Note: Descriptions are shown in the official language in which they were submitted.
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TITLE
FILTER UNDERDRAIN SYSTEM FOR BACKWASH FLOW
AND METHOD FOR MEASURING SAME
FIELD OF THE INVENTION
This invention relates to filter underdrain
systems for granular media filters and, more particularly,
to an apparatus intended to improve backwash water flow to a
filter bed and to a method for assisting in the design of
such apparatus.
BACKGROUND OF THE INVENTION
The traditional rapid sand filter has been a
reliable performer in potable water treatment and the
mechanics of the operation and performance of such a filter
have remained largely unchanged over the years. The filter
is a straining device comprising a bottom underdrain
collection system equipped with slotted strainers or the
like which holds a layer of filter sand. Above the sand
layer is a layer (or layers) of hard coal media which is
coarser. A wash water trough is located above the media
layers and is used to direct unfiltered water into the
filter as well as to channel backwash rinse water to a waste
outlet. A backwashing cycle is required when the filter
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media has substantial head loss during operation, sometimes
occurring several times a day due to particle buildup in the
filter. Backwashing fluidizes the media, rinses out the
particles from the interstitial voids and reclassifies the
layers of media
A problem associated with backwashing is the
non-uniform or uneven water distribution which occurs
because of the momentum of the water discharging from the
perforated header or channel. Water at high velocity across
an orifice will not be discharged through the orifice as
readily as when flowing at lower velocity. Backwash
discharge from the underdrain will be greatest in those
portions of the underdrain furthest away from the backwash
water inlet. Such unequal flows cause undesirable
channelling in the media which reduces the efficiency of the
backwash operation and results in filtering problems.
A further problem with many types of filter is the
requirement for a support gravel layer immediately above the
underdrain upon which the sand layer rests. This
requirement results in a deeper overall bed and increased
material requirements for the filter installation. The need
for a support gravel layer also restricts the available
depth for the sand and coal layers which reduces the
filtration effectiveness.
The above-identified problems are discussed in
various patents. Such prior art patents include United
States Patent 3,956,134 (Sturgill) dated May 1976 and
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entitled UNDERDRAIN FOR WATER FILTRATION SYSTEM; United
States Patent 4,214,992 (Sasano et al) dated August 1978 and
entitled WATER COLLECTING AND DISTRIBUTING APPARATUS
DISPOSED IN A LOWER PORTION OF HIGH SPEED FILTER BASIN;
United States Patent 4,331,542 (Emrie) dated August 1980 and
entitled UNDERDRAIN UNIT WITH AIR/WATER BACKWASH FOR
GRANULAR FILTRATION SYSTEM; United States Patent 4,923,606
(Gresh et al) dated February 1988 and entitled PLASTIC
JACKETED FILTER UNDERDRAIN BLOCK; United States Patent
4,995,990 (Weston) dated April 1989 and entitled AIR AND
WATER DISTRIBUTION CONDUIT; United States Patent 5,068,034
(Walter) dated May 1990 and entitled PURIFICATION UNDERDRAIN
WITH MEANS COMPENSATE FOR FLOW AND PRESSURE DIFFERENCES
BETWEEN LATERALS; United States Patent 5,160,614 (Brown)
dated February 1992 and entitled AIR DUCT BLOCK FOR
AIR/WATER UNDERDRAIN SYSTEMS IN GRAVITY FILTERS; United
States Patent 5,149,427 (Brown et al) dated September 1992
and entitled CAP FOR UNDER DRAINS IN GRAVITY FILTERS;
United States Patent 5,413,710 (Roberts et al) dated May
1995 and entitled LATERAL UNDERDRAIN; and United States
Patent 5,462,664 (Neuspiel) dated October 1995 and entitled
FILTER UNDERDRAIN MODULE AND UNDERDRAIN SYSTEM.
The prior art identified above suffers from other
problems, such problems including that the devices disclosed
are not readily adaptable for retrofitting to existing
filter installations; that the devices are prone to plugging
with grit flushed in during the backwash cycle and are
therefore less resistant to structural failure during the
large upward hydraulic thrust generated during backwash;
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that the devices are expensive to purchase and are difficult
and expensive to install, some requiring tedious grouting
procedures or cumbersome and expensive false bottom
structures; that many of the devices are constructed from
tile or porous tile or the like and are therefore fragile
and subject to breakage during installation while inadequate
corrosion resistance is also present; and that some devices
require support gravel layering.
