Twin City Upblast Propeller Roof Fans - IM-4870 - Manual (Page 7)

Twin City IM-4870 7
Figure 1. Eliminate Slack Figure 2. Belt Deflection
Figure 3. Alignment Figure 4. Belts
Figure 5. 2-Groove Sheaves
Deflection
Deflection =
Belt Span
64
Belt Span
Slack belts wear excessively, cause slippage
and deliver less power. For longest belt life,
always provide proper tension
Mount belts straight. Shafts must be parallel
and sheaves in alignment to prevent unnec-
essary belt wear.
Two-groove variable pitch
sheaves must be opened the
same number of turns on
both sides; otherwise, slip-
page occurs, wearing belts
rapidly.
Do not force belt. Forcing the belt will
break the cords and cause belt failure.
V-Belts
V-belts on these belt driven fans are oil, heat, and static
resistant type and oversized for continuous duty. With
proper installation and maintenance, years of operating
efficiency can be added to the lifespan of the V-belt
drive.
The condition of V-belts and the amount of belt tension
should be checked prior to start-up (see Figure 1). When
it becomes necessary to adjust belt tension, do not over-
tension as bearing damage will occur. Recommended
belt tension should permit 1 ⁄
64
" deflection per inch of
span of the belt at the center of the belt span. To
find this point, measure halfway between the pulley
centerlines as shown in Figure 2. Extreme care must be
exercised when adjusting V-belts as not to misalign the
pulleys. Any misalignment will cause a sharp reduction
in belt life and will also produce squeaky, annoying
noises (see Figure 3). On units equipped with 2-groove
pulleys, adjustments must be made so that there is
equal tension on all belts (see Figure 5).
1. Where tensioning rods are not available, adjustment is
more easily obtained by loosening and adjusting one
side of the motor bracket at a time.
2. Always loosen tension adjustment enough to place
belts on sheaves without running belts over the
edge of either sheave. A new belt may be seriously
damaged internally by careless handling (see Figure
4).
WARNING: When removing or installing belts, never
force belts over pulleys without loosening motor first to
relieve belt tension.
3. Fan speed can be increased by closing the adjustable
motor pulley, or decreased by opening it. Two
and three groove adjustable pitch pulleys must be
adjusted an equal number of turns. (See Figure 5).
Always check load on motor when increasing fan
speed.
CORRECT
INCORRECT