Service - Graco GMax
3900 Instruction Manual

C
B
A
Torque to 20-25 ft-lb
(27-34 N.m)
Torque to 80–90 in-lb
(9–10 N.m)
Fig. 7
NOTE: The needle (C), diffuser/seat (A), gasket (B)
and locknut (D) must be replaced together. They are
included in Kit 218–070.
Disassembly
(See Fig 7 )
1. Follow the Pressure Relief Procedure on page
5.
2. Remove the tip guard assembly. See Fig 2.
3. Squeeze the trigger while unscrewing the diffuser/
seat (A) and gasket (B).
4. Remove the locknut (D) and end cap (23).
5. Tap the rear of the gun with a plastic mallet to
push the needle assembly out the front.
Reassembly
(See Fig 7)
1. Guide the threaded end of the needle assembly
into the front of the gun.
2. Install the end cap, aligning its guides with the
holes in the rear of the gun. Install the locknut (D)
loosely.
3. Squeeze the trigger while installing the gasket (B)
and diffuser/seat (A). Torque the diffuser seat to
20–25 ft-lb (27–34 N.m).

Service

D 4. If the gun handle (6) was removed, hand tighten it
23
4
5. Adjust the needle before using the gun. Procedure
6. Be sure the trigger guard and tip guard are
Adjusting the needle
1. Engage the gun safety latch.
2. Hold the gun with the nozzle straight up so the
3. With light pressure, hold the trigger against the
4. Turn the adjusting nut 3/4 turn counterclockwise.
5. Connect the fluid hose. Install the tip guard and
Fig 8
into the fluid housing (26); it should fit easily. Only
if necessary, loosen the setscrew (4), align the
handle with the fluid housing and torque the
setscrew to 80–90 in-lb (9–10 N.m).
below.
installed before using the gun.
(See Fig 8)
trigger falls onto the safety latch.
latch. Turn the locknut (D) clockwise until there is
enough tension for you to feel and see the trigger
raise slightly off the latch.
prime the system. Trigger the gun and release it.
The fluid flow should stop immediately. Engage the
safety latch and try to trigger the gun. No fluid
should flow. If the gun fails either test, relieve
pressure, disconnect the hose and readjust the
needle.
Engage trigger
safety latch
Arrows indicate
clockwise turn
D