Specifications

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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 7: Drive Belt Adjustment
Ductwork and Attenuation
Discharge ductwork is normally used with these condi-
tioners. Return air ductwork may also be required but will
requireeldinstallationofareturnairductcollar.
All ductwork should conform to industry standards of
good practice as described in ASHRAE Systems Guide.
Thedischargeductsystemwillnormallyconsistofaex-
ibleconnector,atransitionpiecetothenalductsize,ashort
run of duct, an elbow without vanes and a trunk duct tee’d
into branch ducts with discharge diffusers. Transformation
duct must not have angles totalling more than 30 degrees or
severe loss of air performance can result.
All units have multiple fan outlets. The preferred method
for minimum static pressure loss would be individual ducts
at each outlet connected to a larger main duct downstream
(Figure 8).
B
E
D
C
A
Key E projects to
provide a grip for
removing
Single Groove
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.
Air Balancing
Unit sizes 072 thru 290 are supplied with a variable pitch
motorsheavetoaidinairowadjustment.Theyaretypically
setatthelowendoftherpmrangeforeldadjustmenttothe
requiredairow.
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 indus-
try 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 6)
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 6: Sheave Adjustment Detail
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.