Brother MFC620CN Service Manual page 121

(5) Removing air
Another position of the purge cam shifts the slide cams, producing vertical motion of the air vent
rods. Pushing up the air vent rods opens the shut-off valves inside the air vent unit of the
head/carriage unit. Simultaneously adding negative pressure from the tube pump expels air trapped
in the manifolds.
Maintenance unit
Air vent rod
Clutch gear
Air vent unit
Purge gear
Slide cam for color ink
Slide cam for black ink
Purge cam
3-33 Confidential