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This
type incorporates a combined tubular body and indicator humidity
plug. It is screwed into the equipment container from the
outside. Air enters the desiccator through an annular inlet
channel, which is covered by a strip of Polytetrafluorethylene
(PTFE) coated wire mesh to prevent the ingress of rain, dust,
insects, etc.
A tube is connected at one end to the annular channel, and
the other end is covered by metal gauze to prevent particles
of desiccant blocking it. The direction of airflow depends
on the relative pressure differentials between the inside
of the equipment and the surrounding atmosphere. If the external
pressure is greater than the internal pressure, moist airflows
from outside, through the annular channel and breather tube,
to the desiccant. Dry air flows from the desiccant through
a second tube to the equipment interior. If the pressure differential
is reversed, the direction of the airflow is also reversed
until pressure equalization is achieved.
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