FIGURE 4.4
Mobile fi lter cartridge blotter-paper type dryer fi lter press Model BA-2FC2-20. (Courtesy of
Baron USA, Inc., Cookville, TN.)
can handle much greater concentrations than can the conventional fi lter press,
but it cannot remove some of the contaminants as completely as a fi lter press.
Consequently, the centrifuge is generally used for rough bulk cleaning where
large amounts of contaminated oil are to be handled.
Frequently, the output of the centrifuge is put through a fi lter press for the
fi nal cleanup. The centrifuge cannot remove dissolved water from oil; since
the fi nal centrifuge is sealed with water, the oil leaving the centrifuge may be
saturated at the temperature of operation and conceivably could contain
more dissolved water than when it entered. Neither the centrifuge nor the
fi lter press is designed to treat oil chemically.
4.5.1.6 Coalescers
Throughout the power industry, coalescers are replacing centrifuges for use
in removing free water from both lubricating and insulating oils. Coalescing
is a technique that has been borrowed from the aviation fueling fi eld.
Fiberglass cartridges trap small water particles; increasing differential pressure
across the fi lter media forces the particles of water together, and the
large water drops are extruded at the outer surface of the fi berglass element.
Large water drops are retained within a water-repellent separator screen and
collect, by gravity, at the bottom of the fi lter while dry oil passes through the