Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
Z
MULTIBED FILTER BACKI^IASHED BY MOVABLE
ISOLATION HOOD
BACKGROU D OF THE INV~NTION
This invention relates to liquid filtration, and
more particularly to processes for gravity filtration and
filters with a rotating hood for lsolating discrete beds of
filter material during backwashing.
There are inherent economies and advantages in
multiunit filters in which an individual filter unit is
isolated from a common chamber of unfiltered influent
for backwashing, while the remaining unlts continue to -
produce filtered effluent. Since the filter media is
segregated into several discrete beds, the backwash flow
required by any single bed is so small that the beds re~
maining in service can provide sufficient filtered liquid.
The relatively small volume of dirty backwash liquid can
be returned directly to a clarifier or floculator combined
with the filters or to waste without the danger of
hydraulically upsetting the system. Since only one bed is
backwashed at a time, the service flow from the mul~ibed
filter is essentially constant. The multiunit filter design
has been extensively used for totally enclosed strainer or
cartridge type pressure filters of relatively moderate
or small size. It has been necessary in such totally
enclosed pressure filters to use mechanical implements to
force the isolation device into sealing engagement with the
unit being backwashed. However, this multiunit design has
~ '
z
not been employed on gravity filters. One reason for the
lack of use of the multiunit design on large gravity
filters has been the unavailability at a reasonable cost
of suitable prior art mechanical sealing mechanisms that
are easily movable and operable over large surfaces and
distances inherent in the common gravity filter designs.
SUMMARY OF THE INVENTION
Accordingly, it is an object of this invention
to provide an improved liquid filter and an improved
process for backwashing same.
Another object is to provide a multiunit gravity
liquid filter having a movable hood that isolates indivi-
dual units for backwashing.
Another object is to provide a multiunit filter - -
having a movable hood that does not require mechanical
implements to directly force the hood into sealing engage-
ment during backwashing or to release the hood from such
engagement.
Another object is to provide a multicell liquid
filter with a movable backwash isolation hood that is
sealed and released from sealing by hydraulic and gravi-
tational forces.
Another object is to provide a multicell liquid
filter that is simple, relatively low cost, durable, and
that does not have defects found in corresponding prior
art equipment.
Another object is to provide a liquid filter
backwashing process in which a filter cell isolation hood
-- 2 --
.
z
floats out of sealing contact with the cell after bac~-
washing, and sinks into sealing contact under the influence
of gravity.
Another object is to provide a process and
apparatus in which the force required to lift the movable
backwash isolation hood of a multiunit filter is reduced.
Another object is to provide a way of detecting
leakage between the movable backwash isolation hood of a
filter and the surfaces against which it seals.
Another object is to provide an improved mechanism ~
for lifting, rotating and lowering the movable backwash -
isolation hood of a filter.
Another object is to provide a multiunit filter in
which one unit at a time is backwashed and the dirty
backwash liquid is returned to the untreated liquid
flowing to the filter.
Another object is to provide a combined filter-
floculator that discharges only filtered liquid effluent
and sludge.
~ 20 Still other objects and advantages will be revealcd
- in the specification and claims, and the scope of the ;
invention will be set forth in the claims.
Briefly stated, in accordance with one aspect of
the invention, there is provided a multiunit liquid filter which
com~rises a backwash isolation hood mova~le to cover a specific
~ filter unit in need of backwashing, with means for moving the
;! ' hood from one unit to another, means for lifting the hood out
of sealing engagement with a filter unit, and means for moving
the hood into sealing engagement with another unit.
:i. : . . .
3 --
, ~090~i~
Thus broadl~, the inYention contemplates a multibed
gravity liquid filter which comprises a tank having an inlet
and an outlet, means in the tank supporting granular filter
material and definIng therebeneath a filtered liquid chamber
communicating with the outlet, with a wall of the container
extending above the granular filter material so as to define
a chamber for unfiltered liquid, partitions extending upwardly
. ",
from the granular material supporting means so as to divide
the granular filter material into a plurality of beds, with
the upper terminal edge of each partition extending above the
beds into the unfiltered liquid chamber, and with the upper
edges providing sealable surfaces. A backwash isolation hood
for sealing with the sealable surfaces is provided by the
partitions which define any of the beds, a backwash outlet-
is connected to the underside of the hood, and means connects
the backwash outlet to the chamber for unfiltered liquid so as
.~:
to equalize the pressure on opposite sides of the hood and
thereby reduce the force required to lift the hood out of
~ sealing engagement with the partitions. Means lifts the hood
.. .
out of sealing engagement with the partitions, means moves the
hood from one bed to another, and means lowers the hood into -
sealing engagement with the sealing surfaces.
