A single strand of rope or cable doubled back around two sheaves so that
three parts of it pull a load together. Nichols, 1
Usually a three-wire circuit using alternating current with three equal
voltages. This should not be confused with the three-wire service
supplying 110 V and 220 V. This latter is merely a two-voltage
single-phase circuit arrangement and is used almost universally to provide
power and lighting to homes and small business establishments.
Kentucky
Alternating current in which three separate pulses are present, identical
in frequency and voltage, but separated by 120 degrees . Pryor, 3
An inclusion consisting of a liquid with a gas bubble and a crystal within
a crystal. See also:negative crystal; inclusion.
A set of timber used in ground that requires greater support than a
two-piece set or stull will provide. A cap is supported by two posts often
spread apart at the bottom to give greater stability.
See also:timber set; four-piece set. Lewis
a. In surveying, a method used to orient underground workings via three
plumblines suspended in a vertical shaft. Pryor, 3
b. The problem in plane table surveying of locating precisely the point at
which the table is set up, using three fixed points that are visible from
the plane table. Hammond
c. The problem of determining dip and strike of a plane from elevations
determined at three known points not in a straight line.
A method in which the cleanest fraction of the coal with an ash content of
1% to 2% (for hydrogenation, etc.) is separated; the remainder giving coal
with an ash content of 10% to 15% (for boiler firing, etc.) and finally
incombustible shale. Nelson
A system of cyclic mining on a longwall conveyor face, with coal cutting
on one shift, hand filling and conveying on the next, and ripping,
packing, and advancement of the face conveyor on the third shift. The
system restricts coal production to one shift. Nelson
Instrument that automatically regulates a process in proportional,
integral, and derivative terms, thus neutralizing and removing the errors
that arise during operation. Pryor, 3
This type of pump consists essentially of three single-acting ram pumps
side by side, either vertical or horizontal, and driven from a triple
crankshaft with cranks set at angles of 120 degrees . The three-throw pump
can deal with heads up to 1,000 yd (900 m) in a single lift.
Sinclair, 4
A voltage improvement system that consists of the series operation of two
generators. One circuit of a mine is fed from one generator, and a second
circuit is fed from the other generator. The mine track or return is
common to both generators and is connected between the generators. This
method provides high voltage for transmission of power, yet the individual
circuits provide normal low-voltage power. In effect, this is the Edison
three-wire system, wherein the rails form the neutral third wire. The
third wire (mine track) carries only the unbalance between the loads on
the two separate circuits. Kentucky
a. In geochemical prospecting, the limiting anomalous value below which
variations represent only normal background effects and above which they
have significance in terms of possible mineral deposits. Hawkes, 1
b. In analytical chemistry, the limiting sensitivity of an analytical
method, the detection limit. Hawkes, 1
A time-weighted average concentration under which most people can work
consistently for 8 hours a day, day after day, with no harmful effects. A
table of these values and accompanying precautions is published annually
by the American Conference of Governmental Hygienists. NSC, 2
a. The part of a blast furnace at the top of the stack. Dodd
b. The zone of decreased cross section found between the port area and the
furnace chamber in some designs of open-hearth steel furnaces.
Dodd
c. The submerged passage connecting the melting end to the working end of
a glass tank furnace; the refractory blocks forming the sides of the
throat are known as throat cheeks, sleeper blocks, or dice blocks; the
refractories for the top are the throat cover.
See also:submarine throat
d. The least thickness of a weld, the calculation of its strength being
based on the thickness at the throat. Hammond
Point at which the rock is discharged. Its short dimension varies,
depending upon whether the swing jaw is in the open or closed position.
Newton, 2
To obstruct the flow of, as steam to an engine esp. by a throttle valve.
Webster 3rd
A valve designed to regulate the supply of a fluid (as steam or gas and
air) to an engine. Webster 3rd
A passage cut through a pillar to connect two rooms. Fay
An excavation between parallel banks that begins and ends at original
grade. See also:thirling
See:stenton
Quantity of material passed through the mill or a section thereof in a
given time or at a given rate. Pryor, 3