Abstrict
Apparatus for cleaning a filter cloth in a filtering device with
a rotatable drum having an inlet for the liquid to be filtered.
The drum has in its circumferential surface openings through which
the liquid to be filtered is conducted in a filtering direction
out of the drum for filtering through a filter cloth. The cleaning
apparatus includes at least one spray nozzle which is adapted to
spray cleaning liquid onto a portion of the filter cloth in a direction
opposite to the filtering direction. Moreover the apparatus comprises
a driving device for providing a reciprocating motion of the spray
nozzle. The driving device has a coupling which is adapted to transform
the rotary motion of the drum into the reciprocating motion of the
spray nozzle, with such a ratio that the rotary motion of the drum
and the reciprocating motion of the spray nozzle are out of phase
with each other.
Claims
What is claimed is:
1. An apparatus for cleaning a filter cloth in a filtering device
comprising a filtering device having a drum which is rotatable about
its centre axis and which has an inlet for liquid to be filtered
and which in its circumferential surface has openings through which
the liquid to be filtered is adapted to be conducted in a filtering
direction out of the drum for filtering through a filter cloth,
and a cleaning device having at least one spray nozzle which is
adapted to spray cleaning liquid onto a portion of the filter cloth
in a direction opposite to the filtering direction, and a driving
device for providing a reciprocating motion to the spray nozzle,
the driving device having a coupling for transforming rotary motion
of the drum of the filtering device into the reciprocating motion
of the spray nozzle of the cleaning device, and the coupling having
a ratio such that the rotary motion of the drum and the reciprocating
motion of the spray nozzle are out of phase with each other.
2. An apparatus as claimed in claim 1, wherein the reciprocating
motion of the spray nozzle has a motion vector component, which
is in a plane parallel to that portion of the filter cloth which
in a certain rotational position is flushed and which is directed
perpendicular to a direction of motion of said filter cloth portion.
3. An apparatus as claimed in claim 1, wherein the spray nozzle
is arranged on a flush tube which is adapted to conduct the cleaning
liquid to the spray nozzle.
4. An apparatus as claimed in claim 1, wherein the filtering device
further includes at least one disc-shaped filter element, whose
normal direction is parallel and essentially concentric with the
centre axis of the drum, said disc-shaped filter element extending
radially away from and round the drum, the filter cloth being supported
on at least one lateral surface of the disc-shaped filter element
and the cleaning device further includes a flushing ramp for conducting
cleaning liquid to the spray nozzle which is pivotable about a pivot
axis which is parallel with the centre axis of the drum.
5. An apparatus as claimed in claim 4, wherein the pivotable flushing
ramp has at least one flush tube each supporting at least one spray
nozzle and being adapted to conduct the cleaning liquid to the spray
nozzle.
6. An apparatus as claimed in claim 5, wherein the flush tube extends
in a plane which is essentially parallel with the lateral surface
of the filter element.
7. An apparatus as claimed in claim 5, wherein the flush tube has
such a radial extent as to extend along essentially the entire portion
of the lateral surface of the disc-shaped element which is provided
with the filter cloth.
8. An apparatus as claimed in any one of claims 4-7, wherein the
flushing ramp is connected to a wheel which is eccentrically mounted
on a shaft at a distance from the pivot axis of the flushing ramp,
and a rotary shaft at the center axis of the drum supports a wheel
which is non-rotatably arranged thereon, a loop-shaped drive between
the non-rotational wheel and the eccentrically mounted wheel forming
said coupling between the rotary motion of the drum and the reciprocating
motion of the spray nozzle.
9. An apparatus as claimed in claim 8, wherein the wheels have
a ratio-generating ratio of diameters such that the reciprocating
motion of the spray nozzle and the rotation of the drum are out
of phase with each other.
10. An apparatus as claimed in claim 1, wherein said at least one
spray nozzle is arranged on an elongate flushing ramp with a flush
tube which is adapted to conduct cleaning liquid to the spray nozzle
and which is arranged essentially parallel with the centre axis
of the drum.
11. An apparatus as claimed in claim 10, wherein the flush tube
is reciprocable along its longitudinal axis.
12. An apparatus as claimed in claim 10, wherein a drive wheel
is arranged on a drive shaft which via said coupling rotationally
drives the drum, the drive wheel having on its circumferential surface
a circumferential guide means, a follower means being connected
to the flush tube and the follower means engaging with and following
the guide means to provide said reciprocating motion.
