Page 347 - Shale Shakers Drilling Fluid Systems

GLOSSARY 329

Ultra Fine Wire Cloth A group of industrial wire cloth specifications with lighter than normal
wire. The wire diameter of this grade produces the highest percentage
of open area of all other grades for any specific mesh size. This cloth is
used in multiple-layer screens. See.- Market Grade Cloth, Mill Grade Cloth,
Tensile Bolting Cloth, Calendered.

Ultra Fine Solids Particles whose diameter is between 2-44 microns.

Ultraviolet Light Light waves shorter than the visible blue and violet waves of the spec-
trum. Crude oil, colored distillates, residium, a few drilling-fluid additives,
and certain minerals and chemicals fluoresce in the presence of ultra-
violet light. These substances, when present in drilling fluid, may cause
the drilling fluid to fluoresce.

Unbalanced Elliptical Motion An elliptical motion of a shale shaker screen such that the ellipse axes
at the feed end are tilted toward the discharge end of the screen, and
the ellipse axes at the discharge end are tilted toward the feed end. Usu-
ally, these screens are tilted downward to assist solids removal from the
end of the screen. The vibrator is usually located above the center of
gravity of the shaker basket.

Underflow (1) Centrifugal Separators: The discharge stream that contains a higher
percentage of solids than does the feed. (2) Screen Separators: The discharge
stream that contains a lower percentage of solids than does the feed.

Underflow Header A pipe, tube, or conduit into which two or more hydrocyclones discharge
their underflow.

Underflow Opening See.- Apex, Apex Valve.

Undersize Solids Particles (1) Particles, in a given situation, that will pass through the mesh of the
screen in use. (2) Particles, in a given situation, that will remain with the
liquid phase when subjected to centrifugal force.

Underslung Field terminology denoting that the support ribs for the shaker screen are
located above the screen surface. See: Overslung.

Unoccluded Area Unobstructed area of a screen opening.

Unweighted Drilling Fluid A drilling fluid that does not contain commercial suspended solids added
for the purpose of increasing the drilling fluid density.
V.G. Meter See.- Direct Indicating Viscometer.

VAC Alternating Current Voltage.

Valence A number representing the combining power of an atom (i.e., the num-
ber of electrons lost, gained, or shared by an atom in a compound). It is
also a measure of the number of hydrogen atoms with which an atom
will combine or replace (e.g., an oxygen atom combines with two hydro-
gens, hence has a valence of 2). Thus, there are mono-, di-, tri-, and so
forth, valent ions.

Valence Effect Generally, the higher the valence of an ion, the greater the loss of sta-
bility to emulsions, colloidal suspensions, and the like, these polyvalent
ions will impart.