Tip: Air Bubble Growth; Ink Pressure In The Ink Supply Tubes - Brother MFC5490CN Service Manual

---------------------------------------- [ Tip: Air bubble growth ] ----------------------------------------

Liquid ink contains trace amounts of air. The amount varies with the pressure on the ink
because increasing the pressure raises the ink's ability to absorb air from its surroundings and
lowering the pressure forces the ink to give up some of this air.
The ink pressure fluctuations caused by the piezoelectric ceramic actuators repeatedly expand
and contract any air bubbles, growing them larger gradually. This is because the amount of the
air per unit area passing through the boundary surface between the ink and the bubble is always
constant but the boundary surface area decreases or increases when the bubble contracts or
expands, respectively.
That is, when the pressure becomes high, the bubble contracts so that the amount of air moving
from the bubble to the ink decreases in proportion to the boundary surface area decreased. On
the contrary, when the pressure becomes low, the bubble expands so that the amount of air
moving from the ink to the bubble increases in proportion to the boundary surface area
increased.
The design therefore compensates by allowing the purging/flushing of air bubbles during
printing to keep the amount of air dissolved in the ink to a minimum.
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Ink pressure in the ink supply tubes

High
Bubble
Ink
: Pressure
: Air flow
3-17
Low
Bubble
Ink
(Bubble)
Confidential