Note: Descriptions are shown in the official language in which they were submitted.
3~i
"APPARATUS FOR CLEANING FILTERS IN
PRESSURIZED FLUID FLOW SYSTEMS "
Field of the Invention
The present invention relates to filter apparatus
in pressurized fluid flow systems, and, in particular, for
filter apparatus in which the filter element is cleaned by
reversing the flow of liquid therethrough. Even more par-
ticularly, the apparatus is suitable for connection in water
lines which furnish water to buildings.
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1~ 36
~ackqround of the Invention
Filter apparatus is required to prevent impurities
such as particles of sand, iron fiLings, rust particles, etc
which may be carried in the li~lid to reach equipment further
down the line and to cause damage in such equip~ent. SUCh
dirt is deposited on the inlet side of the filter element.
As more dirt is deposited on the filter eleme~t, the pressure
drop across the apparatus increases. Therefore the filter
element must be cleaned from time to time by reversing the
flow of current through it. The reversal of the flow of current
causes the dirt to be loosened from the inlet side of the
filter and to be swept into a reverse flow outlet channeL
which is opened only during the time that the filter clean-
ing takes place. The higher the water pressure during the
reverse flow or cleaning cycle, the better the cleaning
effect. On the other hand, the amount of liquid to be used
for the cleaning process is to be held to a minim~1m.
In conventional filter apparatus of the above de-
scribed type, a cleaning channel element is used whose out-
let is connected to the reverse flow outlet channel and whose
iniet has a relatively small opening. The cleaning channel
element is then moved relative to the surface of the filter
so that the small inlet opening passes over the whole surface
of the latter. Specifically, the cleaning channel element is
passed over the surface o~ the filter step by step by the turn-
ing of a hand wheel, the turning of the wheel also causing
a shut-off leading to the reverse flow outlet channel to be
opened. This process is relatively cumbersome and cannot be
easily automated.
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Summary of the Invention
__
It is an object of the present invention to furnish
filter apparatus cleanable by a reverse flow method in which
the reverse flow takes place continuously and is easily con-
trolled either manually or automatically.
In accordance with the present invention, a filter
is provided which separates a first, inlet chamber, from a second,
outlet chamber. Dirt particles which collect on a first
filter surfaee in contact with the unfiltered water are re-
moved by reverse flow of water from the second chamber to
reverse flow inlets positioned adjacent to the first sur-
face and having an inlet area substantially less than the
total surface area of the filter. The reverse flow inlets
are connected through a pipe to a reverse fLow chamber.
A reverse flow shut-off is provided which has a first po-
sition which allows a reverse water flow through the reverse
flow outlet and a second position which stops the flow.
When the shut-off means are moved from the second to the first
position, a pressure difference is created which causes a
reverse water flow from the second chamber through the filter
to the reverse flow inlet, t~e reverse flow chamber and then
to the reverse flow outlet. The pressure difference also
creates a force acting on the inlets to move the in]ets over
the first surface of the filter from a first to a second
end position, so that the complete filter surface is cleaned.
Reset apparatus is also provided to move the inlets back to
the first po~ition after the reverse flow shut-off has again
been closed.
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In a particularly preferred embodiment, the filter
element is a webbed tube which is stretched over a cylindrical
supporting me~ber having a plurality of through openings and
a supporting rib. The inlets are constituted as sLots in a
S wiper, the sLots being defined by edges which are radially
pressed against the inner surface of the filter to form water-
tight contacts. The opposite ends of the wiper or wipers are
held in a pipe mounted for axial movement relative to the
filter. The open bottom end of the pipe extends into the
reverse flow chamber. Since the opening of the wiper in con-
tact with the filter extends only over a very small part of
the ~ilter surface, the filtering process may be maintained
even during the reverse flow cleaning process.
The wiper is preferably constituted by a plurality
lS of wiper elements each having a slot, all arranged around the
periphery of the pipe at small distances from one another. The
slots form an almost complete circular opening while the spac-
ing permits movement of the individual wiper elements in the
radial direction, so that manufacturing tolerances and possible
dirt deposits on the filter can be accommodated.
The supporting member for the filter in this embodi-
ment has a helical supporting rib so that the wiper is applied
to the filter with constant pressure and th~refore constant
sliding friction.
The hollow cylindrical pipe carrying the wiper pre-
ferably has a closed top so that it constitutes a piston re-
Sponsive to pressure differences which allow axial movement
relative to the filter in two directions.
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1(336
The end of the pipe which is immersed in the re-
verse flow chamber carries a sealing element which sits in
a seat in the region of the reverse flow outlet. An actuating
rod may be provided which is rotatable with respect to the
pipe, axially movable with respect to the sealing element
and may be manually pushed downward or rotated. The sealing
element also has a threaded end which engages a rigidly
mounted receptacle in the region of the water-tight seat~
Opening and closing of the reverse flow outlet is thus achieved
by rotation of the activating rod and is independent of any
axial movement of the rod during the reverse flow process.
