Note: Descriptions are shown in the official language in which they were submitted.
CA 02363588 2001-11-22
TITLE OF THE INVENTION: SELF-CLEANING FILTER
FIELD OF THE INVENTION
The present invention relates to liquid filters, and more particularly to a
self
cleaning liquid filter.
BACKGROUND OF THE INVENTION
Filters used for filtering liquids come in many shapes and sizes. Often, a
filtering
screen or a filtering film is used in the filter, with a porosity which
depends on the desired
filtration quality. This film or screen needs to be cleaned for removal
therefrom of
macroparticulate debris or waste which are filtered from the liquid and which
remain on the
screen or film surface. Indeed, this gradually accumulating debris can
eventually clog the
filtering screen or film, preventing macro-particle-laden or dirty liquid from
flowing through the
screen or film. However, cleaning the screen or film can be time-consuming and
complicated,
as the filtering operations often have to be stopped while cleaning is
underway, and the filter
often has to be opened and partly disassembled to allow one to reach the
filtering screen or film
for cleaning purposes.
SUMMARY OF THE INVENTION
2 0 The present invention relates to a self cleaning filter for filtering
incoming dirty
liquid and distinctly recuperating clean liquid and waste liquid, comprising:
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CA 02363588 2001-11-22
- a housing having an elongated inner chamber defining first and second inner
chamber
portions, and an outer chamber;
- a filtering device mounted to said housing and separating said inner and
outer chambers,
for allowing dirty liquid in said inner chamber to be filtered by flowing
through said filtering
device to form clean liquid in said outer chamber, leaving waste in said inner
chamber;
- first and second inlet ports in said housing for allowing dirty liquid to
flow respectively
into said first and second inner chamber portions;
- a clean liquid outlet port in said housing for allowing clean liquid to flow
out of said
outer chamber;
- first and second waste outlet ports in said housing for allowing waste
liquid to flow
respectively out of said first and second inner chamber portions;
- a piston longitudinally movable along said inner chamber and engaging said
filtering
device for cleaning said filtering device of waste as said piston moves, said
piston separating said
first and second inner chamber portions whereby said first and second inner
chamber portions
have a variable dimension depending on the position of said piston;
- valve means controlling liquid flow through said first and second inlet
ports and through
said first and second waste liquid outlet ports; and
- piston control means for controlling the movement of said piston inside said
inner
chamber;
2 0 wherein said piston can move through said inner chamber in a reciprocating
motion between a
first and a second limit position to expel waste liquid alternately through
said first and second
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CA 02363588 2001-11-22
waste outlet ports, and wherein said valve means will allow either one of:
a) dirty liquid to flow into said first firmer chamber portion and waste
liquid to flow out of
said second waste outlet port; and
b) dirty liquid to flow into said second inner chamber portion and waste
liquid to flow out
of said first waste outlet port.
The present invention also relates to a self cleaning filter for filtering
incoming
dirty liquid and distinctly recuperating clean liquid and waste liquid,
comprising:
a housing having an elongated inner chamber defining first and second inner
chamber
portions, and an outer chamber;
- a filtering device mounted to said housing and separating said inner and
outer chambers,
for allowing dirty liquid in said inner chamber to be filtered by flowing
through said filtering
device to form clean liquid in said outer chamber, leaving waste in said inner
chamber;
first and second inlet ports in said housing for allowing dirty liquid to flow
respectively
into said first and second inner chamber portions;
- a clean liquid outlet port in said housing for allowing clean liquid to flow
out of said
outer chamber;
first and second waste outlet ports in said housing for allowing waste liquid
to flow
respectively out of said first and second inner chamber portions;
a piston longitudinally movable along said inner chamber between a first and a
second
2 0 limit position and engaging said filtering device for cleaning said
filtering device of waste as said
piston moves, said piston separating said first and second inner chamber
portions whereby said
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first and second inner chamber portions have a variable dimension depending on
the position of
said piston;
a control device;
first and second inlet control valves controlled by said control device and
respectively
linked to said first and second inlet ports for controlling liquid flow
through said first and second
inlet ports;
first and second outlet control valves controlled by said control device and
respectively
linked to said first and second waste outlet ports for controlling liquid flow
through said first and
second waste outlet ports; and
- first and second pressure sensors linked to said control device and
respectively located
in said first and second inner chamber portions for measuring the pressure in
said first and
second inner chamber portions;
wherein said piston will move through said inner chamber in a reciprocating
motion for expelling
waste liquid alternately through said first and second waste outlet ports upon
determined pressure
differentials being reached between said first and second inner chamber
portions, and wherein
said control device will control the openings of said first and second inlet
control valves and of
said first and second outlet control valves so as to create desired pressure
differentials in said
first and second inner chambers to ensure a reciprocating motion of said
piston in said inner
chamber to clean said filtering device and to ensure expulsion of waste liquid
through said first
2 0 and second waste outlet ports.
