR STRESS – Shear stress is the shear load per unit area, exerted between the material on one side of an imaginary plane of separation in the part and the material on the other side.
SHORTNESS – A form of brittleness in metal. It is designated as cold, hot and red to indicate the temperature range in which the brittleness occurs.
SKELP – A name of the semi finished steel of which butt-welded pipe is made.
SLAG (dross) – A fused product that occurs in the melting of metals and is composed of oxidized impurities of a metal and a fluxing substance such as limestone. The slag protects the metal from oxidation by the atmosphere since it floats on the surface of the molten metal.
SLIP PLANES – Also called slip bands. These are lines that appear on the polished surface of a plastically deformed metal. The slip bands are the result of crystal displacement, defining planes in which shear has taken place.
SOLID SOLUTION – Found in metals at temperatures below the solidus. Some of the types of solid solutions are continuous, intermediate, interstitial, substitutional and terminal.
SOLIDUS – Seen as a line in a two phase diagram, it represents the temperatures at which freezing ends when cooling, or melting begins when heating under equilibrium conditions.
SOLUBILITY – The degree to which one substance will dissolve in another.
SPALLING – Breaking small pieces from a surface, often caused by thermal shock.
SPECIFIC GRAVITY – A numerical value that represents the weight of a given substance with the weight of an equal volume of water. The specific gravity for pure water is taken as 1.000.
SPHEROIDIZING – Consists of holding carbon steel for a period of time at just under the transformation temperature (heating and cooling). An aggregate of globular carbide is formed from other microstructures such as pearlite.
SPRING BACK – The tendency of a formed metal part to return to some extent to its former shape because of the elasticity of the metal.
SPUTTERING – To dislodge atoms from the surface of a material by collision with high energy particles for the purpose of depositing a metallic film on a part.
STIFFNESS – The ability of a metal or shape to resist elastic deformation. For identical shapes, the stiffness is proportional to the modulus of elasticity.
STRAIN – The measure of the change in the size or shape of a body, referred to its original size or shape. This is unit deformation of a metal when stress is applied.
STRENGTH – The ability of a material to resist external forces. It is called tensile, compressive, or shear strength depending on the load.
STRESS – The load per unit area on a stress strain diagram.
STRESS, TENSILE – Refers to an object loaded in tension, denoting the longitudinal force that causes the fibres of a material to elongate.
STRESS, COMPRESSIVE – Refers to a member loaded in compression, which either gives rise to a given reduction in volume or a transverse displacement of the material.
STRESS, SHEAR – Refers to a force that lies in a parallel plane. The force tends to cause the plane of the area involved to slide on the adjacent planes.
STRESS, TORSION – The shearing stress that occurs at any point in a body as the result of an applied torque or torsional load.
STRESS RAISER – Can be a notch, nick, weld under cut, sharp change in section, or machining grooves or hairline cracks that provide a concentration of stresses when the metal is under tensile stress. Stress raisers pose a particular problem and can cause early failure in members that are subjected to many cycles of stress reversals.
STRESS RELIEF ANNEAL – The reduction of residual stress in a metal part by heating it to a given temperature and holding it there for a suitable length of time. This treatment is used to relieve stresses caused by welding, cold working, machining, casting and quenching.
SUPER-CONDUCTIVITY – Property of zero electrical resistance (and zero magnetic induction) acquired by some metals at very low temperatures.
SURFACE TENSION – Interfacial tension between two phases one of which is a gas.
SAND BLASTING – Process used for cleaning metal surfaces, consists of directing a stream of air under pressure, into which quartz sand is introduced as an abrasive, on to the work.
SCREW CUTTING – Process of cutting a screw thread, usually in a lathe, which involves copying a master screw called the leading or lead screw in the nature of its pitch, but not its profile.
SEAMING – A bending and flattening of an interlocking fold, e.g., a stove pipe seam.
SEAM WELDING – Process of closing a seam by a continuous resistance weld.
SEASONING – Process by which the internal stresses existing in a piece of material (which have been subjected to sudden changes of temperature, as in casting or hardening or have been acted upon by heavy forces in some machining operations) are removed.
SEMI AUTOMATIC – A process in manufacturing that requires some degree of manual input, but acts without this input for at least part of the cycle.
SERRATING – Method of forming by the use of a knurling tool a series of straight serrations on the outer surface of a part, and parallel with it along the axis of a part.
SHAPING – Operations performed on shaping machines.
