Du Pont SORVALL RC-5 Service Manual page 148

Maintenance
&
Repair
Sorvall9
Centrifuges2.
Remove guide shoe mounting bracket
with
screw and lockwasher on motor
assem¬bly
end
bell.3.
Remove screw securing brush wire
terminal.4.
Retract
and stow
upper
brush
spring
in brush
spring
stow
groove.CAUTIONWhen
retracting the lower brush
spring,
exercise care to avoid
snarls,sharp
bends,
and
especially
kinks in the brush
lift
cable.5.
Retract
lower brush
spring.6.
Lift
the brush from the
holder,
wire
attached.7.
If
the
brush is less than 14 mm (9/16
in),
badly pitted, or unevenly
worn,
it
must
bereplaced.
The motor armature
may
have to be machined
if the
commutator is
badlygrooved,
worn. pitted, or burned. Also.
the brush
plate
should be checked for
ab¬normalities.8.
Insert
new brushes into
the holders
so
that the bevelled
ends match
the
curvatureof
the commutator
(see
figure
6-11
).9.
Route the brush wire downward in
a
hooked position and secure
with
terminalscrew.
Do not route brush wire over lower brush
spring
(see figure
6-12).10.
Release each brush
spring
from its stowed
position,
making sure
that
each
brushspring
seats
properly
in Its
respective
channel.11.
Using a spring scale or
other suitable tension
measuring device, measure
tension
oflower
brush
spring
at the knee of
the
spring.
Spring
tension should be
510-623
g(18-22
oz).
Proper tension
is obtained
by
loosening
the
spring
post
with
a 2.39
mm(3/32
in)
hex head (Alien) wrench through the
access opening
in the bottom of
theend
bell
and turning
the
spring post
with
a
1/4 In
open
end
wrench. Secure
thespring
post
when
proper spring
tension is obtained,
then recheck
tension.
Read¬just.
if
necessary.12.
Measure tension of
upper
brush
spring
at
the
knee
of the
spring. Spring
tensionshould
be 56 g ± 5
g
(2 oz). Proper
tension is obtained
by loosening
the hex nut
atthe
top
of the
spring post
and turning
the
spring
collet wheel. Tighten
the hex
nutwhen
proper
tension is
obtained.13.
Recheck
tension
of both brush
springs.
Since both brush
springs
derive
a
tensionrelative
to
positioning
of the
spring
post,
readjusting
the lower brush
spring
createsa
requirement to check and readjust
the
upper
brush spring (see Figure
6-12).NOTESteps
14
through
17
apply only
when
the
optional automatic rate
con¬troller
is
installed.6-10