Figure 1-17.--Pressure-feed cup.
Hose lines: The hose lines used for spray guns
are of two types: one handles air; the other
handles liquids. The air hose is usually made of
braid-covered tubing of either one-braid or
two-braid construction. The fluid hose is made
of a special solvent-resistant material that can
withstand the attacks of paint, lacquer, and
similar liquids.
Air supply: The compressed air that operates
spray guns is supplied by either portable or
installed compressors. The air pressure from the
compressors is usually set from 100 to 125 psi.
The pressure is reduced to spraying pressure by a
pressure-regulator valve. When using air
c o m p r e s s o r s , f o l l ow t h e m a n u f a c t u r e r 's
operating instructions. To spray paint properly,
ensure that the air is dry and free of dust. Since
all air contains moisture and dust in varying
amounts, some means must be provided to
Figure 1-18.--Air transformer.
remove it. This is commonly done by an air
transformer, frequently called an air separator or
compressed air through the air inlet opens. The air then
an air regulator. Air, passing through the
passes through the gun body into the spray head. In the
transformer, enters through an air inlet and
most common types of spray heads (external-mix), the
passes through a series of baffles and a filter
air does not come in contact with the paint inside the
chamber to a regulator diaphragm that adjusts
gun, but is blown out through small holes drilled in the
the pressure. During normal weather conditions,
air cap. The paint is blown out of the nozzle in a thin jet.
the transformer should be drained daily. If the
The force of the air striking the paint breaks the jet into
weather is damp, it should be drained several
a fine spray.
times daily. To drain the transformer, open the
drain valve on the bottom of the unit. Change the
You can control this spray to produce various
packing and filter units also at regular intervals.
patterns by setting the air control screw that regulates
See figure 1-18.
the spreader adjustment valve.
To get a round spray, turn the control screw
SPRAY GUN OPERATION.--When the trigger
counterclockwise.
of a spray gun is squeezed, the air valve that admits
1-19
