Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
113~731
I Background of the Invention
This invention relates generally to filters for
liquids, and more particularly, to gravity filters which
'0 employ filter beds comprising particulate filter media.
Generally, high rate gravity filter~, i.e.,
filters designed to work at high flux rates ranging from 8
to 60 gallons per minute per square foot, include a filter
bed composed of particulate filter media. The filter bed is
typically supported by planar m~embers which extend over the
horizontal cross-section of the filter tan~. In such systems
the fllter liquid is introduced into the tank above the
filter bed and flows downwardly through the filter bed,
through tubular extensiOns or the like provided in the
supporting member into a chamber below the filter bed. Upon
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1 entering this lower tank chamber, the effluent filter liquid
exits through an outlet provided in -the-lower tank chamber.
In the past, the filter bed supporting-member
included a flat plate which, when used in larger size filter
cells, required, in addition to peripheral support flanges
provided on the tank wall surfaces, a relatively bulky
assembly of beams and support columns extending bet~een the
underside of the support plate and the bottom of the tank.
Each support structure is ~uite heavy and has been a costly
and time-consuming item in the manufacture of such liquid
filters.
Further, such filters are usually cleaned by passing
a fluid, such as water or a mixture of air and ~ater, through
the bed in a direction opposite to that used during normal
~5 filter operations. In such reverse-Elow backwashing of
filter beds, it is desirable to design the apparatus so that
the backwash fluids (liquid and air) are evenly distributed
over a horizontal cross-sec~ion o~ tlle Eilter bec1. In an
attempt to attain this goal with resue~ct to the backwasll air,
a multipl:icity of pipes (hereinaEter refcrrcd to ~s secondary
pipes)of varyin~ length have becn providcd extelldincJ horizontally
from a supply header in the ]ower tank chamber wllich Ulli-
formly distribute the a:ir over tl-e area of the filter bed
support plate~ Tubular extensions, mounted within the filter
2~ bed support plate over its entire area, distribute the back-
wash air delivered by the secondary pipes in a uniform
manner to the filter bed through air passages found therein.
~lowever, such filters have proven to be costly since a great
many of such secondary pipes are reyuired to achieve
sufficien-t backwash air distribution.
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An additional problem encountered in the use and
construction of high rate gravity filters is that at least
four valves are usually required in order to control the
flow of the filter and backwash liquids, namely, a first
valve to control the flow of the influent, raw liquid to be
filtered, a second valve to control the flow of the effluent
filtered liquid, a third valve to control the flow of the
influent backwash liquid and a fourth valve to control the
flow of the effluent, used backwash liquid. These valves
are quite expensive since they are usually equipped with
mechanical, automatic command controls that requires the
use of delicate instrumentation and thereby raise the total
cost of constructing and maintaining such filters.
Accordingly, one object of this invention is to
provide a new and improved gravity liquid filter.
Still another object of the instant invention is
to provide a new and improved apparatus for mounting a filter
support plate within a liquid filter.
A further object of this invention is the provision
of a new and improved filter support plate which facilitates
the distribution of backwash air evenly over the filter bed.
A still further object of the instant invention
is to provide a filter support plate which enables the
elimination of secondary air distribution tubular extension
pipes in the lower filter tank chamber.
One other object of this invention is the provision
of a filter apparatus having a reduced number of required
valves for controlling the flow of influent and effluent
liquids.
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il3~731
Summary of the Invention
The filtering apparatus for liquids of the present
invention comprises a filter tank having upper and lower
chambers, a fluid inlet assembly communicating with the
lower tank chamber, the inlet assembly including at least one
header member within the lower chamber which extends substan-
tially horizontally across a substantial portion of the
length of one dimension of the lower chamber, means within the
tank for supporting a filter material bed, which filter bed
supporting means divides the tank into upper and lower
chambers and is at least partially structurally supported by
the header member, means extending through the filter beds
supporting means for providing fluid communication between
the tank upper and lower chambers, a bed of filter material
within the upper tank chamber having a bottom surface defined
and supported by the filter bed supporting means, an influent
filter liquid inlet communicating with the tank upper chamber,
an effluent filter liquid outlet communicating with the tank
lower chamber, and an effluent backwash liquid outlet
communicating with the tank upper chamber.
