During regular operation the air filter 
will gradually saturate with oil. This is
not a problem, on the contrary: a saturated air filter will
capture more oil mist particles out of the air than a clean
filter. However, it may be necessary to adjust the power of the
extractor fan to increase the air flow through the air extractor
unit.
The power of the air extractor fan can be adjusted by turning the
black knob located on the black regulator box which can be found
in the middle of the control compartment. Turning it clock-wise
gives more power; turning it counter-clock-wise gives less power.
The air extractor unit should be adjusted to the minimally
necessary air flow: it should pull out just so much air that
hardly any spray mist escapes from the spraying compartment.