Purchas D. Handbook of Filter Media
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Replaceable Filter Elements 377
relatively large diameter, as in Figure 9.24, and greatly increased filtration area,
with corresponding benefits in respect of dirt-holding capacity and life. The latest
version of this cartridge is the
750
KF filter, also made of meltblown
polypropylene.
The pleated cellulose paper cartridge has been the mainstay of engine fluid
filtration for many years. However, the demands of modern industry and
commerce are such that extended service intervals are becoming normal (1) and
filters are having to change to accept higher dirt loadings, and to achieve higher
efficiencies. New types of cartridge are being developed to meet this need, while
Figure 9.15. All-polypropylene multilayer general purpose filter cartridge.
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Replaceable Filter Elements ~ 79
Figure 9.18. The pleated and spiral formation of paper cartridge for the FS diesel fiM filter.
Figure '4.19. The FS diesel fuel filter.
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Handbook of Filter Media
section, connected to a stacked disc of cellulose medium by a venturi that
increases the flow through the stacked discs.
Other new designs for engine oil filters are the modular incinerable cartridge
(in which all parts of the disposable element are made from incinerable
materials), and the in-place cleanable oil filter, which has an element that can be
cleaned by back-flushing with compressed air.
9.2.4.2 Pleated cartridges for gas filtration
For the greater part of its life, the fabric filter used for the filtration of large
volumes of inlet air or exhaust gas streams has employed filter bags for its
medium. While bags are still an important part of the fabric filter scene, made
largely of non-woven media, there has been a rapid influx of pleated media
cartridges into gas filtration, triggered by the need for higher filtration
efficiencies. The ePTFE membrane media discussed in Chapter 8 have been
Figure 9.20. Dirt collected in all the 'vee'pleats of an FS diesel fuel filter cartridge.
Figure 9.21..4 high pressure hydraulic oil filter with a 'disposable'pleated cartridge.
Replaceable Filter Elements
381
especially successful in this application, because of their higher operating
temperature range.
Resin-impregnated cellulose paper may be sufficiently rigid to be self-
supporting without need of either a central core or spacers to maintain a gap
between adjacent pleats. Illustrative of this is the engine air intake cartridge in
Figure 9.2 5. The function of the spacers is fulfilled by the dimples that can be
seen in the surface of each pleat.
Also self-supporting is the large (324 mm diameter, 673 mm high) cartridge
illustrated in Figure 9.26, containing 22.3 m 2 of filter medium, comprising a
chemically treated blend of cellulose and synthetic fibres. Multiple assemblies of
these cartridges are applied in pulse jet cleaned dust filters, notably for the air
intake to gas turbine power generation systems.
Figure 9.22. A high pressure hydraulic oil filter cartridge.
Figure 9.23. Schematic illustration of ~M Series 700B radial cartridge.
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Handbook of Filter Media
It is not only paper-like materials that can be pleated. Media made from
sintered metal and even ceramic can now be pleated, as shown in Figure 9.17
and, in multi-cartridge assemblies such as Figure 9.2 7, for hot or corrosive gas-
phase processing duties.
Most pleated cartridges used for gas filtration are circular in cross-section.
However, Donaldson has recently described an oval cartridge ~2~, with shorter,
wider pleats, that offers higher filtration efficiency, and greater ease of cleaning.
The medium is a polymer nanofibre, acting as a surface filter. The resultant filter
housings are smaller than corresponding cylindrical cartridge houses would be.
9.2.5 lenticular discs
A lenticular disc is one that has the double convex shape of a lens. This is
advantageous in a filter, since it allows inward filtration to proceed through both
faces, with ample space between them for the flow of filtrate into a central outlet.
A stack of such discs assembled on a perforated core provides a convenient
Figure 9.24.3Mfilter cartridge compared with conventional 2 5, 50 and 75 cm cartridges.
Figure 9.25. A resin impregnated celhdose paper cartridge for an engine air intake filter.
Replaceable Filter Elements 383
method for constructing a compact cartridge of high surface area. This format is
the basis of both throwaway and cleanable long-life cartridges, depending on the
type of media utilized.
The filter sheets made by Carlson from cellulose, described in Chapter 4, are
available as lenticular filter cartridges. Figure 4.7 in Chapter 4 shows a similar
Figure
9.26.
A 'Tenka!l' dust filter cartridge.
Figure 9.2 7. A multiple assembly of pleated sintered metal fibre cartridges for high temperature gas filtration.
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Handbook of Filter Media
throwaway cartridge from Cuno's range of lenticular cartridges based on the
various grades of Zeta Plus filter media, their modular construction being
illustrated in Figure 9.28. A cartridge comprises an assembly of lenticular discs
or cells, each of which is composed of two discs of Zeta Plus medium, sealed
together around a polypropylene separator. The cartridge is pre-assembled
under high compression, and is locked together by three stainless steel bands.
Edge sealing of each cell is effected by an injection moulded polypropylene ring.
A similar format is shown in Figure 9.29, now with activated carbon
incorporated into the Zeta Plus, in order to provide a combination filter,
marketed under the ZetaCarbon brand name. Five different types of carbon can
be incorporated, to decolourize liquid streams, and remove organic
contaminants. These cartridges have no shedding of carbon into the filtrate, and
can be supplied certificated for pharmaceutical use.
Lenticular disc stacks are another type of filter used in the filtration of molten
polymers. Sintered stainless steel is the standard material required to withstand
the high operating pressures (300 bar) and temperatures of the polymer
industry, where, with repeated specialized cleaning, the useful life of a filter is
expected to be perhaps 10 years or more. Accordingly, whilst the same lenticular
format still applies, there are major differences in the detailed engineering. The
most noticeable of these is that the product supplied by the manufacturer is a
number of separate filter discs (which are generally known as segments), from
which the customer can assemble a stack inside a suitable housing, as in Figures
9.30 and 9.31. These segments or discs are produced in two standard diameters,
175 and 200 mm.
To withstand these rigorous conditions, appropriate multi-layered
construction is utilized so as to protect and support the critical layer of filter
medium. As illustrated in Figures 9.32-9.35, four standard options are available
from Pall, these offering different combinations of sophistication versus cost.
Figure 9.28. The modular construction of Cuno 'HT Series' lenticular cartridges.
Replaceable Filter Elements 385
9.2.6
Rigidized elements
While pleated cartridges have been the biggest recent competitor for filter bags in
gas filtration, a small but important part of the market is now using rigidized
elements for this purpose, because of their better operating temperature range.
The version developed by Herding, described in Chapter 5, uses a pleated type of
surface for a self-supporting structure of filter media, able to operate at
moderately high temperatures.
Somewhat similar are the Compact Filter Elements supplied by Madison,
which are available in flat, rectangular shape or as cylindrical elements. They
can be made from needlefelts, spunbondeds or composites, but are mainly
supplied with microporous coated or anti-static media. Their chief claim is that of
much reduced cartridge size for a given filtration area.
Figure 9.29. Cuno 'Zetacarbon' cartridges, incorporating activated carbon with 'Zeta Plus'.
Figure 9.30. A sintered metal segment for polymer filtration.
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Handbook of Filter Media
Figure 9.31. A multi-segnwnt stack assembly for polymer filtration.
Figure
9.32.
The multi-layer construction of Pall's 'Segment' filters for polymer filtration.
Figure
9.33.
The multi-layer construction of Pall's 'Segment-M' filters for polymer filtration.