V — Dictionary of Quarrying Terms

VDU: abbr. visual display unit.

VOD: abbr. velocity of detonation.

vane pump: A pump having a slotted rotor mounted eccentrically in the circular casing, and vanes which are free to slide radially in the slots, forming pockets of variable volume between them.

variable costs: Costs which vary directly with output.

variable-ellipse screen: A mechanically vibrated screen in which the vibrating assembly is mounted above the screen and the motion generated varies along the length of the screen; a flat ellipse at the feed end, a circle at the centre and a steep ellipse at the discharge end.

vector: A line used to represent a vector quantity, ie to represent that quantity in both magnitude and direction.

vector quantities: Quantities which possess two fundamental characteristics, namely magnitude and direction. Examples are force, velocity and alternating electric current and voltage.

vee belt: A power transmission belt having a cross-section in the form of a truncated V running in similar-shaped grooves in pulleys. These belts can withstand higher working stresses and can transmit much more power than a flat belt of corresponding cross-section.

vein: A mineral body, thin in relation to its other dimensions, which cuts across the bedding and in which the minerals are later than the country rock.

velocity: The speed of an object in a specified direction. Units: m/s.

velocity of detonation: The velocity with which the shock wave traverses an explosive charge on detonation.

velocity ratio: see ‘movement ratio’.

venturi: A convergent-divergent duct in which the kinetic energy of a fluid flow is increased at the throat, leading to a drop in pressure energy there; after the throat the reverse takes place. The lower pressure at the throat compared with the pressure in the pipe can be used as a measure of flow rate.

venturi scrubber: A device for removing dust from gases by passing them through a narrow throat into which water is introduced and is atomized by the high-velocity gas stream. Dust particles are trapped in the water droplets and are then carried away by the flow to a centrifugal separator.

vermiculite: A variety of chlorite occurring in the form of radiating tubes or granules. Expanded vermiculite is used as a lightweight aggregate in concrete.

vertical circle: The graduated circular plate used for the measurement of vertical angles by a theodolite.

vertical-shaft impactor: A secondary or tertiary crusher consisting of a rotor or impeller disc mounted on a vertical shaft which is rotated at high speed. Rock is fed on to the centre of the rotor from where it is thrown with high radial velocity to be broken on contact with either the anvils or previously crushed rocks which line the crushing chamber.

vibrating feeder: A steel trough or a grizzly, or a combination of the two, which is vibrated by either an electrical or mechanical unit attached to the frame.

vibratory roller: A self-propelled or towed roller with one or more mechanically vibrated rolls which impart the oscillations to the material being compacted.

vibrograph: An instrument for recording ground vibrations from quarry blasts.

viscometer: An instrument for measuring viscosity.

viscosity: The resistance of a fluid to flow or relative movement within itself; the higher the viscosity, the thicker or less free flowing is the fluid.

viscosity grade: The degree of viscosity of a binder measured by a standard viscosity test.

viscosity index: The higher the index, the more the viscosity changes with temperature. Values range from 0 to 100.

vitreous lustre: The lustre of glass, eg quartz.

void: In an opencast mine, the open excavated area.

volt: The difference of electrical potential or emf between two points of a conducting wire carrying a constant current of one ampere, when the power dissipated between these two points is one watt. Symbol: V.

voltage: The electromotive force of a supply of electricity. Symbol: V. Unit: volt.

voltage drop: The fall in voltage between the ends of a conductor or across an apparatus through which a current is flowing.

voltmeter: An instrument for measuring the voltage or potential difference between two points in a circuit. It is connected across the points being measured.

vug: A natural cavity within a mass of rock usually lined with crystallized mineral.

vulcanization: The treatment of rubber with sulphur compounds in order to change its physical properties; a process used in the manufacture and repair of tyres, conveyor belting etc.