The invention also contemplates a process for gravity
filtration of a liquid in a multiunit filter having a movable
hood that isolates individual filter units during backwashing
which comprises passing liquid under the influence of gravity
. ~ through the units until at least one unit requires backwashing,
~'.. ,
~: moving the hood into sealing engagement isolating the unit in
,;;` need of backwashing from the other units, backwashing the unit
.,',:~
: 30 by flowing backwashing liquid therethrough,equalizing the
. pressure on opposite sides of the hood, lifting the hood out
:
of sealing engagement with the unit, and moving the hood to
":~
-il another unit in need of backwashing.
,~,.. .
:: -
' 1d - 3a -
, .... ..
/
071~
- DESCRIPTION OF THE DRAWING
- Fig. 1 is a partially broken-away, top plan,
schematic view of one embodiment of the invention. ;~
Fig. 2 is a cross-sectional view of the invention
shown in Fig. 1.
-.
Fig. 3 is a cross-sectional view taken along the -~
~ line 3-3 in Fig. 1.
; Fig. 4 is an enlarged, partially broken-away,
cross-sectional view of a drive coupling for the hood.
Fig. 5 is a top plan view of a reduced scale of
the coupling shown in Fig. 4.
,. . .
Fig. 6 is a broken-away cross-sectional view
corresponding to Fig. 2 and including pressure equalizing
and leak detecting means in accord with this invention.
,; Fig. 7 is a top plan schematic view of another
i- embodiment of the invention.
'~ ' '
Fig. 8 is a cross-sectional view of the embodiment
~ shown in Fig. 7.
-1 Fig. 9 is a cross-sectional view taken along the
line 9-9 in Fig. 7.
Fig. 10 is an enlarged, partially broken-away, cross-
;': -
~' sectional view of the hood moving mechanism of the embodi- ~
,,", .
ment of Figs. 7 and 8, appearing with Fig. 6.
Fig. 11 is a cross-sectional view taken along the
.1 line 11-11 in Fig. 10, appearing with Fig. 6.
... .
. .
. . ..
. ~ '.
;~ .
...
,
. .
r ~V9(~7~
DESCRIPl~ION OF THE INVENTION
Figs. 1-5 show an embodiment of a gravity liquid
filter 1 comprising numerous discrete filter beds 2 occupy-
~ .
- ing an open-topped cylindrical container tank 3. Beds 2
~ are preferably granular filter material 4, such as sand,
;^ gravel, coal, activated carbon, or a combina~ion of such
materials, supported on a perforated plate 6 that spans
- the interior of tank 3. Strainers 7 surround each
perforation in plate 6 and prevent escape of filter material
r 10 4. Upstanding radial partitions 8 separate beds 2. The
;~ upper, perpendicular, terminal flanged edge 9 of each
partition 8 extends above the beds 2, and flanged edges 9
,. . .
~ all lie in the same horizontal plane. A peripheral flange
.~` 10 is connected to and in the same plane as flanged edges
g
Liquid to be treated enters filter 1 through an
inlet pipe 11 and exits through a filtered effluent outlet
~.;. .~
pipe 12. A baffle 13 dissipates the energy of the incoming
liquid. The level 14 of the liquid in tank 1 is kept at a
~t 20 predetermined height above edges 9 by an outlet valve 16
~' which has the size of its port controlled in a conventional
v manner by a liquid level sensing float mechanism 17. The
portion 18 of the wall of tank 3 extending above beds 2
defines an unfiltered liquid or floculation chamber 19
,~. ,,; .
which collects an atmospheric pool of liquid of sufficient
;~ depth standing on beds 2 to cause the unfiltered Liquid to
... .
.....
