FAN ASSEMBLY
fan hubs are shipped from the Marley factory with center hub and zinc
shield assembled to the hub plate. if components of the hub assembly
are to be replaced in the field, refer to paragraphs 1,2 and 3 for reas-
sembly instructions.
1. position the protective zinc shield and the fan hub plate on the
center hub with the keyway and socket no. 1 lined up. one of the
bolt hole patterns will be aligned properly in only one position.
2. drive the dowel pins flush into the four smaller holes to accurately
position the hub plate.
3. Apply a thread sealant/adhesive to the cap screws, install and
tighten. see Table 1 for correct center hub torque.
4. Make certain that the identification number on each blade cor-
responds to the identification number in the fan assembly serial
number on the nameplate.
5. u-bolt threads and bearing surface of self-locking nuts are lubri-
cated at the factory prior to shipment.
Touch up all threads and
nut bearing surfaces with a generous coating of the lubricant
supplied with the fan.
6. install blade marked no. 1 in hub socket no. 1. install blade no. 2
in hub socket no. 2, and so on around the fan. install blades with
pitching boss and fan direction arrow on air discharge side of fan.
7.
Be certain that each blade is as far from the center of the fan
as the shoulder on the shank end of the blade will permit
after the locking nuts are tightened.
This is necessary in order
to maintain proper balance.
8. support blade tips in a horizontal plane when u-bolts are tight-
ened. Hold each blade at the proper pitch angle when tightening.
9. Total vertical tip track variation should not exceed tolerances speci-
fied in Table 1. Excessive tip track will cause dynamic imbalance.
SETTING FAN BLADE PITCH
1. The trial pitch angle is the calculated setting for design conditions
(water rate, heat load, air density and contract horsepower). set
the bevel protractor at the trail pitch angle supplied and pitch all
the blades to the same angle. All blades must be pitched to the
same angle when each blade is pointing in the same direction in
the fan cylinder.
2. progressively tighten the self-locking u-bolt nuts to specified
torque. stainless steel fasteners are prone to galling. Be alert to
a sudden rise in nut turning resistance before parts are properly
clamped. This signifies galling. remove nuts and u-bolt and
replace with new ones until satisfactory joint is made. see Table 1
for correct u-bolt torque.
3. recheck the pitch of each blade, as the pitch might change while
tightening the nuts.
Table 1
- specified Torque and Tip Track variation
FAN DIA.
55”-
72”
73”-
84”
85”-
96”
97”-
144”
145”-
168”
Center Hub
Torque
40-50
ft/lbs
40-50
ft/lbs
40-50
ft/lbs
40
ft/lbs
100
ft/lbs
U-Bolt Torque
40
ft/lbs
40
ft/lbs
55
ft/lbs
40
ft/lbs
70
ft/lbs
Vertical Tip
Track Variation
3
⁄
4
”
(±
3
⁄
8
”)
3
⁄
4
”
(±
3
⁄
8
”)
3
⁄
4
”
(±
3
⁄
8
”)
1”
(±
1
⁄
2
”)
1
1
⁄
2
”
(±
3
⁄
4
”)
CHECKING LOAD AT MOTOR
1. operate the fan until motor and Geareducer have reached opera-
tion temperature. Take operating voltage and amperage measure-
ments* for use in calculating motor hp by the following equation:
hp = x nameplate hp
2. The calculated horsepower should equal but not exceed the speci-
fied contract horsepower. Measurements used in above calcula-
tions must be made with hot water flowing through the tower.
repitch blades as required to obtain contract horsepower. reading
taken with no water or cold circulating water will result in an er-
roneous calculate horsepower. degrees change in pitch required
to change motor load one hp: see Table 2.
3. if blades are repitched, self-locking u-bolt nut must be retightened
to specified torque. see Table 1. Touch up u-bolt threads and nut
bearing surface with lubricant consisting of 50% petrolatum and
50% graphite by weight.
FAN REBALANCE
1. if the fan hub plate, center hub, or one or more blades are
replaced, the complete fan assembly may require rebalancing.
other components can be replaced without significantly affecting
balance.
2. if rebalance is required, trail and error attachment of balance
weights at various locations on the hub may produce a satisfac-
tory dynamic balance with the fan operating on the tower. if this
is not satisfactory, the fan assembly can be rebalanced as follows:
A. fan assembly should be mounted on a suitable mandrel match-
ing the hub bore, and the mandrel placed on knife wheels or
level, parallel bars with the fan blades in a vertical plane. This
must be done in a draft free area.
B. Apply balance washers to hub, on same side as blade sockets,
until all tendency for fan to rotate is overcome. This is ac-
complished by allowing the fan assembly to rotate freely on
the knives until it comes to rest with the heaviest portion at
the bottom. Manually rotate the fan 90º so that the heaviest
portion is at either side of the fan centerline. Add weights to
the light side of the hub plate. Holes are provided in the plate
between each blade socket for attachment of weights.
C. if one or more blades are replaced, relocating some of the
blades in other sockets might simplify balance and result in
fewer balance weights being required.
FAN MAINTENANCE
A monthly inspection of the fan should be made to assure continued
trouble-free operation. remove carefully and completely any accumula-
tion of dirt or scale deposits, if balance is affected.
actual volts x actual amps
nameplate volts x nameplate amps
Table 2
- pitch vs. hp
No. of Blades:
6
8
9
10
12
Fan Dia.
Pitch Change Per hp
60”
3
2.5
72”
2.5
2
84”
1
.8
.6
96”
.8
.7
.6
.5
108”
1
120”
.8
132”
.6
144”
.4
168”
A one degree change in pitch will vary the
power required by approximately 3 hp.
CAUTION:
When checking and/or changing blade pitch or when cycling
fan in normal operation, do not exceed 30 sec./hr. total motor starting
time as motor may become overheated.
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