13. An apparatus as claimed in claim 12, wherein the guide means
comprises a wave-shaped groove in the circumferential surface of
the drive wheel.
14. An apparatus as claimed in claim 12, wherein the follower means
comprises a pin fixedly connected to the flush tube.
15. An apparatus as claimed in any one of claims 12-14, wherein
the drive shaft which supports the drive wheel is connected to a
rotary shaft at the center axis of the drum with a ratio such that
the rotation of the drum and the reciprocating motion of the spray
nozzle are out of phase with each other.
16. An apparatus as claimed in claim 1, which comprises at least
two spray nozzles, two neighbouring spray nozzles being arranged
to spray, in a certain rotational position of the drum, cleaning
liquid onto a first and a second portion of the filter cloth, the
reciprocating motion of the spray nozzles having a stroke which
is at least equal to the distance between said first and second
portion of the filter cloth.
Description FIELD OF THE INVENTION
The present invention relates to an apparatus for cleaning a filter
cloth in a filtering device.
BACKGROUND ART
Filtering devices of the type stated by way of introduction are
used especially for filtering of particles from liquids.
Two variants of filtering devices of this type are predominant
on the market.
The one variant is in technical language called rotary disc filter
and is described, for example, in the brochure "Skivfilter"
(in English: Rotary Disc Filter) issued by the Applicant (Hydrotech,
1996). The brochure, p. 2, shows in a perspective view the principle
of such a rotary disc filter, see FIG. 1. The rotary disc filter
10 comprises a horizontal, slowly rotating drum 11, which supports
a number of parallel, disc-shaped filter elements 12 which are successively
arranged in spaced-apart relationship along the centre axis of the
drum and which extend radially away from the drum 11. The filter
elements 12 have on their opposite lateral surfaces relatively large
openings which are covered with a filter cloth 13. The drum 11 has
a number of openings through which the liquid A which is to be filtered
can flow to the interior of the filter elements 12. The filtering
liquid A is conducted through an inlet into the drum 11 and then
falls down to the interior of the disc-shaped elements 12, from
which the liquid A continues out through the filter cloth 13 so
that the particles which are to be fiitered off adhere to the inside
of the filter cloth 13. For cleaning of the filter cloth 13, the
disc filter 10 is provided with spray nozzles 14 which are mounted
on a number of fixed flush tubes 15, which extend between the disc-shaped
filter elements 12. The flush tubes 15 are adapted to conduct flushing
liquid to the spray nozzles 14 and are connected to an elongate
liquid-conducting pipe 16 which extends parallel with the centre
axis of the drum 11. The spray nozzles 14 spray the filter cloth
13 axially from the outside, in a direction opposite to the filtering
direction, and the flushed-away particles are collected in a discharge
trough 17 which is placed inside the drum 11 in the upper portion
thereof.
The other variant is in technical language called drum filter and
described, for example, in the brochure "Trumfilter" (in
English: Drum Filter) issued by the Applicant (Hydrotech, 1996).
The brochure, p. 2, shows in a perspective view the principle of
such a drum filter. See FIG. 2 where the drum 21 has been cut open
to be able to show the flushing equipment arranged outside the drum
21. Thus the drum filter 20 comprises a horizontal, slowly rotating
drum 21, whose circumferential surface has relatively large openings
which are covered with a filter cloth 22. The liquid A that is to
be filtered is passed into the drum 21 and is filtered as it falls
downwards through the filter cloth 22 and out of the drum 21. To
avoid clogging of the filter cloth 22 on the rotating drum 21, this
is flushed clean with the aid of fixedly mounted spray nozzles 23
which are placed on the outside of the drum 21 and above the liquid
level inside the drum 21. The flushing is carried out radially inwards
in a direction opposite to the filtering direction. The dirt which
is flushed away from the cloth 22 inwards in the drum 21 reaches
a discharge trough 24 which is placed inside the drum 21 just above
its centre axis and which draws off the dirt.
The reverse flushing or cleaning can in both cases occur with a
rotating or stationary drum, and the flushing may occur continuously
or intermittently.
A problem which is common to these filtering devices is that the
filter cloth has a tendency to clog in spite of the particular spray
nozzles which flush the filter cloth in a direction opposite to
the filtering direction. Clogging of the filter cloth deteriorates
the efficiency or degree of efficiency of the filtering device.