SHAVING – A finishing operation that cuts a small amount of material from the edge of a stamping to gain finish, accuracy and / or a square edge.
SHEARING – Cutting in a line by two opposed blades somewhat in a manner of the ordinary household shears.
SHELL MOULDING – A form of gravity casting process metal (usually a high melting temperature metal) in which the mould is made of a thin shell of refractory material.
SHIELDED ARC WELDING – Process in which the molten weld metal is protected from deterioration by an envelope of chemically reducing or inert gas such as helium or argon.
SHRINKAGE FIT – Method of fitting a shaft or other part into an undersized hole by heating the outer member until has expanded sufficiently.
SHOT PEENING – A cold working process in which the surface of a finished part is pelted with finely ground steel shots or glass beads to form a compression layer.
SILVER BRAZING – Brazing similar or dissimilar materials by using an alloy of silver or other metals.
SINTERING – The process of fusing compacted material such as metal powders into a solid or porous piece by applying heat sufficient to bond, but not melt, the particles.
SLOTTING – Machine tool operation designed for finishing slots or other enclosed parts not capable of being machined by normal planning or shaping machine.
SLUSH DIE CASTING – Casting process which involves the filling of a metallic mould with liquid metal or alloy, then inverting the mould and pouring out the unfrozen metal from the center.
SMELTING – The process of heating ores to a high temperature in the presence of a reducing agent such as carbon (coke) and of a fluxing agent to remove the gangue.
SOLDERING – Operation of joining two or more parts together by molten metal.
SPINNING – Cold drawing ductile sheet metal blanks into cylinders and other shapes having rotational symmetry in a spinning lathe.
SPOT WELDING – Method of uniting sheet material by a series of localized welds, produced by overlapping the edges of two sheets of metal and fusing them together between copper electrode tips at suitably spaced intervals, by means of a heavy electrical current. It is a form of resistance welding.
STAMPING – Process of shaping metal under a falling weight.
STUD WELDING – Method of attachment of studs, screws, pins and similar parts to plates and components by projection welding or arc welding.
SUNDERLAND PROCESS – Method of generating gears by the use of a rack shaped cutter.
SURFACE GRINDING – Method of grinding designed to carry out the removal of metal from the surface of a part or parts less expensively, and with greater precision than could be achieved by machining processes with cutting tools of steel or by hand or machine filing.
SURFACING – Movement of a lathe tool at right angles to the bed, to work on the face or end surface of the work.
SWAGING – Compacting or necking down metal bars or tubes by hammering or rotary forming.
SWEDGING – A cold die forging operation in which the metal is confined and made to flow plastically into the punch and/or die impressions.
SCALAR QUANTITIES – Those quantities which have magnitude only (and no direction) e.g., distance, area, volume and time.
SENSITIVITY OF GOVERNOR – Ratio of the mean speed to the speed range of the governor over its limits of operation.
SIMPLE AND COMPOUND MECHANISM – A simple mechanism consists of three or four links. All other mechanisms or those consisting of more than four links are compound mechanisms. Compound mechanisms are usually made up of combinations of simple mechanisms.
SIMPLE GEAR TRAIN – A gear train in which there is only one gear on each shaft.
SIMPLE HARMONIC MOTION – A particle having rectilinear motion has simple harmonic motion if its acceleration is proportional to the displacement of the particle from a fixed point and is of opposite sign.
SKEW GEARING – Gearing arrangement in which the axes of the shafts connected by gears are non parallel and non-intersecting.
SLIDING CONTACT – Sliding exists in a direct contact mechanism whenever the bodies have relative motion along the tangent through their point of contact.
SPEED – The rate of change of magnitude of displacement with respect to time.
SPHERICAL MOTION – A point has spherical motion if it moves in three dimensional space and remains at a fixed distance from some fixed point. A body has spherical motion if each point in the body has spherical motion.
SPIRAL GEARING – A type of skew gearing, but differs in one respect i.e., the contact between pitch surfaces is point contact instead of line contact.
SPRING LOADED GOVERNOR – The governor in which the control of the flyballs is by springs operated directly on the balls or on the sleeve.
SPUR GEARING – Gearing arrangement in which the axes of the shafts connected by gears are parallel and the teeth are cut parallel to the axes.
STABILITY OF GOVERNOR – The governor is said to be stable if there is one equilibrium speed for each radius of rotation of the flyballs and this speed increases with the radius.
