Note: Descriptions are shown in the official language in which they were submitted.
20~3~69
FI~T~R UNDEPtD~I~ ~OCI~ :
3AC~GRO~ND 0~ 'rH8 ~ N~I
1. Fi~ld o~ thQ InvRntlon
This lnv~ntlon g~n~3rally r~l~te~ l:o ~ilter
5 bottoms ~or use in ~ilters ~o~ ds, and more
p~rtlcularly to th~ structure o~ a ~iltar block ~or
und~rdrain3 which when assembled ~or~ a ~ilter botto~ for
supporting a bed of f$nely divided filtering ~dia. Tho
filter bottom provid~s liqui~ ~low condults b~low the bed
lo of ~iltering medi~, which conduits ~ake po~sib~e the
colle~tlon af filtere~ liquid an~ t~Q dlstr~bution of gas
and fluid backwa~h. ~he pre~ent invention ia aspeGiall~
directsd to ~ filter bottom providing a virtually
complete, unifo~m distributi~n ~ gas and fluid backwash
medla thr~ughout the ~ntire filter bed while ~aquiring a
minimum amount of en~rgy to ~horoughly and ev~nly
backwash the filtering media. ~he inv~ntion featur~s
~peclal and n~vQl aapects which ara pri~arily directed to
the esta~lishment and maintenance of an usually h~gh :-
degr~e Or uniformity of g~ ~nd ~luid backwa~h
distribution at ~lnl~um energy oxpen~o whila ~arkedly
broadoning t~e range o~ allowable backwash ~low rat~s.
2. Dy~yllL~ L~ G~
Several ass~m~lie~ ~or filter bottoms are known
2S in tha art, particularly, assemblies having indiYid~al
units called ~ilt~r blocka, w~ich ar~ a~e~bled toge~her
and interconnected with tne ap~ropriate ~uppli~ and
drains. ThQ ~iltQr bloc~cs, ~hen a~sembled provid~ an
upper 6ur~ace or supp~rting a ~ilter media . l`h~ ~ilter
30 bott~ upper sur~ace is provit~ed With a~ertur~ ~o allow
the flow o~ iltered lil3uid from th~ ~ilter m~dl~ to p~!l5~
into the filter bcttom where conduits carry the filtered
litluid ~rom the ~ilt~r. The conduits also s~r~re to
provide bao~wa~hing fluids, either qas or liquid or both,
35 to the f ilter media rOr cleaninq.
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206396~
Tho ~ilt~3r bot~om ~s covered with Piltering
media such as a bed o~ relatively coarse agyregate~ (the
particle~ being to~ large to pass through th~ apertures
in th~ top of tho block~, and seYeral additional l~yer~
5 o~ graded material o~ largex ~o ~maller and back tc~
laxger 5iZC farther above the i~ilter bottom.
ConY~ntiona11y, tha liquid to be rllte~ed,
typically wa~er, enters ~om a~ove, pa~ing downwardly
through the ~iltering media, ~hrough ~ha varlous lay~r~
10 of coar3er p~rticle~, then through ths~ ap~rtur~3 ln the
tcps of the bloclc~, through conduits in the ~locks, an~
out through a tak~-of~ fl-lme. Gravity ~low moves the
liquid ts ba treated through the filter.
Periodically, ehe Slow o~ uid to bç~ iltered
15 is shut off and a orashing medium ~ 3 forced ~hrou~h thQ
~llter in revers~ dire~tion.
The wash mediura (typically water~ ~low~ from
'che r~ums into the conduit~ which distr~,but~ ~t lat~rally
away ~rom the flume and ~rom the condult~ up through the
20 separat~ upper ohambers, the bads oS partic:ulata
~i}tering material and out at the top, thoroby carrying
o~f deposlted partlcles dislodged from tho ~ilter raedia.
