Dual media filter cartridge construction

A filter cartridge is provided which includes (a) a wound depth filter or a cylindrical seamless depth filter and (b) a pleated filter having a lower micron retention rating than the depth filter. The depth filter and pleated filter surround a central opening. The cartridge is sealed and an appropriate inlet or outlet is provided in order to assure sequential fluid flow first through the depth filter and then through the pleated filter.

BACKGROUND OF THE INVENTION 
This invention relates to a filter cartridge construction suitable for 
filtering liquids and gases. 
At the present time a wide variety of filter cartridge constructions are 
utilized to purify fluids. These cartridge constructions are designed to 
remove solids and colloidal particles as well as microorganisms. The basic 
two separate and distinct types of cartridges used in filtration of gases 
and liquids are depth filters (typically wound) and surface or screen 
filters (usually pleated). A depth filter is primarily used to remove most 
of the contaminants and particles. It is typically utilized upstream of a 
surface or screen filter. The most important properties for a depth filter 
are its "dirt holding capacity" or throughput, pressure drop and 
retention. The filter design allows contaminants and particles to be 
trapped in stages within the depth of the filter due to the construction 
of the multiple layers of various media types. A wound depth filter has 
multiple layers with the most open media (largest micron retention rating) 
i.e. largest pore size usually the outermost layer, adjacent the liquid 
inlet with the tightest media (smallest micron retention rating, i.e. 
smallest pore size) adjacent the liquid outlet. The tightest media at the 
core adjacent the liquid outlet will have the least amount of surface area 
due to the smallest diameter around which it is wrapped. This layer at the 
core contributes to most of the pressure drop of the cartridge because the 
media has the highest pressure drop and the least amount of filtration 
surface area. Likewise, this layer will significantly reduce the capacity 
of the filter due to both the low filtration surface area and the smallest 
micron retention rating. 
A surface or screen filter will retain virtually 100% of the particles or 
contaminants for which it is rated. The media used in a surface or screen 
filter typically has a high pressure drop and low "dirt holding capacity" 
or throughput because of its high retention efficiency. The media normally 
used in a surface filter comprises glass or polymeric microfibers. The 
normally used medium in a screen filter comprises a polymeric microporous 
membrane. Particles are retained by size exclusion primarily on the 
surface of the screen filter rather than within the depth of the filter. 
Particles are retained primarily on the surface of a surface filter which 
has a controlled pore size. Particles smaller than the controlled pore 
size tend to be trapped within the media of the surface filter. However as 
a result of the controlled pore structure, they provide more predictable 
filtration than depth filters. For the surface or screen filter to be 
economical, the media is pleated to obtain a large filtration surface 
area. Presently, the wound depth filter and the surface or screen filter 
are utilized in series in separate housings to effect the desired level of 
purification. 
The useful life of a filter construction is the time the filter 
construction functions to remove particles of a size for which it is rated 
while avoiding a desired maximum pressure drop between the inlet and 
outlet of the filter construction. When the filter construction either 
fails to retain particles of a size for which it is rated or a pressure 
drop larger than desired results due to particle retention within the 
filter construction, it is replaced. 
It is economically desirable to maximize the useful life of a filter 
construction. Convenient measures of useful life of a filter construction 
are the volume of fluid satisfactorily filtered prior to experiencing a 
pressure drop between its inlet and outlet which equals or exceeds the 
maximum pressure drop desired. 
It is also desirable to minimize the volume of filter used to attain 
satisfactory filtration for a given time in order to minimize the cost of 
filter material. In addition, it is desirable to utilize a single filter 
housing rather than a plurality of filter housings in order to minimize 
filter housing cost and to eliminate the need for conduits and associated 
structures such as valves for connecting the housings. While a single 
housing is desirable, the filter construction positioned therein must be 
capable of retaining particles equal to and larger than a desired size 
while affording an economically satisfactory useful life. 
It has been proposed in U.S. Pat. No. 3,552,553 to provide a dual media 
filtration cartridge formed from a pleated filtration medium positioned 
adjacent a liquid outlet from the cartridge and a porous foam medium 
adjacent a liquid inlet to the cartridge. The foam medium surrounds the 
pleated medium. This filter cartridge is undesirable since the foam medium 
has a random porosity which results in a random micron retention 
characteristic throughout the foam layer. This micron retention 
characteristic is undesirable since retained particles tend to be located 
within a narrow stratum within the foam which results in a portion of the 
foam thickness not being utilized for filtration. 