Preferably, said filtering device is a filtering screen.
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Preferably, said filtering screen comprises a rigid perforated support
structure and
a porous film applied against said support structure.
Preferably, said inner chamber is cylindrical and is circumscribed by said
filtering
screen which is also cylindrical, said outer chamber being located around said
inner chamber,
being toroidal and being circumscribed by said housing which is also
cylindrical.
Preferably, said piston is generally cylindrical and comprises a filtering
device
engaging peripheral surface and a pair of opposite end surfaces that are
inwardly concave.
Preferably, said piston comprises an axial channel defining two extremities
and
axially extending through said piston, and a plunger movable in said axial
channel and having
a pair of opposite seats, with either one of said seats being engageable
against a corresponding
said piston end surface to close a corresponding said axial channel extremity,
said piston further
comprising at least one radial channel radially extending through said piston
between said axial
channel and said peripheral surface.
Preferably, said piston comprises a pair of opposite frusto-conical, outwardly
convex, back-to-back surfaces linked at a common annular filtering device
engaging edge.
Preferably, said piston further comprises a pair of stabilizers on opposite
sides
thereof.
The present invention also relates to a method of filtering incoming dirty
liquid
and distinctly recuperating clean liquid and waste liquid with a self cleaning
filter, the filter
2 0 comprising:
a housing having an elongated inner chamber defining first and second inner
chamber
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CA 02363588 2001-11-22
portions, and an outer chamber;
- a filtering device mounted to the housing and separating the inner and outer
chambers
thereof;
- first and second inlet ports in the housing for allowing dirty liquid to
flow respectively
into the first and second inner chamber portions;
- a clean liquid outlet port in the housing for allowing clean liquid to flow
out of the outer
chamber;
- first and second waste outlet ports in the housing for allowing waste liquid
to flow
respectively out of the first and second inner chamber portions;
- a piston longitudinally movable along the inner chamber between a first and
a second
limit position and engaging the filtering device for cleaning the filtering
device of waste as the
piston moves, the piston separating the first and second inner chamber
portions whereby the first
and second inner chamber portions have a variable dimension depending on the
position of the
piston;
- a control device;
- first and second inlet control valves controlled by the control device and
respectively
linked to the first and second inlet ports for controlling liquid flow through
the first and second
inlet ports;
- first and second outlet control valves controlled by the control device and
respectively
2 0 linked to the first and second waste outlet ports for controlling liquid
flow through the first and
second waste outlet ports; and
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- first and second pressure sensors linked to the control device and
respectively located in
the first and second inner chamber portions for measuring the pressure in the
first and second
inner chamber portions;
wherein said method comprises the following steps:
a) allowing dirty liquid to flow in the first inner chamber portion through
the first inlet port;
b) allowing the dirty liquid in the first inner chamber portion to flow
through the filtering
device to form clean liquid in the outer chamber, leaving waste in the first
inner chamber portion,
whereby pressure in the first inner chamber portion will rise as the filtering
device gradually
becomes obstructed;
c) moving the piston towards the second limit position to increase the size of
the first inner
chamber portion and to free a clean filtering device portion in the first
inner chamber portion
upon the pressure in the first inner chamber portion reaching a determined
value, whereby the
pressure in the first inner chamber portion will remain approximately equal to
said determined
value;
d) allowing waste liquid in the second inner chamber portion to be evacuated
through the
second waste liquid outlet port only when the pressure in the second inner
chamber portion is
equal to or greater than an outlet threshold pressure value;
e) upon the piston reaching the second limit position, allowing the pressure
in the first inner
chamber portion to rise beyond said determined value;
2 0 f) upon an inlet threshold pressure value being reached in the first inner
chamber portion,
preventing dirty liquid to flow into the first inner chamber portion and
allowing dirty liquid to
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flow into the second inner chamber portion through the second inlet port;
