18
McQuay IM 777-4
Operation Guidelines
Note:
Variable pitch fan drives usually are provided for
operation in the mid-speed adjustment range. However,
the drives usually ship with the adjustment opened up for
minimum fan speed. Adjust the drives for the proper
airflow. See
Fan Drive‚ page 23
.
After the First 48 Hours of Operation:
1
Disconnect and lock electrical power source.
2
Check tightness of all bearing, wheel, and sheave setscrews
(or capscrews). See
Table 7, page 19
.
3
Recheck belt tension and adjust if necessary. Belts that are
tensioned sufficiently to slip one to two seconds at startup
perform satisfactorily, extending life and reducing vibration. If
retensioning is necessary, be certain to retain sheave
alignment.
Fan Wheel Alignment
Figure 26: Wheel-to-Inlet Tunnel Relationship—Airfoil Type
Fan Wheels (Housed)
Note: 1. To obtain rated air performance, dimensional relationship must be
held.
2. To obtain dimension A, loosen setscrews in wheel hub(s), shifting
wheel(s) axially as needed, and retightening setscrews.
3. To obtain dimension B, loosen screw and washer fasteners around
periphery of funnel(s), shifting funnel radially as required, and re-
torquing fasteners.
Figure 27: Wheel-to-Inlet Funnel Relationship—Forward
Curved Type Fan Wheels
Note: 1. To obtain rated air performance, dimensional relationship must be
held.
2. Adjust dimension C by loosening wheel hub setscrews, shifting
wheel(s) axially as needed, and retightening setscrews
Figure 28: Wheel-to-Inlet Funnel Relationship—Plenum
Fans
Table 3: Wheel-to-Inlet Funnel Relationship—Airfoil Type
Airfoil
Unit sizes 003 to 035
Unit sizes 040 to 090
Dia.
A
(in)
A
(mm)
B
(in)
B
(mm)
Dia.
A
(in)
A
(mm)
A
(in)
B
(mm)
13.22 4.56
116
0.21
5.33 20.00 7.19
183
0.31
7.87
14.56 5.06
129
0.21
5.33 22.25 7.69
195
0.33
8.38
16.18 5.62
143
0.21
5.33 24.50 8.56
217
0.31
7.87
17.69 6.90
175
0.22
5.59 27.00 9.47
241
0.63 16.00
21.56 7.59
193
0.24
6.10 30.00 10.47
266
0.39
9.91
24.00 8.45
215
0.23
5.84 33.00 11.75
298
0.38
9.65
36.50 12.78
325
0.38
9.65
40.25 14.31
363
0.50 12.70
A
A
B
E q u a l s p a c i n g
a l l a r o u n d
I n l e t
F u n n e l
W h e e l
C
C
I n l e t
F u n n e l
Table 4: Wheel-to-Inlet Funnel Relationship—Forward
Curved Type Fan Wheels
Forward curved
Unit sizes 003 to 035
Unit sizes 040 to 090
Diameter (in)
C
(in)
C
(mm)
Diameter (in)
C
(in)
C
(mm)
9 x 4
0.25
6.35
20 (Class 1 & 2)
0.24
6.10
9 x 7
0.13
3.30 22.38 (Class 1 & 2) 0.41
10.41
9 x 9
0.25
6.35
25 (Class 1 & 2)
0.47
11.94
10
0.22
5.59 27.62 (Class 1 & 2) 0.47
11.94
12
0.35
8.89
30 (Class 1 & 2)
0.47
11.94
15
0.44
11.18
33 (Class 1 & 2)
0.50
12.70
18
0.25
6.35
36 (Class 1 & 2)
0.75
19.05
20 (Class 1 & 2)
0.73
8.54
22 1/2 (Class 1 & 2) 0.59
14.99
24 1/2 (Class 1 & 2) 0.56
14.22
Table 5: Wheel-to-Inlet Funnel Relationship—Plenum Fans
Wheel—funnel overlap
Size
Overlap
13.5
.25
15
.31
16.5
.38
18.25
.44
20
.50
22.25
.56
24.5
.62
27
.69
30
.75
33
.81
36.5
.88
40.25
1.00
44.5
1.12
49
1.25
54.25
1.38
60
1.50
Overlap