Th~ backwash p~ocedure usually includ~s first air
~ackwashing b~f~re wa'c~r ~ackwashing. ~h~ air
25 backwashing step loosens and separates th~ par~icles o~
the ~iltar ~ad and then the subs~quent wa~er backwa3hing
step ~lutdizss the bed and carrles the depo~sited
par~iclos upward and fro~n the bed. In many ins~ance~,
air and watar are us~d si~ultane~llsly. In all steps, th~
30 air and water ~low through thQ bed mus~ b~s uni~ormly
distri~ut6~d over the araa of 'clle bed. Ir the backwashing
flow is not uniformly di stributed, than the filter ~rea~
of low backwash v~locity provide lit~le backwashing
effect and in areas o~ hi~h fluid velocity, the flow will
35 cau~ ar media to be carried upward and lost to
di~posal. Moreover, when thR ~ilter m~dia i5 present in
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2063969
layer~ o~ different particulate materials, sr dl~erent
partlculate ~i~e, non--mlfor~ ba~clcwa~h~ ng can cause
undesired mixing of the partiaulate l~ysrs.
One t:ypQ 0~ th~ prio:r ~rt ~lt~r blocks i5
shown $n U.S. Patent No. 3, l1o, 667 to stuppy. Each
filter hlc~k includes a pzlir o~ parallel upp~r ~nd a pair
of parallel lower condui~s, shown in cro~ ction in
Figure S. Water ~rom the fil~er pl~ses through aporture~
in tha top or each bloclc into ~h~ upper condu~t~, th~n
lo through ports in the ~loors of the uppar ¢onduit~ into
thO lowQr conduits. Th~ liquid then ~low6 fro~ block to
block to a ~lume. Tha ~tuppy ~atent ~l~o propo~es a
liquid backwash b~hQr~in liquid is supplied to the low~r
condu~ts, pas~es l~pWards throug~ the portY to ~he upper
15 conduits and ou~ the apertures to th~ filt~r media.
U. S . Patent No. 4, 065, 391 to Farabaugh
di~clo6~s anothQr con~iguratlon of f~lt~r block whioh
do~s not include upper and lower condult~, but instead
ha~ an ar~ange~ent Or paraLlel pri~a~y and s~condary
conduits positionad horizon~ally adjacent ~ch other and
separated by inclined w~lls. Th~ inclino~ w~118 contain
relativ~ly smaller ga~ ~eterlng orifices and rslatively
larger liquid ~etering orirlces with the li~uid metering
ori~lco~ posit~on~d below the ga3 matering ori1ces.
2S 8ackwa3h ga6 or liquid i~ ~upplied through the primarv
conduit~, passes throu~ the metering oririces into the
second~ry conduits, and from ~ha secondary condult~ into
tha b~d of fllter media. The gas meterin~ ori~ices
control the rate at which a backwash gas passe~ ~rom the
primary to the secondary conduit~. The liyuid metsring
orif ~ ces, ~nd to a lesser extent the gas ~etaring
ori~ices, control the ~low rate o~ a liquid backwashing
med~ um.
The prior art filter block devices are
3 ~ dsf icisnt a~ to backwash operations . For ~xar~pl~, the
stuppy deYice has relati~rely larga li~uid port~ between
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2063~6~
the upper and lawer con~uits. I~ lthough not di~loeod
in the S~uppy patent, a ~as backwash were used with th~
~evic~, the ga~ would be supplied to the lowe~ ¢onduits
but then would p2~ easily through the ~iro~ ew of the
5 r~latlvely large liguld por~s en~ountered to the upp~r
conduits r~sulting in sigrli~Lcantl~y un~3qu3~1 d~ ~3tribution
o~ ga~ through 1:he ril~er h~tt:or~. The uneven
di6trlbution of gac during ~3uch a ~aokw~l~h woul~ ~er~e to
di~rupt the ~llter media where ~oc much gas flow o~curs
10 and to provide inade51ua'ce c:l~aning o~ th~3 f ilt~ ~nedia
whera insuf ~ ent gas dlstribution occur~O
Th~ Farabaugh devis:sa depends on a ga~/liquid
inter~as:a ~o control gaa dlstrlbution durirg ~3
backwa~h. Whar~ ga~ backwashinsf be~ins, since the entire
15 block anà the filta~ing media a~ove it is under water at
that time, each o~ th~ conduits is essentially filled
with water. Wh~n backwash ga~ ls supplied to ~he primary
condui~, a gas~liguià interface ~ ~ ~ormed as shown in
Fiqure 5 o~ the Farabaugh patent, and gas i~ mstered 'co
20 the ~econdary conduits via thc- ga~ meterlng orl~ices ln
the uppe~ portion o~ the w~ll saparaeing ~l~e prlmary and
s~condary conduit3. However, th~ Farabaugh syste~ can
tolerata only a limited rang6~ of baclcwashing ~l~w. I~
that limit is exceeded, the gas/liquid intQrface levsl ls
25 ~orc~3d down to a point at which gag 86capes in~o ~che
secondary conduits th~:ouçlh the over~ized 1 i~uid metering
orifices whlch are als~ located i3~ the wal~ ~eparating
tha primary and secondary conduita. Because o~ the rapid
sscape o~ thQ gas through th~ oversized liquid met~ring
30 o~iflces, unequal dist~ibution of the b~ckwash gas, w$th
its consequ~nt disadvantage~, occur~.
