How To Use The Gun; How To Adjust The Spray Pattern - Graco GMax
3900 Instruction Manual

How to Use the Gun

1. Connect a grounded fluid hose to the gun inlet.
See Fig. 2
2. With no tip installed, start the pump. Flush the
pump according to the instructions supplied with it.
Prime the system with the fluid.
3. Follow the Pressure Relief Procedure on
page 5. Be sure the gun trigger safety is locked.
See Fig. 1.
4. Models 217–593 & 235–990: unscrew the tip guard
(3) and install the tip (A) and the gasket (2) in the
nut of the tip guard. Screw the assembly firmly
onto the gun. Tighten the assembly with a wrench.
See Fig. 2.
NOTE: If the gasket (2) is not installed, the gun will
leak.
5. Models 220–955 and 820–165: install the
SwitchTip (40) and the tip guard (41). See manual
307–848, supplied. See Fig. 2.
41
40
Fig. 2
6. Start the pump. Adjust the fluid pressure until the
spray is completely atomized. Use the lowest
pressure necessary to get the desired results.
Higher pressure may not improve the spray pattern
and will cause premature tip wear and pump wear.
Installation/Operation
2
A
3
7. If adjusting the pressure does not give a good
spray pattern, follow the Pressure Relief Proce-
dure on page 5 and then try another tip size.
8. Use a full-open, full-close triggering action. Hold
the gun about 14 in. (350 mm) from and at right
angles to the work surface. Don't swing the gun in
an arc. Practice to find the best length and speed
of stroke.

How to Adjust the Spray Pattern

1. To adjust the spray pattern direction, follow the
Pressure Relief Procedure on page 5. Loosen
the tip guard retaining nut (B). Turn the tip guard/
tip groove horizontally (C) for a horizontal pattern
and vertically (A) for a vertical pattern. Tighten the
nut.
2. The spray tip orifice and spray angle determines
the coverage and size of pattern. When more
coverage is needed, use a larger spray tip rather
than increasing fluid pressure.
CAUTION
The openings in the tip guard reduce paint buildup on
the tip guard while spraying. Any damage to the
sharp edges of the openings causes paint to collect
at that area. Never hang the gun by the tip guard.
KEY
A Tip guard shown in position for
vertical spray pattern
B Retaining nut
C Tip guard shown in position for
horizontal spray pattern
B
A
Fig. 3
C