24 McQuay IM 672-3
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 39.
2 Verify that all setscrews are torqued to the values shown in
Table 14 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 14.
7
Replace belts and adjust the motor base to tension the belts
properly. See “Fan Drive Belt Adjustment” on page 25
.
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 39: Sheave adjustment
Table 14: 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
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