Our earlier United States Patent 5,019,259
(Hambley) dated May 28, 1991 and entitled FILTER UNDERDRAIN
APPARATUS WITH PARTITIONED DISTRIBUTOR CONDUITS, teaches a
filter underdrain apparatus which includes a steel flute or
arch forming a plurality of horizontal distributor conduits.
The conduits are in juxtaposed, laterally spaced
relationship and are constructed to define alternating
conduits and troughs of a filter underdrain. This apparatus
functions well with or without support gravel and reduces
backwash water maldistribution by varying the diameter of
the water inlet/outlet orifices arranged along the length of
the water conduits. While this apparatus is effective in
overcoming many of the problems of the prior art, the
effective diameter of each individual inlet/outlet orifice
in the flute or arch needed to be calculated and attendant
tool changes were required during the manufacturing process
to accommodate the variations in orifice size along the
flute.
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SUMMARY OF THE INVENTION
According to the invention, there is provided a
filter underdrain assembly for controlling backwash water
flow from a backwash water inlet comprising a plurality of
panel members forming a grid like underdrain, each panel
member having a plurality of apertures, the cross-sectional
area of said apertures in said panel members varying between
said panel members, said apertures of said panel members being
located further away from said backwash water inlet having
a lesser cross-sectional area relative to said
cross-sectional area of said apertures of said panel members
closer to said backwash water inlet.
According to still yet a further aspect of the
invention, there is provided a filter underdrain apparatus
for controlling backwash water flow maldistribution from a
backwash water inlet in an underdrain assembly comprising a
plurality of panel members assembled adjacent each other to
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form a grid like underdrain, each panel member having multiple
punched bridges in a surface thereof, each bridge defining
a pair of water inlet/outlet slotted apertures and wherein
the number and size of said punched bridges and slotted
apertures respectively can be varied from panel member to
panel member, said panel members furthest away from said
backwash water inlet having a lesser number of bridges or
smaller slotted apertures from said panel members nearer to
said backwash water inlet, said panel members being operable
to provide a substantially equalised water flow through the
underdrain assembly from said panel members.
According to yet a further aspect of the invention,
there is provided a filter underdrain assembly for
controlling backwash water flow from a backwash water inlet
comprising a plurality of panel members forming a grid like
underdrain, each panel member having a plurality of
apertures, the number or cross-sectional area of said
apertures varying between said panel members, said panel
members located further away from said backwash water inlet
having a lesser number or smaller cross-sectional area of said
apertures relative to said panel members located closer to
said backwash water inlet, said panel members being operable
to substantially equalize water flow from each of said panel
members of said filter underdrain assembly.
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According to still yet a further aspect of the
invention, there is provided a filter underdrain assembly
comprising an arch extending longitudinally in said
underdrain assembly from a water inlet generally located
adjacent one end of said arch, said arch being positioned
above said underdrain assembly and allowing water from said
water inlet to enter the interior of said arch, said arch
having a plurality of perforations extending the length of
said arch, said plurality of perforations having larger
cross-sectional area nearer said water inlet, said plurality
of perforations having smaller cross-sectional area further
from said water inlet.