Moreover the filter cloth of both variants has a tendency to be
"striped" owing to irregular cleaning, which is a sign
of the filter cloth not being sufficiently cleaned in certain portions.
The above drawbacks in turn result in the filter cloth needing
be replaced too frequently.
For satisfactory cleaning of the filter cloth, a plurality of spray
nozzles must according to the prior art solutions be arranged extremely
close together, which means that the filtering device is rendered
expensive.
SUMMARY OF THE INVENTION
An object of the present invention is suggest a solution to the
above problems by providing an improved apparatus for cleaning a
filter cloth in a filtering device.
The cleaning apparatus according to the invention comprises a driving
device for providing a reciprocating motion of the spray nozzles.
The reciprocating motion allows each spray nozzle to clean a larger
portion of the filter cloth, which results in more efficient cleaning.
Besides, the number of spray nozzles can be reduced.
The driving device has a coupling which is adapted to transform
the rotary motion of the drum into the reciprocating motion of the
spray nozzles. The coupling has such a gear ratio that the rotary
motion of the drum and the reciprocating motion of the spray nozzles
are out of phase with each other. By these two motions not occurring
in step or phase with each other, it is avoided that a certain spray
nozzle flushes the same parts of the filter cloth revolution after
revolution. This means that each portion of the filter cloth is
once now and then subjected to direct flushing by a spray nozzle.
If the motions had occurred in phase, the above-described "striped"
condition of the filter cloth would only have been converted into
curved lines instead, thus causing incomplete cleaning.
The reciprocating motion of the spray nozzles preferably has a
motion vector component, which is in a plane parallel to that portion
of the filter cloth which in a certain rotational position is flushed
and which is directed perpendicular to the direction of motion of
said filter cloth portion. By the filter cloth moving in one direction
and the spray nozzles at least partially moving in a direction perpendicular
thereto, all portions of the filter cloth can be reached by a flushing
jet from a spray nozzle.
The spray nozzles are advantageously arranged on a flush tube which
is adapted to conduct the cleaning liquid to all spray nozzles.
This solution makes the construction compact and robust.
According to a first aspect of the invention, the filtering device
further comprises at least one disc-shaped filter element, whose
normal direction is parallel and essentially concentric with the
centre axis of the drum. The filter element extends radially away
from and round the drum. The filter cloth is supported on at least
one of the lateral surfaces of the disc-shaped filter element. The
cleaning apparatus according to this first aspect advantageously
comprises a flushing, ramp which is pivotable about a pivot axis,
which is parallel with the centre axis of the drum. The pivotability
of the flushing ramp gives the spray nozzles a reciprocating rocking
motion, which results in more efficient cleaning of the filter cloth
and, thus, an improved degree of efficiency of the filtering device.
According to a preferred embodiment of this aspect, the flushing
ramp has flush tubes each supporting at least one spray nozzle.
The flush tubes are intended to conduct the cleaning liquid to the
spray nozzles. Thanks to the rocking motion of the flushing ramp,
a spray nozzle supported on a flush tube is given a reciprocating
motion on the one hand in the radial direction and, on the other
hand, in the tangential direction, thus allowing all portions of
the filter cloth to be reached by a spray nozzle.
For utilisation of the limited space between the disc-shaped elements,
the flush tube is preferably arranged in a plane which is essentially
parallel with the lateral surface of the filter element.
The flush tube has such a radial extent as to extend along essentially
the entire portion of the lateral surface of the disc-shaped element
which is provided with filter cloth. This allows all portions of
the filter cloth to be reached by a spray nozzle supported on the
flush tube, without the flush tube having to make a great and inconvenient
motion.
According to a preferred embodiment of the invention in its first
aspect, said coupling between the rotary motion of the drum and
the reciprocating motion of the spray nozzle is provided by means
of a loop-shaped drive between an eccentrically mounted wheel connected
to the flushing ramp and a wheel non-rotationally mounted on the
rotary shaft of the drum. Since the loop-shaped drive has an essentially
constant length and the wheel connected to the flushing ramp is
eccentrically mounted, the flushing ramp is forced to make said
reciprocating rocking pivoting motion.
To ensure that the rotary motion of the drum and the reciprocating
motion of the flushing are out of phase, the wheels have an uneven,
ratio-generating ratio of diameters. For example, the two diameter
dimensions can be non-divisible by each other.
