CA2063969A1 - Filter underdrain block - Google Patents

Abstract

FILTER UNDERDRAIN BLOCK
ABSTRACT OF THE DISCLOSURE

A filter block having a plurality of exterior and interior walls defining a plurality of interior chambers, said chambers including at least first and second conduits parallel to the longitudinal axis of said block, one disposed above the other, with a third conduit provided to supply gas under pressure to the upper conduit; a top exterior wall of the block having a plurality of aperture distributed thereover. The interior chambers comprise separate conduits for both gas and liquid backwash flows. The interior walls defining the conduits are disposed to provide even distribution of the backwashing gas and to provide bearing support for the top wall of the block.

Description

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.

: : ~
~, . . .
, . . , ~.

:. :
:: : . . ,.:

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 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 : . , 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 . . .

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.

~ ,~
''~

": ` ; . : ' '. .
~. ' '; ' ~, `

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.

~ , 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.

- 7a ~

'. ':' .: : '.

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~.

: . . :..
. .

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 ` ' ' !
' '' . ... ' ' .' . ~ ' '~ ~ ', 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~

.

.
~ .

:

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 '- ~ '` ,'~ ';~ ','' - . :

. , . :
.

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 -. ~ :
:: ;
..
~ ~ .

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 : ~. : :
- . . . . .

:, : . -: .

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.

Claims (8)

1. 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 exterior 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.

2. The block of claim 1 wherein said primary gas conduit is defined by two inclined interior walls providing said primary gas conduit with a vertically tapering cross-section and wherein said gas orifices are disposed in each of said two inclined walls.

3. The block of claim 2 wherein said gas orifices comprise a plurality of upper gas orifices and a plurality of lower gas orifices.

4. The block of claim 3 wherein said upper gas orifices have smaller cross-sectional areas than said lower gas orifices.

5. The block of claim 1 further comprising means for admitting a gas under pressure to the interior of said primary gas conduit.

6. The block of claim 5 wherein said means for admitting a gas is a pipe passing through said top wall and adjacent an end of said block, said pipe having one end thereof in fluid communication with said primary gas conduit.

7. The block of claim 1 further including a plurality of orifices in said top wall for matering a gas, during backwashing, from said block to an overlying filter material.

8. The block of claim 1 wherein said interior walls include a transverse wall extending from one side wall to the opposite side wall and substantially parallel to said top and bottom walls, said transverse wall being vertically spaced from said bottom wall.