McQuay IM 777-4
21
Operation Guidelines
Figure 34: Torque Requirements at 100% WOV for
SWSI Plenum Fans with NESTED Inlet Vane
Fan Vibration Levels
Each unit as shipped is trim balanced to operate smoothly. To
provide satisfactory operation after shipping and installation,
use the accepted industry guidelines for field balancing fans.
See
Table 12
.
Note:
Excessive vibration from any cause contributes to premature fan and
motor bearing failure. Monitor overall vibration levels every six
months of operation. An increase in levels is an indication of potential
trouble.
Vibration Causes
1
Wheel imbalance.
a
Dirt or debris on wheel blades.
b
Loose set screws in wheel hub or bearing-to-shaft.
c
Wheel distorted from overspeed.
2
Bent shaft.
3
Drive faulty.
a
Variable pitch sheaves—Axial and radial runout of
flanges; uneven groove spacing; out of balance. Also
similar faults in driven sheave.
b
Bad V-belts; lumpy, or mismatched; belt tension too
tight or too loose.
4
Bad bearings, loose bearing hold-down bolts
5
Motor imbalance
6
Fan section not supported evenly on foundation
60
0
700
600
500
400
100
900
300
200
T
o
rq
ue
(lb.
/in
.)
Fan Speed (rpm)
800
900
1000
1500
2000
400
500
600
700
300
200
3000
800
1000
2000
3000
4000
5000
54
2
49
0
44
5
40
2
36
5
33
0
30
0
27
0
24
5
To
rque
(i
n-lb
)
Table 12: Vibration Levels
Fan speed (rpm)
Vibration
800 or less
5 mils maximum displacement
801 or greater
0.20 in/sec. maximum velocity
