JOHNSON CONTROLS
6
START-UP (CONTINUED) AND MAINTENANCE
Dampers and Variable Inlet Vanes (VIVs)
- They should
operate freely with blades closed tightly. All dampers and VIVs
should be partially closed during starting periods to reduce power
requirements. This is particularly important for a fan designed for
high temperature operation being “run in” at room temperature
or at appreciably less than design temperature. When air is up
to temperature, the damper or VIV may be opened. Complete
closing of dampers could cause the fan to run rough.
Fan may now be brought up to speed. Watch for anything
unusual such as vibration, overheating of bearings and motors,
etc. Multi-speed motors should be started at lowest speed and
run at high speed only after satisfactory low speed operation.
Check fan speed on belt drive units and adjust motor sheave
to give the desired RPM. Balance system by adjusting damper
or VIVs.
At first indication of trouble or vibration, shut down and check
for cause of difficulty.
MAINTENANCE
Always disconnect or shut off fan before attempting any
maintenance.
A definite time schedule for inspecting all rotating parts should
be established. The frequency of inspection depends on the
severity of operation and the location of the equipment.
Fan bearing alignment should be checked at regular intervals.
Misalignment can cause overheating, wear to bearing dust seals,
bearing failure and/or unbalance.
Fan bearings should be lubricated at regular intervals. Periodic
inspection will be necessary. If grease is found to be breaking
down, replenish grease by pumping new grease into bearing
until all the old grease has been evacuated. See section on
bearing lubrication.
Bearings on high speed fans tend to run hot: 75°F to 100°F
above ambient. Do not replace a bearing because it feels to hot
to touch. Place a contact thermometer against the bearing pillow
block and check the temperature. Before you investigate high
temperature, realize that ball or roller bearing pillow blocks
can have a total temperature of 225°F (107°C). High temperature
bearings are rated at 425°F (218°C).
Foundation bolts and all set screws should be inspected for
tightness.
Fans should be inspected for wear and dirt periodically. Any
dirt accumulated in housing should be removed. The impeller
may have to be cleaned. A wash down with steam or water jet is
usually sufficient, covering bearings so water will not enter the
pillow blocks. Impellers having worn blades should be replaced.
Impellers require careful rebalancing before being returned to
service. Replacement impellers should have the balance checked
upon start-up and corrected as required to operate properly in its
specific application.
Repairing of exterior and interior parts of fans and ducts will
extend the service life of the installation. Select a paint which will
withstand the operating temperatures. For normal temperatures a
good machinery paint may be used. Corrosive fumes require all
internal parts to be wire brushed, scraped clean and repainted
with an acid resisting paint. Competent advice should be sought
when corrosive fumes are present.
Blow out open type motor windings with low pressure air to
remove dust or dirt. Air pressure above 50 psi should not
be used, as high pressure may damage insulation and blow
dirt under loosened tape. Dust can cause excessive insulation
temperatures. Do not exceed OSHA air pressure requirements.
Excessive vibration will shorten the life of any mechanical
device. Correct any imbalance situation before returning fan to
service.
Lubrication of Hinge Bearings on Power Roof Ventilators
Stack cap damper hinge bearings are oil impregnated and
may never need lubrication. A drop or two of 10W30 motor oil
every 6 to 12 months will not hurt the bearings. Check damper
operation to detect binding or checking. Adjust hinge pin bearing
bracket to resume free damper operation.
Shaft Cooling Wheel Option (High Temperature Units)
For some high temperature applications, a shaft cooling wheel
is factory installed. Fan maintenance may require the cooling
wheel to be removed. Be certain to reassemble the cooling wheel
with the fins towards the bearings. Reversing the assembly will
heat rather than cool the shaft. Mark one side of the split in the
cooling wheel and match mark the shaft so that the cooling
wheel can be repositioned on the shaft where it was originally
installed. Changing the angular position of the cooling wheel on
the shaft will affect the dynamic balance of the fan.
Lubrication Lines - Plastic or Copper
Lubrication lines installed at the factory are not filled with
grease at the factory. Caution must be used when first greasing
the bearings to purge air from the lines without blowing bearing
seals or over greasing a bearing.