According to yet a further aspect of the invention,
there is provided a method of equalizing backwash water flow
in a filter underdrain assembly having a water inlet and a
plurality of blocks located relatively closer and relatively
further from said water inlet, each of said plurality of
blocks having an upper surface and a water passageway, holes
extending between said water passageway and said upper
surface, said method comprising blocking a predetermined
number of said holes in a specific number of said blocks such
that the quantity of water flowing from said upper
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surface of said blocks located relatively closer to said
water inlet is substantially similar to said quantity of
water flowing from said blocks located relatively further
from said water inlet.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
Specific embodiments of the invention will now be
described, by way of example only, with the use of drawings
in which:
Figure 1 is an isometric partially sectional view
of a water filter tank or basin incorporating the apparatus
according to the present invention;
Figure 2 is a plan view of a panel member
according to the present invention;
Figure 3 is a bottom view of the panel member of
Figure 2;
Figure 4 is a side view of the panel member of
Figure 2;
Figure 5 is an end view of the panel member of
Figure 2;
Figure 6 is an isometric view of the panel member
of Figure 2;
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Figure 7 is a sectional view taken along 7-7 of
Figure 6;
Figure 8 is a sectional view taken along 8-8 of
Figure 6;
Figure 9 is an isometric exploded view of a panel
member according to the present invention particularly
illustrating the relationship of the panel member and the
seals, relative to the filter underdrain block;
Figure 10 is an isometric view of the assembled
panel member and underdrain block of Figure 9;
Figure 11 is an isometric view of a clamping
bracket used to secure adjacent ones of the panel members of
Figure 1;
Figure 12 is a sectional view of the panel members
in a secured position on the filter underdrain blocks and
further using the assembled position of the clamping bracket
of Figure 11;
Figure 13 is a partial plan view of the grid
structure formed by securing a plurality of panel members to
the filter underdrain blocks;
Figure 14 is an isometric view illustrating an
apparatus used to measure the hydraulic head of water
according to a further aspect of the invention;
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Figure 15 is an isometric view illustrating the
apparatus of Figure 14 in its operating condition with an
inflow of backwash water;
Figures 16A-16E are views illustrating a panel
member according to Figure 2 but further utilising an air
distribution or scouring capability/conduit as used with
water backwash according to a further aspect of the
invention;
Figures 17A and 17B and plan and side views,
respectively, of a panel member utilising air scouring
according to a further aspect of the invention;
Figure 18A is an isometric view of a backwash
water/air system including longitudinal flutes or arches
according to the prior art;
Figure 18B is an enlarged elevation view of the
flute or arch of Figure 18A;
Figure 19 is an isometric view of flutes used in a
backwash water system according to a further development
within the prior art;
Figures 20A-20C are diagrammatic views of a
longitudinal flute or arch according to a further aspect of
the invention which arch is used for test purposes, the
figures not showing the normally used air passageway for
ease of explanation;
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Figures 21A, 21B and 21C are plan, side and
partial bottom views, respectively, of an arch or flute with
air scouring capability according to a further aspect of the
invention;
Figure 22 is a sectional view taken along 22-22 of
Figure 21B;
Figure 23 is a plan view of a typical media bed
illustrating the clay blocks comprising the media bed with
the water orifice holes in the upper surfaces;
Figure 24 is a plan view of a single clay block of
the underdrain;
Figures 25A and 25B are enlarged plan and side
views, respectively, of the clay block of Figure 24;
Figure 26 is an enlarged view particularly
illustrating the plug used to block the holes of the clay
block of Figure 24; and
Figure 27, appearing with Figure 24, is a
sectional view of a seal intended to be located between the
clay block and the panel member which panel member has a
formed ridge or protuberance extending into the seal
according to a further aspect of the invention.
DESCRIPTION OF SPECIFIC EMBODIMENT
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The media bed of an underdrain acts as a filter
medium for obtaining potable water. Filtration occurs when
a feedwater particle is larger than the pores between two
adjacent filtering granules thereby preventing passage of
the particle through the bed. Likewise, when feedwater
particles pass close enough to the surface of a media
granule, the particle may be adsorbed onto the granule.
As the filtering action continues, more and more
spaces or pores between filtering granules become plugged.
As the pores plug, the flow rates through other pores
increase to maintain the set flow rate of the bed.
Particles previously adsorbed in the latter pores are then
subjected to higher flow rates which may strip off the
particles. The number of particles exiting the filter bed
may therefore actually exceed the number of particles
entering the bed. To prevent this, a backwashing operation
is performed. To perform backwashing, filtered feedwater is
pumped up through the bed by reverse flow. This fluidizes
the media and rinses out the dislocated particles from the
interstitial voids. The backwash water is discharged and
the filter'media are then relatively clean thereby to allow
commencement of a more efficient filtering action.
A significant problem associated with the
backwashing operation is the non-uniform or uneven backwash
water distribution which occurs because of the momentum of
the water passing through the perforated header or channel.
Water passing individual orifices in an underdrain at a
relatively high velocity will not be discharged from the
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orifice as readily as when flowing at a relatively lower
velocity. Hence, backwash flow through the filter
underdrain will be greater in those portions of the
underdrain farthest from the backwash water inlet. Over
time this can cause significant disruption of the filter bed
by the aforementioned "channelling" with the accompanying
deterioration in filter performance.