An ~ddltional proble~ with the: Farabaugh QViCo
i8 that standing waves, crea~ed by a variety o~ phenomena
durin~ bac~cwash of the ~ilter sucll ~13 a pra ~ure ~hock
35 fro~n a ~tickincl gas valve or oth~r causes, can further
limit ~ha range of ba~kwash flaw~. When such a ~tanding
2~39~9
wave is ~ormcd during bacXwash, it can rsduce the 12vel
of the liquid~gas int~rfAce up~tream o~ tha wave 60 that
thP large liquid ms~er~ng ori~ice~ ar~ ~xpossd to the sas
flow, again cre~ting unequal dist~ibution o~ bacXwash
gas.
It has also b~en found in th~ opQration o~
iilter bottom~ as tauyht by ~rabaugh that wave~ wbich
froquantly occur on the surf~ce of the li~uid in the
~ilter, by changing temporarily th~ liqu~d pre~ur~ h~ad
over portions of the iilter botto~, can ther~by changQ
the lovol Or the liquld~gas inta~c~ in tha primary
conduit. Th}s fluctuation ln the lev~l of the Ln~er~ace
cyclically exposes t~en covers the over~ized l~quid
m~tering orifico~ in thQ primary oonduit to tha gas abov~
the int~rfac~, and, conse~u~ntly, re~ult~ in
~aldistribution o~ gas bac~wash a3 the o~rsi3~ orifice
i~ expos~d.
~ h~ dependency of t~e Farabaugh d~ign on a
liquid/ga6 intorfacQ also limlt~ the backwash rat~s which
20 car. ba us~d during simultaneQus gas and l~quld ~ck~lu~h.
The typlcal Upp8~ limit for ei~ultanecus bacXwa~h in the
~ara~ugh device i~ ~pproximat~y 5 standard cubic ~et
per minuto (~8CFM~ gas per squar~ foot o~ ~llt~r bottom
upper sUr~ACC and 5 gall~n~ p~r square ~oot o~ ~ilter
2~ botto~ per minute ~aGSF~n). It has been propo~ed that
ralslng ons or ~oth o~ the backwash rat~s simulkan~ously
would lnoreasa ~couring and cleanin~ of th~ ~ilter medl~.
How~v~r, the Farabaugh device, with it~ itation o~ the
gas/liquld interface c~n only acoommodats simultanecus
ba~KWash rates within ~ limited ran~e.
Finally, another proble~ with th0 Farabaugh
devic~ is that, bacAuse of the pre~nc~ o~ the large
liquid m~tering orif1ces in the pr~mary conduit, 1~ is
particularly sus~ceptibls to pro~l e~s ~temming f rom non-
lQvel ins~allation o~ the ~ilter blocX~. At column 5,line 1~, Farabaugh states th~t th~ liquid m~oring
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orifices are preferably placed about 3 1/2 inches below the
gas metering orifices. Accordingly, even slight errors in
installation of the filter blocks can markedly reduce the
vertical distance between the lowest gas orifice and the
highest liquid orifice which share the same gas/liquid
interface. This non-level installation significantly
reduces the safe operating range for gas backwashing to
avoid escape of the gas through the liq~id orifices.
Although modifications of the Farabaugh device have been
proposed, extending the vertical distance between the gas
and liquid metering orifices to almost 9 inches, the same
problems still occur.