,'"'`
5 _
'
` ' ~ Q~0712
. ., ~
~,' ~
- percolate under the influence of gravity through material
; 4. Plate 6 defines therebeneath a filtered liquid
chamber 21 in communication with outlet 16. Conventional
accessories, such as a guard rail 22 and catwalk 23 should
be provided when required.
When tank 3 is filled, liquid accumulates in
.~ , .
- chamber 19 until there is sufficient static head to cause
it to pass through filter material 4, leaving most or
all of the undesired contaminants on or in beds 2. When
the amount of filtered contaminants on or in beds 2
.; .
reaches somes predetermined quantity, it is necessary to
-; begin backwashing, one bed at a time.
~ A hollow backwash hood 25 is mounted for rotation
¦ around the center of filter 1. The flat undersurface 26
. ~
~; of hood 25 is perforated to permit liquid to flow into
;- hood 25, and a pliable gasket 27 extends around the periphery
of undersurface 26 for sealing against flanged surfaces
,,. ,~.................................................................. ..
`~ 9 and 10. A protruding cylindrical collar 28 extends ~, .".; .
~ perpendicularly from the inner end of hood 25 into center
,.. ~ .
pipe 29. Collar 28 acts as a guide and a bearing for
'j hood 25 and also enables liquid to flow out of hood 25
, . . . ~
into pipe 29. The space between pipe 29 and collar 28 is
sealed by a suitable gasket that permits collar 28 to
~:,, -
rotate and to move up and down in pipe 29. A backwash
outlet pipe 30 is connected to center pipe 29, and a
~; backwash valve 31 opens and closes outlet pipe 30.
Hood 25 is turned by a gear-motor 32 that is
controlled by a conventional timer, pressure, or liquid- -
:
level actuated electrical circuit. Gear-motor 32 rotates
- 6 -
.,; ............................ . . . . . . .
` 3~(J907iZ
a first hollow, open-ended shaft 33 that is connected in
a gas-tight manner to a second hollow, open-ended shaft
34 by a coupling 35. The upper end of shaft 34 slides
vertically up and down in sleeve 36 of coupling 35. The
lower end of shaft 34 is attached to hood 25, and the
inside of shaft 34 communicates with the inside of hood 25
through a port 37. A slotted indexing disc 38 attached
to pipe 34 and a positioning switch 39 shut off gear-motor
32 when hood 25 is moved to the correct position over the -
next bed 2 in need of backwashing. Limit switch 40 unted .
on support 41 detects the vertical position of disc 38
as it moves vertically up and down with hood 25 and provides ~ .
a signal that gasket 27 is disengaged from the surfaces 9
when switch 40 is actuated by contact with disc 38. The
upper end of shaft 33 extends above gear-motor 32 into an
airtight housing 42. An electrically operated vent valve
43 is connected to the inside of housing 42 through a
T-connection 44. An electrically operated valve 45
j connects the inside of housing 42 to a source of pressured
air or other gas through T-connection 44.
When a bed 2 has been sufficiently backwashed to
render it suitable for return to filtering service, the
conventional control circuit closes valves 31 and 43 and
opens valve 45. Gas under pressure passes into housing 42
- and enters pipe 33. The gas pressure is transmitted into
pipe 34 and expells liquid therefrom. Pressurized gas
enters hood 25 through port 37 and displaces backwash
~ liquid through the filter material 4 in bed 2 into chamber 21,
- 7 -
thus breaking the seal between surfaces 9 and 10 and gasket -
27. When sufficient gas has entered hood 25, the hood
floates up a short distance out of contact with surfaces
9 and 10. This vertical movement of hood 25 carries pipe
34 and attached disc 38 upwardly until limit switch 40
contacts and is actuated. Tripping of limit switch 40
causes the control circuit to actuate gear-motor 32,
which rotates shafts 33 and 34 until movement of indexing
disc 38 trips positioning switch 39. Actuation of switch
39 stops gear-motor 32 when hood 25 is properly positioned
over the next bed 2 in need of backwashing and also
causes the control circuit to close pressure valve 45 and
`!
open vent valve 43. When valve 43 is opened, the interior
of hood 25 is vented to the atmosphere. The static head
from the liquid in chamber 19 forces liquid into hood 25
and displaces gas up pipe 34 and out through valve 43.
