26
McQuay IM 777-3
Service and Maintenance
MVP Variable Speed Sheaves
Mounting:
1
Verify both driving and driven sheaves are in alignment and
the shafts are parallel. The centerline of the driving sheave
must be in line with the centerline of the driven sheave. See
Figure 35.
2
Verify that all setscrews are torqued to the values shown in
Table 16 before starting drive. Check setscrew torque and
belt tension after 24 hours of service.
Adjusting:
1
Adjust motor base forward to release belt tension. Remove
the belts for easier adjustment.
2
Loosen, but do not remove both of the locking setscrews
A
in the outer locking ring by using a hex key or torque
wrench with a hex bit.
3
Adjust sheave to desired pitch diameter by turning the outer
locking ring. Use a spanner wrench or drift inserted into the
three holes that are located 120° apart on the ring.
4
Any pitch diameter can be obtained within the sheave
range. One complete turn of the outer locking ring changes
the pitch diameter 0.233".
5
Do not open sheaves more than the following:
•
Do not open
B
sheaves more than 4 3/4 turns for the
A
belts or 6 turns for the
B
belts.
•
Do not open
C
sheaves more than 9 1/2 turns.
•
Do not open
5V
sheaves more than 6 turns.
•
Do not open
8V
sheaves more than 8 turns.
6
Tighten BOTH locking screws
A
in the outer locking ring
before operating the drive. Use a torque wrench and tighten
to the value shown in Table 16
.
7
Replace belts and adjust the motor base to tension the belts
properly. See “Fan Drive Belt Adjustment” on page 27.
8
Do not loosen any screws other than the two locking screws
A
in the outer locking ring when adjusting the sheave pitch.
Do not operate the drive until the locking screws have been
set to the torque specifications.
Figure 35: Sheave Adjustment
Table 16: Screw Torque Values
Nominal screw size
(dia–-thds/in)
Socket head cap screws
Flat head socket
screws
Hollow head set screws only
Lengths equal or greater than dia.
For lengths (L)) less than dia.
Seating torque
Seating torque
Seating torque
Seating torque
Length (L)
Seating torque
(in–lbs)
(in–lbs)
(in–lbs)
(in–lbs)
(in–lbs)
(in–lbs)
(in–lbs)
1/4–20NC
150
12.5
100
87
7.3
3/16
50
5/16–11NC
305
25.4
200
165
13.8
1/4
90
3/8–16NC
545
45.4
350
290
24.2
1/4, 5/16
150, 250
1/2–13NC
1300
108.3
N/A
620
51.7
N/A
N/A
5/8–11NC
N/A
N/A
N/A
1225
102.1
N/A
N/A
Motor
Must be
parallel
Adjustable
Sheave
Center lines
must coincide
Bearing
Must be
parallel