According to a second aspect of the invention, the filter cloth
is supported on the circumferential surface of the drum, at least
one spray nozzle being arranged on an elongate flushing ramp with
an elongate flush tube which is intended to conduct cleaning liquid
to the spray nozzles and which is arranged essentially parallel
with the centre axis of the drum. This solution makes the construction
compact and robust.
The flush tube is preferably reciprocable along its longitudinal
axis for providing the reciprocating motion of the spray nozzles,
which results in more efficient cleaning of the filter cloth and,
thus, a higher degree of efficiency of the filtering device.
According to a preferred embodiment of this second aspect, a drive
wheel is arranged on a drive shaft which via said coupling rotationally
drives the drum. Advantageously the drive wheel has on its circumferential
surface a circumferential guide means, and the cleaning apparatus
further comprises a follower means connected to the flush tube.
To provide the reciprocating motion of the spray nozzles, the follower
means engages with and follows the guide means.
The guide, means preferably comprises a wave-shaped groove formed
in the circumferential surface of the drive wheel, and the follower
means advantageously comprises a pin fixedly connected to the flush
tube.
By using a guide means and a follower means, which according to
a preferred embodiment consist of a groove and a pin, a motion-transferring
coupling is obtained, which is simple, robust and reliable.
To achieve the condition that the rotation of the drum and the
reciprocating motion of the flushing ramp are out of phase with
each other, the drive shaft supporting the drive wheel is connected
to the rotary shaft of the drum with a non-uniform gear ratio. This
non-uniform gear ratio causes a spray nozzle not to flush the same
portion of the filter cloth revolution after revolution as the drum
rotates.
According to a preferred embodiment of one of the two aspects of
the invention, the cleaning apparatus comprises at least two spray
nozzles, two neighbouring spray nozzles being arranged to spray,
in a certain rotational position of the drum, cleaning liquid onto
a first and a second portion of the filter cloth. The reciprocating
motion of the spray nozzles has a stroke which is at least equal
to the distance between said first and second portion of the filter
cloth. This stroke causes all portions of the filter cloth to be
reached by direct flushing by means of one of the spray nozzles.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be described in more detail with reference
to the accompanying schematic drawings which for the purpose of
exemplification illustrate currently preferred embodiments of the
invention according to its two aspects.
FIG. 1 is a perspective view which schematically illustrates the
principle of a prior-art rotary disc filter.
FIG. 2 is a perspective view which schematically illustrates the
principle of a prior-art drum filter.
FIG. 3 is a front view of a rotary disc filter provided with a
cleaning apparatus according to a first aspect of the invention.
FIG. 4 is an end view of the rotary disc filter shown in FIG. 3.
FIG. 5 is a front view which shows a drum filter provided with
a cleaning apparatus according to a second aspect of the filtering
device.
FIG. 6 is an end view of a drum filter shown in FIG. 5.
FIG. 7 is a partial view on a larger scale of the drum filter shown
in FIG. 5.
FIG. 8 is a basic sketch which shows the reciprocating motion of
the spray nozzles illustrated in FIG. 7.
DESCRIPTION OF PREFERRED EMBODIMENTS
FIGS. 3 and 4 show a filtering device, a so-called rotary disc
filter, according to a first aspect of the invention. The essential
function of a disc filter of this type is shown in FIG. 1. The disc
filter 100 has a slowly rotating drum 110 which supports a number
of disc-shaped filter elements 120, whose normal direction is parallel
and concentric with the axis of rotation 111 of the drum 110 and
which on their lateral surfaces 121, which are axially directed
and have a radial extent, support a filter cloth 122. The liquid
A which is to be filtered is conducted through an inlet 112 to the
interior of the drum 110. From the interior of the drum 110 the
filtering liquid is conducted through openings 113 in the circumferential
surface 116 of the drum 110 to the interior of the disc-shaped filter
elements 120. From there, the filtering liquid A is then finally
conducted in a filtering direction out through the filter cloth
122. Any particles in the filtering liquid A adhere to the inside
of the filter cloth 122.
If the disc filter 100 is used without cleaning or reverse flushing,
more and more particles will be collected on the inside of and in
the pores of the filter cloth 122. This would imply that the degree
of efficiency of the filter decreases and that it would be necessary
to frequently change the filter cloth 122. To avoid that the filter
cloth 122 must be changed too frequently, it is flushed intermittently
or continuously from the outside in a direction opposite to the
filtering direction by means of spray nozzles 133. The particles
that are flushed away from the filter cloth 122 are collected and
drained off by a discharge trough 115 which is placed inside the
drum 110 in the upper portion thereof.