It has also been proposed in U.S. Pat. No. 3,334,752 to provide a dual 
filter construction in a single housing. The filter construction comprises 
a pleated paper tube filter positioned on a hollow core and an upstream 
filter comprising napped wound yarn which surrounds the pleated filter. 
The wound yarn portion functions to remove slimy constituents while the 
pleated paper filter functions to remove even minute solid particles. The 
yarn, which has the same porosity through the depth of the upstream 
filter, is wound to form rhombic openings which diminish in 
cross-sectional area when proceeding from an outermost surface to the 
surface of the upstream filter positioned adjacent the pleated filter. 
Thus, the yarn utilized does not have progressive lower micron retention 
characteristics as one progresses toward the pleated filter. 
It would be desirable to provide a filter cartridge construction which 
avoids the undesirably high pressure drop such as that due to the tightest 
filtration medium positioned adjacent the liquid outlet from the filter 
cartridge. Furthermore, it would be desirable to provide a filter 
cartridge having a significantly improved useful life as compared with 
filter cartridge of the prior art having at least about the same retention 
efficiency. Such filter cartridges would provide substantially improved 
economic benefit from the standpoint of increased satisfactory throughput 
fluid volume capacity while minimizing the cost of filter cartridge 
support apparatus to achieve this capacity. 
SUMMARY OF THE INVENTION 
This invention comprises a filter cartridge construction and filter 
assembly having a filtration medium formed of (a) a depth filter 
comprising either a cylindrical, seamless fibrous depth filter comprising 
a nonwoven fibrous mass or a wound depth filter and (b) a pleated screen 
or surface filter which are retained within a common housing. One end of 
the cartridge of this invention is sealed with a cap while the opposing 
end is sealed with a cap having a fluid inlet or outlet. The filtration 
medium is positioned around a hollow core which is in fluid communication 
with the filtration medium and the fluid inlet or outlet within the cap at 
one end of the filtration medium. The hollow core extends substantially 
the length of the cartridge. The depth filter comprises a layered filter 
having a plurality of filtration media, each having a different percent 
retention efficiency retention rating. The layers of the depth filter are 
either formed either of (a) wound or layered flat filtration sheets or (b) 
of a fibrous mass of nonwoven polymeric fibers secured together by 
mechanical entanglement or intertwining or a wound depth filter. The 
surface or screen filter comprises one or a plurality of pleated layers 
each being formed of a medium having a lower retention rating than that of 
the layers of the depth filter medium. The pleated filters are formed from 
surface or screen filters wherein the media have a controlled pore size of 
pores at the surface of the media. The filter cartridges of this invention 
provide substantially improved characteristics of reduced pressure drop, 
substantially equal retention efficiency and increased capacity (life) as 
compared to prior art filter cartridges formed from depth filters and 
surface or screen filters which are lain flat rather than being pleated 
and which are positioned within a common housing.

DESCRIPTION OF SPECIFIC EMBODIMENTS 
The present invention provides a filter cartridge construction which 
comprises (i) a depth filter comprising either (a) a wound depth filter or 
(b) a cylindrical seamless fibrous depth filter formed from a fibrous mass 
of fibers and (ii) a pleated surface or screen filter positioned on a 
hollow core. The depth filter comprises a plurality of media (layers) each 
having a different micron retention size so that the permeability or 
retention of the media layers is largest adjacent a fluid inlet to the 
cartridge and is smallest adjacent the pleated surface or screen filter. 
Thus, large particles will be retained adjacent a feed inlet and 
progressively smaller particles will be retained as the feed passes 
through the filter cartridge. The inclusion of a pleated surface or screen 
filter in the construction rather than a filter which is lain to follow 
the surface contour of the core results in substantially lower pressure 
drop initially and over time within the cartridge. In addition, the 
retention capacity of the filter cartridge of this invention is 
substantially increased over a construction which utilizes a wound or 
layered arrangement of flat filtration sheets or of a cylindrical seamless 
fibrous depth filter having essentially the same retention efficiency. 