The previously known filter block arrangements
suffer from sensitivity to non-level alignment of the
blocks. Even small divergences from level alignment of the
blocks leads to significantly non-uniform backwashing
performance, particularly when the backwash medium is a
gas. Accordingly, it is an object of an aspect of this
invention to provide a filter underdrain block structure
which when assembled and arranged to form a filter bottom,
maximizes uniform distribution of backwashing gas and
backwashing li~uid, fluidizes the filtration media over the
underdrain block, dislodges dirt and debris entrapped in
the filter media, and thoroughly cleans the media.
It is an object of an aspact of the present
invention to provide a filter block underdrain with a
reduced sensitivity to non-level block alignment,
particularly with regard to gas backwashing. An object of
an aspect of the invention is to provide a filter block
weighing less than conventional filter blocks yet having a
good structural integrity thereby being easier to handle
and easier to install than conventional clay filter blocks.
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Other objects and advantages of the present
invention will be apparent from the following detailed
description and from the appended drawings.
SUM~RY OF THE I_ENTION
An aspect of the invention is as follows:
A block for use in draining and backwashing a
filtering media in a filtering bed of the type where liquid
may be supplied to the filtering media from a position
vertically above the media and passed down through the
media to an underdrain system including a plurality of said
blocks, said block comprising: a plurality of exterior
walls defining a hollow interior and having a longitudinal
axis, said axterior walls including a top wall, a bottom
wall and a pair of side walls extending between said top
wall and said bottom wall; a plurality of interior walls
defining an upper portion and a lower portion, said lower
portion having at least two primary liquid conduits and
said upper portion having at least one secondary liquid
conduit with a primary gas conduit disposed within said
secondary liquid conduit, said interior walls including a
plurality of gas orifices between said primary gas conduit
and said secondary liquid conduit and further including a
plurality of liquid orifices between each primary liquid
conduit and said secondary liquid conduit.
The present invention, generally described,
provides a filter block having both upper and lower
conduits or chambers and having conduits for distribution
of liquid backwash which are separate from a conduit for
distribution of gas backwash.
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In a preferred embodiment, the upper chambers
comprise a primary gas conduit and two secondary conduits.
The lower chambers comprise two primary liquid conduits.
The primary gas conduit is in communication with the
secondary conduits via appropriately sized gas orifices to
allow the flow of gas from the primary gas conduit to the
two secondary conduits. Liquid orifices are provided
between the secondary conduits and the primary liquid
conduits to allow the flow of liquids between the secondary
conduits and the primary liquid conduits.
Filtered liquid passes through apertures in the
top of the filter block, into the secondary conduits,
through orifices into the primary liquid conduits and from
block to block to a flume. The primary gas conduit
essentially does not contribute to the flow of liquids
during filtering operations.
During backwash operations, gas or liquid
backwash can be carried on simultaneously or
independently. Gas backwash flow is supplied to the
primary gas conduits and is passed from block to block
across the filter bottom. Backwash gas passes from the
primary gas conduit through the gas orifices to the
secondary conduits. Liquid backwash flow is supplied to
the primary liquid conduits and is distributed thereby
evenly across the filter bottom. Backwash liquid passes
from the primary liquid conduits through liquid orifices
into the secondary conduits, through the apertures in the
top surface of the filter bottom to the ~ilter media.
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2~63~69
Having separate prl~ary condui~s ~or th~ gas
bacXwash and ths llquid backwa~h~ wlth th~ pximary g~
conduit specially doslgned with all ori~ C~5 ~her8~rOm
con~titut~ng ~as ori~ices, ~ o~pared to h~ing only
on~ primary conduit de~igne~ to accompli6h both liquid
and ga~ ba~kwash), provides signii'icant advantag~s o~cr
ths prior art. ThQ present invention allows ~or
groatly inerQased range Or ga~ backwash flow r~te~,
increa~d ~multanaou~ gas~liquid backwa~h rate~, the
minimiza~lon of pro~lems inherent ~n ~y~tem~ d~p~nd~n~ on
a gas~liquid int~r~ac~ during backwash, and numerous
other advantages.
B~IB~ D~8CRI~TION 0~ ~U~ DRAW~N~9
Figur~ a p~r~pect1~ view o~ one
embadimant of the pre6~nt i~v~ntion:
Figuro 2 shows a cross-sectlon Or t~o ~ilter
block o~ Figure 1 tak~n along lines 2-2 Or Flgure l;
Figurs 3 i~ a ViRW along lineY 3-3 oS Figure 1;
and
Figur~ 4 i8 a eid~ vi~w, partly broXen away and
par~ly in seation, of a series o~ filtQr block~ connect~d
end-to-end with lay~r~ of ~ilter m~dia on top.