With reference now to Figure 1, the filter
underdrain system according to the present invention is
generally illustrated at 44. It is shown within a bed 20 of
filter media which includes a top layer 22 of anthracite
coal followed by a layer of sand 24. A supporting gravel
layer is not illustrated below the sand layer 24 which
gravel, however, may optionally be provided if desired.
Filters according to the prior art generally use a
top layer of anthracite 22 over a layer of sand 24 as
illustrated. However, filters may operate without the
anthracite layer 22. A layer of fine heavy material, such
as garnet or ilmenite may also be used under the filter
sand. Other filters may operate with materials such as
manganese dioxide, magnesium oxide, activated carbon and the
like.
The filter underdrain 44 and the bed 20 are
located in a concrete, open top tank or basin generally
illustrated at 26 which is defined by bottom slab 28, side
walls 30 and end walls 32. A partition 34, parallel to side
wall 30, defines an overflow trough or gullet 36 for
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receiving backwash water from semicylindrical metal,
concrete or fiberglass troughs 38, which troughs 38 extend
transversely of the basin 26 above bed 20 as is illustrated.
The troughs 38 distribute the incoming water and discharge
the collected backwash water.
A further trough or flume 40 is provided in the
bottom of the basin 26 at one end thereof for receiving the
backwash water. Filtered water is discharged from flume 40
via pipe 42. Pipe 42 is also used to introduce backwash
water back into the flume 40, the media and then to the
trough 40 and basin 26.
Referring to Figures 2 through 8, a filter
underdrain panel according to the present invention is
generally illustrated at 44. It takes a generally
rectangular form which is defined by end walls 46, side
walls 48 and inner panel 50. Inner panel 50 has an upper
surface 52 and a lower surface 54. An elongate brace member
56 is centrally located on lower surface 54 of inner panel
50 and transverse to end walls 46. Brace member 56 is used
for rigidity purposes.
Inner panel 50 further includes a multiple of
generally rectangular apertures in the form of punched
bridges 58 (Figure 4), the bridges 58 being substantially
equidistant from each other and arranged by row and column.
Each bridge 58 defines a pair of slotted water inlet/outlet
apertures 60 (Figure 7) through the upper and lower surfaces
52, 54 of the inner panel 50. The slotted apertures 60 are
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of a dimension sufficiently small to substantially prevent
the passage of filter media thereby allowing for the
elimination of a support layer of gravel above the panels 44
which gravel is principally used to support the sand layer
resting thereon.
The end walls 46 and side walls 48 of panel member
44 also conveniently include a single row of similarly
punched apertures or bridges 58 to provide for cleaning of
the filter media between adjacent panel members 44.
A perimeter flange 62 has a generally L-shaped
configuration in cross-section and extends outwardly from
the end walls 46 and side walls 48 as is illustrated.
A gasket retention wire 64 (Figure 9) of generally
circular cross section is attached to the undersurface of
the horizontal portion of perimeter flange 62. A sealing
gasket 68 is positioned between the underdrain block 66 and
the sealing wire 64 as will be explained.
OPERATION
The filter underdrain panels 44 are installed on
the upper surface of conventional underdrain blocks 66 with
each panel 44 being dimensioned so as to form a cap for each
of the underdrain blocks 66 (Figure 9). A substantially
watertight seal is formed between the panel 44 and the
underdrain block 66 by inserting sealing gasket 68 made from
rubber or other elastomer material between the lower surface
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of the horizontal wall of the perimeter flange 62 of the
panel 44 and the upper surface of the underdrain block 66.
The sealing wire 64 applies point pressure on the gasket 68
to ensure that the gasket 68 conforms to surface
irregularities of the underdrain block 66 as well as to the
undersurface of the horizontal wall of the perimeter flange
62.