Furthermore, these improved performance characteristics are attained 
without adversely affecting the retention performance of the filtration 
medium. It has been found, in accordance with the invention, that the 
useful life of the filter cartridge of this invention is at least about 
50% longer, preferably about 100% longer than a prior art filter wherein 
the portion of the depth filter having essentially the same retention 
efficiency as the pleated filter portion of this invention is positioned 
to follow the surface contour of the hollow core. Thus, the filter 
cartridge of this invention permits the use of fewer cartridges for a 
particular application and at a lower cost as compared to the filter 
cartridges of the prior art. Percent retention efficiency and Beta Ratio 
are measures of the ability of a cartridge to capture and retain 
particles. The Beta Ratio concept was introduced by the Fluid Power 
Research Center (FPRC) at Oklahoma State University (OSU) in 1970. 
Originally developed for use on hydraulic and lubricating oil filters, the 
test has been adapted by many cartridge manufactures to measure and 
predict cartridge filter performance in aqueous-base feeds. The Beta Ratio 
is defined by the FPRC as the number of particles greater than a given 
size (x) in the feed, divided by the number of particles greater than the 
same size in the effluent. Both percent retention efficiency and Beta 
Ratio values are calculated for specific particle size ranges. 
The following equations show the relationship between Beta Ratio and 
percent retention efficiency: 
##EQU1## 
The filtration medium utilized in the present invention comprises a depth 
filter in an initial stage and a second stage surface or screen media 
having a pleated construction. The depth filter can be a wound filter or a 
cylindrical seamless fibrous depth filter. The filter medium of the depth 
filter having the largest micron retention is positioned adjacent an inlet 
to the filter cartridge. The filter medium of the depth filter having the 
smallest micron retention is positioned adjacent the pleated filter. The 
micron retention characteristic of a filter can be raised by varying the 
diameter of fibers used to form the filter and/or the extent of comparison 
of the fibers such as by winding a filter media sheet tighter or looser 
around a core. A tighter wound filter media sheet gives a higher percent 
retention efficiency. Any intermediate filter media are positioned 
according to percent retention efficiency so that incoming fluid is passed 
sequentially through filter media having progressively smaller micron 
retention and lastly through the filter having the smallest micron 
retention. Thus, the overall filter cartridge presents a percent retention 
efficiency which comprises a progressive gradient from the inlet to the 
outlet wherein the percent retention efficiency progressively increases. 
Representative media useful for forming the depth filter include fibers of 
polyolefins such as polyethylene or polypropylene, cellulose, cotton, 
polyamides, polyesters, fiberglass or the like. 
The depth filter element utilized in the apparatus of this invention can be 
charged or uncharged. A charged depth filter is formed of a composition 
which serve to attract particles in the feed to be retained by the filter. 
When utilizing a charged depth filter, the retention efficiency of the 
overall depth filter is increased. Any conventional means of charging the 
fibers or the like which form the depth filter can be utilized including 
chemical modification of the surface of the filter medium as is disclosed 
for example by U.S. Pat. No. 5,137,633 which is incorporated herein by 
reference or by corona discharge in the presence of oxygen or ozone. 
The cylindrical fibrous depth filter is free of seams and is formed of 
fibers which produce a fibrous mass of fibers. This embodiment of the 
depth filter is characterized by a gradation of micron retention 
characteristics throughout its thickness in the radial direction. This 
gradation can be achieved either by varying the void volume of the 
cylindrical fibrous depth filter medium as a function of thickness in the 
radial direction or by maintaining a constant void volume and varying the 
size of the fibers as a function of depth filter thickness in the radial 
direction. In either embodiment all that is necessary is that the 
gradation of micron retention characteristics is produced. The gradation 
is effected such that the liquid to be filtered first encounters a layer 
of the depth filter having the largest micron retention characteristic (i. 
e. largest pores) and encounters layers having progressively smaller 
micron retention characteristics (i.e. smallest pores) prior to being 
directed into the pleated filter. The seamless cylindrical fibrous depth 
filter can be formed by any conventional means such as is disclosed in 
U.S. Pat. No. 3,933,557; 4,032,688; 4,726,901 or 4,594,202 which are 
incorporated herein by reference. 
