VALVE GEAR – The mechanism or combination of parts by which a reciprocating or to and fro motion is imparted to the valve from the rotary motion of the shaft.

VOLUMETRIC EFFICIENCY – The ratio of the actual number of cubic meter of free air (at 1.03 ks.cm abs and 15° C) compressed per unit of time to the number of cubic meter of piston displacement during that time.

VACUUM BRAKE – is the device in which the braking effect is due to the difference of pressures that acts on the opposite sides of a diaphragm. In this unit, one side of the piston or diaphragm is exposed to atmospheric pressure while the other side to a pressure which is below the atmospheric pressure.

VARIABLE RATE SPRINGS – provide a low rate for ordinary service and higher rate for heavy obstruction or loads. These consist of a conventional spring and below which is placed a small auxiliary spring with several leaves. Under heavy loads, the auxiliary or helper spring strengthens the main spring more and more as the main spring is compressed.

VARIABLE RATIO STEERING – A steering gear that provides a different ratio during parts of a turn.

VALVE CLOSING PRESSURE – is the fuel pressure at which the fuel injector needle valve snaps back on its seat. For the differential valve stem, this is less than the nozzle opening pressure.

VALVE CLOSING ORIFICE NOZZLE – In this nozzle, the needle valve sits directly on the top of the orifice. This prevents any fuel in the sac volume escaping into the cylinder after the valve is closed.

VALVE OPENING PRESSURE – is the fuel pressure at which the needle valve of the injector lifts off its seat.

VARIABLE INJECTION TIMING – Altering the injection timing as the engine speed changes (advancing timing as speed increases), by a set of flywheel weights mounted on the injector pump camshaft, to obtain better performance.

VARIABLE SPEED GOVERNOR – Governs both the idle and maximum speeds as well as the range in between.

VENT – Channel made in the sand in the vicinity of a mould to allow steam, gases etc., generated when sand and molten metal come into contact with one another, to escape.

VENT ROD – A piece of wire or rod to form the vents i.e., holes in the sand, for the escape of gases.

VENT WAX – Wax in rod shape placed in the core during manufacture. In the oven the wax is melted out leaving a vent or passage.

VANADIUM – A rare metal used as an alloying element in steel to improve shock resistance and forgeability.

VULCANATES – Vulcanates are materials which reduce plasticity of the rubber compound, while maintaining its elasticity.

VALVE STEM SEAL or SHIELD – A device placed on or surrounding the valve stem to reduce the amount of oil which can get on the stem and thereby work its way down into the combustion chamber.

VARNISH – A build up of oxidized oil or fuel.

VISCOSITY – Resistance of oil to flow. The thickness of oil is determined by its rate of flow, a thick oil has a greater viscosity than a thin oil. Unit of viscosity is centipoise.

VISCOSITY INDEX – A measure of the change of viscosity with temperature of an oil compared with two reference oils having the same viscosity at 210°F one of naphthenic base and the other of paraffinic base.

VISCOSITY INDEX IMPROVERS – Additives added to an oil, to reduce the change of viscosity with increase in temperature.

VISCOSITY RATING – An oil classification based on the time it takes for an amount of oil to flow through a capillary tube, under specified conditions, the higher the rating, the thicker the oil.

VAPOURIZATION – To change a liquid into a vapour, often by the addition of heat.

VAPOURIZING BURNER – A burner in which the fuel oil is vaporized by heating in a retort. It may be a mixing or non mixing type.

VAPOUR LOCK – A condition in the fuel system in which gasoline has vaporized and turned to bubbles in the fuel line or fuel pump, so that the fuel delivery to the carburettor of a SI engine is prevented or retarded.

VOLATILITY – refers to the ease with which a liquid vaporizes. A liquid which vaporizes at a relatively low temperature has a high volatility. This liquid is said to be highly volatile.

VELOCITY COMPOUNDED IMPULSE TURBINE – The turbine in which the kinetic energy created by the expansion of gas in nozzles is absorbed in two or more rows of moving blades so as to reduce the speed of the turbine rotor.