~ ~.
When all or almost all of the gas has been expelled from
hood 25, it will sink under the influence of gravity
until gasket 27 rests on the flanged surfaces 9 and 10
; 20 surrounding the next bed in need of backwashing. This
lowers disc 38 and thereby actuates switch 40, thus
`I providing a signal which opens valve 31. The lower
- static head at valve 31 draws filtered liquid from -
chamber 21 up through the strainers 7 into the bed 2
being backwashed. The filtered liquid flushes contaminates
from such bed into hood 25, down center pipe 29, and out
through pipe 30. The greater static pressure in chamber
19 forces hood 25 against flanged surfaces 9 with sufficient
:,
- 8 -
force to seal gasket 27. However, no harm results if
gasket 27 does not seal perfectly, because the unfiltered
liquid which would then leak into hood 25 mixes with the
dirty liquid resulting from backwashing of the filter bed
and is expelled from filter 1 through pipe 30. If desired,
as for example when the liquid being filtered is sewage or
when solids are being floculated in chamber 19, the dirty -~
- liquid leaving through pipe 30 can be pumped directly
back into chamber 19 for continued treatment, in which
case valve 31 can be replaced by or used with a pump.
Solids or floc which accumulate in chamber 19 can be
removed by an air lift pump or other conventional means.
Fig. 6 shows how the force required to lift hood
25 can be reduced, and also how the degree, if any, of
il
~ leakage between hood 25 and flanges 9 can be detected.
r~l The force required to lift hood 25 is reduced by equaliz;ng
,~, .
the pressure on opposite sides of hood 25 at the same
time as, or just before, valves 31 and 43 are closed and
valve 45 is opened. This is accomplished by connecting
electrically operable valve means 50 to backwash pipe 30
by conduit 51 and to chamber 19 by conduit 52, and by
opening valve means 50 before starting to raise hood 25.
This immediately overcomes the effect on hood 25 of the
static head in chamber 19, and reduces the force required
to lift hood 25 to an amount equal to its weight plus the
friction and inertia of the moving parts. This reduces
the amount of air which must be pumped into hood 25 and
hence the time needed to index the hood to the next filter
;
_ 9 _
'
to be backwashed. Valve 50 is closed before backwashing
of the next unit is started.
An indicating pressure differential switch 53 is
connected by a conduit 54 to filtered liquid cllamber ~1,
and to conduit 51 between valve means 50 and pump 30 by
a conduit 55. When valve 50 is closed and hood 25 is
seated on edges 9, switch 53 will indicate zero pressure
differential when there is no leakage under hood 25. The
greater the leakage the greater will be the pressure
differential indicated by switch 53. Switch 53 cnn ~c
connected in a conventional circuit which can sound an
alarm, or prevent the start of the backwash cycle if the -
pressure differential, and hence the leakage, is above
a predetermined amount. An indicating pressure differential
switch suitable for use as described herein is obtainable --
. from Ellison Instrument Company of Boulder, Colorado, as
their "EAGLEEYE" ( ) Mod~l 77c.
; Figs. 7 and 8 show another embodiment of the invention
to be a combined gravity liquid filter and floculator 60
20 having numerous discrete filter beds 61 occupying an open- -
topped cylindrical container tank 62. Beds 61 are made of
; the same materials as in the embodiment of Figs. 1 through
5, and are supported on a perforated plate 63 that spans
the interior of tank 62. Strainers 64 surround each -
perforation in plate 63. Upstanding radial partitions 65
separate beds 61, and the upper terminal edges 66 of each
partition 65 extend above beds 61 and lie in the same
horizontal plane. The upper terminal edge 67 of a
,r,". . - 10 -
cylindrical wall 68 and an outer peripheral rim 69 are
connected to, and terminate in the same plane as, edges
66. Rim 69 is spaced from side wall 70 of tank 62 to
provide clearance for the hood seal.
