Water filter abstract
A composite water filter for reducing the cyst content for drinking
water utilizing a non-woven microfiber layer prefilter wrapped over
a porous carbon block filter to retain at least 99.95% of cyst-size
particles while retaining a relatively low pressure drop and high
Water filter claims
1. A high efficiency, low pressure drop water purification filter
for cyst reduction comprising: an inner porous carbon block element
made of bonded carbon particles having a nominal size range of about
40 .mu.m to 600 .mu.m and a block density in a range of about 0.3
gm/cm.sup.3 to 0.75 gm/cm.sup.3; an outer wrap comprising a non-woven
fiber layer enclosing the carbon block and capable of retaining
particles as small as 3 .mu.m; and, said fiber layer supported on
said carbon block to prevent collapse and sealed at the interface
between the layer and the block at both axially opposite ends and
along opposed enclosing edges of the layer.
2. The filter as set forth in claim 1 wherein said fiber layer
comprises glass fibers.
3. The filter as set forth in claim 1 wherein said fiber layer
comprises meltblow plastic fibers.
4. The filter as set forth in claim 1 wherein said porous carbon
block element comprises a hollow cylindrical block.
5. The filter as set forth in claim 1 including a highly porous
backing layer enclosing the fiber layer.
6. The filter as set forth in claim 5 wherein said backing layer
comprises a spun bonded paper layer.
7. The filter as set forth in claim 1 wherein the fiber layer is
covered on both faces with a highly porous backing layer comprising
spun bonded paper layers.
Water filter description
BACKGROUND OF THE INVENTION
 The present invention relates to filters for the purification
of drinking water and, more particularly, to the use of a pre-filter
media with a carbon block filter element to remove cysts, permit
the use of a less dense carbon block, and to improve flow rate and
 Historically, carbon block filters, comprising carbon particles
bonded under pressure, have provided a filtration media that has
performed a multitude of tasks in the water treatment industry.
Carbon block is used to reduce heavy metals, chlorine, volatile
organic compounds, sediment, cryptosporidium, giardia and other
protozoan cysts, and improve taste and odor. The block structure
must be dense and composed of very small particles to remove cysts
and therefore the resultant pressure drop across the block is very
high for a given water flow rate. In addition, these high density
blocks will tend to filter out all types of particulate matter present
in the water with high filtration efficiency. This results in premature
plugging of the block pores and more frequent filter changes.
SUMMARY OF THE INVENTION
 An improved dual stage filtration carbon block is disclosed
that allows for reduced pressure drop while still maintaining the
filtration efficiency to remove cysts. Recently, a class of filtration
media has emerged that improves the filtration efficiency of particulate
matter. This media is typically melt blown fiber or glass fiber
deposited on or between spun bonded papers.
 The present invention utilizes this media as a pre-filtration
wrap around a carbon block. The resultant filter possesses properties
unlike that of present production carbon block in that it filters
and retains cysts and other small particles on the outer wrap and
utilizes the carbon block inner core as the chemical filter. Current
production blocks sometimes are constructed with a pre-filter wrap;
however, the wrap that is utilized is only used for course sediment
removal and to cover the block for aesthetic reasons. This invention
utilizes a wrap specifically formulated for fine particle removal.
The result of this invention is a true dual stage filter where the
density of the carbon block and resultant pressure drop of the carbon
block filter can be much lower than a block that is currently designed
to remove cysts.
 In a presently preferred embodiment, a high efficiency,
low pressure drop water purification filter particularly adapted
for cyst reduction includes an inner porous carbon block element
that is made of bonded carbon particles having a nominal size range
of about 40 microns to 600 microns and a block density in the range
of about 0.3 gm/cm.sup.3 to 0.75 gm/cm.sup.3; and outer wrap utilizing
a non-woven fiber layer that encloses the carbon block and is capable
of retaining at least 99.95% of particles as small as 3 microns;
and wherein the fiber layer is supported on the carbon block to
prevent collapse and is sealed at the interface between the layer
and the block at both axially opposite ends and along opposed enclosing
edges of the layer.
 The non-woven fiber layer may comprise glass fibers or melt
blown plastic fibers of, for example, polypropylene. Preferably,
the non-woven fiber layer is provided with a highly porous backing
layer or layers to provide support and protection for the non-woven
layer. The backing layer may comprise a spun bonded paper layer
and the interface of the non-woven fiber layer with the carbon block
may also be covered with a highly porous backing layer or the same
or similar spun bonded paper layer.