In one method for forming the cylindrical, seamless fibrous depth filter, 
for example, a molten thermoplastic composition is spun from a 
multiplicity of orifices arranged at an angle to a rotating mandrel. The 
orifices are positioned at a plurality or distances from the mandrel. Gas 
is directed at the orifices in a direction generally in the direction of 
projection of the fibers from the orifices to attenuate and disrupt the 
fibers into discrete lengths. The fibers are collected and wound on the 
mandrel to form a generally spirally wound cylindrical layer of randomly 
intertwined spun fibers and to form the seamless cylinder which can be 
removed from the mandrel. If desired, the mandrel can be formed of the 
pleated filter layer surrounded by a porous screen so that the filter 
cartridge of this invention can be formed simultaneously with forming the 
cylindrical, seamless fibrous depth filter. Micron retention 
characteristics for a given layer of the cylindrical fibrous depth filter 
can be controlled by controlling the rate of exit of fibers from a 
particular set of orifices which produce a given layer, thereby to control 
the void volume in that layers 
In a second method, the cylindrical seamless fibrous depth filter is formed 
in a manner whereby the voids volume throughout the filter thickness in 
the radial direction is essentially constant. The desired micron retention 
characteristic gradation is achieved by varying the size of the fibers 
throughout the cylindrical fibrous depth filter thickness in the radial 
direction. The smallest fibers produce a layer having the smallest micron 
retention characteristic while the largest fibers produce a layer having 
the largest micron retention characteristic. The fibers are formed by 
extruding a molten thermoplastic composition from a fiberizing die. The 
fibers are attenuated by a gas stream directed to a rotating, 
reciprocating mandrel. The fibers are cooled prior to their collection on 
the mandrel to a temperature below which the fibers bind to each other to 
substantially eliminate fiber-to-fiber bonding. The cooled fibers are 
collected on the mandrel and are subjected to a compression force to 
effect a substantially constant void volume through the thickness of the 
cylindrical, seamless fibrous depth filter in the radial direction. The 
cylindrical fibrous depth filter can be formed on the pleated filter 
surrounded by a screen which, in turn is mounted on the mandrel. 
Alternatively, the cylindrical, seamless fibrous depth filter can be 
formed directly on the rotating mandrel and subsequently removed 
therefrom. 
Typically the voids volume of the cylindrical fibrous depth filter move 
between about 60 and 95% and varies no more than about 1 to 2%. Typically, 
the fibers range in diameter between about 1.6 and 16 micrometers. 
The wound depth filter is formed by winding one or a plurality of filter 
sheets formed of fibers to form a generally cylindrical structure. The 
filter sheet or sheets have varying pore size such that the micron 
retention characteristic of a portion of the depth filter is a function of 
radial position within or on the depth filter. The portion of the wound 
depth filter positioned adjacent an inlet to a filter cartridge including 
the wound depth filter has the largest micron retention characteristic 
while the portion of the wound depth filter having the smallest micron 
retention characteristic, i.e., smallest pore size, is positioned adjacent 
the pleated filter. Any intermediate portions of the wound depth filter 
are positioned according to pore size so that incoming fluid is passed 
sequentially through portions of the depth filter having progressively 
smaller micron retention characteristics and lastly through the portion of 
the filter having the smallest micron retention characteristic. 
Representative media useful for forming wound depth filters include the 
fibers set forth above for the cylindrical seamless fibrous filters. 
The surface or screen filter comprises one or a plurality of pleated 
constructions having a membrane filter sheet and one or more spacer layers 
to support the membrane filter sheet. The pleats can be in a corrugated 
shape or spirally positioned and can have a loop cross-section or a folded 
cross-section such as an M-shaped cross-section. As used herein, the terms 
"pleat", or "pleated" is intended to include all such cross-sectional 
shapes or positions. The pleated structure provides increased surface area 
which is initially exposed to fluid exiting from the depth filter as 
compared to a flat or curved non-pleated sheet construction. This pleated 
structure, in combination with the wound depth filter or the cylindrical 
seamless depth filter within a single housing, significantly reduces the 
rate of pressure drop during filtration without adversely affecting 
retention efficiency of the filter. When a plurality of pleated final 
filters are utilized, they are arranged concentrically adjacent relative 
to each other such as by being interleaved between each other or 
maintained as separate layers. 
