Similar to the edge filter in appearance, in that it has an array of disc-shaped components held on a central core, the stacked disc filter differs because the discs are actually hollow, with filter media over the faces of the disc. It employs individual
discs, porous on both sides – that are stacked over a perforated inner tube – with intermediate spacing washers creating a flow space between each pair of discs.
Flow is between and subsequently through the filter discs and into the inner tube. The discs typically have a fine metal wire screen supported on a coarser back-up screen to provide effective use of the full filtration area. The complete disc assembly is then clamped together inside an outer, cylindrical straining screen that prevents passage of larger particles into the spaces between the discs.
Performance is nominally that of the mesh elements or filter screen apertures, typical standard openings being from 0.25 to 0.025mm, equivalent to ratings of approximately 250 and 25 um respectively. With this form of construction, however, performance materially improves as dirt collects on the screen surfaces, providing increasingly finer filtration.
This particular form of filter is thus a mesh aperture controlled one, rather than an edge type. It does provide a large surface area in a compact volume, with a moderately low pressure drop.
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