BRIEF DESCRIPTION OF THE DRAWINGS
 FIG. 1 is a vertical sectional view through a water purification
filter made in accordance with the present invention.
 FIG. 2 is a graph showing net pressure drop versus flow
rate comparing prior art filters with a filter of the present invention.
 FIG. 3 is a graph showing flow rate versus inlet pressure
and comparing the performance of prior art filters with filters
of the present invention.
 FIG. 4 is a graph showing the cyst reduction performance
of prior art filters versus filters of the present invention.
 FIG. 5 is a graph showing flow rate versus total flow volume
in prior art filters and filters of the present invention operating
to remove cysts.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
 Referring to FIG. 1 a filter 10 made in accordance with
the present invention includes a porous carbon block 11 surrounded
by an outer wrap 12 which act together to provide a filter for high
cyst removal capability and relatively low pressure drop. The carbon
block 11 and outer wrap 12 are enclosed together in an upper end
cap 13 and a lower end cap 14 so that radial flow of water to be
filtered from the outside of the filter 10 to the inside of the
carbon block 11 must pass first through the outer wrap 12 without
by-pass. The filter 10 is typically sealed in the end caps 13 and
14 with a polyolefin hot melt adhesive 24. Similarly, the edges
of the outer wrap 12 which includes a non-woven fiber layer 19
as will be described in greater detail, must be sealed with a butt
joint or overlapping joint where the opposed edges of the outer
wrap 12 meet. The sealed joint may utilize an adhesive or may comprise
a heat seal. The filter 10 is of a type adapted to be placed in
a hollow housing or sump (not shown) and enclosed with a housing
cap (also not shown), the housing cap providing an inlet to the
outside of the filter for untreated water and an outlet from the
hollow interior 15 of the carbon block for filtered water all in
a manner well known in the art.
 The carbon block 11 is made from fine particulate carbon
mixed with a suitable binder, such as polyethylene, and formed under
heat and pressure into a solid porous block. Variations in the particle
size and the formation conditions result in carbon blocks of varying
density and porosity. In the porous blocks preferred for use in
the present invention, the carbon particles are preferably in a
size range of about 40 microns to about 600 microns and the formed
carbon block has a density in the range of about 0.3 gm/cm.sup.3
to about 0.75 gm/cm.sup.3. Carbon blocks made in accordance with
the foregoing specifications are generally considered to be unsuitable
for cyst removal. However, the actual density of carbon blocks useful
in this invention will vary quite widely depending on the type of
the carbon (i.e. the density and size of the carbon particles) and
other materials used in the construction of the block. The current
applicable standard for cyst removal in a filter for domestic drinking
water use requires removal of more than 99.95% of cysts, based on
the nominal particle size as small as 3 microns. However, these
carbon blocks are desirable nevertheless for their ability to remove
other contaminants such as heavy metals, chlorine, VOCs and sediment
while exhibiting a desirable low pressure drop.
 In accordance with the present invention, a low density
carbon block 11 is combined with an outer wrap 12 utilizing a non-woven
fiber layer 19 that is capable of filtering and retaining at least
99.95% of particles as small as 3 microns. The combination of a
pre-filter for cyst removal utilizing a non-woven fiber layer 19
as part of the outer wrap 12 and a low density carbon block 11 provides
a unique combination that permits cyst removal at relatively low
pressure drop and without premature clogging of the filter.
 One particularly suitable non-woven fiber layer 19 is a
micro-glass material made by Lydall, Inc. and sold under the trademark
LYPORE. This material comprises a dense mat of extremely fine glass
fibers (with a nominal diameter of about 1 .mu.m) laid down in a
mat having a thickness of 24 mils (0.6 mm) to provide a mean pore
size of 2 microns. The fibers are held in the mat with an adhesive
binder, such as EVA.