The placement of panels 44 in the Figure 1
embodiment follows the placement of the underdrain blocks 66
and will result in a perforate grid like formation of panels
44 (Figures 12 and 13). The panels 44 are secured to the
underdrain blocks 66 by drilling a perpendicular hole into
the mortar 70 (Figure 12) between adjacent underdrain blocks
66, inserting and cementing in place a non-expanding anchor
72 and utilizing a clamping bracket 74 fastened to the
anchor 72 by a threaded nut. Clamping bracket 74 (Figure
11) includes an elongate portion of rigid channel material
having semicircular or elliptical cutaways 76 on either side
thereof to define four(4) pads or contact areas 78, two at
each end, and being substantially centered about hole 80.
Hole 80 is dimensioned to allow insertion of the bracket 74
over the anchor 72 such that each of the contact areas 78
engage one corner of a perimeter flange 62 on four adjacent
panels 44 while the side cutaways 76 allow clearance of the
end walls 62 of panel members 44. Other methods of
attachment could clearly be used.
The dual slotted apertures 60 (Figure 7) act as
water inlets during the filtration cycle and water outlets
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during the backwash cycle. Accordingly, the sizes of such
apertures 60 are relevant since water flowing at relatively
high velocity past an aperture will not be discharged
through that aperture as readily as the same volume of water
flowing at a lower velocity past the same sized aperture.
Thus, the number and size of the punched bridges
58 and their slotted apertures 60 incorporated into any
given panel member 44 define the ratio of open space to
closed space for the particular panel 44 and thereby
controls the degree of water distribution into the above
media bed acceptable in the particular underdrain system
from each panel 44 and further prevents "jetting" of the
water into the media bed. By increasing or decreasing the
number of apertures 60 in any given panel 44 or, likewise,
by varying the size of the slotted apertures 60, the
quantity of water passing can be varied as desired.
Alternatively, the number of apertures 60 may be
varied in a specific panel 44 in the event it is desirable
to do so. It is important, however, to determine the number
and/or size of the apertures in order to allow more water to
escape when water velocity is higher and to allow less water
to escape when the water velocity is lower, the objective
being to obtain a relatively constant head of water over the
length and cross section of the blocks 66 in the basin 26.
A further consideration is to make such size sufficient to
prevent the egress of the media through the panels 44.
To measure the hydrostatic head along the various
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cells and, therefore, to determine the desired release of
water from the panel members 44, reference is made to
Figures 14 and 15. Each of the cells generally illustrated
at 82 comprise an elongate, generally rectangular housing 84
having a closed upper end 86 and an open lower end 88, the
open lower end 88 being dimensioned with a perimeter seal 90
of a size for a typical filter underdrain block 66 (Figure
9). The height of the housing 84 is such that since the
housing 84 is intended to be attached to a filter underdrain
block 66 and operates during the filter backwash cycle, the
height should conveniently extend above the filter bed 20
(Figure 1). In practice, it has been found that a housing
84 having a height of nine (9) feet is sufficient for most
applications.
A float member 92 is suspended within the confines
of the housing 84 and is free to rise and fall responsive to
the backwash water flow into the bottom of housing 84. An
elongate graduated rule 94 is attached to the float member
92 with one end of the rule 94 extending through the closed
upper end 86 of the housing 84. The intervals between
graduations on rule 94 are conveniently three(3) inches
apart. Rule 94 will rise and fall with float 92.
A reference pointer 96 is attached to the upper
end 86 of the housing 84 adjacent the graduated rule 94
extending through the upper end 86 of the housing 84. The
pointer 96 allows determination of the rise and fall of the
float member 92 within the housing 84.
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The float member 92 and the attached graduated
rule 94 are generally centralized within the housing 94 by a
rod 98 mounted transverse to the sides of the housing 84. A
central ring member 83 encircles the body of the graduated
rule 94. Thus, sideways movement of the float member 92
within the housing 84 is restricted to a preset limit.
Conveniently, mounting the rod 98 approximately seventy-
eight(78) inches from the lower end 88 of the housing 84
allows sufficient lift distance for float member 92.
As described in association with Figure 1,
filtered backwash water is periodically introduced into the
troughs or channels 42 running beneath the false bottom and
escapes upward into the filter bed via orifices in the
underdrain 66 to fluidize the filter bed 20 and break loose
particles trapped in the filter media. Since water flowing
at a relatively high velocity across an orifice will not be
discharged through the orifice as readily as when flowing at
a lower velocity, flow from the underdrain elements 66
closest to the backwash water inlet 42 will tend to be less
than the flow through those underdrain elements farthest
from the inlet 42 thereby resulting in a difference in head
and flow maldistribution. The cell 70 allows quantification
of the extent of flow maldistribution by measuring the float
movement thus allowing for appropriate corrective action
such as increasing or decreasing the number and/or size of
the perforations or apertures 60 (Figure 7) in panels 44.
