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VALVE:
In
baghouses,
frequently
the
pilot
valve
and
the
diaphragm
valve
pulse
are
considered
as
one,
simply
called
“valve.”
van
der
Waals:
Adhesive
forces
that
exist
between
the
particle
and
fiber.
VANEAXIAL
FAN:
Axial
fan
with
either
inlet
or
discharge
guide
vanes
or
both,
includes
fixed-pitch,
adjustable-pitch
and
variable-pitch
impellers.
VAPOR:
Substance
in
gaseous
form.
VAPORIZATION:
The
change
of
a
substance
from
the
liquid
to
a
gaseous
state.
One
of
the
three
basic
contributing
processes
of
air
pollution,
the
others
being
attrition
and
combustion.
VAPORS:
The
gaseous
form
of
substances
which
are
normally
in
the
solid
or
liquid
state,
and
which
can
be
changed
to
these
states,
either
by
increasing
the
pressure
or
decreasing
the
temperature
alone.
Vapors
diffuse.
VARIANCE:
Permission
granted
for
a
limited
time,
under
stated
conditions,
for
a
person
or
company
to
operate
outside
the
limits
prescribed
in
a
regulation.
Usually
granted
to
allow
time
for
engineering
and
fabrication
of
abatement
equipment
to
bring
the
operation
into
compliance.
VELOMETER:
A
simple
instrument
for
for
determining
the
velocity
of
gas
in
a
duct.
Its
operation
is
similar
to
an
inclined
manometer,
except
that
it
automatically
converts
the
reading
to
velocity.
VENA
CONTRACTA:
The
smallest
flow
area
for
flow
through
a
sharp-edged
orifice.
VENTILATION:
Supplying
and
removing
air
by
natural
or
mechanical
means
to
and
from
any
space.
VENTURI:
Device
used
to
theoretically
increase
the
efficiency
of
a
compressed
air
pulse.
Designed
with
converging
circular
sides
to
a
throat
and
then
diverging
sides.
Designed
such
that
when
a
pulse
is
introduced
at
the
top,
a
negative
pressure
zone
is
created
outside
the
top,
and
secondary
air
is
induced
into
the
venturi,
increasing
cleaning
energy.
VENTURI
SCRUBBER:
A
wet
type
dust
collector
that
can
obtain
very
high
efficiency,
but
requires
large
horsepower
to
do
so.
The
gas
and
dust
particles
are
accelerated
in
a
venturi
throat,
where
finely
atomized
water
is
introduced
and
water/dust
collisions
take
place.
VERTICAL
CARTRIDGE
COLLECTOR:
A
cartridge-type
dust
collector
where
the
cartridge
filters
hang
vertically.
The
contaminated
air
typically
enters
the
bottom
of
the
unit
and
moves
in
an
upward
airflow
pattern.
Vertical
cartridge
collectors
have
been
shown
in
an
EPA-sponsored
research
project
to
cause
particle
redisposition
during
pulse
cleaning
and
are
less
effective
than
downward
airflow
collectors.
VIBRATION:
Alternating
mechanical
motion
of
an
elastic
system,
components
of
which
are
amplitude,
frequency
and
phase.
VISCOSITY:
The
characteristic
of
all
fluids
to
resist
flow.
VOCs
(VOLATILE
ORGANIC
COMPOUNDS):
A
group
of
chemicals
that
react
in
the
atmosphere
with
nitrogen
oxides
in
the
presence
of
heat
and
sunlight
to
form
ozone;
does
not
include
methane
and
other
compounds
determined
by
EPA
to
have
negligible
photochemical
re-activity.
Examples
of
VOCs
include
gasoline
fumes
and
oil-based
paints.
VOLT:
A
unit
of
electrical
potential
or
pressure.
110
or
230,
460
volts
are
normally
found
in
the
U.S.
VP
(VELOCITY
PRESSURE):
The
kinetic
energy
pressure
of
air
in
motion.
VP
is
used
to
get
the
velocity
of
a
gas
stream.
Velocity
(SFPM)
=
4005
vVP
Velocity
(AFPM)
=
1096
vVP/?
?
=
Actual
density
of
the
air
(lb/ft3
)
VP
=
Inches
of
water
column
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