| Vacuum annealing |
Annealing carried out at subatmospheric pressure. |
| Vacuum carburizing |
A high-temperature gas carburizing process using furnace pressures between 7 and 55 kPa during the carburizing portion of the cycle. |
| Vacuum pump |
A pump for exhausting air and non-condensable gases from a vessel to be maintained at sub-atmospheric pressure. The pirani and thermal-conductivity gauges are vacuum gauges used to measure the absolute pressure within a vacuum system (vacuum level), usually expressed in torr or Pa. |
| Vacuum relief valve |
A valve that admits gas to a system under vacuum, should the degree of vacuum become excessive. |
| Vacuum servo |
A vacuum-operated servomotor which is used in a motor vehicle to provide a brake effort greater than the capability of the driver. |
| Valve |
Any of various manual or automatic devices that are able to initiate, regulate, or stop the flow of a fluid through a conduit or from a closed container. |
| Valve plug |
A conical or cylindrical plug, in which there are transverse holes, in a valve, such as a plug valve. Flow through the holes occurs when the plug is rotated. |
| Valve spring |
The spring that restores a valve to its closed position after having been opened, and is also intended to prevent valve bounce. |
| Vane engine (vane motor) |
A rotary engine in which high-pressure hydraulic fluid in the spaces between spring-loaded sliding vanes held in an offset rotor acts on the vanes, causing the rotor to revolve within a cylinder. The design is much like a sliding-vane compressor, as is that of a vane pump, used to pump liquids. |
| Vapour |
The gas-like phase of a substance at a temperature below its critical point. A vapour can be condensed to a liquid or a solid by increasing its pressure or reducing its temperature. |
| Vapour static pressure |
(Unit Pa or bar) A pressure analogous to hydrostatic pressure, where the fluid is a vapour such as steam. A term used in geothermal applications. |
| Vapour static pressure |
(Unit Pa or bar) A pressure analogous to hydrostatic pressure, where the fluid is a vapour such as steam. A term used in geothermal applications. |
| Vapour–pressure curve |
For a pure substance, the curve of saturation pressure plotted vs saturation temperature. |
| Vapour-pressure thermometer |
(vapour-filled thermometer) A type of fluidexpansion thermometer in which the working fluid is a volatile liquid. |
| Variance |
A measure of the squared dispersion of observed values or measurements expressed as a function of the sum of the squared deviations from the population mean or sample average. |
| V-belt |
A drive belt having a trapezoidal cross section which runs in pulleys with V-shaped grooves. Higher torques can be transmitted than with a flat belt. |
| V-block |
A block having a 90° V-shaped recess; used in a workshop to hold round workpieces. |
| Vector |
Any physical quantity, such as velocity, acceleration, force, or momentum, that is specified in terms of both its magnitude and its direction. The convention of printing vector quantities in boldface was introduced by the physicist Josiah Willard Gibbs. |
| Vehicle |
A means of conveyance for transporting goods and people, generally with wheels powered by a petrol, diesel, or steam engine, or by an electric motor, or by a hybrid combination of an electric motor and a diesel or petrol engine. |
| Velocity defect (Unit m/s) |
In a viscous flow, such as a boundary layer or wake, the reduction in velocity, due to friction, compared with that of the free stream. |
| Velocity ratio |
1. The ratio between the input velocity to a machine, train of gears, etc. and the output velocity. 2. The ratio between the displacement of an applied force at one part of a mechanism and the movement of the load at a different part. |
| Vent |
A small valve that allows the release of pressurized fluid from a pipe, pressure vessel, etc., often to the atmosphere. |
| Ventilation |
A system for circulating fresh air in a room, building, passenger vehicle, orother enclosed space. |
| Venturi |
A convergent–divergent flow nozzle, usually circular in cross section, with a relatively short convergent section (the confuser) upstream of a throat followed by a gradually diverging section (the diffuser). Such nozzles usually have flanges at either end for installation in a pipeline. Applications include flow meters and ejectors. When a fluid flows through a convergent duct at subsonic speed, there is an increase in velocity accompanied by a decrease in pressure (Venturi effect). |
| Verification |
Checking or testing an instrument to ensure conformance with a specification. |
| Verified loading range |
For testing machines, the range of indicated loads for which the testing machine gives results within the permissible variation specified. |
| Vernier |
A short auxiliary scale that slides along the main instrument scale to permit more accurate fractional reading of the least main division of the main scale. |
| Vertical engine |
A piston engine having the cylinders above the crankshaft. |
| Vibration |
1. A periodic change with time of the displacements of elements making up a component or structure. 2. The study of the oscillatory motion of bodies and systems and the frequencies, amplitudes, and forces associated with them. |
| Vibration isolation |
The prevention of transmission of vibration from one component of a system to another part of the same system, such as a building or other structure. Isolation may be achieved using dampers (vibration damping) or by active feedback-control methods. Mechanical vibration is often attenuated by means of components immersed in oil such as in dashpots (viscous damping). Vibration suppression can be achieved (a) using dampers and absorbers tuned to a particular frequency to suppress vibratory forces in structures and other systems (passive suppression) or (b) by the measurement of vibration at key locations in a structure and the application of cancellation forces (active suppression). |
| Vibration-testing machine (vibrator) |
Any machine that subjects components or systems to vibration at known amplitudes and frequencies in order to determine the response. vibratory equipment Vibrating process equipment, such as shakers, used to separate small and large particles, or feeders to supply particulate or granular material that may otherwise clog. |
| Vibrograph |
An instrument that records vibrations in a system over time. |
| Vibrometer |
A device used to measure the motion of a vibrating surface, typically using a contactless laser-based technique. |
| Vice |
A workshop tool used to hold a workpiece and consisting of two jaws, one fixed and the other moved by turning a screw. |
| Vickers hardness number |
(diamond hardness number, DHN, VHN, VPN) (Unit kg/mm2 originally, sometimes now Pa) Indentation hardness given by load divided by the surface area of the permanent impression obtained when the indenter is in the form of a square pyramid whose opposite faces make an angle of 136° with one another. The mean length d of the diagonals of the indentation is determined, from which VPN = 0.927(2W/d2) where W is the load, since the base of the pyramid has an area equal to 0.927 times the surface area. |
| Vickers hardness test |
An indentation hardness test employing a 136° diamond pyramid indenter (Vickers) and variable loads, enabling the use of one hardness scale for all ranges of hardness—from very soft lead to tungsten carbide. Also know as diamond pyramid hardness test. |
| Viscoelasticity |
A property involving a combination of elastic and viscous behavior. A material having this property is considered to combine the features of a perfectly elastic solid and a perfect fluid. A phenomenon of time-dependent, in addition to elastic, deformation (or recovery) in response to load. |
| Volume (Unit m3) |
The amount of space occupied by a specified mass of substance or by an object. |
| Volume flow rate |
(volumetric flow rate, , ) (Unit m3/s) The volume of a material, usually a fluid or powder, that flows across a surface or through a pipe or other duct per unit time. |
| Volumetric efficiency |
For a piston engine, the ratio of the volume of the induced charge per induction stroke, determined at a reference pressure and temperature, to the swept volume. |
