Ransburg Aerobell 168 Atex Approved 13350 - Manual (Page 33)

AIR HEATER
REQUIREMENTS
Turbine drive air expands as it moves through the
turbine wheel cavity and as it exits the turbine from
the exhaust port. This expansion will cause cool-
ing of the exhaust air and the surfaces it contacts.
This same expansion cooling can occur across
the shaping air exit ports. This cooling effect can
cause surface temperatures to fall below the dew
point of the booth, which will result in condensa-
tion on the interior and exterior of the atomizer,
machine, and its components. It is even possible
that the temperature of the supply air may be be-
low the booth dew point, even without additional
expansion cooling.
Condensation is especially probable in waterborne
applications when booth temperature and relative
humidity levels are typically maintained very high.
This condensation will allow sufficient conductivity
of the surfaces such that they act as an erratic
ground source potential. This can cause damage
to the equipment.
It is therefore, a requirement that turbine exhaust
air temperature be maintained above the booth
dew point to prevent condensation from forming
on atomizer surfaces. Doing so will eliminate
moisture as a potential defect in painted surfaces
as well as extending equipment life. Thus, it is
recommended that air heaters be installed into the
atomizer air supply lines, i.e. Turbine air. The air
heaters must be of sufficient capacity capable of
raising the incoming air temperature at least 40°F
(4.4°C) at a flow rate of 60 SCFM per applicator.
The actual air heater process setting depends on
applicator fluid flow rate load, booth conditions,
turbine airflow settings, and incoming air tempera-
ture. The heater should be set as low as possi-
ble, sufficient to maintain the applicator surface
temperatures above the dew point in the booth.
Example: With the incoming air temperature at
72°F (22.2°C), an Aerobell 168 with 65mm bell cup
rotating unloaded at 60 krpm has a turbine outlet
temperature drop of approximately 28°F (-2.2°C)
(@ 40 krpm unloaded, DT ~ 14°F (-.10°C).
Referring to the ASHRAE Psychometric chart,
the saturation temperature range (dew point) of
a spray booth maintained at 70-75°F / 65-70%
RH is 62-68°F (21.1-23.9°C / 65-70° RH is 16.7-
20°C). Thus it is almost certain that the surface
temperatures of the applicator will fall below the
dew point of the booth, and an air heater will be
needed in this case.
To prevent condensation, Ransburg air heater
assembly should be assembled after the air filters.
(Reference the current “Air Heater Assembly”
service manual for further information.)
† Failure to use an air heater may cause
damage to equipment or ruin the finished
component being processed.
NOTE
Aerobell 168 - Installation
Ransburg
LN-9247-13 30