VOLUME OF FLOW--The quantity of fluid that
VALVE, UNLOADING--A pressure control valve
passes a certain point in a unit of time. The volume
whose primary function is to permit a pump or
of flow is usually expressed in gallons per minute
compressor to operate at minimum load.
for liquids and cubic feet per minute for gases.
VAPOR LOCK--A condition in the fuel system in
VOLUMETRIC EFFICIENCY--The ratio between
which gasoline has vaporized, as in the fuel line, so
the amount of fuel-air mixture that actually enters
that fuel delivery to the carburetor is blocked or
an engine cylinder and the amount that could enter
retarded.
under ideal conditions.
VELOCITY--The rate of motion or speed at any
WATER JACKET--A jacket that surrounds the
instant, usually measured in miles per hour or feet
cylinders and cylinder head(s), through which
per second or minute.
coolant flows.
VENTURI--A tube having a narrowing throat or con-
WATER MANIFOLD--A manifold used to distribute
striction to increase the velocity of fluid flowing
coolant to several points in the cylinder block or
through it. The flow through the venturi causes a
cylinder head.
pressure drop in the smallest section, the amount
being a function of the velocity of flow. In a
WATER PUMP--In the cooling system, the pump that
carburetor, it is the restriction in the air horn that
circulates coolant between the engine water jackets
produces the vacuum responsible for the movement
and the radiator.
of fuel into the passing airstream.
WHEEL ALINEMENT--The mechanics of keeping
VIBRATION DAMPER--A weighted device that is
all parts of the steering system in correct relation
attached to the engine crankshaft at the end
with each other.
opposite its power output. Its purpose is to absorb
WHEEL BRAKE--A brake that operates at the
engine vibration.
wheel, usually on a brake drum attached to the
VISCOSITY--A measure of the internal friction or
wheel.
resistance of a fluid to flow.
WHEEL CYLINDER--In hydraulic brake systems,
VISCOSITY INDEX--A measure of the
the hydraulic cylinder that operates the brake shoes
viscosity-temperature characteristics of a fluid as
when hydraulic pressure is applied in the cylinder.
referred to that of two arbitrary reference fluids.
WINCH--A mechanism actuating a drum upon which
VISCOSITY, KINEMATIC--The absolute viscosity
a cable is coiled, so that when a rotating power is
divided by the density of the fluid. It is usually
applied to the drum, a powerful pull is produced.
expressed in centistokes.
WOBBLE PLATE--That part of a certain type of
VISCOSITY, SAYBOLT UNIVERSAL SECONDS
pump that drives pistons back and forth as it rotates
(SUS)--The time in seconds, for 60 milliliters of
to produce pumping action. It is a disk, or plate, set
oil to flow through a standard orifice at a given
at an angle on a rotating shaft.
temperature.
WORK--The result of a force acting against
VOLATILITY--A measurement of the ease with
opposition to produce motion. It is measured in
which a liquid turns to vapor.
terms of the product of the force and the distance it
acts.
VOLTAGE REGULATOR--A device used in con-
nection with a generator to keep the voltage
WORM GEAR--A gear having concave, helical teeth
constant and to prevent it from exceeding a
that mesh with the threads of a worm; also called a
predetermined maximum.
worm wheel.
VOLT--A unit of potential, potential difference, or
electrical pressure.
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