Liquid to be treated enters through inlet pipe 71,
and filtered effluent exits through outlet pipe 72. The
level 73 of the liquid in tank 62 may be kept at a pre-
determined height by an outlet valve 74, which has the size
of its port controlled in the same manner as described
above with reference to valve 16. The portion o~ wall 70
extending above beds 61 defines an unfiltered liquid and
;~ floculation chamber 75 which collects an at spheric pool
of liquid of sufficient depth standing on beds 61 to cause
, ~ .
the unfiltered liquid to percolate under the influence of
gravity through the filter media. Plate 63 defines there-
beneath a filtered liquid chamber 76 in communication with
outlet 72.
~` Incoming liquid from pipe 71 passes into header
pipe 77 and then into distribution pipes 78 and 79. A
generally cylindrical vertical floculation column 80 is
centered in tank 62, and its top edge 81 terminates
below liquid level 73. Cables 83 support column 80 from
beams 84 which span tank 62. Pipe 78 enters a header 85
:; on the outside of column 80. Liquid flows from pipe 78
~ .
,.;,.
'~ into header 85 and then through holes 86 into adjustable
. ............................... .
nozzles 87. Liquid and solids expelled from nozzles 87
.; . .
cause a turbulent upward swirling and mixing of the con-
, tents of column 80, which promotes floculation. Pipe 79
... - 11 -
,
~3 ~'71 ~
enters a header 89 on the outside of an outwardly flaring
end portion 90 of column 80. Liquid and solids flow through
holes 91 and continue to promote floculation as the liquid
and solids leave column 80 and enter floculation chamber 75,
where the solids continue to floculate as they settle on
the top of filters 61. Sedimentation also occurs in
column 80, and solids fall through a quiescent zone 92 .. ...
defined by an outwardly flaring bottom portion 93. The
solids settle into a collection chamber 94 defined by
10 cylindrical wall 68, which serves as an inner end wall of -
filters 61 and of their common filtered liquid chamber 76.
. Liquid and solids are drawn under bottom portion 93 from
chamber 75 by the upward swirling flow from nozzles 86; some
of such solids settle into collection chamber 94. An
inverted conical wall 96 guides the settled solids toward
the center where they are withdrawn in conventional manner
through a sludge blowdown pipe 97. Chemicals which promote
floculation may be added to the liquid in pip~ 71, or in -
column 80, or in chamber 75
After liquid has filled chamber 75, there is :.
sufficient static head to cause it to pass downwardly
through filter beds 61 into chamber 76 and out through pipe ~
72, leaving most or all of the undesired contaminants on :
or in the beds. Solids in floculation chamber 75 also
sedimentate on to beds 61, and a peripheral, tilted
.~ baffle 99 attached to wall 70 directs the settling solids
towards the center of tank 62. When the amount of contami-
: nants on or in beds 61 reaches some predetermined quantity,
-~ it is necessary to begin backwashing, one bed at a time.
~ - 12 -
~ 2
A hollow backwash hood 100 is mounted for rotation
around the center of tank 62 underneath portion 93. The
underside 101 of the hood is perforated to permit entry
of backwash liquid. An inverted U-shaped flange 102 is
pie-shaped like the top of each filter 61, as defined by
edges 66 and portions of rims 67 and 69, and extends
around the underside of hood 100. A pliable gasket 103
held within flange 102 seals against the upper terminal
edge of the filters. A protruding cylindrical collar 105
extends perpendicularly from the inner end of hood 100
into a center pipe 106. Collar 105 acts as a guide and
a bearing for hood 100 and also directs backwash liquid
flowing out of hood 100 into pipe 106. The space between
pipe 106 and collar 105 is sealed by suitable gasket
means that permits collar 105 to rotate and also to move
up and down in pipe 106. A backwash outlet pipe 107 is
connected to pipe 106, and a three-way backwash vaIve
108 opens and closes pipe 107. Opening of valve 108
causes filtered liquid to flow upwardly from chamber 76
through plate 63 and thus to backwash a bed 61. A recircu-
lation pump 109 may be used to recirculate all or some ofthe dirty backwash liquid and solids through return pipe
110 to header pipe 77, from which the backwash liquid and
solids mix with incoming liquid and are distributed through
! .1,
pipes 78 and 79 into floculation column 80. When all of
the backwash liquid and solids are recirculated into
chamber 80, the only effluents from combined filter-
,
floculator 60 are treated liquid from pipe 73 and sludge. ~
from pipe 97.
