exhaust
and
recirculating air. This balance is
critical
because
too
much
positive
or
negative
pressure
in
the
work
area could
mean
an
outflow
of
pathogens
or
an
inilow of room contamination.
The
balancing
damper
adjusts
the
volume
of
the
exhaust
air
so
as
to
maintain
the
proper
supply
and
calculated
intake
air
velocities. The
damper
is
preset
at
the
factory
and
should
not
be
changed
unless
the
proper
airflow balance carmot be
achieved
after
new
filters
are
installed.
On
those
occasions
when
adjustment
becomes necessary,
adjustments
can
be
performed
by
a
damper
quadrant
located
on
the
top
of the unit.
The
procedure
is as follows:
1.
Loosen
the
quadrant
wing
nut.
2.
To
decrease
exhaust
airflow,
move
the
quadrant
arm
towards
the front of the unit
(clockwise rotation).
3.
To increase
exhaust
airflow,
move
the
quadrant
arm
towards
the
rear
of
the
unit
(cotmter-clockwise rotation).
4.
When
final
adjustments
have
been
achieved,
make
sure
to
tighten
the
wing
nut
on
the
damper
quadrant.
5.
If,
after
adjusting
the
darnper,
both
supply
and
exhaust
are
high
or
low,
adjust
the
speed
control.
Troubleshooting
Here
are
some
suggestions
based
on
our
experience
with
the
use
and
misuse
of
biological
safety
cabinets.
DANGER!
Whene71er
the
potentially
contaminated
areas
of
your
cabinet
1nust
be· entered, 1nake s;.tre 1
that
the
unit
is
first
decontaminated
by
use
of
j
appropriate
1nethods.
1
When
a
smoke
test
indicates
that
there
is
air
flowing
from
the
interior
of
your
cabinet
into
the
surrounding
room
-
1.
Make
sure
that
the
shipping
cover
is
removed
from
the
exhaust
filter
and
that
no
other
objects
are
blocking
the
airflow.
2_
If
your
cabinet is cmmected to
an
in-house
exhaust,
make
sure
that
there
is
adequate
exhaust
suction
and
the
system
is
not
producing
back
pressure.
Also,
be
sure
the
dampers
are open. Re-balance
the
exhaust
system
to
handle
an
adequate
volume
of
air
and
static
pressure
(suction).
Consult
with
building
maintenance
people.
3. The
exhaust
filter
mav
be
loaded
with
dirt
if
the urtit has
been
in
service
for
some
time.
Decontaminate,
and
replace all filters.
4.
There
may
be
high
cross-drafts
in
the
room
which are
causing
the
outflow
of
smoke.
Check the airflow balance, following
the
procedure
recommended
earlier
in
this
chapter. Eliminate
the
source
of
the
cross-
draft.
When
there
is
low
airflow
within
the
work
area
and
through
the
exhaust
filter
-
1. Check the
incoming
line
voltage.
Low
voltage
may
cause
the
blower
to
operate
at
a
slower-than-designed speed.
Although
this
should
be
corrected in
the
building's
electrical
system,
you
may
be able to
compensate
by
adjusting
the
blower
speed
control
clockwise
until
proper
velocity is reached.
The
control
is located on
the
left
side
of
the
light
canopy.
2.
The reduced airflow
may
be
caused
by
damaged
or leaking filters.
Decontaminate
the
unit
and
replace the filters
at
once.
If
there
is
no
air
flow
within
the
work
area
-
1.
If
the lights
and
electricaJ
outlets
also fail to
operate,
make
sure
the Llnit is
plugged
into
a
dedicated eJectricaJ outlet
(grounded
20
amp,
115 Volt,
60
Bz). Also
make
sure
that
the
blower
switdl
is
turned
on.
The
yellow
indicator above
the
button
should
be lighted.
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