Friday, 23 April 2021, 12:00 PM
Site: IMI eLearning
Course: IMI eLearning (IMI eLearning)
Glossary: Automotive Glossary




Battery voltage.

V Belt

A continuous loop drive belt with a 'vee' section. The sides of the belt grip the side faces of 'vee' pulleys to provide a friction drive method.


Power voltage.


A continuous loop drive belt with a 'vee' section. The sides of the belt grip the side faces of 'vee' pulleys to provide a friction drive method.


Vehicle Identification Number."


Reference voltage.


Vehicle log book/registration certificate. Issued by the Driver and Vehicle Licensing Agency.




In everyday usage, vacuum is a volume of space that is essentially empty of matter, such that its pressure is much less than atmospheric air pressure. The word comes from the Latin term for empty.

Vacuum Advance

Automatic engine ignition timing adjustment using the inlet manifold pressure to sense engine load. The pressure, as a vacuum, is applied to a diaphragm assembly to move the base plate in the ignition distributor.

Vacuum Assisted Brakes

A brake booster system that uses inlet manifold vacuum in a brake servo unit to increase the driver's braking effort. The vacuum can also be provided from a vacuum pump on diesel engines.

Vacuum Gauge

An instrument for measuring pressure (below atmospheric pressure) of a fluid or a gas.

Vacuum Motor

A motor that is operated by a vacuum such as to move or drive something.

Vacuum Pipes

See Vacuum Hoses

Vacuum Pump

Test equipment that can be used to apply a vacuum.

Vacuum Regulator

A device that either controls vacuum so a set level or one that uses vacuum to regulate another operation.


Vane Air Flow Sensor.


Term describes a material that has a free electron.


This is the performance of an extremely thorough cleaning, polishing and waxing of an automobile, both inside and out, to produce a showroom-quality result.


The degree of darkness or lightness of a colour.


A control device that restricts or cuts off the flow of a liquid or gas.

Valve Ball

A ball used to create a seal inside a valve.

Valve Block

Collection of valves in one unit that operate a common system (automatic transmission for example).

Valve Bounce

Bounce of a valve in its seat when closing. Usually occurs as a result of the engine speed being too high or the valve spring losing tension through age or deterioration.

Valve Gear (Train)

The mechanism from a cam to a valve in an engine that transmits the movement of the cam to open the valve.

Valve Guide

The tube or sleeve in the cylinder head that locates a valve centrally in its seat. The valve slides in the guide during opening and closing.

Valve Head

The top or disc end of a valve that seals the gases in the cylinder head.

Valve Lag

The term applied to valves which remain open after the piston has passed tdc or bdc at the end of a stroke in the four stroke cycle.

Valve Lead

The term applied to valves which open before the piston has passed tdc or bdc at the beginning of a stroke in the four stroke cycle.

Valve Lifter

Cam follower or tappet.

Valve Margin

The thickness of the valve head between the valve face and the head surface.

Valve Needle

The control pin in, for example, a fuel injector. The needle works against an accurately shaped component to control flow.

Valve Overlap

The term used to describe the angle of crankshaft rotation when the inlet and exhaust valves are both open.

Valve Seat

The bevelled surface annular face in the cylinder head that closes each port and into which a valve seats and seals the port.

Valve Seat Insert

A steel insert fitted in aluminium and some iron cylinder heads to form a durable seating for the inlet and exhaust valves.

Valve Spring

The spring that closes and holds closed the valve. It fits around the valve stem above the guide and between the cylinder head and valve spring retainer.

Valve Stem

The shaft of a valve.


A flat component used as part of a pump that moves a liquid or fluid.

Vane Pump

A type of positive displacement pump formed by an eccentric rotor driving two or more vanes fitted inside a housing. The eccentricity of the rotor and vanes forms the pumping chambers of the vane pump.


See Vapour.


Fuel that is broken down to very fine particles and distributed into the intake air stream of an engine.


Fuel that is broken down to very fine particles and distributed into the intake air stream of an engine.


Minute airborne droplets of a liquid or liquid that has been heated to a gas state.

Vapour Lock

Vapour formation in a fuel line caused by heat. The effect is similar to an air lock and acts to prevent fuel delivery. To clear the vapour lock the fuel line must be bled or allowed to cool.


Variable assist power steering

Variable Choke Carburettor

A carburettor with a variable diameter venturi (choke tube). The variable diameter is obtained by inlet manifold vacuum being applied to one side of a diaphragm or piston and atmospheric pressure to the other side. This arrangement produces a constant depression and relatively accurate fuel metering.

Variable Resistor

A resistor that can have its value changed manually.

Variable Venturi

A venturi (narrowing of a tube) that can be changed. Usually refers to a carburettor. See also Variable Venturi Carburettor.

Variable Venturi Carburettor

See Variable Choke Carburettor.


A burnt gum deposit from petrol that forms in the inlet tract of carburettors and on piston skirts.