. - 13 -
.; . '
~S~3r~7~
Hood 100 is raised, lowered and rotated by the
- mechanism shown in Figs. 10 and 11. A hollow, open-ended -
. shaft 112 is attached perpendicularly at its lower end
~ to hood 100, and the inside of shaft 112 communicates with
;~ the inside of hood 100 through a port 113. A hole 114 in
shaft 112~ay connect the inside of hood 100 to a source of
- pressurized gas that is controlled by valves (not shown)
corresponding to valves 43 and 45, so that hood 100 may
also be raised by air pressure in the manner described
above with regard to the embodiment of Figs. 1-5. The -
~ upper end 115 of shaft 112 is attached to and movable with
: a first cylinder 116. A first piston 117 in cylinder 116
is secured to one end of a rod 118, and the other end of
. rod 118 is connected to plate means 120. First piston
117 and cylinder 116 and shaft 112 are axially aligned at
the center of tank 62, but the inside of shaft 112 does
., not communicate with the inside of cylinder 116. A
, : .
pair of identical, parallel guide rods 122 are spaced on
` opposite sides of, and are parallel to, shaft 112. Rods
122 are attached to plate 120 at their upper ends, and
' their lower ends are reduced to define indexing pins 123
which fit into holes 126 in plate 127. There are two holes
.. in plate 127 corresponding to each filter bed 61, and holes
126 are uniformly spaced around the circumference of a
. circle which is centered at the center of shaft 112. Plate
j .
. 127 is journaled for partial rotation around shaft 112,
and shaft 112 slides through holes 128 and 129. Plate 127
''
- 14 -
, . . .
is supported by a bearing 130, which rests on plate means
131, which in turn is supported over tank 62 by beams 84.
A pair of identical, spaced, parallel plates 132 are
secured to shaft 112 and slidably receive guide rods 122,
which pass through bushings 133 that connect plates 132
to each other. A limit switch actuating rod 135 is also
attached to, and spans the space between, plates 132.
A projecting arm 136 integral with plate 127 is
connected by a pin 137 to an end of a rod 138. The other
end of rod 138 is connected to a second piston 139 in a
second cylinder 140, which is-attached by a bracket 141
to plate means 131. A pair of threaded, adjustable rotation
j limit stops 142 and 143 attached to plate means 131 ac-
curately set the extent of travel of arm 136, and hence
the amount that indexing plate 127 can rotate. Conventional
air pressure lines 144 and 145 are connected to opposite
ends of first cylinder 116, and conventional air pressure
lines 146 and 147 are connected to opposite ends of second
cylinder 140.
A valve 148 connected by conduit 149 to backwash
pipe 107 and by conduit 150 to chamber 75, equalizes the
pressure on opposite sides of hood 100 when it is opened
in the same manner described above with regard to valve 50.
A pressure differential indicating switch 151 connected
between chamber 76 and conduit 149 indicates the amount
` of leakage under hood 100 when valve 148 is closed in the
same manner described above with regard to switch 53.
. , .
- 15 -
Air is forced under pressure into the opposite
ends of first cylinder 116 in a first predetermined sequence
that raises and lowers hood 100, and air is forced under
pressure into the opposite ends of second cylinder 140
in a second predetermined sequence coordinated with the -
first sequence that causes hood 100 to rotate or index
from one filter 61 to another. These sequences are con-
trolled by a conventional electrical control circuit.
Assuming that hood 100 is seated on a filter 61 and
backwashing is taking place, the parts of the mechanism
.~
would be in the positions shown in Figs. 10 and 11. Air
pressure applied through line 145 moves first piston 117
. , : .
upwardly and this raises plate 120 until it contacts limit
switch 153, which shuts off the air; raising of plate 120
... .
~' lifts indexing pins 123 at the ends of guide rods 122
,~. out of the holes 126 which correspond to the filter 61 then
.. . .
.