D~AIL9D DE~CR~SON o~ INVE~IO~
With reference now to the dr~wing~ whar~in llke
numoral3 designate aorresponding parts ~hroughout the
several views, there is s~own in Figure 1 a pre~rred
smbodiment o~ a ~ilter block 10 o~ thQ present i~v~ntion
and which ha6 a top w~ provided with ~ plu~ality of
apertures, one of which is indica~ed at 14, distributed
in a substantially even pattern ov~r th~ top wall 1~.
ThQ block may b~ intagrally formed by in~ection ~olding
With a p~lr oS side wall~ 1~ and a bottom w~ll 18 with a
plurality o~ rein~orcing ribs 20, ~1 ~orm~d on the
sxtsrior ~ur ace o~ t~e walls 12 r 16 and 1~.
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2~63969
Additionally, a plurality of rein~oraing ribs 23 ~y be
formed on th~ interior surface of wall~ 16 and 18. Rib~
23 may or may not extend th~ full length of blocX 10.
At one ~nd, a r~ceiving ~oll~r 22 is pro~id~d
S h~vin~ dl~nsions ~o snugly lnter~it with an ~d~acent
block which will have an end con~e1gura~on to c~osely
int~rfit ~i~hin thQ collar 22. ~his clo~ ~it
~u~s~an~ially pr~vonts eit~er gas or ll~uid ~r~ entering
or exi~ing the intorior of ~he as~e~bl~d ~lcck~ during
~se. Grouting ~nd/or an adhesive is emplcyed t~ pr~vide
a ~luid-tight joint betwesn th~ ends of the blocks. It
will be understood that an oppositQ and 2~ of each block
10 may be molded to the d~sir~d si~e and shape to
1nterfit with the collar 22 o~ an ad~ac~nt block to
f~c~l~tate th~ ass~bly o~ an intarlocklng relati~nship
along an axis o the ~ilter bed.
With reference now to Figuro 2, ~ar~ is shown
a cro~s-sectional v~ew along lin~ 2-2 o~ Figure
wherein a ~ransverso wall 24 Qxtends f~o~ ons slde wall
~6 to the opposite ide wall 16 to dividQ the in~erior
the ~l~ck 10 into an uppar and a lowor porti~n. ThQ
lower portion is further divided hy a partiticn 26 into a
~nir o~ primary liquid ~nduit8 o~ chamb~r~ 2a and ~0
which are substantially rectangul3r in oro~s-ce~tion and
which extend parallel to thQ longitudinal axis of the
bloc~ 1~ and to each other along th~ 16ngth o~ the block
lo. The lower portion may ~ s~ill furthor divided by
another partition (no shown) t~ enhance the ~tructural
integrity of bloc~ 10. ~h~ upper portion i~ further
divided by a palr or angularly extendi~ wall~t 32 and 34
into threa chambers, secondary conduitg 36 and 40, and a
primary gas c~nduit 38, all o~ whlch ~lso extend paraltel
to the lQngitudinal axi~ o~ the block and extend along
the l~ngt~ of each block 10. Secondary conduit~ 36 and
reoeive wat~r or liquid pass~ng down through the
filter bed and through th~ aper~ure~ 14 provided ln wall
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2~63~
12. Primary gas conduit 38 :3e~e!3 to di~trl3~ute ba-::kwa~h
gas axially along the length s~f the ~ilt~r block 10 and
through apertures in walls 32 and 34 into secondary
condu~ts 36 and 40. A~ is also apE~arent in ~igur~ 1, an
S end portion 27 o~ wall 2~ is reeesoed from th~ end o~
~llt~r block 10 to allow ths co~nmUnic~tion o~ fluid~
between prlmary liquid conduits 23 and 30.
Secondary conduit 36 18 in çommuni~::ation
through a plurality or li~auid 3siE$ces 48 with primary
lo liquid condult 28 while a plurality o~ li~id ori~i~es 50
in wall 24 provlde Plow communlca~ion between con~Uits 40
and 3D. L~quid orir~c~s 48 and ~ are provided in svenly
spaced rela~ion along wall 2~.