STATICS – Study which deals with forces which act on the various parts, when these parts are assumed to be without mass.
STRAIGHT LINE MECHANISMS – Linkages having a point that moves along a straight line or nearly along a straight line, without being guided by a plane surface (e.g., Watts’s mechanism, Scott Russell mechanism).
SAFETY HEAD – Unit which is not fixed to the top of the cylinder but is held down by heavy springs and allows the passage of liquid refrigerant or oil, which it does by lifting bodily whenever the pressure in the cylinder becomes abnormally high.
SEALED UNIT – The compressor unit in which the compressor, usually rotary, and the driving motor are contained within a welded steel shell.
SECONDARY REFRIGERANT – Chilled liquid like water which is circulated to distant units where the air is to be cooled in individual rooms.
SEMI HERMETIC COMPRESSOR – The compressor unit in which the motor and compressor are a single unit, but the motor is detachable from the compressor and therefore capable of field repairs.
SHELL AND COIL CONDENSER – A cylindrical shell, usually vertical, containing a water coil, and within the shell the refrigerant is condensed.
SHELL AND TUBE EVAPORATOR – An evaporator having a cylindrical casing, containing a number of tubes through which the liquid to be cooled flows and the refrigerant is contained within the casing.
SHRADER VALVE – A spring loaded valve through which a connection can be made to a refrigeration system, also used in vehicle tyres.
SIGHT GLASS – In a car air conditioner, a viewing glass or window set in the refrigerant line, usually in the top of the receiver dehydrator, the sight glass allows a visual check of the refrigerant passing from the receiver to the evaporator.
SILICA GEL – Desiccant which operates by adsorption of water molecules.
SINGLE THICKNESS FLARE – The part of the tubing that forms the flare is the thickness of the tubing.
SPRAY HEADER – Perforated pipe mounted along the ceiling of the cargo compartment of a transport.
STEAM JET SYSTEM – Uses a device in which the extremely rapid flow of a vapour through a narrow tube reduces the pressure and permits evaporation of a liquid, produces a cooling effect.
STRONG AQUA – An ammonia and water solution with a concentration of almost 30 percent ammonia, used in ammonia absorption cooling system.
SUCTION LINE – Runs from evaporator to compressor, returns the heat laden gases from the evaporator.
SUCTION SERVICE VALVE – Manual shut off valve installed on the compressor. Also called suction valve.
SUCTION THROTTLE VALVE – The compressor is in continuous operation and the valve is opened and closed by sensing the actual evaporator operating pressure.
SULPHURDIOXIDE – An old refrigerant that was used to recharge units.
SUPERHEATING – The rise in temperature resulting from the addition of heat to the refrigerant vapour either in the evaporator or in the suction line.
SUPERHEAT SWITCH – Designed to protect the A/C system compressor against damage when the refrigerant charge is partially or totally lost.
SUPER INSULATION – Alternate layers of radiation shields and spacer material operating in a high vacuum.
SURGE CHAMBER – A drum or container into which liquid enters from the metering device in order to recirculate the refrigerant in a flooded evaporator.
SWAGING – A means of shaping copper tubing so that two pieces may be joined without the use of a fitting.
SECONDARY IGNITION CIRCUIT – Part of the ignition circuit consisting of secondary windings of ignition coil, spark plug wire, spark plug terminal and spark plug.
SECONDARY WINDING – Part of an ignition coil, a winding of fine wire wound many thousands of turns around a laminated steel core.
SIDE DRAUGHT CARBURETTOR – also called horizontal carburettor, consists of a horizontal mixing tube, with the float chamber on the side of it.
SINGLE POINT INJECTION – has one or two injectors mounted inside the throttle body assembly. Fuel is sprayed into one point or location at the centre of the engine intake manifold. Single point injection (SPI) is also called throttle body injection (TBI).
SPARK ADVANCE – The adjustment in ignition timing made by the timing device for changes in load, speed or other conditions.
SPARK DURATION – The length of time spark occurs at a spark plug.
SPARK PLUG – The assembly, which includes a pair of electrodes and an insulator, that has the purpose of providing a spark gap in the engine cylinder.
SPARK PLUG HEAT RANGE – The distance heat must travel from the centre electrode to reach the outer shell of the plug and enter the cylinder head.
SPARK PLUG REACH – is the length of the threaded portion of the spark plug. This is the distance between the end of the plug threads and the seat or sealing surface of the plug.
