SB--7--626 Page 14
SECTION 5
MAINTENANCE
GEAR INSPECTION
Inspection of the timing gears may be accomplished
simply by removing the gear case.
Refer to
FIGURE 10. Remove the bolts from the gear case and
detach it from the head plate. Timing gears and gear
end bearings are now exposed. On completion of
maintenance work, be certain that the gear case is
restored to its original position. Use a paste--type
gasket compound on the mating surfaces. Always
relubricate before starting.
IMPELLER INSPECTION
Series 4500 impellers can be inspected through the
inlet or outlet ports. This will reveal such conditions as
out of time, excessive or insufficient clearances,
abrasion of parts from passing foreign material, etc.
REPAIR
Assembly
When rotation of the impellers is
required in the assembly process,
insure that all personnel are clear of
lobes and gears to guard against
serious injury.
Timing
The impellers of the unit are separated by pre--deter-
mined exact clearances built into the machine. The
timing of a unit is the setting of one impeller with respect
to the other so they do not touch or knock during normal
operation. The impellers are held ‘in time’ by timing
gears which are secured to the shaft by grip rings inside
the gear hubs. See FIGURE 10. Retiming is neces-
sary to restore proper impeller lobe to lobe clearances
after a unit has been jammed and the removal of the
strain or foreign material does not stop the knocking or
pounding during operation.
Determining Proper Impeller Clearances
-- Refer to
FIGURE 12, page 15. Impellers are shown viewed
FIGURE 10 -- LOCATION OF TIMING GEAR BOLTS
Impeller Clearances
Imp. Tip
Discharge
Gear
Each
Timing
Blower
End
Minimum
Minimum
Size
Min.--Max
Inlet/Disch Open/Closed
Inches
Inches
Inches
6
.006--.008
.008/.006
.011/.005
7
.007--.008
.010/.006
.013/.006
8
.007--.008
.011/.006
.014/.006
FIGURE 11 -- GEAR END CLEARANCE
from the drive end of the blower. Always face the drive
shaft end when determining clearances.
Clearances between impellers are measured at points
o--o and c--c when the impellers are positioned at 45
_
angles as shown. This is done by measuring with a
feeler gauge between o--o, then rotating the impellers
a quarter turn and gauging between c--c. Adding the
measurements obtained will give the total clearance.
Units are timed for rotation in one direction only, and are
marked with a rotational arrow above the drive shaft.
In these units, o--o should have 2/3rds of the total