The filter bed supporting means may include a
corrugated plate which is at least partially structurally
supported by the header member or, alternatively, the filter
bed supporting means may include substantially horizontally
extending beam members which are at least partially
structurally supported by the header member and a substantially
plainer plate which is at least partially supported by the
beam members.
1~3(~731
The drawings and the following detailed description
are directed not only to the invention claimed in the
present application, but also to embodiments of the filtering
apparatus for liquids which are the subject of a co-pending
divisional Canadian patent application, filed by the
applicant Hydrotechnic Corporation, entitled "Filtering
Apparatus for Liquids."
Description of the Drawings
A more complete appreciation of the invention and
many of the attendant advantages thereof will be readily
appreciated as the same becomes better understood by
reference to the following detailed description when con-
sidered in connection with the accompanying drawings wherein:
Fig. 1 is a plan view, partially broken away, of
one embodiment of the liquid filter of the present invention;
Fig. 2 is a section view taken along line 2-2 of
Fig. l;
Fig. 3 is a detail view in cross-section of area
A in Fig. 2 showing a filter bed support plate and
cooperating structure of the present invention;
Fig. 4 is a section view taken along line 4-4 of
Fig. 3;
Fig. 5 is a plan view, partially broken away, of
another embodiment of a liquid filter according to the
present invention;
Fig. 6 is a section view taken along line 6-6 of
Fig. 5;
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Fig. 7 is a detail view of area B of Fig. 6
showing another filter bed support plate and cooperating
structure of the present invention; and
Fig. 8 is a section view taken along line 8-8 of
Fig. 7.
1~3V73~
l Description of the PreEerred Embodiments
Referring now to Figs. 1-4, a liquid filter,
generally denoted as lO, according to one embodiment of this
invention is shown. Liquid filter lO is illustrated as a
relatively large rapid gravity filter having a multiplicity
of cells 12 (2 shown in Fig. l) designed to work at high
flux rate ranging from 8 to 60 gallons per ~inute per square
foot. However, as will become clearer hereinbelow, various
features of the present invention may be employed in sm~lle~-
size liquid filters. Further, the following description will
generally make reference to a single cell 12, it being under-
stood that additional cells may be provided having substan-
tially identical structure and incorporating the features of
the present invention.
Liquid filter 10 is generally constructed having
an upstanding tank 14 of reinforced concrete construction
having a bottom wall 16, outer, side walls 18 and interior
partitions 20 between adjacent cells 12. It is understood
that although the liquid filter cells are shown as having a
square cross-sectional configuration and as being formed of
concrete, other configurations and materials may be employed
within the scope of the present invention.
In general, in liquid filters of this type, the
raw fluid which is to be filtered (hereinafter referred to
2~ as "filter liquid") is introduced in the upper portion of
tank 14 and flows through a bed of particulate filter media,
such, for example, as sand or gravel, wherein entrained
liquid and/or solid impurities are removed by the action
of the media. The filtered liquid passes from the filter
bed into the lower portion of tank 14 through appropriate
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1 passages from where it is removed. The filter bed is
adapted to be cleaned by passing a fluid, such as water
or a mixture of air and water, through the bed in a
direction reverse of that during normal filtering operations.
Still referring to Figs. 1-4, the filter bed 22
is supported within tank 14 by a filter bed support element
which, in the present embodiment, comprises a corrugated
plate 24, which plate comprises one feature of the present
invention. As best shown in Figs. 2-4, the corrugated filter
bed support plate 24 which divides tank 1~ into upper and
lower chambers 34, 36, respectively, may itself be supported
by at least one air header 26 which functions, as described
in detail hereinbelow, as an inlet for air during the
reverse-flow backwashing of the filter bed. The air header
26 is in turn supported by the upper ends of a plurality of
support columns 28 whose lower ends bear against the upper
surface of tank bottom wall 16. ~dditionally, a perforated
plate or screen 25 (shown in phantom in Fig. 3) may be
placed over corru~ated plate 2~, bu~ such arran~ement is
optiona]-
Air header 26 provides a convenient and economical
support apparatus for the filter support plate which, in the
past, was usually supported by flanges formed in the cell
` walls and/or additional support structures. Such headers
are often found in liquid filters of the type of the present
invention and are employed for the introduction of air during
the reverse-flow backwash of the filter bed. In the case
where only a single header is provided, it preferably
traverses over the horizontal cross-sectional area of the
cell in the vicinity of one of the center lines thereof.