SQUISH – is the radial inward or transverse gas motion that occurs towards the end of the compression stroke, when a portion of the piston head approaches the cylinder head closely.
STATIC TIMING – The test of ignition timing made with a buzz box or a continuity light while the engine is at rest.
STRATIFIED CHARGE ENGINE – In a gasoline fuel, spark ignition engine, a type of combustion chamber in which the flame starts in a very rich pocket or layer of fuel air mixture and after ignition, spreads to the leaner mixture filling the rest of the combustion chamber. The diesel engine is a stratified charge engine.
SURFACE IGNITION – is the ignition of the air fuel mixture by any hot spot in the combustion chamber.
S/V RATIO – The ratio of surface area of the combustion chamber to its volume, with the piston at the top dead centre. Often used as a comparative indicator of hydrocarbon (HC) emission levels from an engine.
SAFETY VALVE – A circular valve connecting the steam space of a boiler and loaded to such an extent that when the pressure of steam exceeds a certain point, the valve is lifted from its seat and allows the steam to escape. The valve is loaded either by weight or by a spring. The release of steam saves the boiler from explosion.
SCALE – Incrustation within a vessel caused by the mineral substances from the water. Scale is a result of the chemical effect of the heat and concentration. A hard coating, chiefly calcium sulphate. If the scale is excessive, it leads to overheating of the metal and ultimate failure.
SCOTCH BOILER – A horizontal boiler in which the combustion chamber at the end of the boiler shell is entirely surrounded by water.
SCUM SCOOP – Apparatus for blowing out water from the surface to remove fine particles of scale forming foreign matter.
SEPARATOR – The device that removes as much moisture as possible from steam after it leaves the boiler.
SINGLE TUBE BOILER – Boiler made up of plain tubes, and the gases flow from one end to the other end of the tubes.
SOCKET STAY – Also called stay bolt consisting of a rod and socket.
STATIONARY BOILER – A boiler which is installed permanently on a land installation.
STAY BOLT – Short stay bars to support flat surfaces that are only a short distance apart, such as inner and outer sheets of water legs in a locomotive boiler. Generally have screw threads cut at one end, and sometimes at both ends, to receive a nut.
STAY ROD or THROUGH STAY – A plain rod 1 ¼" to 2½" in diameter having nuts and washers for fastening the ends to the plates.
STAY TUBE – A thick tube with threads on the ends, one end being larger than the other so that the tube may be slipped through the large hole.
STEEL ANGLE STAY – Two lengths of steel angle riveted together forming a T-shape piece and riveted to the plate.
STEAM – Water in a semi gaseous condition. It is a vapour than a gas, that is a substance between the purely liquid and gaseous states. Wet steam.
STEAM BOILER – A closed vessel in which steam or other vapour is generated continuously for use external to itself by the direct application of heat resulting from the combustion of fuel (solid, liquid, or gaseous) or by the use of electricity or nuclear energy.
STEAM GAUGE – A device for indicating gauge pressure as distinguished from absolute pressure.
STEAM LOOP – An ingeneous thermal pump consisting of an arrangement of piping wherein condensate is returned to the boiler.
STEAM SEPARATOR – An apparatus for separating out moisture that may be carried in suspension by steam flowing in pipelines, and for preventing this moisture from reaching and perhaps damaging engines, pumps, or other machinery that may be driven by the steam.
STEAM SPACE – The space above the water level in a boiler where steam gets collected until it is drawn off through the steam main.
STEAM TRAP – An automatic device which allows the passage of water but prevents the passage of steam. It is used to drain pipes of condensate.
STOP VALVE – A non-return valve having a hand wheel and screw stem which acts only to close the valve.
SUBMERGED TUBE BOILER – A vertical boiler having tubes extending from the lower tube sheet to an upper submerged tube sheet.
SUPER CRITICAL BOILER – A boiler that operates above the super critical pressure of 3206. 2 psi and 705.4°F saturation temperature.
SCOOP CONDENSER – A type of marine condenser with a flow of circulating water induced through an enclosed chamber by the movement of the vessel, rather than externally as with a keel condenser.
SIMPLE IMPULSE TURBINE – A steam turbine in which the expansion of the steam takes place in one set of nozzles only.
SIMPLE MULTISTAGE TURBINE – A steam turbine in which the pressure energy of the steam is progressively transformed into kinetic energy in two or more pressure stages, there being one wheel to each stage.