g) allowing the dirty liquid in the second inner chamber portion to flow
through the filtering
device to form clean liquid in the outer chamber, leaving waste in the second
inner chamber
portion, whereby pressure in the second inner chamber portion will rise as the
filtering device
gradually becomes obstructed;
h) moving the piston towards the first limit position to increase the size of
the second inner
chamber portion and to free a clean filtering device portion in the second
inner chamber portion
upon the pressure in the second inner chamber portion reaching a determined
value, whereby
pressure in the second inner chamber portion will remain approximately equal
to said determined
value;
i) allowing waste liquid in the first inner chamber portion to be evacuated
through the first
waste liquid outlet port only when the pressure in the first inner chamber
portion is equal to or
greater than the outlet threshold pressure value;
j) upon the piston reaching the first limit position, allowing the pressure in
the second inner
chamber portion to rise beyond said determined value;
k) upon the inlet threshold pressure value being reached in the second inner
chamber
portion, preventing dirty liquid to flow into the second inner chamber portion
and allowing dirty
liquid to flow into the first inner chamber portion through the first inlet
port;
1) repeating steps (a) to (k) until no more dirty liquid is desired to be
filtered; and
2 0 m) continuously collecting clean liquid from the outer chamber through the
clean liquid outlet port.
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DESCRIPTION OF THE DRAWINGS
In the annexed drawings:
Figure 1 is a perspective view of the filter of the present invention, with a
portion
of the filter housing and a portion of the filtering screen being removed to
show the filter inner
chamber and the cleaning piston;
Figure 2 is an exploded perspective view of the filter of figure l;
Figure 3 is a schematic longitudinal cross-sectional elevation of the filter
of figure
l;
Figures 4-6 are views similar to figure 3, sequentially suggesting the liquid
flow
directions in the filter together with corresponding piston positions and
movement directions;
Figures 7 and 8 are respectively a perspective view and a cross-sectional view
of
a filter cleaning piston according to a first embodiment of the invention;
Figures 9 and 10 are respectively a perspective view and a cross-sectional
view
of a filter cleaning piston according to a second embodiment of the invention,
with figure 10
being at an enlarged scale and additionally showing the portion of the filter
screen adjacent to
the piston; and
Figures 11 and 12 are respectively a perspective view and a cross-sectional
view
of a filter cleaning piston according to a third embodiment of the invention.
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DETAILED DESCRIPTION OF THE EMBODIMENTS
Figures 1-3 show a self cleaning filter 10 according to the present invention.
Filter 10 comprises a horizontally disposed cylindrical housing 12 having
first and second ends
12a, 12b. A perforated cylinder or screen 14 having a smaller diameter than
housing 12, is
coaxially installed inside housing 12, with housing 12 and screen 14 being
radially spaced-apart.
A Y-shaped dirty liquid inlet tube 20 has a main inlet portion 22 connected to
a
dirty liquid source (not shown) feeding dirty liquid to be filtered. Main
inlet portion 22 is also
connected to co-extensive first and second elbowed branches 24a, 24b that are
in turn connected
to first and second frusto-conical caps 26a, 26b. Caps 26a, 26b are
respectively connected by
their integral peripheral flanges 28a, 28b with bolts 34 to first and second
annular flanges 30a,
30b that are in turn fixed to cylinder 12 at its first and second ends 12a,
12b respectively.
Annular elastomeric seals 32a and 32b are respectively installed between
flanges 28a, 30a and
28b, 30b. Figure 2 shows that the cap flanges 28a, 28b radially inwardly
protrude relative to
annular flanges 30a, 30b, so as to form inwardly protruding annular shoulders
in casing 12 near
its extremities 12a, 12b.
Figure 3 shows that screen 14 extends longitudinally inside cylinder 12
between
annular flanges 30a, 30b to which it is attached, so as to separate the
toroidal volume forming
an outer chamber 35 and located around screen 14, from the cylindrical volume
located inside
screen 14 and forming a cylindrical inner chamber 37 that extends into hollow
caps 26a, 26b.
2 0 The inlet tube first and second branches 24a, 24b, defining dirty liquid
inlet ports, are thus in
fluid communication with the filter inner chamber 37, which may in turn
fluidingly communicate
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CA 02363588 2001-11-22
with outer chamber 35 through screen 14. In fact, liquid located in inner
chamber 37 can only
access outer chamber 35 through cylindrical screen 14.
