Displacement Pump - Graco GMax
3900 Instruction Manual

Removal
1. Flush pump.
2.
Relieve pressure; page 4.
3. Fig. 16. Cycle pump with piston rod (222) in its
lowest position.
4. Fig. 16. Remove suction tube (30) and hose (33).
33
Fig. 16
Repair
See manual 308798 for pump repair instructions.
Installation
WARNING
If pin works loose, parts could break off due to
force of pumping action. Parts could project
through the air and result in serious injury or prop-
erty damage. Make sure pin and retaining spring
are properly installed.
CAUTION
If the pump locknut loosens during operation, the
threads of the bearing housing will be damaged.
Make sure locknut is properly tightened.
1. Fig. 19. Pull piston rod out 1.5 in. Screw in pump
until holes in bearing cross link and piston rod
align.
Fig. 19

Displacement Pump

222
30
1.5 in.
5. Fig. 17. Use screwdriver: push retaining spring up
and push out pin (29).
Fig. 17
6. Fig. 18. Loosen locknut by hitting firmly with a
20 oz (maximum) hammer. Unscrew pump.
Fig. 18
2. Fig. 17. Push pin (29) into hole. And push retaining
spring into groove all the way around connecting
rod.
Fig. 20. Screw jam nut down onto pump until stops.
Screw pump up into bearing housing until it is stopped
by jam nut. Back off pump and jam nut to align pump
outlet to back. Tighten jam nut by hand, then tap 1/8 to
1/4 turn with a 20 oz (maximum) hammer to approxi-
mately 75 5 ft–lb (102 N m).
Fig. 20
Fig. 21. Fill packing nut with Graco TSL until fluid flows
onto the top of seal.
Fig. 21
29