113
EXAMPLE:
Given:
Belt Span
16 in.
Belt Cross-Section A, Super Belt
Small Sheave PD
5 in.
Small Sheave RPM:
1530
Belt Condition:
New
Deflection =
Belt Span/64
Solution:
a. From Table 31, find that deflection force for a new
type A, super belt with 5-in. small sheave PD is 8 lb.
a. Deflection =
16
/
64
or
=
1
/
4
in.
TENSION MEASUREMENT PROCEDURE
1. Measure the belt span (see Fig. 56).
2. Position bottom of the large o-ring on the span scale at the
measured belt span.
3. Set the small o-ring on the deflection force scale to zero.
4. Place the tension checker squarely on one belt at the center of
the belt span. Apply a force on the plunger and perpendicular
to the belt span until the bottom of the large o-ring is even
with the top of the adjacent (next) belt or with the bottom of a
straight edge laid across the outside diameters of the v-belt
sheaves.
5. Remove the tension checker and read the force applied from
the bottom of the small o-ring on the deflection force scale.
6. Compare the force you have applied with the values given in
Table 31. The force should be between the “Used Belt” and
“New Belt” values shown. The maximum value is shown for
“New Belt” and new belts should be tensioned at this value to
allow for expected tension loss. “New Belt” tensions should
be used at initial installation and after job start or 1 to 3 min
-
utes of operation. Used belts should be maintained at the
value as indicated in the chart. “Used Belt” tensions should
be used for the 8-hour and subsequent checks. If the belt span
was measured in centimeters, then use the kilograms of force
values for comparison.
NOTE: The ratio of deflection to belt span is 1:64 in either units of
measurements.
7. Whenever possible, jog start for a few revolutions or prefera
-
bly run drive for approximately 1 to 3 minutes and then re-
tension in accordance with Steps 1-6. Running the drive for a
few revolutions or minutes will help seat the belt(s) in the
groove(s). This relatively early re-tensioning may reduce or
minimize the amount of re-tensioning required in the first 24
hours of drive service.
Direct Drive Fan Alignment
Direct drive fans are aligned in the factory. However, Carrier rec
-
ommends checking alignment before starting the unit.
1. Ensure the radial distance between fan wheel and inlet cone
appears visually equal in all directions.
2. Ensure that the fan wheel to inlet cone overlap is within the
correct range. See the section Direct Drive Plenum Fans on
3. Motor and fan are balanced as an assembly. If either changes,
rebalancing is required.
Fan Airflow Measurement Piezometer Ring
The Piezo system is based on the principle of a flow nozzle. The
inlet funnel is used as the flow nozzle, and the flow can be calcu
-
lated by measuring the static pressure drop through the inlet fun
-
nel. The pressure drop is measured from the tap located on the
face of the inlet funnel to the piezometer in the throat. The front
pressure tap, located on the face or outer portion of the inlet ring,
is connected to the high-pressure side of the transducer and the
piezometer ring is connected to the low-pressure side.
CALCULATION WHEN USING THE PIEZOMETER
For standard air (
= 0.075 lb/ft
3
):
• K (K Factor) value: Obtain from Table 6 on page 25.
•
P (Delta Pressure): The differential in static pressure
from the piezometer and the front pressure tap (in. wg).
If the K factor is not shown in Table 6, perform a pitot tube tra
-
verse either before or after the fan where the airflow is most uni
-
form (preferably in the straightest portion of the duct) and at the
same time note the Delta Pressure read by the control system. Use
the following formula to calculate the K Factor:
Outdoor Hoods and Louvers
Three options are available: fixed rear intake hoods, intake lou
-
vers, and collapsible exhaust box hoods. All hoods and louvers
have an intake screen to prevent unwanted entry of birds and
debris. There is an additional screen available to prevent snow
from entering the intake louver. It is attached to the outside of
the louver. It can be factory or field installed. The intake hoods
have easily serviceable demisters via small hinged doors. In
-
take louvers are a wind-driven rain design that will allow no
more than 0.01 oz per sq ft of free area water penetration at
1250 fpm. This is the maximum velocity required by AMCA
(Air Movement and Control Association) 511. Higher veloci
-
ties are possible without significant water intrusion.
Most fixed rear hoods (Fig. 57) and intake louvers (Fig. 58)
ship installed and should require no further assembly. If a rear
hood is shipped attached to the skid, do not install the rear
hood in the air-handling until the rest of the unit and splits have
been completely assembled. Otherwise, the combination of just
the hood and mixing box may become a tipping hazard.
Collapsible exhaust box hoods ship covering the exhaust outlet
of the unit and/or inside the unit and require some basic assem
-
bly. Fasteners, washers and gasket material for installation of
the hood come taped inside the exhaust section. Figure 59
shows an exploded view of the assembly in its shipping posi
-
tion, and how the various parts assemble to form the hood.
CAUTION
Do not exceed maximum fan speed rpm with variable
frequency drive. Equipment damage may result.
CFM K
P
=
K
CFM
P
=
UNIT
GASKET
AIRFLO
W
INTAKE HOOD
SCREW TYPICAL
ENTIRE PERIPHERY
OPEN DOOR TO
REMOVE DEMISTERS
Fig. 57 —
Rear Intake Hood (Size 30 Shown)
A39-
2347ef