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1 The unique corrugated construction of plate 24 renders it
sufficiently rigid so that it may support relatively wide
filter beds while itself being supported only by the header.
Additionally, when the filter cells are relatively
small, it has been found that the corrugated nature of plate
24 provides sufficient rigidity to the plate by itself,
so that it is not necessary to provide additional support in
any form. In such cases, air header 26 may be built with
lighter pipe and spaced a distance below corrugated plate 24.
Turning to Figs. 3 and 4, a detailed view of one
air header 26 supporting corrugated filter bed support plate
24 is shown. The lower surface of corrugated plate 24 defines
a plurality of channels 30, the base portions 31 of channels
30 being mounted on the top of air header 26. In order to
provide fluid communication between upper and lower tank
chambers 34, 36, tubular extensions 38 are mounted in and
pass through plate 24. Each extension has an axial passage
formed therein and upper and lower Eluid ports 40, 42
respectively conununicating with the passage.
The header is urovidcd with air outlets, such as
nipples 27, through which the air exit~s into the lower tank
chamber. Nipples 27 are located adjacent to corrugated
plate 24 in a manner such that they extend into channels 30
defined by the lower surface oE the corrugated plate. During
the reverse flow backwashing of the filter, air exits from
header 26 through nipples 27 and is conducted in a uniform
fashion through channels 30 over the bottom surface of
corrugatelplate ~4. The air is transmitted into the upper
tank chamber through tubular extensions 38 and, due to its
uniform distribution through channels 30, is uniformly
: ~ 113C~731 ~ `
1 distributed over the horizontal cross section of the filter
bed. Thus, by virtue of channels 30, the need for secondary
air pipes previously necessary to provide uniform backwash
alr distribution over the filter bed is eliminated.
As mentioned hereinabove, another feature of the
present invention is that the number of relatively expensive,
mechanical valves and complementary instrumentation, which
control the liquid flow of the filter and backwash liquid is
reduced from four to two per filter cell in comparison to
conventional liquid filters of this type. Again referring to
Figs. 1 and 2, a flume 44 for the influent filter liquid is
preferably provided on the outside of and integral with the
tank side walls 18 at a height somewhat above the top of
filter bed 22. Openings 46 define influent filter liquid
inlets and fluidly interconnect the interior of tank upper
chamber 34 and flume 44. Float-type valves ~8 having raised
seats 50 adapted to sealingly engage openings 46 are pivotally
attached, as by pins 52, directly beneath each opening 46.
Backwash launders or troughs 5~ are provided in upper tank
chamber 34 having upper ed~es somewhat above the level of
openings 46, ~or reasons which will become clearer hereinbelow.
An outlet pipe 56 for the effluent filtered liquid
passes through tank side wall 18 into lower tank chamber 36
and,similarly, inlet pipes 58 and 68 (which leads to header-
26) for influent backwash liquid and air respectively are
.. . .
provided. Main supply pipes 60, 62 carry the influent back-
wash liquid and air to be supplied to header 26, respectively,
and are located adjacent to the liquid filter and may be
enclosed within an integral, housing 64, a portion of which
is shown in Figs. 1 and 2.
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.
1 In the filtering operation, the influent filter
liquid travels throu~h flume 44 and is dispensed over filter
bed 22 through opening 46 passing float valve 4~ which is
normally open. The filter liquid passes through filter bed
~5 22, the sold impurities entrained therein being removed by
the filter media. The filtered liquid passes into lower tank
chamber 36 through tubular extenslons 38 and exits through
the effluent filter liquid ~utlet pipe 56.