SINGLE WHEEL IMPULSE TURBINE – A steam turbine having a set of nozzles and one row of moving blades fixed to the rotor. The moving blades deflect the steam and therefore cause a change in momentum and consequently produce force i.e., motive force.
SPRAY POND – A pond which is provided with spray apparatus so that the hot cooling water from the condenser is sprayed over the surface of the pond and cooled.
STAGE EFFICIENCY – Ratio of the rate of doing work per kg of steam (diagram work) to the energy supplied to the stage per kg of steam, in a steam turbine. Also called GROSS STAGE EFFICIENCY. This is product of nozzle efficiency and blade efficiency.
STEAM CONDENSER – Device in which the exhaust steam from an engine or a turbine is condensed and air and other non condensable gases are removed in a continuous process.
STEAM JET VACUUM PUMP – Pump system in which one or more steam jets moving at a high velocity (1000 m/s) entrain the saturated non condensable gases, and the mixture passes through an expanding tube in which the velocity is reduced with a resulting increase in pressure and finally the mixture is let out into the atmosphere. Also called STEAM JET AIR EJECTOR.
STEAM LAP – The distance by which the admission edge of the D slide valve overlaps the edge of the steam port when the valve is in the mid position, which is the middle of its travel.
STEAM RATE OF AN ENGINE – The weight of steam supplied to a steam engine per horse power hour.
STEAM TURBINE – A prime mover in which gradual changes in the momentum of a fluid are utilized to produce rotation of the movable member.
STEAM TURBINE EXTERNAL LOSSES – Losses which do not affect the steam conditions while it flows through the turbine, includes mechanical losses and losses due to the end leakages.
STEAM TURBINE INTERNAL LOSSES – Losses connected with the steam conditions while it flows through the turbine. These include losses in regulating valve, nozzles, moving blades, carry-over losses from one stage to another, rotor and guide blade clearance losses, loss due to steam wetness and exhaust losses.
SURFACE CONDENSER – A device for condensing steam, in which the steam and the cooling water do not come into contact with each other, but are separated by metal surfaces.
SURFACE CONDENSER SINGLE PASS TYPE – Type of surface condenser in which the cooling water flows in one direction only through all the tubes.
SURFACE CONDENSER TWO PASS TYPE – Type of surface condenser in which the cooling water flows in one direction through part of the tubes and returns through the remainder.
SATURATION TEMPERATURE – Temperature of the liquid surface corresponding to the pressure of the vapour in contact with it.
SATURATED PHASE – is any phase of a substance existing under saturated conditions, wherein two or more phases of a pure substance can exist together in equilibrium.
SATURATED STEAM – Steam, as it is generated from water, just barely on the steam side of the fence.
SATURATED VAPOUR – Vapour whose temperature and pressure are in accordance with the temperature vapour pressure relationship for the particular substance. Vapour in contact with its liquid is saturated.
SECONDARY DIMENSIONS – are those quantities which are described using primary dimensions.
SEMI-PERFECT GAS – is one which follows the ideal gas relations with specific heats being functions of temperature.
SENSIBLE HEAT – Heat energy that causes a change of temperature of a solid, liquid or gas, changes the speed with which molecules move. When unit weight of a substance is heated by one degree to gain, the sensible heat is equal to the specific heat.
SENSIBLE HEAT OF WATER – Heat added to one kg of water from 0°C to the boiling point at the given pressure. Also called ENTHALPY OF WATER.
SOLIDS – are substances in which the molecules are closely packed and may not move freely. Molecules can only vibrate about a mean position. Very large force is required to change the shape of a solid substance.
SPECIFIC HEAT – The ratio of the amount of heat which will raise the temperature of a given weight of a substance by one degree to the amount of heat which will produce the same raise in temperature in the same weight of water.
SPECIFIC HEAT OF SUPERHEATED STEAM – Amount of heat required to raise the temperature of superheated steam, at constant pressure by 1°C.
SPECIFIC PROPERTY – is the value of any extensive property divided by the mass of the system. This is an intensive property, e.g., specific volume, specific weight.
SPHEROIDAL STATE – The condition of a liquid, as water, when being thrown on a highly heated metal surface, it rolls about in spheroidal drops or masses, at a temperature several degrees below ebullition and without actual contact with the heated surface. This phenomenon is due to the repulsive force of heat and the intervention of a cushion of vapour.
