Ransburg Aerobell 168 A12787 - Manual (Page 34)

Aerobell 168 - Installation
31 LN-9270-12.3
INSTALLATION (continued)
AIR HEATER
REQUIREMENTS
Turbine drive air expands as it moves through
the turbine wheel cavity and as it exits the tur-
bine from the exhaust port. This expansion will
cause cooling of the exhaust air and the surfac-
es 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 condensation on the interior and
exterior of the atomizer, machine, and its com-
ponents. It is even possible that the tempera-
ture of the supply air may be below the booth
dew point, even without additional expansion
cooling.
Condensation is especially probable in water-
borne 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 ex-
haust 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 paint-
ed surfaces as well as extending equipment life.
Thus, it is recommended that air heaters be in-
stalled into the atomizer air supply lines, i.e. Tur-
bine air. The air heaters must be of sufficient
capacity capable of raising the incoming air tem-
perature 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 condi-
tions, turbine airflow settings, and incoming air
temperature. The heater should be set as low
as possible, 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 As-
sembly" service manual for further infor-
mation.)
N O T E
Failure to use an air heater may cause dam-
age to equipment or ruin the finished compo-
nent being processed.