In the reverse-flow backwashing of the filter bed,
the influent backwash fluid which may include backwash liquid,
such as water, introduced through inlet pipe 58, and air
introduced through header 26 passes from lower tank chamber
36 into upper tank chamber 34 through tubular extensions 38,
and moves upwardly through filter bed 22 dislodging and
cleaning the particulate filter media. When the backwash
fluid level increases within upper tank chamber 34 over the
level of the liquid in the influent flume 44, the float
valves ~8 are automatically closed, their buoyancy causing
them to pivot so that the raised seats S0 pivot into sealing
arrangement within opellings 46. The backwash fluid level
continues to rise until the fluid (containing the impurities
dislodged from the filter bed) over10ws i~to backwash
trough 54 from where it is directed to a backwash launder
pipe 66 (Fig. 1).
2S As mentioned hereinabove, in prior liquid filters
of this type, mechanical control valves were necessary to
control the flow of influent filter liquid into the tank
upper chamber and to control the flow of the effluent back-
wash fluid. However, by the construction described above,
both these valves may be eliminated. This results from the
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. .
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1 fact that the backwash troughs 54 are loca-ted at a level
- higher than the level of the liquid in the cell during
filtration. Thus, as the backwash fluid level risesj the
float valves are automatically self-closed thereby
prohibiting the introduction of dirty backwash water in the
raw water influent flume.
Referring now to Figs. 5 through 8, a liquid
filter of generally the same type as discussed above and
incorporating the valve system and structural air header
features of the present invention is shown. Thus, elemen~s
in this embodiment will be designated by the same numerals
as identical or corresponding elements shown in F1gs. 1
through ~, primed.
~nother embodiment of a filter bed support assembly
is incorporated in the liquid filter 10' illustrated in
Figs. 5-8. As seen in Figs. 5 and 6, influent backwash
llquid and air inlet pipes 58' and 68' communicate with the
lower tank chamber 36' and, similarly, an effluent filter
liquid outlet pipe 56' is provided. An inf~uent filter
liquid flume ~' directs filter liquid through openings 46'
past float valves ~8' and over filter bed 22'. The
filtering and reverse ~low backwashing operations are sub-
stantially the same in the use of liquid filter 10' as was
described in connection with the liquid filter 10 shown in
Figs. 1-~, the effluent backwash *luid being removed by
backwash troughs 54'.
Reerring to Figs. 6-8, a filter bed support plate
80 having a substantially planax configuration is provided
and is supported by a series of relatively small, light
beams 82, preferably having a channel shape cross-section,
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1 which themselves are preferably supported ~y at least one
header 26' which is mounted on support columns 28'.
Header 26' may be provided with perforations 84 in its wall
in lieu of nipples 27 as shown in Figs~ 3 and 4 in,the
previously described embodiment as will be understood by
those skilled in the art. Although several horizontally
extending support light beams are used in this embodiment,
the support structure for the filter bed support plate 80
' is still much lighter and less expensive than conventional
apparatus in present use because of the use of the air
header as air pipe and as a structural beam.,
As seen in Fig. 7, header perforations 84 are
provided inbetween beams 82. Adjacent pairs of beams 82
in cooperation with the lower surface of support plate 80
define channels 88 which transverse the underside of support
plate 80. Thus, in a similar manner as in the embodiment
shown in Figs. 1-4 and described above, during the reverse
flow backwashing of the filter, air exits from header 26'
'through perfora~ions 8~ and is conducted in a uniform fashion
through channels ~8 over the bottom surface of support plate 80.
The use of the air headers as support elements for
the,filter bed support plate has been found to substantially
reduce the cost of manuEacturing liquid filters of the type
described hereinabove. The simplification in both design and
construction resulting from such use is substantial.
Obviously, numerous modifications and variations of
the present invention are possible in the light of the above
teachings. It is therefore to be understood tha~ within the
- ' scope of the appended claims the invention may be practiced
otherwise and as specifically described herein.
.
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