VOLUMETRIC EFFICIENCY – Ratio of the equivalent volume of free atmospheric air finally delivered by a compressor to the volume of free atmospheric air entering the suction pipe of the compressor.

V ENGINE – An engine with two banks of cylinders set at an angle to each other to form a V.

VALVE – A device that can be opened or closed to allow or stop the flow of a fluid (liquid or gas or vapour) from one to another place.

VALVE CLEARANCE – The clearance between the rocker arm and the valve stem tip in an overhead valve engine: The clearance in the valve train when the valve, is in the closed position. Also called VALVE LASH.

VALVE FLOAT – The condition that exists when an engine valve does not follow the cam profile, failure of the valve to close at the proper time.

VALVE GRINDING – Refacing a valve in a valve facing machine.

VALVE GUIDE – The cylindrical part in the cylinder block or head in which the valve is assembled and in which valve stem moves up and down.

VALVE LIFTER – Also called lifter, tappet, valve tappet and cam follower. A cylindrical part of the engine, which rests on a cam of the camshaft and is lifted, by cam action, so that the valve is opened.

VALVE LIFTER FOOT – The bottom end of the valve lifter, the part that rides on the cam lobe.

VALVE OVERLAP – Number of degrees of crankshaft rotation through which both the intake and exhaust valves are open together.

VALVE ROTATOR – Device used in place of the valve spring retainer, it has a built in mechanism to rotate the valve slightly each time it opens.

VALVE SEAT – The surface in the cylinder head or cylinder block against which the valves face comes to rest.

VALVE SEAT INSERT – Metal rings inserted in the valve seats, usually exhaust, they are of special metal which can withstand high temperature and exhibit minimum wear at these temperatures.

VALVE SEAT RECESSION – Also known as lash loss, the tendency for the valves, in some engines run on unleaded gasoline, to contact the seat in such a way that the seat wears away, or recesses into the cylinder head.

VALVE STEM – The long, thin cylindrical section of the valve that fits and moves in the valve guide.

VALVE TIMING – The timing of valve opening and closing in relation to piston position in the cylinder.

VALVE TRAIN – The valve operating mechanism of an engine, from the camshaft of the valve.

VEE CYLINDERS – Cylinders positioned at angles to each other forming the shape of the letter V.

VIBRATION DAMPER – is attached to the crankshaft in order to control the torsional vibration caused by the power impulses.

VOLUMETRIC EFFICIENCY – Ratio between the amount of fresh charge that actually enters an engine cylinder and the theoretical amount that could enter under ideal conditions.

VACUUM GAUGE – Gauge used to measure the amount of vacuum in any vessel in which a pressure lower than atmospheric pressure is produced by evacuation of air, vapour and gas.

VERNIER – Small-scale, for making accurate measurement, carrying a certain number of graduations equalling in their combined length a different number of graduations, usually one more or one less, on the main scale of the instrument to which the Vernier is attached.

VERNIER CALIPER – Precision measuring instrument consisting of a beam or rule having a fixed jaw at one end, and a straight jaw to which is attached a Vernier scale.

V-BLOCK – Block of metal having a V-shaped groove cut in its top surface in which can rest a circular shaft.

V-SUPPORT – Steady in the form of a V, to support the work near the cutting tool.

VICE – A mechanical device of many designs and sizes in which work-pieces are clamped for hand and machine operations.

VICE CLAMP – Piece of soft material so shaped as to enable it to fit over each of the hardened jaws of a vice in order that work-pieces may be gripped without damage.

V-WAYS – The top part of the bed of a lathe, planer or other machine bed which acts as a bearing surface for aligning and guiding the moving parts, such as the carriage of a lathe.

VALVE – Any device or arrangement used to open or close an opening to permit or restrict the flow of a liquid, gas or vapour.

V-BLOCKS – Square or rectangular shaped blocks of steel that are usually hardened and accurately ground. These have 90° V groove through the center and are provided with clamps for holding round workpiece for laying out, drilling, milling etc.

VISE – A mechanical device of many designs and sizes in which work pieces are clamped for hand or machine operations.

