COALESCING FILTERS
A 0.3-µm-rated coalescing filter element is standard in all coalescing units. They remove 99.99% of oil and solid contaminants larger than 0.3 µm. An optional 0.01-µm-rated element provides extremely fine filtration, but at some reduction in air flow. However, in GUARDSMAN, GUARDSMAN II, SERIES 380, and VANGUARD filters there are available extended bowls with higher capacity coalescing elements for significantly increased air flows. Coalescing filters have epoxy-resin-coated, borosilicate, glass fiber elements. Liquids and solids are removed from the air stream by several different actions, namely:
IMPACTION: Particles larger than 1 µm collide with and adhere to the fibers of the element.
INTERCEPTION: Particles 0.3 µm to 2 µm in size are molecularly attracted to the fibers of the element, and this causes them to adhere.
DIFFUSION: Particles 0.001 µm to 0.3 µm in size move by random Brownian motion, thereby contacting and adhering to the fibers of the element.
DRAINING: Tiny droplets of oil coalesce (merge) until they form drops large enough to fall off the filter element and into the bowl sump. The automatic drain then expels them.
The filter element will continue to coalesce liquids until solid contaminants accumulated in the filter element cause the pressure drop across the element to become excessive. At this point the filter element must be changed. A built-in differential pressure gauge will indicate when the point is reached that requires the element to be changed.
IMPORTANT NOTE:
A general purpose filter must be installed ahead of a coalescing filter to ensure good performance and to extend the life of the coalescing element.