The depth filter comprising the wound depth filter or the cylindrical 
seamless pleated filter and the pleated filter are contained within a 
housing provided with a fluid inlet and a fluid outlet. The housing and 
seals assure that fluid to be filtered passes sequentially through the 
depth filter and then through the pleated final filter while preventing 
fluid by-pass. The inlet can be positioned at the outer surface of the 
housing or within a centrally located portion of the housing while the 
outlet is positioned remote from the inlet to effect fluid passage as 
described above. 
The filter cartridge of this invention has a substantially larger useful 
life as compared to a filter cartridge which is a 100% depth filter 
wherein a portion of the depth filter has essentially the same retention 
efficiency as the pleated filter portion utilized in the present 
invention. Retention efficiency comprises the percentage retention by the 
filter cartridge of particles of a given size range admixed in the fluid 
being filtered. Applicants have found that by converting a portion of a 
depth filter having a small pore size relative to the remaining portion of 
the depth filter to a pleated filter construction, the useful life of the 
resulting filter cartridge is at least 50% longer and, more generally at 
least about 100% longer, than the useful life of the 100% depth filter. 
Generally, the portion of the 100% depth filter which has substantially 
the same retention efficiency as the pleated filter utilized in the 
present invention is about 20 to about 50% of the entire depth filter. 
A convenient repeatable method for measuring the useful life of a filter 
cartridge including a depth filter cartridge and a filter cartridge of 
this invention is to challenge the filter cartridge with relatively pure 
water. The pure water can be product water from a reverse osmosis process 
which is substantially free of particulate and colloidal impurities to 
which is added a known concentration of hard particles having a known size 
range. A standard test dust of particles having a known size range is 
available from the AC Spark Plug Division of General Motors Corporation 
and is identified as AC Fine Test Dust, Lot 1307. The test dust is admixed 
with the relatively pure water so that the final mixture contains 80 ppm 
test dust. The mixture then is used to challenge a filter cartridge in 
accordance with Example 2. The useful life is conveniently determined by 
measuring the volume of the water-est dust mixture passed through the 
filter cartridge until an undesirable pressure drop is experienced between 
the inlet and outlet of the filter cartridge, e.g. 40 psi. The retention 
efficiency of the filter cartridge is determined by monitoring the 
concentration of test dust of varying size range in the feed to the filter 
cartridge and in the filtrate obtained from the filter cartridge. A 
convenient means for measuring test dust concentration as a function of 
particle size range is with a standard light scattering particle counter 
such as a Model 4100 monitor with Model 376 BCL particle sensor available 
from HIAC Royco Corporation. 
A convenient comparison test for determining an alternate useful life of a 
filter cartridge when exposed to water containing both colloidal particles 
and hard particles is to challenge a filter cartridge to normal tap water 
which usually contains these contaminants. Since the composition of tap 
water varies from day to day, it is difficult to reproduce useful life 
measurements for a filter cartridge over time. However, for a given time 
and tap water composition, an accurate comparison can be made of the 
useful life of a plurality of cartridges when challenged with the same tap 
water. Applicants have found that when a filter cartridge of the present 
invention is challenged with tap water, its useful life is typically about 
50% longer or more as compared to a 100% depth filter cartridge having a 
layer which has essentially the same retention efficiency as the pleated 
filter used in the filter cartridge of this invention. 
Referring to FIGS. 1 and 1A, the filter cartridge 10 of this invention 
includes an exposed outer surface 12 and an outlet 14. A would depth 
filter or a cylindrical seamless depth filter 16 includes the exposed 
outer surface 12. A pleated surface or screen filter 18 is positioned 
adjacent the outlet 14 and is supported by core 20. The core 20 includes 
holes 23 for fluid passage. The cap 19 seals the top surfaces 22 of 
filters 16 and 18 so that incoming fluid is required to pass first through 
surface 12. The cap 21 having outlet 14 thereon seals bottom surface 23 of 
filters 16 and 18 so that filtered fluid is required to pass through 
outlet 14. The cartridge 10 is positioned within housing 21 so that outlet 
14 is positioned within housing outlet 26. Housing 20 is provided with 
fluid inlet 28. Flow of fluid to be filtered is exemplified by the arrows 
29, 29A and 29B shown in FIG. 1A. 