A plurality of housings 72, each being utilized to
acquire a measurement of the rate of flow backwash water
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through an individual underdrain element 66, will provide
head information across the underdrain system. Each of the
individual elements or clay blocks of the underdrain system
need not be tested. Rather, disparate test points are
conveniently chosen. Thus, measurements are first made
along a row of underdrain blocks nearest the backwash water
inlet 42 followed by sample measurements in an area of
blocks further from the backwash inlet 42. Conveniently,
this general procedure may be repeated in columnar fashion
in order to provide a more complete hydraulic water flow
model representative of the existing backwash flow from the
underdrain.
The lower end 76 of the housing 72 of each cell 70
is removably attached to the upper surface of a respective
underdrain element 66 and a substantially watertight seal is
provided. A reference level is established across each cell
70 by float 78 and the backwash cycle is commenced. As
backwash water enters each cell 70 from underdrain element
66, the float 78 rises. The rate of rise of float 78 and
thus the rate of flow of backwash water into each cell 70 is
determined by recording the rise over a predetermined period
as rule 82 moves upwardly through the upper end 74 of the
housing 72 and past the reference pointer 83.
Enough measurements are recorded to build a
representative hydraulic model of backwash flow
distribution. Thereafter, corrective action is taken to
reduce any maldistribution in the backwash flow by
selectively restricting flow through certain of the
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underdrain panels 44 which results in increased flow through
the remaining elements. The testing procedures may be
repeated following panel installation to confirm that the
corrective modifications have resulted in substantially
uniform flow distribution across the underdrain system.
A further embodiment of the invention relates to
the V-shaped arches illustrated in our United States Patent
5,019,259 and also illustrated in Figures 18A and 18B. In
the prior art embodiment shown in those figures, there is
disclosed a plurality of arches 101 joined together with
brackets 102 and positioned over the underdrain filter media
comprising clay blocks 105. The arches 101 have an air
passageway 103 in addition to the water passageway 104 which
allows air scouring to occur during the backwash operation.
Air scouring can improve the removal of impurities in the
filter media.
One problem with the arches illustrated in Figures
18A and 18B, however, was that media retention by the arches
101 suffered; that is, the media could frequently pass
through the air and water openings 110, 111 in the arches
101 so that, over time, the media would become reduced to
such an extent that media replacement was necessary. A
further problem related to the need for multiple tool
changes in producing the air and water holes 110, 111 in the
arches 101 throughout the length of each individual arch
101.
To prevent the egress of media and to assist with
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reducing the number of tool changes, plates or panels 112
were attached to the arches 101 illustrated in Figure 19 on
each side of the upwardly directed portions meeting at the
apex. Each of the plates 112 had a series of rectangular
perforations or apertures 113 punched therein which total
cross-sectional area would relate to the area of the water
openings 111 in the arches 101. The water openings 111
remained in the arches 101 but their cross-sectional area
was constant throughout the length of arch 101 which
assisted the manufacturing process. The openings in the
plates 112 were varied thereby to prevent media egress and
also to adjust water release to obtain a constant discharge
flow rate throughout the length of the arches 101. The
number of apertures 111 in the plates 112 was likewise
varied so as to allow fewer apertures further from the water
inlet. In this case, the apertures 111 were all the same
size.
While the plate attachment process described
overcame the problems of media egress and tool changes,
however, there were unnecessary manufacturing steps still
present and the panels 112 were relatively expensive to
produce and install due to their configuration.
Reference is now made to Figures 20A-20C wherein a
typical arch 200 is shown. This particular arch 200 is a
test arch used to determine proper replacement for arch 101
of Figures 18 and 19 as will be explained hereinafter but
the comments made concerning arch placement and position
also apply to arches normally used in actual operations.
