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8
Figure 6
Adjusting Fan Blade Pitch
The trial pitch is the calculated setting for design conditions
(water rate , heat load, air density, and brake horsepower). The trial
pitch is provided (see page 2).
1–Select a position on the fan circumference and rotate each blade
to this common location when setting or checking blade pitch. Sup-
port the blade tip to maintain a common rotation plane while setting
the fan pitch. The pitch is set within 2″ (51mm) of the blade tip by
placing a bevel protractor on top of a parallel sided straight edge
that extends across blade width as shown in Figure 6.
2–Pull the blade outward so the safety shoulder is in contact
with the blade clamp, then set the pitch. See Figure 5. Blades
should be within ± 1/4° of the desired pitch angle. After the de-
sired setting is obtained, progressively tighten the 3/4″ hex nuts to
120 ft·lb
ƒ
(163 N·m) torque. Recheck the pitch angle. If required,
loosen the hex nuts and reset the pitch as necessary until the proper
pitch angle is obtained with the 3/4″ hex nuts at 120 ft·lb
ƒ
(163 N·m)
torque.
3–Repeat step 2 for all blades.
4–Check the vertical blade-tip track variation. The allowable verti-
cal variation from a reference plane is ±1″ (25mm). If a blade’s tip
track is out of tolerance, loosen the 3/4″ hardware and change the
blade tip support location higher or lower as required to adjust the
tip track. Recheck blade pitch angle.
BEVEL
PROTRACTOR
STRAIGHT
EDGE
BLADE
2"
TIP
PITCH ANGLE