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 (4) Remove end bell covers from motor,
f. Installation.
disconnect brush electrical leads, then lift brushes from
(1) Position motor and fan on foundation housing.
brushholders.
(2) Install the mounting hardware. Do not tighten.
(5) Remove mounting screws from commutator
(3) Connect inlet and outlet ducts to the housing.
end bell, then remove end bell and brushholder from motor
(4) Tighten mounting hardware.
shaft.
(5) Reconnect all electrical connections.
(6) Remove screws from drive end bell, then
g. Replacement of START-STOP Switches.
carefully push armature through field frame, and remove drive
(1) Remove as follows:
end bell and armature from the frame.
(a) Remove cover screws and lift cover off
(7) Disconnect internal electrical leads, then
housing.
remove field coils from pole piece.
(b) Tag and disconnect the electrical leads.
(8) Pull drive end bell from armature shaft.
(c) Remove mounting screws, then lift
(9) Remove brushholders from the commutator
switch from the housing.
end bell, marking position for reassembly.
(2) Install as follows:
(10) Bend tabs on lockwashers back, remove
(a) Position new switch in housing over the
bearing locknuts and the lockwashers from armature shaft.
mounting holes and secure with the mounting screws.
(11) Use a puller to remove bearings from the
(b) Reconnect electrical leads to terminals
armature shaft (TM 55-506).
and remove tags. Tighten terminals securely.
d. Cleaning, Inspection, and Repair.
(c) Position switch cover and secure with
(1) Blow accumulation of carbon dust and dirt
the cover screws.
from field coils with dry low pressure (10 psi) compressed air.
(3) Replace START-STOP buttons as required.
(2) Dampen a clean lint free cloth in a solvent
conforming to FED SPEC P-D-680, then wipe all parts free of
5-73. Controller
dust and dirt.
a. General. All centrifugal type blowers are controlled
(3) Inspect bearings for wear, or roughness of
by a magnetic starter; a START-STOP station, and an
rotation. Replace a worn or defective bearing.
emergency STOP station. The closing of the START button
(4) Inspect brushes for chipping, or excessive
closes the circuit to the magnetic coil of the line contactor,
wear. Replace worn or defective brushes. Note that brush
causing the contacts to close. The magnetic coil circuit is
springs give proper tension. Replace worn, weak, or defective
maintained by an auxiliary contact on the line contactor after
springs.
the START button has been released. Pressing the STOP
(5) Inspect
brushholders
for
cracks
or
button at the START-STOP station, or at the emergency
deformation. Replace defective brushholders.
STOP station, breaks the circuit to the magnetic coil of the
(6) Inspect windings of field for damaged
line contactor, causing it to open and stop the motor. When
insulation, shorts (TM 55-506), and leaks. Replace defective
the motor is running, current passes through the heating
field, or coil.
element of an overload relay in the controller. Excessive
(7) Check that armature is not shorted. Inspect
current will cause the normally closed contacts of this relay to
the commutator for roughness, pitting, or excessive wear.
open, breaking the circuit to the line contactor magnetic coil,
Replace a defective armature.
thus stopping the motor. These contacts, once opened, must
e. Reassembly.
be reset by pressing the RESET button on the controller
NOTE
panel. Insufficient voltage will also cause the line contactor to
drop out. The controllers for the exhaust blowers have an
Pack bearings with grease in accordance
added feature of speed control. Turning the dial switch
with LO 55-1925-204-12.
towards SLOW causes resistance to the armature circuit and
(1) Assemble by reversing the order of
reduces the motor speed.
disassembly.
b. Cleaning, Inspection, and Repair.
(2) Sand new brushes to contour of the
(1) Keep interior of controller clean by blowing out
commutator, then blow out carbon dust and sand. Adjust
with dry, low pressure compressed air.
brush tension (TM 55-506). To 1 1/2 to 2 1/2 oz Spring Scale
(2) Inspect contacts for pitting or burned points,
pull.
and contact spring tension. Replace defective contacts or
NOTE
springs.
After installing fan hub on shaft, rotate by
(3) Check arcing contacts to see that they
hand to determine that fan is squarely
mounted, and does not rub the housing.
5-157
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