Wall~ 32 and 34 adjacant wall 24 are eac:h
15 provided with a plural ity Or gas orl~lces along the
lerlgth oP th-~ block a~ at 33 ana 35. These gas o~i~ices
ara ~ized s~o that during ha~kwa~;h operatlo~s whar~ gas i9
suppliad to primary gas condui~ 38, the in~ected ~as
forcef~ the wat~r out o~ primary gas c:ondul~ 38 and an
20 even distribution o gas i~ accompli~hed along the length
of pri~nary gas conduit 38 ~hrough gas ori~ice~ 33 and 35.
In a pref~rrod em~odim~nt o~ ~ present
invention, each filter block is designad tc provid~ t~e
width o~ 1 oot (mea~ured ~n th~ d~ r~tlon o~ wa}l 24) o~
25 filter bottom. Sec:ondary ccnduits 36 and 40 ~ach hav~
appr3xim~tely 16.9 s~luar~ inches Q~ cro. ~-~eot~onal area.
Primary gas conduit 3~ ha~ approxi~ately 17 . 4 s~uar~
inches of cross-~ectional area. Primary li~uid conduit
28 and 3 0 each provid~ ~pproximately 22 . 6 ~quare inches
30 o~ cross-sectional ~rss. ~n thc preferred embodiment,
upper gas orifi~es 35 havo a diamate~ o 3/32 inah and
are spaced at four oriP~ ce~ per ~xial 3~aot o~ ~ilter
block. Lo~er gas orifice:s~ 33 h~e ~ di~mater of 1/8 inch
and are also spaced at ~our orific~s pzr axial foot o~
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2~639~9
~ilt~r block. Llquld o~l~lces 48 and 50 hnv~ ~ dlameter
of 3~4 inch and are spaced a~ tw~ or.iric~s per ~xial foot
of filtsr block.
In th~ pre~erred embodiment, it has been found
that the slightly larger diameter o~ lower g~ ori~ce~
33 over tha diametex o~ Uppe~e ga5 ori~ice5 35 is ~'
beneficial ~o a rapid QVacUatiOn Oe liguid fxo~n primary
ga3 conduit 38 during ga~ backwashing. It has ~ean ~ound
that a 53 foot length oP prima~y ga~ condult 3~ ln a
~ilter block a~sembly can b~ ovacuat~d o~ liquid at
normal gas ~ackwa~h pressurss within ten Qeconds fro~ the
start of g~s backwa~h oper~t$ons. ~lso, prlmary gas
conduit 3~ is esssntially ~uLly evacuat~d o~ liquid at
the extremely low g~ backwash rate o~ 1 ~CF~.
15Since prim~ry g~s conduit 3~ antially
completely ev2cua~ad o~ liquid during qa~ b~okwa~hing, a
number of pro~Ie~s inher~ in prior art d~igna are
ovsrco~e. ~he othærwi~Q se~erz e~fec~ og non-l~vQl
inst~llation oF the ~ilter blocks i~ almo~t ~ompl~tely
overcome. So also, are ~he effect~ o~ sur ace wavo~ on
the fllt2r llquid oYe~ccme. Addition~lly, ~ince the~e is
no signirlcant gasJli~uid i~t~rface in primary gas
c~nduit 38 during gas b~c~wash, thQ proble~ o~ standing
waves is avolded.
~5~aving s2parate conduits for g~ and lisUid
ba~kwa~hing allows lndependen~ adjustment o~ ~ither or
both o~ tho gas or llgui~ rlow rate~ during ~okwash
oparations, an option not po~sible with the prior art
~avic~. It has been ~ound t~a~ the deslred ~low rates
o~ 5 SCFM ga~ and ~imultaneous lG GSFM can be
accompliehed in the d~ign of th~ pre~erred embodiment.
It ha~ bo~n ~ound that gas bacXwa~h rates o~ ~-10 ~CFM
can b~ reali2ed in the pre~en~ inventlon.
