Milton Roy Dosing Pump GB402

Ensure all shut-off valves are closed and all pressure has been bled from liquid end.

Drain oil from the pump by unscrewing the drain plug (20) and O-Ring (19).

Set the stroke adjusting knob to 100%.

Disconnect the suction and discharge piping.

Unscrew the six diaphragm head bolts.

Remove the diaphragm head assembly from the pump body.

Turn the motor fan by hand until the end of the diaphragm assembly (261) is fully forward, and unscrew the diaphragm from the connecting rod (60).

Ensure correct assembly of check valve components

Use new O-Rings for each reassembly to ensure a tight, leak-free seal

Refer to Figure 10 for proper assembly order of suction and discharge check valves

Check for potential issues if check valve cartridges are installed incorrectly

Assemble coupling onto check valve assembly

Refer to Figure 9 or 11 before starting disassembly

Unscrew the union nut (435) to separate the union end (445) from other liquid end parts

Unscrew the ball guide (424) from the liquid end

Screw the union nut part way onto the end of the ball guide with the seat, ensuring it is loose

Place the ball guide/union nut on a flat surface with the union nut down

Insert a thin, blunt instrument into the small center hole of the ball guide

Tap the screwdriver gently with a hammer to release the ball and seat from the ball guide

Fit new O-Rings into position on the ball guide and seat

Drop the ball into the curved inner chamber end of the ball guide

Sit the ball guide on a flat surface with the ball facing upwards

Position seat on the ball guide, trapping the ball inside

Press the seat into the ball guide with firm, even pressure

Position the union end onto the correct end of the ball guide

Ensure all shut-off valves are closed and all pressure is bled from the liquid end.

Disassembly (Refer to Figures 7 and 8)

Set the stroke adjusting knob to 100%.

Disconnect the suction and discharge piping.

Unscrew the six diaphragm head bolts.

Remove the diaphragm head assembly from the pump body.

Turn the motor fan by hand until the end of the diaphragm assembly is fully forward, and unscrew the diaphragm assembly from the connecting rod.

Reassembly (Refer to Figures 7 and 8)