As illustrated in figures 1-3, filter 10 comprises first and second waste
outlet tubes
36a, 36b connected to first and second caps 26a, 26b. Waste outlet tubes 36a,
36b are connected
to a suitable waste disposal facility (not shown). Filter 10 also comprises a
Y-shaped clean
liquid outlet tube 38 that has a main outlet portion 40 which is connected to
coextensive first and
second elbowed branches 42a, 42b. Tube branches 42a and 42b are fluidingly
connected to the
cylinder outer chamber 35, and more specifically through the lower portion of
flanges 28a, 30a,
annular seals 32a, 32b and flanges 28b, 30b. Main outlet portion 40 is also
connected to a
suitable clean liquid recuperation facility (not shown).
First and second inlet control valves 44a, 44b are provided on the inlet tube
first
and second branches 24a, 24b. Also, first and second outlet control valves
46a, 46b are provided
on the waste outlet tubes 36a, 36b.
A piston 48 is installed inside screen 14 and can reciprocatingly move axially
therein between two opposite limits positions in which piston 48 abuts against
the radially
inwardly protruding shoulders of cap flanges 28a and 28b, respectively. When
moving inside
screen 14, piston 48 sealingly slides along the inner surface of screen 14 and
rakes and pushes
any debris in screen 14 towards a corresponding one of the cylinder ends 12a,
12b.
A removable filtering film 50 is applied against the inner surface of screen
14, to
2 0 allow for a selected filtering capacity by choosing a film 50 having a
desired porosity. Thus,
screen 14 in fact acts as a support structure for film 50, although a suitable
filtering screen 14
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lacking a filtering film could also be envisioned. A film 50 which is
independent from the screen
support structure 14 has the advantage of being more easily removable and
replaceable, either
to install a new film when the old one is worn or damaged, or to change the
porosity of the
filtering process.
Pressure sensors 52a, 52b (figure 3) are provided in end caps 26a, 26b and are
linked to a programmed electronic control device 54 which is linked to and
commands valves
44a, 44b, 46a and 46b. Control device 54 can be for example a programmable
automaton or a
computer.
In use, the purpose of filter 10 is to filter dirty liquid being fed through
the inlet
tube main portion 22. Clean liquid will be expelled out through main outlet
tube 40, and waste
liquid will be expelled through waste outlet tubes 36a, 36b. The waste liquid
will be formed of
the waste or debris retained by screen 14 and film 50, and by a certain
proportion of dirty liquid.
Preferably, the proportion of dirty liquid expelled will be as low as
possible.
As shown sequentially in figures 3 to 6, dirty liquid can be filtered while
the inner
surface of film 50 will be cleaned by reciprocating piston 48. At any given
time, incoming dirty
liquid will be directed to either one of inlet tube branches 24a and 24b, but
never to both at the
same time. This selective liquid inlet flow orientation is controlled by
control device 54 which
commands inlet control valves 44a, 44b accordingly, as detailed hereinafter.
Also, at any given
time, waste liquid flows out through either one of waste outlet tubes 36a and
36b, or through
2 0 none of them, but in any event never through both at the same time. This
selective waste liquid
outlet flow orientation is also controlled by control device 54 which commands
outlet control
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valves 46a, 46b accordingly, as also detailed hereinafter. Finally, filtered
liquid continuously
flows out through outlet tube 38 during the filtration process.
In an initial condition of filter 10, first inlet control valve 44a is opened,
second
inlet control valve 44b and outlet control valves 46a and 46b are closed, and
piston 48 is
positioned as shown in figure 3 (although it could be positioned elsewhere -
this initial position
being chosen for the purposes of the present explanation). The housing inner
chamber 37 is
sealingly divided into two portions by piston 48, a left-hand side (in the
annexed drawings) first
inner chamber portion 37a, and a right-hand side second inner chamber portion
37b.
Dirty liquid starts to flow from main inlet tube 22 through first inlet tube
branch
24a, the hollow first cap 26a and into the first inner chamber portion 37a.
Once it is in first inner
chamber portion 37a, the liquid flows into the housing outer chamber 35
through film 50 and
screen 14, being filtered in the process to form clean liquid in outer chamber
35. The clean
liquid then flows through outlet tube 38, through both branches 42a and 42b,
to be conveyed to
a suitable clean liquid receiving area.
