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Damp
  Gases (other than air) in mines, usually in dangerous concentrations. Prefixes are attached to indicate various gases and situations (Black damp, white damp, fire damp, after damp, stink damp)
 
De-superheater
  A device for removing the excess heat in steam as its pressure is reduced.
 
De-vent
  To close the vent connection of a pressure control valve permitting the valve to function at its adjusted pressure setting.
 
Deadband
  The region or band of no response where an error signal will not cause a corresponding actuation of the controlled variable.
 
Decompression
  The slow release of confined fluid to gradually reduce pressure on the fluid.
 
Delta
  The amount of change in a number, size or position.
 
Deposit
  Natural mineralization under the ground in sufficient quantities to warrant further exploration.
 
Detectors
  Chemical or electronic instruments used to detect dangerous concentrations of mine gases.
 
Detonator
  Device containing a small charge used to detonate an explosive. Types include: blasting caps, delay electric blasting caps, exploders, electric detonators, etc.
 
Development drilling
  Drilling for the purpose of accurately estimating mineral reserves.
 
Diamond
  Hardest known mineral, composed of pure carbon.
 
Differential current
  The algebraic summation of the current in the torque motor; measured in MA (milliamperes).
 
Differential cylinder
  Any cylinder in which the two opposed piston areas are not equal.
 
Diffusion
  Movement of moisture from areas of high to low concentration or temperature.
 
Dilution
  Waste rock that is unavoidably removed and mixed in with the ore. This lowers the grade of the ore.
 
Directional valve
  A valve which selectively directs or prevents fluid flow to desired channels.
 
Disseminated ore
  Ore spread more or less uniformly through the waste rock (gangue). Opposite of Massive ore.
 
Dither
  A low amplitude, relatively high frequency periodic electrical signal, sometimes superimposed on the servo valve input to improve system resolution.  Dither is expressed by the dither frequency (Hz) and the peak-to-peak dither current amplitude (ma).
 
Dore
  Unrefined gold or silver bullion bars which still need further processing to become pure metal.
 
Dragline
  Large surface mining equipment used to remove overburden above a deposit. Has a long boom and large bucket which is thrown outwards, then dragged back towards the machine.
 
Drain
  A passage in, or a line from, a hydraulic component which returns leakage fluid independently to reservoir or to a vented manifold.
 
Dredging
  Process of using a machine to dig up and sift through placer deposits in a watercourse.
 
Dressing
  Treatment of ores to concentrate their minerals into concentrates and to collect waste to be discarded as tailings.
 
Drill
  Machine using rotation, percussion (hammering) or a combination of both to make holes.
 
Drill hole
  A small diameter hole created when recovering a core for geological information. Also a hole used to plant explosives.
 
Dump
  Waste material extracted during mining and placed on the surface in a large pile. Also known as a waste dump, pile, heap, tip, spoil, pike, etc. Also the actual act of unloading or the mechanism for unloading a load.
 
Dump truck
  A large earth moving vehicle whose carrying box can be tilted to discharge its load.
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