Variable Air Volume (Vav) Start-Up; Rpm Changes; Drive Sheave Alignment And Belt Tension - McQuay SWP 018 Installation And Maintenance Manual

Variable air volume (VAV) start-up

Enter the duct static pressure setpoint value and parameters
through the keypad:
Air/Water Flow
Duct static pressure
Ducts tsp SPT
When the appropriate number of VAV terminal boxes are
opened by setting down there respective thermostats, the
vanes should go to the maximum airflow. Upon closing
enough VAV boxes by setting their respective thermostats
up, the inlet vanes should go to the minimum airflow posi-
tion.

Rpm changes

All units are provided with fixed pitch sheaves selected for
the specified operating conditions. If a new fan rpm selection
is required a new sheave selection will need to be field
installed. Adjust belt tension as described below.

Drive sheave alignment and belt tension

Drive sheave alignment should be checked using the four-
point method shown in Figure 30. When measuring from the
straight edge to the belt, the dimensions A, B, C and D must
be equal for correct alignment.
Check drive for adequate run-in belt tension. Use the follow-
ing procedure to determine proper belt tension:
Step 1. Measure span length (t) as shown in Figure 31.
34
Step 2. From Figure 31, the deflection height (h) is always
1/64" per inch of span length (t). For example, a 32"
span length would require a deflection of 32/64" or
1/2".
Step 3. Determine the minimum and maximum recom-
mended pounds force using Table 14. Find the mini-
mum recommended deflection force for the belt
section and type based upon the small sheave diame-
ter. For intermediate sheave diameters and/or drive
ratio combinations, the minimum force may be inter-
polated.
Step 4. Using a spring scale, apply a perpendicular force to
any one of the belts at the midpoint of the span as
shown in Figure 31. Compare this value with the val-
ues found in Step 3.
a. If the value is below the minimum, the belts are
too loose and should be tightened.
b.If the value is higher, the belts are too tight and
tension should be decreased.
When new belts are installed, the initial tension will drop.
Check tightness of all setscrews on the fan hub, bearing
sleeves and retighten belts after 48 hours of operation.
Note: If after all tension adjustments, the belts slip or
squeal when starting, increase tension slightly and
replace the belts if they are worn or glazed.
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