As waste or debris accumulate on the inner surface of film 50 during liquid
filtration, the latter gradually becomes obstructed, thus reducing the rate at
which liquid flows
towards the housing outer chamber 35. As a consequence of this reduced
outgoing liquid flow
rate in first inner chamber portion 37a, the incoming liquid flow rate
eventually becomes greater
than the outgoing liquid flow rate, and pressure gradually rises inside first
inner chamber portion
2 0 37a. At one point, pressure inside first inner chamber portion 37a becomes
sufficient to
overcome the friction forces retaining piston 48, and the latter is pushed
towards the right-hand
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side, as shown in figure 4.
As piston 48 moves towards second waste outlet tube 36b, a clean filtering
film
portion is freed where piston 48 has vacated film 50 in first inner chamber
portion 37a. This
allows liquid to flow therethrough, still being filtered in the process.
Eventually, this clean
filtering film portion also becomes obstructed, pressure rises in first inner
chamber portion 37a,
and piston 48 is again pushed towards second waste outlet tube 36b, freeing a
new clean film
portion.
Piston 48 thus moves towards the right-hand side until it abuts against the
annular
shoulder formed by the radially inwardly protruding portion of the second cap
flange 28b, as
shown in figure 5. At this point, dirty liquid continues to flow into first
inner chamber portion
37a. However, as dirty liquid continues to flow into first inner chamber
portion 37a, the pressure
therein rises even more, eventually reaching an inlet threshold value as
measured by the first
sensor 52a.
Once this inlet threshold pressure value is reached in the first inner chamber
portion 37a, control device 54 commands first inlet control valve 44a to close
and second inlet
control valve 44b to open. Dirty liquid consequently flows into second inner
chamber portion
37b (now only including the hollow cap 26b portion). Also, as the inlet valves
are switched,
control device 54 reads the pressure in first inner chamber portion 37a with
first sensor 52a, and
2 0 compares it to a determined outlet threshold pressure value, which is much
lesser than the inlet
threshold pressure value; thus, since the pressure in first inner chamber is
greater than the outlet
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CA 02363588 2001-11-22
threshold pressure value, first outlet control valve 46a is commanded to open
by control device
54, and waste liquid pours out into first waste outlet tube 36a, until the
pressure in first inner
chamber portion 37a reaches the outlet threshold pressure value. From then on,
first outlet
control valve 46a only opens to allow outflow of waste liquid if the pressure
measured in first
inner chamber portion 37a is greater than the outlet threshold pressure value,
and otherwise
remains closed.
Piston 48 gradually moves towards the left-hand side, as shown in figure 6, as
the
pressure increases in second inner chamber portion 37b due to waste at least
partly obstructing
film 50 in second inner chamber portion 37b through the filtering of liquid
through film 50. The
process is thus repeated, although piston 48 now moves in the opposite
direction.
As it is gradually displaced towards the left-hand side, piston 48 will this
time not
only vacate a clean film portion. Indeed, piston 48 will also rake the inner
surface of filtering
film 50 in the first inner chamber portion 37a which is filled with waste, and
will push waste in
the first inner chamber portion 37a towards first waste outlet tube 36a,
consequently maintaining,
in combination with the regulated outflow of waste liquid through first outlet
control valve 46a,
the pressure in first inner chamber portion 37a near the outlet threshold
pressure value.
It is understood that a certain amount of liquid is expelled with the debris
out
through waste outlet tubes 36a, 36b, often forming a mud-like liquid.
Piston 48 continues to be pushed towards first waste outlet tube 36a, with
waste
2 0 liquid being either continuously (especially if the waste liquid is very
homogeneous) or
sporadically expelled through first waste outlet tube 36a, until piston 48
abuts against the annular
CA 02363588 2001-11-22
shoulder formed by the radially inwardly protruding portion of the first cap
flange 28a. At this
point, dirty liquid continues to flow into second inner chamber portion 37b,
although the first
outlet control valve 46a remains closed since pressure in the first inner
chamber portion 37a
(now only including the hollow cap 26a portion) then stops to increase due to
the now motionless
piston 48. However, as liquid continues to flow into second inner chamber
portion 37b, the
pressure therein rises even more, eventually reaching the inlet threshold
value as measured by
the second sensor 52b.