The spray nozzles 133 are fixedly mounted on a number of flush
tubes 132 which each, in turn, at their one end are mounted on a
flushing ramp 130 which is placed along the disc filter 100 outside
the disc-shaped filter elements 120. The flushing ramp 130 comprises
an elongate flushing ramp pipe 131 which extends parallel with the
centre axis of the drum 10 and which conducts flushing or cleaning
liquid to the flush tubes 132, which in turn conduct the cleaning
liquid to the spray nozzles 133. The flushing ramp 130 is mounted
in a number of suspension bearings 134 so as to be pivotable about
its longitudinal axis 135. The flush tubes 132 extend from the flushing
ramp 130 radially inwards between the disc-shaped filter elements
120 and in parallel along the entire portion of the lateral surfaces
121 of the filter elements 120 which supports the filter cloth 122.
The disc filter 100 has a motor 102 which drives the rotary motion
of the drum 110. The drum 110 has a pulley 141 which is non-rotationally
connected to the rotary shaft 111 of the drum and which via a drive
belt 142 is connected to another pulley 143, which is eccentrically
and freely mounted on a pivot pin 144. The pivot pin 144 is parallel
with the centre axis 111 of the drum 110 and is supported at a distance
from the flushing ramp 130 by an arm 145 which is mounted on the
flushing ramp 130. Since the length of the belt 142 and the diameters
of the pulleys 141, 143 do not vary during operation, the position
of the pivot pin 144 in relation to the drum 110 must vary, and
since the pivot pin 144 is fixedly connected to the flushing ramp
130 via the arm 145, the flushing ramp 130 will be forced to make
a reciprocating rocking motion.
By the two pulleys 141, 143 having a ratio-generating ratio of
diameters which is non-divisible, a coupling is obtained between
the rotary motion of the drum 110 and the rocking motion of the
spray nozzles 133 which are not in phase. This causes all portions
of the filter cloth 122 to be cleaned once now and then by a jet
from a spray nozzle 133. As a result, the filter cloth 122 will
not be "striped" owing to non-uniform cleaning, which
arises when different portions of the filter cloth 122, revolution
after revolution as the drum 110 rotates, are subjected to different
degrees of flushing.
The pivoting motion of the flushing ramp 130 about its longitudinal
axis 135 makes the flush tubes 132 oscillate in a plane parallel
with the lateral surfaces 121 of the filter elements 120. A spray
nozzle 132 will make a reciprocating motion and, consequently, flush
different portions of the filter cloth 122. Thanks to the suspension
of the flush tubes 132 and the flushing ramp 130, the spray nozzles
133 will make a reciprocating motion which has a radial and a tangential
component. Since the filter cloth 122 relative to a stationary spray
nozzle 133 has a tangential vector of motion, the spray nozzle 133
will make a motion which, relative to the filter cloth 122, at least
partially has a radial component. The motion of a spray nozzle 133
should thus, for different portions of the filter cloth to be reached
by a spray nozzle, during some part of its motion have an angle
relative to the motion described by that portion of the filter cloth
122 which in a certain rotational position is flushed. An angular
difference between two vectors of motion means that a first vector
of motion at least has one component which is perpendicular to the
second vector of motion.
FIGS. 5 and 6 show a filtering device, a so-called drum filter,
according to a second aspect of the invention. The essential function
of a drum filter of this type is illustrated in FIG. 2. The drum
filter 200 comprises mainly a slowly rotating drum 210. The liquid
A which is to be filtered is conducted via an inlet 212 into the
interior of the drum 210 which in its circumferential surface 216
has openings 213 covered with a filter cloth 222. The filtering
liquid A is passed through the openings 213 covered with the filter
cloth 222, any particles getting stuck on the inside of the filter
cloth 222.
Just like in the case of the disc filter 100, use of the drum filter
200 without cleaning or reverse flushing would mean that gradually
more and more particles would collect on the inside of and in the
pores of the filter cloth 222, which would result in the degree
of efficiency deteriorating. Also for the drum filter 200, reverse
flushing occurs by means of spray nozzles 233 which are placed on
the outside of the drum 200 so that they flush the filter cloth
222 in a direction opposite to the filtering direction.
