VACUUM AUGMENTER -- An air
ejector placed in a steam condenser to produce a higher degree of vacuum than
is obtainable by the use of an air-pump alone.
VACUUM PHOTOCELL -- High-vacuum photoemissive cell in which
anode current equals total photoemission currents, so that strict
proportionality between current and incident illumination is obtained.
VALVE BOUNCE -- The unintended opening of an engine valve due
to inadequate rigidity of various parts in the valve gear. The deflected parts
allow the valve to seat too early and when their strain energy is released, the
valve opens again. This bounce causes valve breakage, seat wear, and irregular
function.
VALVE DIAGRAM -- For a steam-engine slide-valve, a graphical
method of correlating the throw and angle of advance of the eccentric, the lead
and laps of the valve, and the points of admission, cut-off, compression, and
release. The Bilgram, the Reulesux and the
Zeunet valve diagrams are examples of the method.
VALVE-GEAR -- The linkage by which the valves of an
engine derive their motion and timing from the crankshaft rotations. All
steamships have a valve-gear although Stephenson named his
valve-gear a link-motion.
VANE PUMP -- A type of pump used, e.g., as a vacuum or oil
pump or as a compressor, in which a slotted rotor is mounted eccentrically in a
circular stator (or a similar geometrical arrangement), and vanes sliding in
the rotor slots divide the crescent-shaped fluid space into variable
volumes.
VAPORIZATION -- The process of a solid or liquid becoming a
gas.
VAPOR PRESSURE -- The pressure exerted by a vapor, either by
itself or in a mixture of gases. The term is often taken to mean saturated
vapor pressure, which is the vapor pressure of a vapor in contact with its
liquid form. The saturated vapor pressure increases with rise of
temperature.
VELOX BOILER -- A forced circulation boiler in which very high
rates of heat release and heat transfer are obtained by the use of a
supercharged furnace and high gas velocities, resulting in exceptionally low
unit weight and high efficiency.
VENTURI METER -- One in which flow rate is measured in terms
of pressure dropp across a venturi, or tapered throat, in a pipe.
VISCOSITY
-- The degree to which a fluid resists flow under an applied force.
VOLATILE -- A volatile substance is one that is capable of
being evaporated or changed to a vapor at a relatively low temperature.
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