STATE OF A SYSTEM – refers to the unique condition of the system at any particular moment. The state is indicated by the properties such as temperature, volume, pressure, internal energy, enthalpy and entropy. These are point functions.
STEADY FLOW SYSTEM – is an open system in which the rate of mass transfer and energy transfer remain constant with respect to time.
STEAM – The vapour of water. It is a colourless expansive invisible gas.
STEAM TABLES – Tables containing values of various properties of saturated steam such as boiling point, specific volume, sensible heat, latent heat and total heat calculated for a wide range of pressures.
STEADY FLOW PROCESS – is a flow process wherein the conditions within the control volume do not vary with time.
STORED ENERGY – is the energy which is contained by the medium within the system boundaries. Examples are potential energy and internal energy.
STP – The standard temperature and pressure refer to the conditions of temperature 15°C (288 K) and pressure 760 mm of mercury.
SUBCOOLED LIQUID – is a liquid existing at a temperature lower than its saturation temperature (or, in other words, at a pressure higher than its saturation pressure).
SUPERHEAT – Addition of heat to a fluid after it has completely vaporized. In this situation, temperature increases but pressure does not.
SUPERHEATED VAPOUR – Vapour removed from contact with its liquid and at a temperature higher than that which corresponds to its pressure as indicated by the temperature – pressure vapour relationship for that particular substance.
SUPERHEATED STEAM – Steam at a temperature higher than the saturation temperature for the given pressure.
SURROUNDING – is everything outside the boundary which may influence the behaviour of the system. Transfer of mass and energy may take place between the system and boundary.
SYSTEM IN EQUILIBRIUM – means it does not undergo any change on its own accord.
SYSTEM IN CHEMICAL EQUILIBRIUM – is an isolated system which may contain substances that can react with one another chemically, but all these chemical reactions cease after a certain time.
SYSTEM IN MECHANICAL EQUILIBRIUM – is an isolated system, when left to itself, may change with time all its properties such as pressure, elastic stress etc., but these changes may cease after a certain time.
SYSTEM IN THERMAL EQUILIBRIUM – is an isolated system, wherein there may be variations of temperature from point to point, but these variations vanish after a certain time.
SYSTEM IN THERMODYNAMIC EQUILIBRIUM – is one which is in mechanical equilibrium, thermal equilibrium and chemical equilibrium.
SCAVENGING – Inertia caused movement of gases through cylinder and exhaust system of a two stroke cycle or four stroke cycle engine by the incoming fresh charge.
SEALED BEAM – A modern automotive headlight. The lens, reflector and filament form a single unit.
SEDIMENT BOWL – A cup located at the bottom of the fuel petcock, designed to prevent flow of dirt and water into the fuel line.
SHAFT DRIVE – Use of a drive shaft, universal joints, and gears to connect gearbox output shaft to rear wheel.
SHOCK ABSORBER – Rear suspension unit made up of a coil spring and a hydraulic damper. It prevents spring oscillations.
SINGLE ROW CHAIN – A conventional roller chain with one row of rollers.
SOLID ROLLER CHAIN – Roller chain using a one piece roller and bushing assembly.
SPINDLE (steering fork) – A shaft which is secured to upper and lower triple clamps. It pivots on bearings mounted in the steering head.
SPOKE – A metal part, often a wire, that runs between the rim and hub of a spoked wheel to transfer force to the hub.
SPOKE CROSSING PATTERN – Number of spokes crossed on the same side of the hub by anyone spoke.
SPOKED WHEEL – A wheel consisting of a rim, spokes, nipples and hub. Spokes are laced between hub and rim and are attached to the rim by nipples.
SPOKE TORQUE WRENCH – A small torque wrench used to adjust accurately the spoke tension.
SPONGY LEVER or PEDAL – A soft or spongy feeling when the brake lever or pedal is depressed. It is usually due to air in the brake lines.
SPROCKET – A circular plate with teeth machined around outside to engage links of a chain.
SPRUNG WEIGHT – The weight of the two wheeler components that are supported on springs, includes the fork tube, engine, triple clamp and frame.
STAMPED FRAME – A frame stamped from pieces of sheet metal which are welded together to provide support for engine and suspension.
STAMPED WHEEL – A wheel assembly using stamped sheet metal spokes in place of small wire type spokes. A stamped wheel resembles a cast alloy wheel in appearance.
STEERING DAMPER – A device which uses friction or a hydraulic damper to reduce steering oscillation.
