Sorvall RT/T6000D - System Descriptions; Mechanical Systems; Refrigeration System

SORVALL®
Centrifuges
System
Descriptions:
Mechanical
Section
6
SYSTEM
DESCRIPTIONS
This
section provides
theoretical descriptions
of the
mechanical and
electrical
systems
In
the
RT/T6000.
RT/T6000B, and
RT/T6000D
centrifuges.
The
descriptions are
Intended
to
assist trained
service
engineers
with
troubleshooting.
Mechanical
Systems
6-1.
Refrigeration System
The
refrigeration
system
Is
composed
of
the
following:
•
a
standard Tecumseh
1/4
hp
refrigerant condensing
unit
•
an
expansion
valve
(preset
at
the
factory
for
9°C
superheat
and
a
maximum
operating pressure
of 35
psig)
•
an
aluminum,
wrap-around
evaporator
secured
around an
aluminum
bowl
that
serves
as a
rotor chamber,
heat
exchanger,
and
guard
bowl.
The
refrigeration
system
is
charged
with 8
ounces
(+0,
-2
oz.)
of
refrigerant
12.
Normal
operating
pressure
with
an
H-1000B
Rotor
at
3200
rpm
is
9-11
psig
suction
and
110-130
psig
head
pressure
at
O'C
chamber
temperature.
In
operation,
280 CFM
(cubic feet
per
minute)
of
air
is taken
in
at
the
front of
the
centrifuge
and exhausted
at
the
rear.
This
air
picks
up
all the
heat from the
condenser as
well
as
the
compressor,
the drive
motor
and
the
electronics.
A
remote
bulb
on
the
suction
line
senses
temperature
of the
suction
line
gases
and modulates
the
orifice in
the
expansion
valve to
provide constant
superheat
under
varying
rotor
speeds.
The
small orifice in
the
expansion
valve is
protected from freezing or
clogging
by
a
filter/dryer.
The
refrigeration
cycle operates
as
follows:
During
the
refrigeration
cycle,
the
temperature
and
pressure
of
the
refrigerant are
varied,
causing
the
refrigerant
to alternate between
a
liquid
and
a
gaseous
state.
(For
a
break¬
down
of the
locations
of
liquid refrigerant
and
refrigerant
gas
In
the
refrigeration
system,
refer
to
figure 6-1.)
In the
evaporator,
low
pressure
liquid refrigerant absorbs heat from the
rotor chamber
and
becomes
a
low
pressure
gas.
The
compressor
pumps
the
gas
out
of the
evaporator
into the
compressor,
where
the
pressure
is
increased.
This
high
pressure
refrigerant
is then
discharged
to the
condenser,
where
the
condenser
fan
cools the
gas
back
to
a
high
pressure
liquid.
High
pressure
liquid refrigerant
is
dispensed
to
the
evaporator
by
an expansion
valve,
which
drops
the
pressure
of the
refrigerant
so
it
can absorb heat
once again
from
the
rotor
chamber.
See figure
6-2
for
a
simplified schematic
of the
compressor
assembly
wiring.
6-1