Referring to FIG. 1B, the cartridge 30 of the prior art includes a depth 
filter or a cylindrical seamless depth filter 32 which includes an outer 
surface 34. A wound or cylindrical seamless surface or screen filter 31 is 
positioned adjacent screen 36 having holes 37. 
In order to determine the pressure drop, capacity and retention performance 
characteristics of the filter cartridges of FIGS. 1 and 1B, within the 
housing of FIG. 1A the following comparison test was effected as Example 
1. 
EXAMPLE 1 
The filter cartridges identified in Table 1 as Cartridge 1 (invention) is 
shown in FIG. 1 but utilizing a wound depth filter rather than a seamless 
cylindrical fibrous depth filter and Cartridge 1B (prior art) is shown in 
FIG. 1B were tested by being positioned within the housing shown in FIG. 
1A. The wound depth filter is utilized for convenience and, for purposes 
of this test is equivalent to utilizing a cylindrical seamless filter. The 
cartridge were produced from the media described in Table 1. 
TABLE 1 
______________________________________ 
Media A Media B Media C Media D 
Media Type Nonwoven Meltblown Meltblown Meltblown 
______________________________________ 
All media 
polypropylene 
Retention less than 47% 72% 92% 
Efficiency 5% 
0.7 micron 
particles 
2 media layers 
Cartridge 1 20 wraps 2 wraps 2 wraps 2 pleated 
invention layers 
Cartridge 1B 20 wraps 2 wraps 2 wraps 2 wraps 
prior art 
______________________________________ 
The filtration surface area of media D in cartridge 1 is 490 in.sup.2 and 
filtration area for cartridge 1B is 58 in.sup.2. The retention efficiency 
of cartridge 1 and cartridge 1B was substantially the same. 
The cartridges were tested with the following test methods: 
Test Methods: 
1. Water Pressure Drop 
Clean water at 21.degree. C. was flowed through the cartridge at 2 gallons 
per minute. Upstream (inlet) and downstream (outlet) pressures were taken. 
The differential pressure across the cartridge (upstream pressure minus 
downstream pressure) is reported in Table 2. 
2. Retention Efficiency 
An aqueous solution containing 0.1 ppm of AC fine test dust available from 
the AC Spark Plug Division of General Motors Corporation was flowed 
through the cartridge at 3.0 gallons per minute at a temperature of 
22.degree. C. A Model 4100 monitor with a Model 346 BCL particle sensor 
light scattering particle counter was used to determine the number of 
particles upstream (inlet) and downstream (outlet). The reduction of 
particles downstream is reported in Table 2 as a % retention efficiency of 
0.7 micron particles. 
3. Capacity/Throughput (Life) 
Tap water was flowed through the cartridges at 2 gallons per minute at 
21.degree. C. while the differential pressure was monitored. (Differential 
pressure is upstream (inlet) pressure minus the downstream (outlet) 
pressure.) All cartridges tested simultaneously in separate housings to 
eliminate tap water variability effects. The flow of water continues until 
the differential pressure increases 8.0 psi greater than the initial 
pressure drop at which time the total volume of water (gallons) which has 
flowed through the cartridge is reported in table 2. 
TABLE 2 
______________________________________ 
Cartridge 1B 
Cartridge 1 (Prior Art) 
______________________________________ 
Water pressure 1.3 psid 8.8 psid 
drop 
Retention efficiency 98.3% 99.8% 
of 0.7 micron 
Throughput in gallons 270 gal. 30 gal. 
to 8 psi 
______________________________________ 
As shown in Table 2, cartridge 1 had essentially the same retention 
efficiency as the prior art but had a useful life nine times longer than 
the cartridge on the prior art and provided a much lower pressure drop 
during use. 
EXAMPLE 2 
This example illustrates that the filter cartridge of this invention has a 
significantly greater useful life as compared to a filter cartridge of the 
prior art having essentially the same retention efficiency. 
The filter cartridges shown in Table 4 formed with layers having the 
characteristics shown in Table 3 were configured to form a wound depth 
filter cartridge and the filter cartridge of the invention. Tables 3 and 4 
also show the construction of the pleated filter per se and the portion of 
the depth filter (Meltblown C and D) having essentially the same retention 
efficiency of the pleated filter per se. While these two layers have 
essentially the same retention efficiency, they differ in construction in 
that Meltblown layers C and D are wound and the pleated filter has a 
pleated configuration. 