~ being backwashed. Air pressure applied through line 146
. .
l moves second piston 139 away from the end of cylinder 140
s~
'i attached to bracket 141, and this pushes rod 138 out of
cylinder 140; this moves arm 136 until it hits limit stop
;j~ 143, as shown in phantom in Fig. 11, and indexes the next
,~j pair of holes 126 under ends 123. Rod 135 hits limit
~, switch 154 which shutsoff the air in line 146. Air
. l
pressure applied through line 144 moves piston 117 down-
wardly until plate 120 contacts limit switch 155; this
~ . -
~,~ lowers pins 123 into the just positioned holes 126. When
-.1.'' .
the filter bed 61 being backwashed is sufficiently clean
to be returned to service, as determined by a conventional
,;ii
,~ - 16 -
''"':
,
-
.~ 9~
timer or pressure actuated control circuit, valve 148 is
opened and thus equalizes the pressure on opposite sides
of hood 100; valve 108 is now closed. If air is also being
used to raise hood 100, it would now be pumped through
hole 114 into shaft 112 and thus into the hood through port
113; at the same time, air pressure applied through line
144 would raise cylinder 116 with respect to piston 117
until the upper plate 132 contacts limit switch 156, and
thus would raise or unseat hood 100. Although plates 132
slide upwardly with cylinder 116 and shaft 112, pins 123
.
remain seated in holes 126. Air pressure applied through
line 147 moves piston 139 so as to retract rod 138 into
cylinder 140 and thus rotate or index plate 127 until rod
135 actuates limit switch 154 and arm 136 hits limit stop
` 142; this rotation of plate 127 also rotates rods 122 and
plates 132 which are secured to shaft 112. Thus, hood 100
~ is indexed to a position over the next filter 61 in need
- of backwashing. If air pressure was also being used to
raise hood 100, it is no longer supplied through hole 114
,- 20 so hood 100 will begin to sink under the influence of
gravity. To speed the seating of hood 100, air pressure is
applied through line 145 which forces cylinder 116 down-
wardly until the hood and gasket 103 are firmly seated.
Valve 148 is now closed, valve 108 is opened, and back-
washing begins and continues until the control circuit
causes the above sequences to be repeated.
` It has thus been shown that by the practice of this :~
. .
invention a multibed liquid filter can be backwashed in a
.~ '
` - 17 - ~
.
7 1 ~
process that uses gas to float a backwash isolation hood
out of sealing engagement with a filter bed without requiring
mechanical implements that directly move the hood vertically.
; The process also causes the hood to sink into sealing
engagement under influence of gravity and hydraulic pressure
without the use of devices that exert mechanical force
directly on the hood. The hood can also be raised and
lowered by a unique mechanism that employs two pistons in
cylinders and a perforated indexing plate, either with or
without gas pressure. This makes it practical to use -
rotating backwash isolation hoods with relatively large
(e.g. over 20 feet in diameter) opèn-topped, gravity filters
utilizing granular filter media. Filters in accord with
this invention have relatively low overall height, and do
not require separate tanks for storage of backwash liquid.
The amount of backwash liquid used is low because minimum
free board above the pie-shaped, discrete filter beds is
achieved by uniform liquid collection across the tip of
the beds by the pie-shaped, perforated backwash hood. The
embodiments shown in the drawing include features that lower
cost by making efficient use of materials and space. For
~' example, rods are not needed to support perforated plates
.;, 6 and 63, because they are attached to the underside of
partitions 8 and 65, which function as-rigid plate girders.
When the unfiltered liquid chambers 19 and 75 also function
, ....
. .,
as floculation chambers, the dirty backwash liquid can be
~ recycled so that the only waste from the system is sludge.
,,,
. ' ~
- 18 - ~
'7 1 ~
While the present invention has been described with
reference to particular embodiments, it is not intended to
illustrate or describe herein all of the equivalent forms
or ramifications thereof. For example, the flange 102 and
edge 66 sealing arrangement shown for the embodiment of
Figs. 7-11 could be used with the embodiment of Figs. 1-6,
and the hood undersurface 26 and flanges 9 of the Fig. 1-6
embodiment could be used with the embodiment of Figs. 7-11.
Also, the words used are words of description rather than
limitation, and various changes may be made without departing
from the spirit or scope of the invention disclosed herein.
It is intended in the appended claims to cover all changes
~ as fall within the true spirit and scope of the invention.
.~,
. .~.
:"
'';''
. . .
~:,
'
,.
~ ''
,: - 19 -
.
