N — Dictionary of Quarrying Terms

NPV: abbr. Net present-day value. The value at the present time of future cash flows.

NVQ: National Vocational Qualification requiring both evidence of knowledge and ability to carry out a job i.e. performance.

national grid: 1 Lines of reference drawn on a map to permit the precise location of particular features. 2 High-voltage electrical power distribution system.

natural asphalt: A bituminous deposit formed in oil-bearing strata by the disappearance of volatiles.

near-mesh material: Material approximating in size to the aperture size in the screen deck, usually within ±25% of the aperture size.

network: A network, as used in planning an operation, is a diagram in which each line representing an activity begins and ends at a circle, which represent the start and finish of an event. The network shows the logical sequence of events and the time for each event is included in the network.

network analysis: A technique used by managers as an aid in planning and controlling their operations. It allows the control cycle to be completed rapidly and therefore frequently.

newton: The force which imparts to a body of a mass of lkg an acceleration of 1m/s². Symbol: N.

nip angle: The angle between the faces of a crusher.

nip point: A point of hazard on a conveyor where the clearance between the moving belt and the static structure, such as a chute, or at the convergence of the moving belt and a drum, is such that parts of a person could be trapped.

nitroglycerine: A liquid high explosive, prepared by treating glycerine with a mixture of concentrated nitric and sulphuric acids; used as a basic sensitizer in some commercial explosives.

nitrous fumes: Poisonous reddish-brown fumes which are produced when ANFO containing insufficient oil is detonated and when nitroglycerine explosives burn instead of detonating.

nominal screening size: A notional size at which it is intended to divide a feed by screening.

nominal size: The limit or limits of particle size used to describe a product of a sizing operation.

nomogram: Chart of scaled lines for facilitating calculations. A simple nomogram consists of three straight lines arranged in such a way that, when a straight-edge is placed so as to join values of two of the variables, the corresponding value of the third variable can be read off at the intersection of the straight-edge and the third line.

non-return valve: A valve which allows flow in a pipe in one direction only. One use of this type of valve is on the delivery side of a pump used to dewater a deep pit to prevent the column of water in the delivery pipe flowing back. In hydraulic systems the valve element is usually a ball which is returned to its seat by a light spring when flow ceases.

Nonel system: A non-electric system of applying short-delay detonators to down-the-hole in intiation of quarry blasts. See ‘shock tube’.

normal fault: A fault which hades towards the downthrow side.

northing: see ‘latitude’.

notifiable: a term created by the Quarry Regulations 1999 to describe a tip or excavation that presents a significant hazard and must, therefore, be notified to the Inspectorate. Likely to include all structures described as ‘classified’ under previous regulations.