What differs the drum filter 200 from the previously described
disc filter 100 is that the filter cloth 222 is arranged immediately
above the openings 213 in the circumferential surface 216 of the
drum 200 instead of being expanded on disc-shaped filter elements
120. This means that the flushing must in terms of construction
be designed in a slightly different manner to function in the way
that characterises the invention.
Thus, the spray nozzles 233 are fixedly mounted on an elongate
flushing ramp 230 directly on an elongate flush tube 232 which is
intended to conduct cleaning liquid to the spray nozzles 233 and
which is parallel with the rotary shaft 211 of the drum 210. To
provide the previously described difference in directions of motion
between the spray nozzles 233 and the filter cloth 222, the flush
tube 232 is reciprocable along its longitudinal axis 234. As a result,
the filter cloth 222 rotating with the drum 210 and, the spray nozzles
233 move in two directions, whose vectors of motion are perpendicular
to each other.
As is evident from FIG. 7, the drum filter 200 has a motor 202
which via a belt drive 253 drives the rotary motion of the drum
210. The drive shaft 246 extending from the motor 202 supports a
drive wheel 247 which in its circumferential surface 248 has a circumferential,
wave-shaped groove 249. The flush tube 232 has a coupling element
250 which supports a pin 251 which is fixedly connected to the flush
tube 232 and which serves as a follower, and the groove 249 of the
drive wheel 247 serves as a guide means.
The drive shaft 246 is via a belt drive 253, between a pulley 252
non-rotatably supported on the drive shaft 246 and a portion 254
on the circumference of the drum 210, connected to the rotary motion
of the drum 210.
The pulley 252 and the drum 210 have such a ratio-generating ratio
of diameters that the rotary motion of the drum 210 and the reciprocating
motion of the flush tube 231 occur out of phase with each other.
A common feature of the described embodiments of the invention
is that the reciprocating motion of the spray nozzles 133; 233 has
such a stroke B between its end positions, which is so great that
that portion of the filter cloth 122; 222 which is flushed by a
spray nozzle 133; 233 when the flushing ramp 130; 230 is in the
one end position D coincides with that portion of the filter cloth
122; 222 which is flushed by a neighbouring spray nozzle 133'; 233'
when the flushing ramp is in the other end position E.
If the stroke B is equal to the distance C between those portions
of the filter cloth 122; 222 which two neighbouring spray nozzles
133, 133'; 233, 233' flush in a certain rotational position of the
drum 110; 210 (see FIG. 8), this means that all portions of the
filter cloth 122; 222 once in a while is flushed by a spray nozzle
133; 233. A greater overlap in the stroke B causes still more efficient
cleaning of the filter cloth.
For the drum filter 200, the motions of the filter cloth 222 and
the spray nozzles 233 are perpendicular in relation to each other,
the desired stroke B being defined by the reciprocating motion of
the spray nozzles 233.
On the other hand, for the disc filter 100 the rotary motion of
filter elements 122 cooperate with the oscillating motion of the
spray nozzles 133 to provide the relative motion. During the oscillating
motion, a certain spray nozzle 133 passes different radii positioned
between an innermost and an outermost radius of the filter element
120. The distance between that portion of the filter cloth 122 which
is cleaned by said spray nozzle 133 in the innermost position thereof
and that portion which is cleaned by said spray nozzle 133 in the
outermost position thereof should be at least as great as the distance
between those portions which in a certain rotational position of
the drum 110 are cleaned by two neighbouring spray nozzles 133,
133'. As a result, the cleaned portions overlap each other. This
oscillating stroke means that those portions of the filter cloth
122 which are cleaned by two neighbouring spray nozzles 133, 133'
in the respective end positions of the reciprocating motion of the
spray nozzles 133, 133' at least touch each other.
It will be appreciated that modifications of the embodiments of
the invention described above are conceivable within the scope of
the invention, which is defined in the appended claims.
For instance, the belt operation according to the preferred embodiment
of the invention in its first aspect can be replaced by other loop-shaped
drives, such as a chain drive or the like (not shown).
For the drum filter, the coupling between the rotary motion of
the drum and the reciprocating motion of the flush tube can be accomplished
by means of an optional transmission which gives an uneven gear
ratio since the distance between the drive shaft and the rotary
shaft of the drum is constant.
The invention according to these two main aspects has a common,
basic function which solves the same basic problems and which gives
the same advantages. What differs the above-described aspects of
the invention is the constructional features which depend on the
type of filtering plant for which the cleaning apparatus is to be
used. |