TABLE 3 
______________________________________ 
Dioctyl Air 
Polypropy- Thick- Phthalate perme- 
Media lene/Con- Weight ness (DOP) ability 
Type struction g/m.sup.2 mils Penetration CFM/ft.sup.2 
______________________________________ 
A Spunbonded 
30 8.0-10.0 2200 
B Spunbonded 35 11.0 360 
C Meltblown 20 6.0 88% 
D Meltblown 20 6.0 71% 
E Meltblown 79 6.5 0.35 
(Calendered) 
______________________________________ 
Spunbonded fiber diameter is 10 to 20 microns 
Meltblown fiber diameter is 2-7 microns 
Meltblown (Calendered) is a gradient density material with 4 different 
media types all calendered together 
TABLE 4 
__________________________________________________________________________ 
MATERIAL TYPES 
Spunbonded 
Spunbonded 
Meltblown 
Meltblown 
Meltblown 
A B C D E 
# of Layers 20 20 35 25 1 pleated 
__________________________________________________________________________ 
Inlet of Filter to----------------------------------------------- 
--Outlet of Filter 
Filter Cartridge 
Description 
Depth Wrapped Depth X X X X 
(Prior Art) 
Depth/Pleat Wrapped Depth X X X 
(Invention) over pleated 
Wrap 1 Wrapped Inside X X 
media only 
Pleat P Pleated media X 
only 
__________________________________________________________________________ 
The depth filter (prior art) and depth/pleat filter C (invention) were 
positioned in the same size housing having a length of 4.0 inches, a 
diameter of 2.8 inches and an inner core diameter of 1.4 inches. 
In an initial test, the retention efficiencies were determined for the 
prior art wound depth filter cartridge, the filter cartridge of the 
invention, the pleated filter per se and the portion of the wound depth 
filter believed to have essentially the same retention efficiency as the 
pleated filter. 
Retention efficiency was measured in accordance with the procedure set 
forth in Example 1 except that the measurement was effected for a particle 
range from 0.6 to 5.0 microns. Retention efficiency as % is shown in Table 
5. 
TABLE 5 
______________________________________ 
% Retention Efficiency for each Particle size band 
Particle Size Microns 
0.6-0.8 0.8-1.0 
1.0-2.0 
2.0-5.0 
______________________________________ 
Pleat P, pleated only 
70.2 88.4 96.5 99.9 
Wrap I, inside wrap media 
C & D 62.4 87.3 91.5 99.9 
Depth/Pleat (Invention) 78.0 92.3 99.5 99.9 
Depth (Prior Art) 65.5 89.8 95.8 99.9 
______________________________________ 
As shown in Table 5, the Pleat P, pleated only filter has essentially the 
identical retention efficiency as the Wrap I, inside wrap media C&D 
filter. The surface area of the Pleat P, pleated only filter was 6.0 
ft.sup.2. 
In an initial test, the pressure drop of both the prior art depth filter 
cartridge and the filter cartridge of this invention were measured with 
reverse osmosis (RO) water which was introduced into the filter at a rate 
of 4 gallons per minute. The pressure drop with the filter cartridge of 
this invention was 3.5 psi while the pressure drop of the depth filter 
cartridge was 7.7 psi. Thus the pressure drop of the filter cartridge of 
this invention was 55% lower than the pressure drop of the prior art depth 
filter cartridge. 
In order to determine the useful life of each of the prior art depth filter 
cartridge and the filter cartridge of this invention, they were installed 
into the same sized housing with a 1 gallon per minute flow controller 
downstream. RO water with a challenge RO water-dust mixture containing 80 
ppm dust particles was filtered at a constant flow of 1 gallon per minute. 
Both pressures upstream of the filter cartridge and downstream of the 
filter cartridge were measured. The filtration was conducted in two test 
runs wherein the filtration in the depth filter cartridge was continued 
for a time until a pressure drop between the cartridge inlet and the 
cartridge outlet was 40 psi. Filtration with the filter cartridge of this 
invention was continued until a pressure drop between the cartridge inlet 
and the cartridge outlet was 40 psi or less. The results of the first run 
are shown in FIG. 7. As shown in FIG. 7, the throughput in gallons until 
40 psi was reached for the prior art depth filter was 16 gallons while the 
throughput for the filter cartridge of this invention at only 18 psi was 
50 gallons. These results show at least about a 200% increase of useful 
life for the cartridge of this invention as compared to a prior art depth 
filter cartridge having equivalent retention efficiency. 