Once this inlet threshold value is reached in the first inner chamber portion
37a,
control device 54 will command second inlet control valve 44b to close and
first inlet control
valve 44a to open. The cycle is thus re-started, although this time the second
inner chamber
portion 37b is already filled with waste, which will be initially partly
emptied through waste
outlet tube 36b until the pressure inside second inner chamber portion 37b
decreases to a value
near the outlet threshold pressure value. The waste will then be gradually
raked and pushed out
through second waste outlet tube 36b by piston 48, as explained hereinabove in
the case of the
waste in first inner chamber portion 37a.
Thus, through the programmed control device 54 which commands valves 44a,
44b, 46a, 46b according to the pressure measured in the first and second inner
chambers 37a,
37b, liquid can be filtered efficiently, with the filter inner surface being
cleaned by the
reciprocating movement of piston 48.
2 0 Tests have been accomplished wherein the outlet threshold pressure value
was
set at 20 pounds per square inch (psi) and the inlet threshold pressure value
was set at 60 psi.
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The pressure required for the piston to be moved was approximately 40 psi. A
20 psi pressure
differential between the first and second inner chamber portions 37a, 37b was
consequently
necessary to overcome the friction forces applied against piston 48 to make it
move.
It is noted that the inlet and outlet threshold pressure values are calibrated
according to the pressure required to overcome the friction force exerted on
piston 48 according
to the specific nature of the liquid to be filtered, and that while piston 48
moves along inner
chamber 37 in one direction, a pressure equilibrium sets up in both the first
and second inner
chambers 37a and 37b. Indeed, the dirty liquid flowing into first inner
chamber portion 37a, for
example, will not increase the pressure in first inner chamber portion 37a
above a certain
pressure value, for example 40 psi. Indeed, as soon as the pressure in first
inner chamber rises
sufficiently to move piston 48, the latter will free a clean film portion
which will allow the liquid
to flow therethrough, and the size of the first inner chamber portion 37a will
increase: the liquid
flow out of first inner chamber portion 37a and this size increase of first
inner chamber portion
37a will effectively participate in reducing the pressure in first inner
chamber portion 37a. On
the other hand, additional dirty liquid flowing into inner chamber portion 37a
will participate to
increase the pressure therein. Consequently, the pressure generally stabilizes
at a determined
value, for example 40 psi. Meanwhile, in second inner chamber portion 37b, the
pressure
substantially stabilizes at the outlet threshold pressure value, as explained
hereinabove, for
example 20 psi. This pressure equilibrium is maintained while piston 48 moves
along inner
2 0 chamber 37, until piston 48 abuts against one of the shoulders formed by
flanges 28a, 28b.
Figures 7 and 8 show piston 48, according to one embodiment of the present
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CA 02363588 2001-11-22
invention. It can be seen that piston 48 comprises a main body 56, which can
be made of nylon
according to one embodiment, and which has a generally cylindrical shape
defining inwardly
concave first and second conical sides 56a and 56b and a peripheral surface
56c. The concave
conical surfaces 56a, 56b register with the housing first and second inner
chambers 37a and 37b
respectively, and provide a greater surface area for enhanced effect of the
pressure applied by the
liquid on piston 48, and a centrally concentrated pressure gradient applied by
the piston on the
waste liquid during waste ejection. Piston 48 also comprises a pair of spaced-
apart annular
elastomeric seals 58, 60 provided in annular grooved ribs 62, 64 integrally
formed on the axial
extremities of peripheral surface 56c.
Figures 9 and 10 show a piston 48' according to a second embodiment of the
invention. Piston 48' is similar to the first embodiment of the piston 48,
having a generally
cylindrical main body 66 defining a peripheral surface 66c and two inwardly
concave conical end
surfaces 66a, 66b, and also having peripheral grooved ribs 68a, 68b housing
annular seals 70a,
70b. Piston 48' furthermore comprises a plunger 72 made of a central rod 72c
having opposite
conical seats 72a, 72b, with rod 72c being axially movable through an axial
channel 74 made
centrally through piston 48', so as to act as a valve. Plunger rod 72c is
diametrally smaller than
axial channel 74 so as to provide a radial play around rod 72c. Also, at least
one radial channel,
for example two radial channels 76, radially extend between axial channel 74
and peripheral
surface 66c, and are centrally disposed relative to end surfaces 66a and 66b,
so as to allow liquid
2 0 to flow from axial channel 74 towards the peripheral groove 77 formed
between ribs 68, 70,
outer surface 66c and film 50. Piston 48' can be used instead of the first
embodiment of piston
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CA 02363588 2001-11-22
48, especially when the dirty liquid includes a lesser proportion of solids or
smaller solid
particles.
