Quantcast Preventive maintenance and inspections of controls

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TM 5-684/NAVFAC MO-200/AFJMAN 32-1082
of these items may be necessary at times, particu-
ties. Communication, not electric, lines are used,
such as telephone pairs; coaxial cable; radio, micro-
larly after a faulty operation. These tests will have
to be conducted when the machine or equipment
wave or power line carrier signals; and fiber optics,
sometimes as a part of a local area network (LAN).
being controlled can be removed from service.
Monthly inspection should be adequate. Annual
11-11. Preventive maintenance and inspec-
testing of the insulation will detect defective wiring
tions of controls.
before the insulation breaks down.
e. Thermally-operated devices. Thermostats, ther-
A well planned schedule of maintenance and inspec-
tions will pay large dividends in fewer interruptions
mal overload units, and temperature devices oper-
ate on the heating effect of electric current. Inspect
and longer equipment life. More frequent inspec-
tions may be necessary for apparatus that receives
units about once a month for dirt, excess heating,
hard service or is located in dirty, dusty, or damp
freedom of moving parts, corrosion, wear, and con-
dition of the heating elements. As elements which
locations. Only specially trained personnel should
attempt to service and maintain control equipment.
normally operate only when an overload or trouble
takes place in the equipment being controlled, they
a. Wiring diagrams and tools. Complete wiring
must be in good operating condition at all times.
diagrams are necessary to adequately service con-
f. Motor-operated devices. Motor-operated timers,
trols. Simplified schematic diagrams, showing all
current and potential coils and contacts, are also
thrusters, valves, and brakes are included in this
very desirable for maintenance work. These dia-
category. Periodic inspections should be made for
grams expedite locating and correcting trouble.
evidence of dirt, heating, corrosion, wear, noisy op-
Keep wiring diagrams up-to-date and indicate any
eration, and vibration. Such inspections should en-
changes that have been made in the system subse-
sure correct voltage, freedom of moving parts,
quent to its installation. Proper tools and test equip-
proper lubrication, adequate gaskets, and satisfac-
ment must be available for servicing special equip-
tory condition of gearing. Cleanliness is particularly
important in mechanical linkages. Trial operation of
ment. An adequately equipped laboratory or shop,
with portable test apparatus, is necessary for major
moving parts may be necessary to detect trouble. As
this may necessitate temporary removal from ser-
vice, actual operation tests if necessary should be
b. Connections. Periodically, and after any wiring
coordinated with scheduled equipment outages.
changes, connections and circuits should be com-
Monthly inspections should be satisfactory, but for
pletely checked for proper operation. Maintaining
extremely dirty locations more frequent inspections
an installation free and clear of dirt, dust, grease,
are desirable.
and other contaminants will help ensure proper op-
eration. Loose connections may occur at times, and
g. Mechanically-operated devices. Mechanically-
should be corrected as soon as possible to avoid
operated devices include master, selector, knife,
serious damage to other equipment.
limit, speed, flow, float, and pressure switches;
drum controllers; push buttons; and manual start-
c. Contacts. Control equipment power contact
ers. Inspections of these parts for dirt, heating, cor-
surfaces are usually of silver, copper, weld-resistant
rosion, restriction of moving parts, contact and
alloys, or other electrically sensitive materials. Sil-
alignment wear, general condition, sealing, sludge,
ver tips should never be filed or cleaned with abra-
and lubrication are required. Each individual case
sive materials. Crocus cloth is best for cleaning sil-
must be studied on its own merits to determine if
ver contacts. Copper and weld-resistant tips may be
the seriousness of the condition justifies an inter-
filed; however, care must be taken to ensure that
ruption of operation for maintenance. In some
only enough oxide is removed to attain good contact.
cases, temporarily disconnecting the control circuit
The so-called electrically sensitive materials, in-
long enough for repairs may be possible. Inspections
cluding gold, platinum, and rhodium, are used for
every 6 months should be satisfactory, but more
special applications where good electrical connec-
frequent inspections may be necessary where con-
tion with low contact pressure is desired. The
tamination is severe.
manufacturer's instructions should be followed for
treating these contacts. Inspections and perhaps
h. Static accessories. Static accessories include
cleaning as often as monthly may be required for
resistors, rectifiers, capacitors, arc chutes, shunts,
contacts which switch heavy currents frequently.
interlocks, transformers, fuses, wiring, and bus
d. Magnet-operated devices. Magnet operated
cables. Inspect for dirt, heating, corrosion, proper
components such as relays, coils, solenoids, and
clearances, and loose connections. The urgency of
brakes should be inspected periodically for dirt,
any required corrective measures should be estab-
heating, freedom of moving parts, corrosion, wear,
lished in accordance with the seriousness of the
noise, and general overall condition. Tests on some
condition. In general, inspections should be made


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