The results of the second run are shown in FIG. 8. As shown in FIG. 8, the 
pressure drop of 40 psi with the prior art depth filter was obtained at 20 
gallons throughput while the throughput with the filter cartridge of this 
invention at 40 psi was 57 gallons. These results show at least about a 
190% increase of useful life for the cartridge of this invention as 
compared to a prior art depth filter cartridge having equivalent retention 
efficiency. 
In final comparison tests, the useful life of the wound depth filter of the 
prior art was compared with the useful life of the filter cartridge or 
this invention when challenged with the same Bedford Mass. tap water 
containing colloidal and hard particles at a flow rate of 3 gallons per 
minute. Capacity/Throughput (life) was determined by the method set forth 
in Example 1. 
As shown in FIG. 9 the throughput attained in one run when reaching a 40 
psi pressure drop across the prior art depth filter cartridge was 235 
gallons while the throughout with the filter cartridge of this invention 
with the same pressure drop was 330 gallons. This result shows at least 
about a 40% increase in useful life when exposed to colloidal particles 
with the filter cartridges of this invention as compared to a prior art 
filter cartridge having equivalent retention efficiency. 
As shown in FIG. 10 the throughput attained in a second run when reaching a 
40 psi pressure drop across the prior art depth filter cartridge was 205 
gallons while the throughout with the filter cartridge of this invention 
with the same pressure drop was 375 gallons. This result shows at least 
about an 80% increase in useful life as compared to a prior art filter 
cartridge having equivalent retention efficiency. 
Thus, the filter cartridge of this invention exhibit a significantly 
extended useful life as compared with prior art depth filters when exposed 
to either hard particles or hard particles and colloidal particles. 
Referring to FIG. 2, the pleated final filter cartridge 40 of the prior art 
is shown. The cartridge 40 is presently utilized as a final filter in 
series with the cartridge 10 shown in FIG. 1B. The cartridge 40 comprises 
a pleated screen or surface filter 42 which surrounds a core 44 and is 
provided with a sealing cap 46 and a second cap 48 having an outlet 50. 
Referring to FIG. 3, the filter cartridge 52 includes a wound depth filter 
or a cylindrical seamless depth 54 filter having a plurality of layers 
having differing micron retention characteristics and a spiral pleated 
screen or surface filter 56. If desired, a porous sleeve can be interposed 
between depth filter 54 and screen or surface filter 56 to provide support 
and promote fluid flow. The cartridge 52 includes core screen 36. 
Referring to FIG. 4, an alternative filter cartridge 60 of this invention 
is shown. The cartridge 60 includes a pleated screen or surface filter 62 
and the wound depth filter or cylindrical seamless depth filter 64 which 
are separated by and supported by screen 68. The cartridge 60 includes 
core screen 36. 
Referring to FIG. 5, an alternative filter cartridge 70 of this invention 
is shown. The cartridge 70 includes the wound depth filter or cylindrical 
seamless a depth filter 72 and a screen or surface filter layer which 
includes two pleated screen or surface filters 74 and 76 which are 
arranged concentrically adjacent relative to each other. The pleated 
filters 74 and 76 are separated from depth filter 72 by screen 78. Screen 
80 separates pleated surface or screen filter 82 from pleated filters 74 
and 76. Thus, as shown in FIG. 5, the filter cartridge of this invention 
can have a plurality of pleated layers and each pleated layer can comprise 
one or more pleated filters. 
Referring to FIG. 6, the filter cartridge 86 has an inlet 88 positioned at 
the central portion thereof rather than having the outlet positioned at 
the central portion thereof as exemplified by the filter cartridge 10 of 
FIG. 1. The filter cartridge 86 includes a pleated surface or screen 
filter 87, a wound depth filter or cylindrical seamless depth filter 89 
and a support screen 90. Flow of fluid to the filters is in a direction 
the reverse of the arrows 29, 29A and 29B shown in FIG. 1A.