Vane Air Temperature Sensor.


Viscous Converter Clutch


Vehicle control module. An electronic control unit that controls a wide range (or all) of the vehicle functions.


Volts Direct Current

Vee Belt

Drive belt made with a V section.


Another name for the binder, into which all of the other ingredients of a paint mixture are added. This includes pigment solvents, diluents, resins, driers, etc.

Veiling (cobwebbing)

The formation of a web or strings in a paint as it emerges from a spray gun, usually caused by too high viscosity, low atomising air pressure or a combination of both.


Speed in a designated direction.

Vent Pipes

Pipes used to ventilate something such as a fuel tank or crankcase.


Air circulating freely in room, disc, etc.


Convergent-divergent nozzle which accelerates air flow and lowers static pressure in gases or vapours flowing through it. In a carburettor the venturi provides the depression in the air flow pressure causing the fuel to be drawn from its float chamber into the air stream.


Any form of communication that uses words, i.e. speaking and writing in the form of letters, newspapers, emails etc.


High frequency oscillating wave producing sound or pulsating feeling.

Vibration Damper

A device, usually fitted to a rotating shaft (crankshaft) that dampens the vibrations produced in the shaft by rotary imbalance or a pulsed drive.


Vehicle Identification Number

VIN (Vehicle Identification Number)

Unique code assigned to each vehicle by its manufacturer to identify the model, year, production sequence and other vehicle specific information.


A class of monomers which can be combined to form vinyl polymers. Widely used to make chemically resistant finishes, tough plastic trim and other vehicle components.

Viscomatic Lock

A drive mechanism that uses fluid to create a lock at a certain speed.


A viscometer (also called viscosimeter) is an instrument used to measure the viscosity of a fluid.


The flow rate of a liquid. The addition of solvents and/or diluents will reduce the viscosity or fluidity of the paint. Paint viscosity must be carefully adjusted and controlled to allow proper atomisation and flow-out.

Viscosity cup

A precision device used to measure the viscosity of a liquid by timing how long it takes the liquid to drain out of the cup in a continuous stream. The standard Viscosity cup in use in the UK paint industry is known as a BS B4 or DIN 4 cup, which has a 4mm orifice for the paint to flow through.

Viscosity Index

A measure of the change in the flow rate (viscosity) of a liquid with temperature rise. The higher the viscosity index the smaller is the change in viscosity.

Viscous Coupling

A drive coupling that uses a fluid to transmit drive. Also sometimes a fluid coupling.

VOC Content

The measure of volatile organic compounds (VOC's) in solvent-borne paints. Usually measured as the weight in kilos of non-exempt solvent per tonne of paint.


Readily changes to vapour or gas at ambient temperatures.


The tendency of a liquid to evaporate. Liquids with high boiling points have low volatility and vice-versa. Volatility affects flash-off time and fire hazard consideration.


Electromotive force expressed in volts. Potential difference.

Voltage Drop

The voltage that is lost when an electrical current passes through a resistance.

Voltage Regulator

An electrical or electronic device to maintain a generator output within a narrow voltage range.

Voltage Stabiliser

A mechanical (bimetal) or electronic device used to maintain voltage at a set level. In instrument systems this prevents readings changing as system voltage changes.

Voltage Stabilizer

A mechanical (bimetal) or electronic device used to maintain voltage at a set level. In instrument systems this prevents readings changing as system voltage changes.


Instrument for measuring electric potential. Can usually be set to read AC or DC on different ranges.


Unit of electromotive force. Potential difference.


The capacity of a space as a numerical calculation.

Volume Solids

The percentage, on a volume basis, of the non-volatile material in a paint.

Volumetric Efficiency

The ratio of the actual amount (mass) of air entering an engine cylinder against the actual swept volume of the cylinder.

Volumetric Sensing

A system used by alarms to sense movement inside the vehicle.


The Vehicle and Operator Service Agency


Voltage Regulator


Vehicle Sensor


Vehicle Specific Information, provided to NTs to aid the correct assessment of a vehicle under test.


Vehicle Speed Sensor.


An MOT Test Certificate which includes the English/Welsh dual language version (VT20W).


An MOT Test Certificate for issue during a period of Emergency Testing.


A notice of refusal of a MOT Test Certificate including the Welsh counterpart (VT30W).


An Advisory Notice – issued to advise of items of concern identified during the test that do not justify the refusal of a test certificate.


MOT Inspection Check List used by a NT during a test for vehicles other than motor bicycles (see VT40M).


Motor bicycle MOT Inspection Check List used by a NT during a test.


Vehicle Test Station

VTS Device

The Computer device installed at each VTS on which each test must be registered, from which MOT documentation is produced and to perform certain administrative functions.


The treatment of rubber and rubber compounds to make them capable of being moulded. Also used to refer to the sealing of a tyre or tube repair with an adhesive and heat process.


Variable Valve Control


Variable Valve Timing