Page 348 - Shale Shakers Drilling Fluid Systems

330 SHALE SHAKERS AND DRILLING FLUID SYSTEMS

Velocity Time rate of motion in a given direction and sense. It is used as a mea-
sure of the fluid flow, and may be expressed in terms of linear velocity,
mass velocity, volumetric velocity, and so forth. Velocity is one of the
factors that contributes to the carrying capacity of a drilling fluid.

Velocity Head Head (relating to pressure when divided by the density of the fluid) cre-
ated by movement of a fluid, equal to an equivalent height of static fluid.

Venturi Streamlining up to given pipe size following a restriction (as in a jet in
a mud hopper) to minimize turbulence and pressure drop.

Vibrating Screen A screen with motion induced as an aid to solids separation. See: Shale
Shaker.

Vibration Isolaters Elastomers, ranging from solid to air-pressured, or springs that allow the
shale shaker screens to vibrate but do not transmit the vibratory motion
to the rest of the machine.

Vibrators Weights rotated about an axis that does not pass through the center of mass.

Viscometer An apparatus to determine the viscosity of a fluid or suspension. Vis-
cometers vary considerably in design and testing methods.

Viscosifiers Material added to a drilling fluid to increase the low-shear-rate viscosity.

Viscosity The ratio of shear stress to shear rate is defined as the viscosity of a fluid.
If the shear stress is measured in dynes/sq. cm and the shear rate in
reciprocal seconds, the ratio is the viscosity in poise. Viscosity may be
viewed as the internal resistance offered by a fluid to flow. This phenom-
enon is attributable to the attractions between molecules of a liquid, and
is a measure of the combined effects of adhesion and cohesion to the
effects of suspended particles, and to the liquid environment. The greater
this resistance, the greater the viscosity. (2) A characteristic property of
a fluid, liquid, or slurry crudely defined as resistance to flow (by accu-
rate definition the ratio of shear-stress to shear-rate). See: Apparent Vis-
cosity, Plastic Viscosity, API Bulletin RP-13B.

Viscosity-Gravity (V.G.) The name more commonly used for a direct indicating viscometer. See:
Meter Viscometer.

Viscous Flow See/ Laminar Flow.

Volatile Matter Normally gaseous products given off by a substance, •— t uo gas break-
ing out of live crude oil that has been added to a drilling fluid. In distil-
lation of drilling fluids, the volatile matter is the water, oil, gas, and so
forth, that is vaporized, leaving behind the total solids, which can con-
sist of both dissolved and suspended solids.

Volt The unit of electrical "pressure" or electromotive force. One volt produces
a current flow of one ampere through a resistance of one ohm.
Volume Percent The number of volumetric parts of the total volume. Volume percent is
the most common method of reporting solids, oil, and water contents of
drilling fluids. See: Weight Percent, Ppm.
Vortex A cylindrical or conical shaped core of air or vapor lying along the cen-
tral axis of the rotating slurry inside a hydrocyclone.