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The length of arch 200 may vary according to the size of the
filter and a plurality of such arches are laid side by side
to cover the width of the filter. Arch 200 conveniently
includes the air passageway found beneficial for air
scouring. However, rather than the plurality of water holes
110, 111 of Figure 18B, there are a plurality of rectangular
openings 202 provided of identical size which are positioned
intermittently along the entire length of the arches 200.
As well, attachment holes 203 are provided which are used to
attach plates 204, shown in greater detail in Figure 20C.
This embodiment allows media retention thereby
preventing the migration of media through the previous holes
in the arches 101. As well, the individual plates 204 which
are readily connected to the arches 200 may be individually
designed with greater or lesser cross-sectional area in the
perforations or apertures punched therein and which plates
204 may likewise be provided with a greater or lesser number
of apertures 202 which may be of the same size. Thus, the
amount of water exiting the plates 204 and used for backwash
can be designed to be relatively consistent along the entire
length of arch 200 by specifically providing plates 204 with
predetermined cross-sectional openings which plates 204 are
then positioned on the arch 200 where desired.
Specifically, the plates will ordinarily be designed with
greater cross-sectional area by way of increased number of
apertures 202 near the entranceway of the water to the arch
200 and with a decreased number of apertures 202 near the
end of the arch 200 downstream from the entranceway. Once
the desired water discharge is obtained, arches as generally
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illustrated at 500 in Figures 21A and 21B are produced.
Arches 500 have a plurality of apertures 501 punched
directly into the arches 500, which apertures 501 are
conveniently horizontal and in double rows as is
illustrated, although vertical apertures could also be used
as well as apertures of virtually any orientation. The
individual apertures 501 will be the same size but the
number of such apertures 501 will typically vary, there
being an increased number of apertures 501 near the water
inlet 503 (Figure 21C) and a reduced number of apertures 502
at the far end of the arches 500 as is illustrated.
The arches 500 are easier to manufacture, with the
previously existing holes of variable diameter along the
length being replaced with openings of consistent size but
varying in number. The number of apertures selected may
follow head measurement as previously described in
association with Figures 14 and 15 or by using the removable
plates 204 of Figures 20A-20C.
Yet a further embodiment of the invention relates
to the addition of air passageways in the panel members 44
(Figure 9) as illustrated in Figures 16A-16D and 17A-17B.
Since air scouring has been found useful to increase the
efficiency of the backwash operation, an air passageway is
provided in panel member 300 in the form of an inverted hat
section 301 (Figure 16B) into which air is introduced. In a
first configuration, openings 302 are provided in the hat
section 301 to release the introduced air under pressure
sidewise beneath panel 300. In a second configuration as
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illustrated in Figures 16D and 16E, air openings 303 are
provided in the panel member 300 itself directly above the
hat section 301 such that the air passing through the hat
section 301 exits the section 301 upwardly from the panel
where scouring takes place. This latter configuration has
the advantage in that the punching operations are carried
out on only one member, namely panel 300, so production
costs are reduced.
A further embodiment of the invention is
illustrated in Figures 17A-17B. In this embodiment, the
panel members 400 are significantly larger than the panel
members 44 (Figure 2). These panel members 400 cover a
greater amount of the underdrain 66 since several filter
underdrain elements or clay blocks 66 may be covered by the
panel 400. A greater amount of water therefore passes
upwardly through the panel member 400 and to allow for the
increase in air scouring necessitated by the increase in
water flow, three(3) inverted hat sections 401, 402 are
used, the two side sections 402 being located equidistant
from the center section 401. Otherwise, the operation is
identical to the operation of the embodiment of Figures 16D
and 16E; that is, air is introduced into each of the hat
sections 401, 402 and escapes from openings 403 in the panel
400 directly above each inverted hat section 401, 402.
Although the panels 44, 300, 400 of the present
invention are illustrated as being positioned as caps on
conventional filter underdrain blocks 66, the panels will
function effectively in the control of backwash flow
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maldistribution without the underdrain blocks 66 and will
provide effective backwash water distribution control in any
situation wherein the elements can be mechanically fastened
and suitably sealed to an appropriate substructure.
Likewise, while the panels 44, 300, 400 are illustrated in
generally rectilinear form, the number and size of the
perforations and apertures may be provided in panels of
different configuration such as semicircular or triangular
panels.