 The outer wrap 12 may alternately include a non-woven fiber
layer 19 comprising melt blown plastic fibers. Such a material may
comprise, for example, polypropylene fibers with a nominal diameter
of about 3 .mu.m. The other physical properties of the non-woven
plastic fiber layer are similar to those of the non-woven glass
fiber layer. Both the non-woven glass fiber and non-woven plastic
fiber layers 19 are typically laid on a backing layer 16 comprising
a highly porous spun bonded paper. It is preferable to provide a
similar backing layer 16 to the other side of the non-woven fiber
layer 19 to protect the interface of the wrap 12 with the carbon
 Referring now to FIGS. 2-5 the performance of filters 10
made in accordance with the present invention and utilizing either
a glass fiber outer wrap or a fine melt blown plastic outer wrap
12 are compared with (1) similar carbon blocks with no wrap or a
coarse fiber wrap, and (2) with high density blocks (suitable for
cyst removal, but having a high pressure drop) having a coarse melt
blown wrap or no wrap whatever. In each of the graphs of FIGS. 2-5
the various plots are numbered consistently to show a high density
block with no wrap 17 a high density block with a coarse wrap (the
wrap per se not capable of retaining cysts) 18 a low density block
20 with no outer wrap, a low density block 21 with a coarse outer
wrap (the same wrap as filter 18), a low density block 22 of the
present invention using a non-woven glass fiber layer 19 in the
outer wrap 12 and a low density block 23 of the present invention
having a fine melt blown micro-fiber layer 19 in the outer wrap
 The high density blocks 17 and 18 are outside the ranges
of particle size and block density set forth above, whereas, the
low density blocks 20-23 are all within those ranges.
 Referring specifically to FIG. 2 the pressure drops through
the high density blocks 17 and 18 are seen to be much higher than
pressure drops across any of the low density blocks 20-23. The addition
of a coarse melt blown outer wrap (not capable of retaining cysts)
does not significantly increase the pressure drop of either the
high density or low density blocks. The addition of the non-woven
glass fiber layer 19 to the low density block 22 and the addition
of the non-woven meltblown fiber layer 19 to the low density block
23 increases the pressure drop slightly, but the pressure drops
remain significantly less than pressure drop across the high density
blocks 17 and 18.
 Referring to FIG. 3 both high density blocks 17 and 18
produce less than 2 gpm flow of water at 30 psi inlet pressure.
The low density blocks 20 and 21 with no wrap and with a coarse
wrap, respectively, produced over 8 gpm flow at 30 psi inlet pressure.
The low density blocks 22 and 23 respectively, having the non-woven
layers 19 of glass fibers and melt blown fibers of the present invention
produced between 5 and 7 gpm at 30 psi pressure. These flow rates
are only slightly lower than for the low density blocks with no
wrap or coarse wrap, but substantially higher than either of the
high density blocks 17 and 18.
 FIG. 4 shows the results of the cyst reduction tests for
the same six filter blocks tested in the preceding FIGS. 2 and 3.
For these tests, surrogate cysts comprising three micron latex microspheres
were utilized. Both high density blocks 17 and 18 passed the cyst
removal requirement of more than 99.95% removal, however, these
dense blocks are specifically constructed for cyst removal as indicated
above. The low density blocks 20 and 21 having, respectively, no
wrap or a coarse wrap failed completely the cyst removal test. These
blocks exhibited extremely poor performance that continued to degrade
through the course of the tests from an initial reduction of 60%-75%
to as low as 0%. By comparison, the low density block 22 with the
fine non-woven glass fiber layer 19 and the low density block 23
with the fine melt blown non-woven plastic fiber layer 19 both passed
the cyst removal test requirement of greater than 99.95% removal
for all four sample points. These results show a very significant
increase in performance over identical low density blocks 20 and
21 having no wrap or a very coarse melt blown wrap. These tests
also show that a low density block 22 or 23 with an appropriate
non-woven fiber layer 19 will provide essentially the same cyst
removal performance as the high density blocks 17 and 18 but with
a much lower pressure drop as shown in FIG. 2.
 Referring now to FIG. 5 tests were run to compare the flow
rate through the various filters with total filtered volume to determine
how rapidly the filters plugged when operating to remove cysts.
Both high density blocks 17 and 18 began with relatively low flow
rates of 1-2 gpm and very quickly plugged to drop to a flow rate
of 0.5 gpm after less than 200 gallons total flow. The low density
block 20 with no outer wrap also plugged very quickly at less than
200 gallons total flow even though it began at a much higher flow
rate of greater than 8 gpm. The low density block 21 with a coarse
outer wrap also had a high initial flow rate of greater than 8 gpm,
and performed best of all the filters tested and was able to process
700 gallons before plugging. This filter, however, has no cyst removal
capability. Both low density blocks 22 and 23 utilizing the fine
non-woven glass fiber layer or the fine meltblown non-woven plastic
fiber layer of the present invention exhibited initial flow rates
between 5 and 6.5 gpm and plugged at slightly more than 300 and
450 gallons total flow, respectively. Both of these filters 20 and
23 with cyst removal capability, performed much better than the
high density cyst removal filters 17 and 18 which plugged at about
only half the total flow.