V-WAYS – The top of the bed of a lathe, planer or other machine tool which acts as bearing surface for aligning and guiding the moving parts such as the carriage of a lathe.

VERTICAL MILLING MACHINE – Milling machine in which the cutter spindle rotates about a vertical axis (as on most drilling machines), but which in certain other respects has much in common with a plain miller.

VERTICAL TURRET LATHE – A lathe with a vertical spindle and ways that carries the work in a chuck and has cutting tools mounted in a five position turret and side heads.

VIBRATION DAMPER – A specially designed device mounted to the front of an engine crank-shaft to reduce torsional vibration.

VACUUM LIFTER – End of line attachment, a convenient means of handling sheet stock of various kind (steel, non-ferrous metals, glass etc.) along with cartons, boxes etc. To lift a load, the vacuum cup is applied to its surface, and the vacuum generator is set into operation, creating a vacuum in the cup.

VERTICAL LIFT – A ferries’-wheel type conveyor that moves goods from the receiving area to the checking area.

VALENCY – The capacity of an atom to combine with other atoms to form a molecule. The inert gases have zero valence, valence is determined by considering the positive and negative atoms as determined by the atoms gaining or losing of valence electrons.

VISCOSITY – The property of the fluids, either liquid or gaseous, which causes them to resist instantaneous change of shape or instantaneous rearrangement of their parts, due to internal friction.

VOID – A cavity or hole in a substance.

VULCANIZATION – The process of treating crude or synthetic rubber or similar plastic material chemically to give it useful properties, such as elasticity, strength and stability.

VECTOR QUANTITIES – Those entities which have magnitude and direction. (e.g., displacement, velocity, acceleration and force). Vector quantities are represented by a straight line with an arrow head (magnitude is represented by its length and direction by the arrow head).

VELOCITY – When a particle is in motion, the rate of change of its displacement with respect to time. It is a vector quantity.

VELOCITY RATIO OF GEAR TRAIN – Ratio of the angular velocity of the first gear in the train to the angular velocity of the last gear.

VACUUM PUMP – A device used to evacuate systems in preparation for charging them with a refrigerant.

VALVE RETAINER – A device which limits the lift of the valve.

VACUUM ADVANCE – A method of advancing the ignition timing by applying engine vacuum to a diaphragm mounted on the distributor.

VACUUM GAUGE – In automotive engine service, a device that measures intake manifold vacuum and thereby indicates action of engine components.

VAPOUR LOCK – A condition in the fuel system in which gasoline has vaporized and turned to bubbles in the fuel line, or fuel pump so that fuel delivery to the carburettor is prevented or retarded.

VAPOURIZATION – is the process of changing the liquid or atomized fuel into a vapour.

VENTURI – In the carburettor, the restriction in the air horn that produces the vacuum responsible for the movement of gasoline into the passing air.

VENTURI PRINCIPLE – The physical law which states that air moved through a constriction increases in speed and decreases in pressure at the point of constriction.

VACUUM BREAKER – An automatic device used to protect the main engine or turbine from flooding when a jet condenser is used.

VACUUM KEEL CONDENSER – A type of keel condenser having tubular condensing surface, a return pipe for the condensate, the end of which connects with a wet air pump.

VELOCITY COMPOUNDED IMPULSE TURBINE – Steam turbine in which the total heat drop takes place in the nozzles, but the velocity (energy) generated is utilized in two or more rings of blades attached to the rotor.

VACUUM – A space devoid of matter, that is, a space in which the pressure is zero absolute.

VAPOUR – A gaseous condition of a substance near its point of liquefaction.

VAPOURIZATION – Change of state from liquid to vapour or gas.

VAPOUR PRESSURE – Pressure exerted by the vapour of any particular liquid on the containing vessel, as a result of the molecules near its surface freeing themselves from the attraction of their neighbours and flying off into space. Its magnitude depends solely on the temperature of the liquid surface.

VOLUMETRIC EFFICIENCY – The ratio of the volume of gas actually pumped by a compressor or pump to the theoretical displacement of the piston of the compressor or pump or reciprocating IC engine.