BAC FXVT 288 Series Operating And Maintenance Instructions Manual page 26

Excessive noise or vibration at initial operation is an indication of one or more of the following:
1. Misalignment
2. Imbalance of the fan or other rotating parts
3. Improperly adjusted fan blades
4. Operation at mechanical equipment resonant speed
If noise or vibration persists shut the unit down and correct the cause before further operation.
On installations with two speed motors, when slowing from high speed, allow a minimum of 15 seconds time delay
for the fan to slow down before energising the low-speed winding. When reversing the direction of rotation, allow
the fan to come to a complete stop before restarting the motor.
Variable Frequency Drive Operation
On installation with variable speed motors, do not operate standard gear drives below 450 RPM motor speed
(gear input speed). Modifications to the lubrication system or special gear oil pumps are required for operation at
input speeds lower than 450 RPM.
Continued operation at a resonant speed condition will result in torsional vibrations within the gear, which can be
damaging to all components of the system. The most common indicator of torsional vibrations is an unusual
rumbling or grinding noise from the gear drive at a sharply defined speed. The noise will disappear when the speed
is increased or decreased. This noise is not indicative of a defect but results when the vibratory torque exceeds the
drive torque causing the gear teeth to clash together very rapidly. On variable speed applications, operation close
to a resonant speed should be avoided and transition through a resonant speed range should be swift.
At start-up, the variable frequency drive should be increased through the range from 0 RPM to maximum motor
speed. As the speed is increased, the gear drive system should be observed to note the onset of any unusual
rumbling or grinding at specific speeds. These resonant speeds (+/- 10%) should be "locked out" by the variable
speed drive. Please refer to the variable frequency drive manufacturer's recommended start-up procedure for
further information.
ROTATION OF FAN(S) AND PUMP(S)
Fans must rotate without obstruction and both fans and pumps must rotate in the correct direction, which is
indicated by arrows on the equipment. Check proper functioning as follows:
1. Stop fan(s) and pump(s).
2. Turn the fan by hand to ensure rotation without obstruction. Remove obstruction, if present.
3. Start the pump(s) and check for the proper rotation as indicated by the arrow on the pump cover. If rotation is
wrong, stop pump and correct electrical wiring.
4. Start the fan(s) and check for proper rotation as indicated by the arrow on the fan housing. If rotation is wrong
stop fan(s) and contact BAC.
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W W W . B A L T I M O R E A I R C O I L . E U
CAUTION