These differ from straight overcurrent relays in that they are primarily
used for ground protection. They are designed to measure fault current in
one or two sections. Whether faults will cause flow in one or two
directions is determined by system conditions. The two-directional relay
is used on transmission lines where ground-fault currents flow in either
direction. These relays provide directional as well as overcurrent
protection. Other directional relays provide phase protection.
Circular galleries made at different levels in a mine that enable empty
trucks to be pushed out of the cage on one side while full ones are pushed
in on the other side, thus ensuring a more rapid journey of the cage.
Circuits also aid air circulation. Syn:roundabouts
A roadway support consisting of an H-section girder of circular form and
usually made in three parts. The joints are secured by fishplates and
bolts. This type of steel arch is useful for withstanding pressures from
roof, sides, and floor. With close lagging between the rings, the finished
roadway resembles a tube. See also:steel arch
A revolving cone with feeder fingers around the base periphery connected
at the apex through a universal joint to a revolving arch breaker arm.
See:ditcher
An apparatus used for the same purpose as a picking belt and consisting of
a flat horizontal rotating annular plate. See also:picking belt
BS, 5
A shaft excavated as a cylinder. The circular shaft is equally strong at
all points; convenient for concrete lining and tubbing, both of which can
be made relatively watertight; and offers the least resistance to airflow.
Nelson
A type of landslide that may occur in embankments or cuttings in clay or
homogeneous earth. See:slip surface of failure
The same as a straight tunnel kiln, except that it has a movable, circular
platform instead of cars.
Fluid pumped into a borehole through the drill stem, the flow of which
cools the bit, washes away the cuttings from the bit, and transports the
cuttings out of the borehole. See also:reverse circulation
circulation fluid; circulation medium; drill fluid; drilling fluid.
Long
A casing-to-drill-rod coupling. When attached to the top of the casing, it
is used during the process of pumping cement slurries or circulating water
through the casing, forcing the fluid to flow out of the casing into the
drill hole between the outside of the casing and the walls of the
borehole. Also called stuffing box; tight head. Long
a. In mineral processing, use of a closed circuit to check mineral issuing
from a specific treatment and to return to the head of the treatment those
particles that do not satisfy the maintained conditions for release to the
next stage of treatment. Pryor, 3
b. In ore dressing, oversize material returned to a ball mill for further
grinding. Newton, 1
Medium in circulation in or outside a separating bath, at or about the
specific gravity of that in the separating bath. BS, 5
a. A pump (usually centrifugal) used to circulate water through the
condenser of a steamplant. Nelson
b. A pump used to circulate water in a coal washer or ore concentration
plant. Nelson
c. A pump used to circulate mud or water through a drilling column. Also
called slush pump. Syn:mud pump
Scrap arising at steelworks and foundries during the manufacture of
finished iron and steel or of castings; consists of the sheared-off ends
of rolled and other worked products, rejected material, etc.
See also:capital scrap
The water in the water circuit of a preparation plant. BS, 5
a. The passing of any liquid or gas from the surface to the end of the
drill string and back to the surface in the process of drilling a
borehole. Long
b. The movement of air currents through mine openings. Long
c. In rotary drilling, the process of pumping mud-laden or other fluid
down the drill pipe, through the drilling bit, and upward to the surface
through the annulus between the drill-hole walls and the drill pipe.
AGI
The fluid pumped through and to the end of the drill string and back to
the surface in the process of drilling a borehole. CF:drilling mud
Long
The result of drilling or circulation fluid escaping into one or more
formations by way of crevices or porous media. Brantly, 1