It will also be ~ppar~nt from Figure 1 that the
ri~s 21 along the uppor por~ion of the blo~k lO are in
stagqered relation~hip relativ~ t~ thQ rl~5 ~0
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2063~9
surrounding th~ side wall and bottom wall 18 alon~ t~
lower portion o~ tho block. In addition, a plurality o~
~paced perpen~icul~rly exten~ing flanga ~emb~rs 52 are
provided along each sid~ wal 1 16 i30mgdiately ~ove the
S posl~-lon wher~ the lower rib~ 20 ter~inate. Th~s~ will
not only assist in handling th~ inclividual block6 but in
placement and positioning of the blooka alon~ the botto~
of tha fllter bed. In addi~io~, the sids wall 16 may be
provlded with a plurall~y o~ indent:ations 3~ a~ ~hown in
Figure 1 to ~a~llitate intimate contac~ w~h y~outing
material ~hen t~e block is asse~bled ~n a ~ilter bed
bottom.
With reference now to Figure 3, there ; 9 ~hown
a sectional view along llnes 3-3 o~ Figure l,
illustrating the coopQratien o~ 2n alr inlet tube 5fi,
which may be provided wi~h a ~mporary cap 58, with an
opening 60. The lower ~n~ o~ th~ tub~ 56 i~ secur~d
a~o~t th~ openlng 60 provided through tho upper wall i~
whereby communicatien with tha intarlor o~ p~i~ary gas
conduit 38 is e~fected. The upper en~ of ~ube 35 will be
connec~d to a pres~uri~e~ air or gas supply. As an
alternative, in thi~ embodiment as well as the embodiment
described b~low, gac ~ay be introducsd into primary ga~
conduit 38 thro~gh a plpe that is provlded with spaced
2 ~ opening~ with the pipe extendin~ in primary ga~ conduit
38 parallel to t~e wall 24. It will b~ under~tood, as
shown in F$gure 4, that each ~ectlon o~ ~lter block ln
the filter botto~ do~6 not need to include an alr inlet
tube 5~.
~ha ~ilter ~lock o~ th~ pre~nt inv~ntion is
~urther characteriz2d by the ratio oP ~he eum o~ th~
cross-section~l area~, o~ ~he s~condary conduits ~6 and
40 relative to the primary liquid conduits 28 an~ 30.
This uniqu~ ra~io o~ cross-~actional areas allows for
signi~icant reduction in head 1098 during th~ backwash
cycle. Specifi.cally, the ratio of the combined cro6s-
~ 12 -
. ~ :
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2~63969
sec~onal area~ o~ primary conduits 28 and 30 to the
combined cross-~ectional a~eas o~ th~ econdary liquid
conduits 36 and 40 ranga~ fro2~ about 1 to 5:1 and,
pre~erably, th~ ratlo ranges from about 1.5-3.5:1.
A ~ilter bottom ~ust pro~ridQ uniform
distribution o~ backwash gas ~nd liquid, ~or ex~pl~ air
and water, over ths entire area o~ th~ ~llter. ~s is
wel} known, lack o~ unif~mity aan ~;~riously impair the
e~ectivene6s o~ the ~iltQr becau~;~ varlous portions o
10 th~ b~d may ret~in depo~i~ed particul~t~ oven aît~r a
backwa~h cycle. The useful lif~ o~ a ~ilter i~ dir~ct~y
proport~onal to the uniformity of dist~bution of tl~e
~acXwash medium. ~ocalize~ vari~tion~ in d$8tribut~0n or
the backwash flow will disrup~ ~the ~iltra~lon s,upport
15 media l~yers, necessit;~tin~ fre~u~nt r~placemont and/or
regra~ing. ~ uniform di~ri~ution o~ backwash gas and
liquid is dependent upon uniforr~ dlstributlon oY the
backwa~;h liquid ~rom primAry 1 ondult~ 28 and 30
into secon~ary condu~t~ 36 and ~0. Acc~ordin~3 to ~e
20 pres~nt imention, this i~s more readily aohi~val~l~ by
malntaining air or gas under pr~squre in primary gas
canduit 38 and the distribution of t~at ga~ through g~s
orl~lces 33 and 3~ into ~iecon~ry condui~ 36 and ~0.
