Figure 14-33.—Suction-feed spray gun.
SUCTION FEED.—The suction-feed spray gun
is designed for small jobs. The container for the paint
is connected to the spray gun by a quick-disconnect
fitting, as shown in figure 14-33. The capacity of this
container is approximately 1 quart. The fluid tip of
this type of spray gun protrudes through the air cap, as
shown in figure 14-34. The air pressure rushing past
the fluid tip causes a low-pressure area in front of the
tip. This causes paint to be drawn up through the fluid
tip, where it is atomized outside the cap by the air
pressure.
PRESSURE FEED.—The pressure-feed spray
gun is designed for use on large jobs where a large
amount of spray material is to be used. The spray
material is supplied to the gun through a hose from a
pressurized tank.
This spray gun is designed to
operate on high-volume, low-pressure air. This type
of equipment eliminates the evaporation of the
volatile substances of the mixture before striking the
surface because the paint and air are mixed in the
tanks. In other words, a wetter coating is applied.
Spray Gun Maintenance
Fluid leakage at the front of the gun is an
indication that the fluid needle is not seating properly.
This may be caused by a fleck of dried material in the
nozzle, or the fluid needle packing may be too tight.
It may also be caused by a bent fluid needle, a broken
fluid needle spring, or the wrong size fluid needle for
the fluid tip.
Air leakage results from an improperly set air
valve.
This may be caused by a bent valve stem,
broken spring, or damaged valve or valve seat.
Jerky or fluttering spray is caused by an obstructed
fluid passage, loose tip, damaged seat, or air in the fluid
line. Air can be inducted into the line from several
sources: a loose packing nut, dried packing, loose or
damaged coupling nut, loose or damaged fluid tube, or
the cup tipped too far. See figure 14-35. Faulty spray
14-38
