Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02270811 1999-04-30
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 a.s
required when the filter media has substantial head loss
during operation, sometimes occurring several times a day
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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
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;
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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; 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
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breakage during installation while inadequate corrosion
resistance is also present; <~nd that some devices
require support gravel layering.
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Our earlier United l3tates Patent 5,019,259
(Hambley) dated May 28, 1991 <3nd entitled FILTER
UNDERDRAIN APPARATUS WITH PP.R'~ITIONED DISTRIBUTOR
CONDUITS, teaches a filter underdrain apparatus which
includes a steel flute or arch forming a plurality of
horizontal distributor conduii;s. The conduits are in
juxtaposed, laterally spaced relationship and are
constructed to define alternai~ing 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 rs:quired during the
manufacturing process to acconunodate the variations in
orifice size along the flute.
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SUMMARY OF TFIE INVENTION
According to one aspect of the invention, there
is provided apparatus for detE~rmining backwash water flow
distribution through an underdrain assembly comprising a
substantially watertight housing for removable attachment
to said underdrain assembly, << seal between the lower end
of said housing and said underdrain and an indicator to
measure the rise and fall of water within said housing
responsive to water introduced to said housing from said
underdrain.
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According to a further aspect of the invention,
there is provided a method of measuring backwash water
flow through a filter underdrain assembly comprising the
steps of removably attaching pit least one housing to said
underdrain, initiating a backwash cycle and measuring the
rate of water flow from said underdrain into said
housing.
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BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
Specific embodiment: of the invention will now
be described, by way of examp__e only, with the use of
drawings in which:
Figure 1 is an isomE~tric partially sectional
view of a water filter tank o~~ basin incorporating the
apparatus according to the preaent 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 ~~iew of the panel member of
Figure 2;
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Figure 6 is an isometric view of the panel
member of Figure 2;
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
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according to a further aspect of the invention;
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
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
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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 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
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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 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.
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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 4:? is also used to introduce
backwash water back into the ~:lume 40, the media and then
to the trough 40 and basin 26,
Referring to Figure:a 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 surfaced 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 rigidit5~ purposes.
Inner panel 50 further includes a multiple of
generally rectangular aperturses 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 defins~s a pair of slotted water
inlet/outlet apertures 60 (Figure 7) through the upper
and lower surfaces 52, 54 of t:he inner panel 50. The
slotted apertures 60 are of a dimension sufficiently
small to substantially prevent: the passage of filter
media thereby allowing for ths, elimination of a support
layer of gravel above the panels 44 which gravel is
principally used to support tree sand layer resting
thereon.
The end walls 46 anc'~ side walls 48 of panel
member 44 also conveniently ir..clude a single row of
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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 or sealing 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.
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 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
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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 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
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thereby controls the degree of water distribution into
the above media bed acceptable in the particular under-
drain 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 panel 44
or 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 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
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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 94.
The pointer 96 allows determination of the rise and fall
of the float member 92 within the housing 84.
The float member 92 and the attached graduated
rule 94 are generally centralized within the housing 84
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
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the pipes, troughs or channels 42 running beneath the
false bottom and escapes upward into the filter bed via
orifices in the underdrain block 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 blocks or elements 66
closest to the backwash water channel or 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
82 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 84, each being utilized
to acquire a measurement of the rate of flow backwash
Water through an individual underdrain block or 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.
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The lower end 88 of the housing 84 of each cell
82 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 82 by float 92 and the
backwash cycle is commenced. As backwash water enters
each cell 82 from underdrain element 66, the float 92
rises. The rate of rise of float 92 and thus the rate of
flow of backwash water into each cell 82 is determined by
recording the rise over a predetermined period as rule 94
moves upwardly through the upper end 86 of the housing 84
and past the reference pointer 96.
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
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
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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, respectively, 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, respectively,
in the arches 101 throughout the length of each
individual arch 101.
To prevent the egress of media and to assist
with reducing the number of tool changes, plates or
panels 112 were attached to the arches 101 illustrated a.n
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 113 in the plates 112 was likewise varied so as
to allow fewer apertures further from the Water inlet.
In this case, the apertures 113 Were all the same size.
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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. 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 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 110, 111 in the arches 101 of Figure 18A and 18B.
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 205 punched therein and which
plates 204 may likewise be provided with a greater or
lesser number of apertures 205 which
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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 204 will ordinarily be designed
with greater cross-sectional area by way of increased
number of apertures 205 near the entranceway of the water
to the arch 200 and with a decreased number of apertures
205 near the end of the arch 200 downstream from the
entranceway. Once the desired water discharge is
obtained, arches as generally 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 501 as
seen at the far end of the arches 500 as is illustrated.
The arches 500 are easier to manufacture, with
the previously existing holes or apertures 501, 502 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 the apparatus
illustrated in Figures 14 and 15 or by using the
removable plates 204 of Figures 20A-20C.
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Yet a further embodiment of the invention
relates to the addition of air passageways in the panel
members 44 (Figure 9) is illustrated in Figures 16A-16E.
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 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 under each panel 400, the two side
sections 402 being located equidistant from the center
section 401. Otherwise, the operation is identical to
the operation of
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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 (Figure 6), 300 (Figure
16A) and 400 (Figure 17B) 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
maldistribution without the underdrain blocks 66 and will
provide effective backwash water distribution control in
any situation wherein the panels 44, 300, 400 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 (Figure 26) 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
underdrain blocks 600 is reduced a predetermined amount.
Likewise, other underdrain blocks
CA 02270811 2005-09-22
- 26 -
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 area with its concomitant advantages.
Thereafter, panel members 44, 300, 400 which may all
contain the same number and size of apertures can be used
over the underdrain blocks 600 to prevent media egress
and to allow air scouring 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
CA 02270811 2005-09-22
- 27 -
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 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
CA 02270811 1999-04-30
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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
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, a.s 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.