Also, by maintaining primary gas conduit 38 under
25 adequats gas pressure slight ~ariat~on~ in tha lQvelnlacs
of ad~ac~nt blockg will not caUs~ signifi~:an~ variation~
in tha distribu~ion o~ ~he backwash ~low. In addition,
it has been found that whereas ~rior block ~truotures
could c~nly tolerat~ a ~eed rate o~ 3-5 SCF~X per squara
30 ~oot over the ~ilter bed, the pra~ent invention can
accoramodal:~ gas backwash ra~s o~ 1-10 SCFM per square
foot of tha f ~ ltQr ~ad without signi~lcant disruption of
the filt~r layers or unaccQptably high en~rgy los~se~ in
gas distributio~
2~39~9
The ~ er block 10 o~ the pressnt ~nvention
may bQ made o~ ~ired clay or ~ llgh~ weisht, h~qh
den~ity, in~ection molded pla~tic such as polyethylene o
~lgh molecular weight. The polyethylen~ i~ more easy tc~
S handle and more du~abl~ during tr~n~portation and
installatlon. Alternativ~ly~ the exterior ~d intsrior
walls o~ block 10 may be ex~rudeld to form ~ontin~u~
lengths o~ rllter block.
Wlth rarerence now to Flgur~ ~, ther~ are ~hown
o ~wo block~ 10 of t~e presen~ invantion connect~ end to-
end wit~ rlanga 23 insart~d in~o ~ollar 22 of ~n ~djacent
blo~k 10. ~ ~racket member 60 may b~ e~pl~yed to 6ecure
the end~ of the block in abuttlng relation~hlp as shown.
Th~ ribs 20 extendin~ around the lower 2ortion o~ e~ch
block will rest on a preYiou~ly construoted floor 62 in a
tan~ 6B. Rows o~ bloc~s assambled as shown in ~guro 4
w~ll Qxtend across the rloor ~2 o~ th~ tanX 68 with tha
on~ of the rows conneoted to a c~mon header ~0 whlch in
turn is conn~cted throug~ a duct 72 to a pump 74. I~
will ba undsrstood that t~is arrange~ene iS illustratiYe
~n that other design~ ~ay be employed.
Conventionall~, a plurali~y Or layer~ o~
particulatQ material 76 are depo~l~Pd over th~ toy walls
of all th~ rows o~ blocks 10 to a level deemad su~ici2nt
~5 to effect tha degree of cl~ansing raquired for tha liquid
to be treated. Tha blc~c:X 10 lo~ated ad~a~ent on~ of the
walls of the tank wilL be connect3d through ~ ts; tube 56
to a 30urae o gas ~;uch ai~3 air under pr~ssure by a tube
5~ provided for each row of blo~:k~; 10. Suitable valving
30 controls would; of coursc, be employed and sinco these
are of convent~ c~nal con~;truction, they n~c~d not be
~urther descri~d hcroin. Al~arnatively, thcl tube 56 may
b~ omi~ted and the ga~ ~upplied to primary gas conduit 38
by a flume and 51QeVe arrangemcnt in tanX ~8 or by
s~para~e air blocks positioned betwe~n ~ank 68 an~ the
end of ea~h row of f~ltar blo~k~ 10
- 14 -
: ~. : :
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:, : . -: .
In the embodiment described above, the apex of
the primary gas conduit 38 is formed integrally with the
top wall 12 and thereby provides support for the wall 12
which carries the weight of the filter media thereon.
Thus, the blocks 10 may be constructed of lighter
material without sacrificing structural stability.
The present invention, having primary liquid
conduits on the lower level of the filter block and the
primary gas conduit substantially in the upper level of
the filter block, also provides the advantage that
portions of side walls 16 of the primary liquid conduits
can be cut away between adjacent filter blocks to allow
further equalization (by flow across the rows of filter
blocks) of liquid backwash flow during backwash
operations.
In alternate embodiments of the present
invention, the primary gas conduit can be fashioned in
cross-section so that its apex does not extend to the top
wall of the filter block. In such case, the secondary
conduits can comprise either one or two conduits.
Additionally, the primary gas conduit can be of numerous
different cross-sectional designs, and it may in some
cases consist of a cylindrical conduit centrally disposed f
within the secondary conduit. It is preferred, although
not necessary, that the primary gas conduit be
symmetrically disposed about a vertical plane extending
through the axis of the filter block.
In other embodiments of the present invention,
the primary liquid conduits can comprise a single conduit
as can the secondary conduits.
Having described the invention, it will be
apparent to those skilled in this art that various
modifications may be made thereto without departing from
the spirit and scope of this invention as defined in the
appended claims.
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