In yet a further embodiment of the invention,
reference is made to Figures 23 through 26. In this
embodiment, panel members which have been previously
described have apertures that are all the same size and
number may be positioned over the clay underdrain blocks 600
as viewed in Figure 23. In order to allow for the correct
water flow from the underdrain blocks 600, the holes 601
(Figure 24) are selectively plugged using the nylon plug or
insert 602 with a screw 603 which acts to expand the plug or
insert 602 when it is inserted. With reference to Figure
25A, two holes 604 have been plugged and the remaining holes
610 remain open and not plugged. Thus, the water flow from
the block 600 is reduced a predetermined amount. Likewise,
other underdrain blocks 600 may have a greater or lesser
number of holes plugged, the objective being to have water
outflow from the underdrain blocks 600 substantially
constant over the entire underdrain are with its concomitant
advantages. Thereafter, panel members which may all contain
the same number and size of apertures can be used over the
underdrain to prevent media egress and to allow air scouring
CA 02543681 1999-04-30
27 -
if desired.
Reference is made to Figure 27 in which a seal 700
is located between the panel member 701 and the underdrain
block (not shown). The panel member 701 is manufactured
with a rise or ridge 702 in its circumferential area 703.
The ridge 702 applies pressure on one side of the seal 700
which assists in the retention of the seal 700 and which
also assists the sealing action between the seal 700 and the
underdrain block.
While the method of measuring hydraulic head on
the underdrain system described herein uses a rule and an
indicator, it should be understood that this elementary and
basic measurement technique serves to best explain the
technique. It is clearly contemplated that a more
sophisticated measurement technique could be used, such
technique using electrical analog or digital signals and
such measurements being recorded through an appropriate
computer interface or other recording medium. Likewise, a
float need not be used. Rather, a stationary resistance
measuring strip, for example, could be positioned within the
measuring cell, thereby sensing the depth of water over time
and transmitting such information to a receiving station
located on or remotely from the transmitter. Other sensing
devices are clearly usable if desired.
While the term "filter underdrain" is commonly
used, the invention is not restricted to filters. Various
types of water/waste and process equipment utilise improved
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backwash distribution which do not use filters. Examples of
such equipment include up flow or down flow contact
clarifiers, activated carbon contactors, ion exchange units,
iron removal units, including those of the
greensand/catalyzed sand type, catalyst bed contactors,
including desilicizers; and neutralizing media contactors.
Thus, it is intended that the term "filter underdrain" be
used and understood to encompass units other than filters.
Further, in some process equipment vessels such as
upflow mode filters and contact clarifiers, the underdrain
serves a different function than in downflow, that is, it
serves to distribute incoming service flow as well as
backwash. Backwash in filter is a periodic reverse flow of
filtered water through the media to flush out trapped
impurities. The term is used in ion exchange and carbon
contactors as well, but in filters, dirt is flushed from the
bed by backwash. In ion exchange, carbon contactors and the
like, water is typically filtered in advance so backwash
serves to loosen and then resettle the bed to eliminate
packing and flow channelling so that contact is improved and
short circuiting averted in carbon contactor units. In ion
exchangers a backwash is required to wash any dirt from the
bed, but more to loosen and then resettle the bed so that
regenerant contact is maximized and regenerant short
circuiting avoided.
While the apparatus illustrated in Figure 1
illustrates a common backwash filter system, the panels
according to the present invention are adaptable to other
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configurations, such configurations including a transversely
extending trough or flume or embedded pipe across the center
width with filter outflow and backwash inlet at the side; a
trough or flume or embedded pipe running the length of the
filter down the center line, or along one side, or
externally down one side; and circular filters with cross
diameter inlet/outlet flume or trough or embedded pipe with
the underdrain of the present invention running transversely
to such trough or flume.
A variety of materials may conveniently be used to
fabricate the filter underdrain panels 44. Painted or
galvanized steel, aluminum, fiberglass, various types of
plastics and fiber reinforced plastics, concrete are
examples. The preferred material, however, is 304 or other
grade stainless steel because of the strength and high
corrosion resistance properties of this material.
While the invention has been disclosed by way of
various specific examples, such embodiments are illustrative
of the invention only and should not be taken as limiting
its scope. Many modifications will readily occur to those
skilled in the art to which the invention relates and it
should be limited only by reference to the accompanying
claims.