STEERING HEAD – The tube at the top and front of the frame that supports the steering stem and is welded at a specific angle to provide the proper fork angle.
STEERING OFFSET – Distance between steering axis and axis on which the axle pivots. Steering offset is accomplished by offsetting axle or triple clamps.
STEERING RAKE – Angle of steering axis from vertical, given in degrees.
STEERING STEM – A shaft positioned through the steering head that enables the front end to turn.
SUSPENSION SYSTEM – A system that consists of front forks, shock absorbers, springs and the swing arm, used to support the two wheeler on its axles and wheels.
SWING ARM – The assembly that links the rear wheel to the frame and allows the rear wheel to move up and down, and prevents the wheel from moving laterally and flexing at the pivot point.
SWING ARM PIVOT – Forward part of swing arm, where it is attached to the frame and pivots on bushings or bearings.
SYMMETRICAL HUB – A wheel hub (wire wheel) which has spoke holes on each side of the hub at the same distance from hub center.
SEAL WELD – Any weld designed primarily to provide a specific degree of tightness against leakage.
SEAM WELD – A continuous weld between or upon overlapping members, in which coalescence may start and occur on the faying surfaces, or may have proceeded from the outer surface of one member.
SEMI AUTOMATIC ARC WELDING – Arc welding with equipment that controls only the filler metal feed. The advance of the welding is manually controlled.
SEMI BLIND JOINT – A joint in which one extremity of the joint is not visible.
SERIES SUBMERGED ARC WELDING – A submerged arc welding process variation in which electric current is established between two consumable electrodes which meet just above the surface of the work-pieces which are not part of the electric circuit.
SHIELDED CARBON ARC WELDING – A carbon arc welding process in which shielding is effected by the combustion of a solid material fed into the arc or from a blanket of flux on the work-pieces or both.
SHIELDED METAL ARC CUTTING/WELDING – Cutting or welding effected by heating the work-pieces with an arc between a covered metal electrode and the workpiece. Shielding is obtained from decomposition of the electrode covering,
SHIELDING GAS – Protective gas used to prevent atmospheric contamination.
SHORT CIRCUITING TRANSFER ARC WELDING – Metal transfer in which molten metal from a consumable electrode is deposited during repeated short circuits.
SHRINKAGE VOID – A cavity type discontinuity normally formed by shrinkage during solidification.
SILVER BRAZING – Brazing process that employs silver alloys. Also called hard soldering or silver soldering.
SLAG INCLUSION – Non-metallic material entrapped in weld metal or between weld metal and base metal.
SLOT WELD – A weld made in an elongated hole in one member of a joint fusing that member to another member. The hole may be open at one end.
SOLDER – A filler metal used in soldering which has a liquidus not exceeding 450°C.
SOLDERING – A group of welding processes that produces coalescence of materials by heating them to a suitable temperature and by using a filler metal having a liquidus not exceeding 450°C and below the solidus of the base metals.
SOLID STATE WELDING – A group of welding processes that produces coalescence at temperatures essentially below the melting point of the base metal being joined, without the addition of a brazing filler metal. Pressure may or may not be used.
SPATTER – The metal particles expelled during fusion welding, that do not form a part of the weld.
SPELTER – is common brass, the first material used to make a brazed joint in ferrous material.
SPOT WELD – Weld made between or upon overlapping members in which coalescence may start and occur on the faying surfaces or may proceed from the surface of one member. The weld cross section (plan) is approximately circular.
SPRAY TRANSFER ARC WELDING – Metal transfer in which molten metal from a consumable electrode is propelled axially across the arc in small droplets.
STACK CUTTING – Thermal cutting of stacked metal plates arranged so that all the plates are severed by a single cut.
STAGGERED INTERMITTENT WELD – An intermittent weld on both sides of a joint in which the weld increments on one side are alternated with respect to those on the other side.
STRINGER BEAD – A type of weld bead made without appreciable weaving motion.
STUD WELDING – A general form for the joining of a metal stud or similar part to a workpiece. Welding may be effected by arc, resistance, friction or other suitable process, with or without external gas shielding.
SUBMERGED ARC WELDING – An arc welding process in which the arc and molten metal are shielded by a blanket of granular, fusible material on the work-pieces.
SURFACING – Application by welding, brazing or thermal spraying of a layer(s) of material to a surface to obtain desired properties or dimensions as opposed to making a joint.