Specifications

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Installation
Air Balancing
Unit sizes 072 thru 120 are supplied with a variable pitch
motorsheavetoaidinairowadjustment.Theyaresetatthe
factory as shown in Table 1.
Whenthenaladjustmentsarecomplete,thecurrentdrawof
the motors should be checked and compared to the full load
current rating of the motors. The amperage must not exceed
the service factor stamped on the motor nameplate.
Upon completion of the air balance, it is a common industry
recommendation that the variable pitched motor sheave be
replacedwithaproperlysizedxedsheave.Amatchingxed
sheave will provide longer belt and bearing life and vibration
free operation. Initially, it is best to have a variable pitched
motor sheave for the purpose of air balancing, but once the
balancehasbeenachieved,xedsheavesmaintainbalancing
and alignment more effectively.
Sheave Adjustment (See Figure 5)
1. All sheaves should be mounted on the motor or driving
shaft with the setscrew “A” toward the motor
2. Be sure both driving and driven sheaves are in alignment
and that shafts are parallel.
3. Fit internal key “D” between sheave and shaft, and lock
setscrew “A” securely in place.
Adjusting
1. Loosen setscrews “B” and “C” in moving parts of sheave
and pull out external key “E”. (This key projects a small
amount to provide a grip for removing.)
Figure 5: Sheave Adjustment Detail
B
E
D
C
A
Key E projects to
provide a grip for
removing
Single Groove
Table 1: 60 Hz Unit - Sheave Adjustment
Unit Size Motor HP RPM Range
Factory Motor Sheave
Settings (RPM) Position
072
1½ 756-902 785 4-Turns Open
3 907-1081 904 5-Turns Open
096
1½ 698-832 858 1½-Turns Open
3 907-1081 904 5-Turns Open
120
3 756-901 814 3-Turns Open
5 907-1081 904 5-Turns Open
2. Adjust sheave pitch diameter for desired speed by opening
moving parts by half or full turns from closed position. Do
notopenmorethanvefullturns.
3. Replace external key “E” and securely tighten setscrews
“B”overkeyandsetscrews“C”intokeywayinxedhalf
of the sheave.
4. Put on belts and adjust belt tension to 4 lbs. – 0.7 lbs.
(18N–3N)fora1⁄2"to3⁄4"(13mmto19mm)belt
deectionheight.
5. Todeterminethedeectiondistancefromnormalposition,
use a straightedge or stretch a cord from sheave to sheave
to use as a reference line. On multiple-belt drives an
adjacentundeectedbeltcanbeusedasareference.
6. Future adjustments should be made by loosening the
belt tension and increasing or decreasing the pitch
diameter of the sheave by half or full turns as required.
Readjust belt tension before starting drive.
7. Be sure that all keys are in place and that all setscrews
are tight before starting drive. Setscrews and belt
tension must be checked after 24 hours of operation.
8. When new V-belts are installed on a drive, the initial
tensionwilldroprapidlyduringtherstfewhours.Check
tensionfrequentlyduringtherst24hoursofoperation.
Subsequent retensioning should fall between the minimum
and maximum force.
Figure 6: Drive Belt Adjustmment
Deflection
Force
h
D
d
Span Length (t)
C
t
64
h =
C
2
-
D-d
2
t =
)
(
Where: t = Span length, inches (mm)
C = Center distance, inches (mm)
d = Smaller sheave diameter, inches (mm)
h = Deflection height, inches (mm)
Note: The ratio of deflection to belt span is 1:64.