In use, as shown more particularly in figure 10, when piston 48' abuts against
a
housing cap flange, for example second cap flange 28b, the pressure rises on
the left-hand side
of piston 48' in first inner chamber portion 37a until the pressure reaches
the inlet threshold
value, as described hereinabove. Control device 54 then switches the active
inlet control valves,
so that the second inlet control valve 44b becomes active and the first inlet
control valve 44a,
inactive. Dirty liquid then flows into second inner chamber portion 37b while
the pressure
remains higher in first inner chamber portion 37a. In such a case, plunger 72
will be pushed
towards the right-hand side as shown in figure 10, due to the greater pressure
on the left-hand
side of piston 48'. Seat 72a will consequently block axial channel 74 on the
left-hand extremity
thereof, while seat 72b will clear the opening of axial channel 74. Incoming
liquid will
consequently be allowed to flow from second inner chamber portion 37b through
channel 74
around plunger rod 72c, then radially outwardly through radial channels 76, 76
into groove 77,
where it will be expelled through film 50 and screen 14, being filtered in the
process.
It is understood that if the dirty liquid were to have an important
concentration
of solids or large solid particles, then piston 48' would not be appropriate
since these solids
would remain in groove 77, eventually clogging the diametral channel 76 and
rendering same
useless, in addition to increasing the friction force between piston 48' and
film 50 due to the
2 0 presence of solid particles trapped in groove 77.
Figures 11-12 show a third embodiment of a piston 48" according to the present
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CA 02363588 2001-11-22
invention. Piston 48" comprises a main body 78 having a pair of outwardly
convex frusto-
conical end surfaces 78a, 78b and a relatively thin peripheral edge 78c. A
pair of cross-shaped
rigid stabilizers 80a, 80b are installed on corresponding end surfaces 78a,
78b of main body 78
by means of a bolt (not shown) extending through stabilizers 80a, 80b and an
axial bore 82 made
in main body 78. Piston 48" is used when the waste on film 50 is particularly
tough to remove,
since the thinner raking edge 78c concentrates the raking force instead of it
being spread out on
a larger surface such as the one of pistons 48 and 48' of the first two
embodiments. Stabilizers
80a, 80b are provided to prevent piston 48" from tilting on one side or the
other due to the
otherwise unstable engagement of the thin edge 78c against screen 14.
In the embodiment shown in the drawings, the support screen 14 and filtering
film
50 are shown as being two distinct elements. However, it is understood that
any suitable filtering
device with required filtering features could be used.
In the embodiment of the invention shown in the drawings, the filter is
positioned
horizontally. This is desirable since it facilitates the clean liquid
collection in outer chamber 35.
If the filter were to be positioned vertically or in a vertically inclined
fashion, some
configuration changes and pressure-related calibrations would have to be made
to ensure a proper
working of filter 10, although a workable vertical filter could be obtained
according to the
present invention.
In one embodiment of the invention, filter 10 is used in combination with
another
2 0 centrifugal filter that can separate denser solids from liquids and
consequently extract a high
concentration of solids. In this embodiment comprising the combination of
filter 10 with a
CA 02363588 2001-11-22
centrifugal filter, the dirty liquid is initially directed into the
centrifugal filter, where the denser
solids are recuperated and where a cleaned liquid outlet port is connected to
the dirty liquid inlet
port 22 of filter 10. The liquid exiting the centrifugal filter is directed
into filter 10 through its
dirty liquid inlet tube, where it is filtered as described hereinabove, to
recuperate clean liquid.
Both the waste liquid outlet ports 36a and 36b of filter 10 are connected to
tubes that convey the
waste liquid back into the centrifugal filter, where the mud-like waste liquid
is separated to
extract waste solids and to recuperate the liquid therefrom, the liquid being
redirected through
filter 10 again. Consequently, with these two serially connected filters, the
global dirty liquid
inlet port is connected to the centrifugal filter, the global waste outlet
port is also connected to
the centrifugal filter, while the global clean liquid outlet port is connected
to the self cleaning
filter 10.
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