While the pipe and thus the wiper elements moved axially rel-
ative to the filter, the latter is subjected to reverse flow
from the clean to the dirty side where the wiper inlets touch
the filter surface, while at the same time, coarser dirt
particles are scrubbed off by the wiper and reach the reverse
flow outlet by another route. A damping element is arranged
either in the pipe or on the operating rod, so that the axiai
movement is uniform.
To decrease the in~ernal friction losses as much as
possible, it is necessary that the parts which move in an
axial direction with respect to one another are precisely con-
centric. For this purpose, a common headpiece is provided
which contains both the inlet for the unfiltered liquid and
the outlet for the filtered liquid and which has concentric
openings in which the filter element and the filter cup which
houses the filtering apparatus are removably mounted.
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The novel features which are considered as charac-
teristic of the invention are set forth in particular in the
appended claims. The invention itself, however, both as to
its construction and its method of operation, together with
additional objects and advantagas thereof, will best be
understood from the following description of specific em-
bodiments when read in connection with the accompanying
drawing.
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Brief Description of the Drawinq
Figs. 1 - 4 are vertical cross sections of four
embodiments of the present invention;
Fig. 5 is a top view of the filter cup of the
embodiment of Figs. 1 - 3, with the headpiece removed;
Fig. 6 is a vertical cross section of a further
embodiment of a filter apparatus;
Fig. 7 is a cross section through the control valve
of the filter apparatus of Fig. 6;
lQ Fig. 8 is a vertical cross section of a further pre-
ferred embodiment of the present invention;
Fig. 9 is an enlarged cross section in the region
of the outlet of the cleaning channel element of Fig. 8, with
modifiad shut-off mechanism.
Description of the Preferred Embodiments
The filter apparatus shown in the various drawings
is designed for connection to water lines, in particular to
water lines for use in buildings. It is the object of the
apparatus to protect the water lines and any apparatus connec-
ted thereto, from impurities and dirt in the water. The
apparatus consists mainly of a filter cup 10, a filter 12
inserted in filter cup 10, reverse flow apparatus 14, and
a headpiece 18 with pipe connections 16, to which filter
cup 10 and filter 12 are fastened.
In the embodiments illustrated in Figs. 1 - 5,
filter 12 is fastened to a pipe-shaped support 20 made of
synthetic material. The upper end 22 of support 20 is in-
serted in an opening 26 of headpiece 18~ Opening 26 opens
into unfiltered water inlet 24. The lower end of support 20
consists of a hollow cylinder 30 braced against the bottom 34
of filter cup 10 by a sealing ring 32 and having a bottom
opening 28. Bottom opening 28 is connected through a coup-
ling 36 to a pipe connection 38 which is fastened to the
bottom 34 of filter cup lQ and leads to the reverse flow
outlet channel. A manually operable lever 40 controls a
shut-off 42 which is connected to pipe connection 38. Shut-
off 42 may consist of a valve, cock or lever. Instead of
being manually operable, it could be an automatically oper-
able solenoid operating, for' example, on the basis of a
timing or pressure difference control.
A filter 12 divides the inside of filter cup 10
into two separate chambers, namely an inlet chamber 44 in-
side of filter 12 and a filtered water chamber 48 connected
to,filtered water outlet 46 exter~al to fiLter 12.
During the filtering operation, the inlet water
passes through inlet 24 into inlet chamber 44, flows through
filter 12 from the inside towards the outside and finally
flows in a filtered state through outlet 46. Any particles
suspended in the inlet water are held back by the inner
surface of the filter. Coarser particles sink downward into
a reverse flow chamber 49 defined by hollow cylinder 30. As
36
more dirt is deposited on the filter, the pressure difference
across the equipment increases. Therefore filter 12 must
be cleaned from time to time by a reverse flow process. This
is accomplished by the reverse flow apparatus 14 internal to
filter 12.
Reverse flow apparatus 14 consists of a channel
piece 50 which is axially movable relative to filter L2.
Channel piece 50 consists of a piece of open pipe 52 insert-
able into hollow cylinder 30 and at least one toroidal
channel 54 which is open over its whole periphery towards
filter 12 and pro~ects radially o~er the pipe jacket. Open-
ing 56 of ring channel 54 can be made to pass over all of
the surface of filter 12 on the inlet si~e by axial movement
of channel piece 5G. Ring channel 54 and pipe 52 are connec-
ted by a plurality of radial channels 58 which are arranged
at predetermined angular intervals to one another, spaces 60
between the channels allowing water to flow from inlet 24 to
filter 12. A cone-shaped flow distributor 62 whose top points
towards inlet 24 equalizes the flow over the filter surface.
When shut-off 42 is closed, channel piece 50 is in
the upper initial position illustrated in Figs. 1 to 3. In
this position the lower end of pipe 52, which carries a
sealing ring 64,is completely withdrawn from hollow cylinder 30
except for downward projecting guide members 66. Water can
thus flow from chamber 44 into chamber 49 through a toroida~
gap 68. Coarser dirt particles can reach chamber 49 through
this gap even during the filtering phase.
The reverse flow phase is initiated by opening shut-
3~
off 42. This causes the inlet, unfiltered water to flow
through gap 48 into chamber 49 and rinses out the dirt
particles which have accumulated in the chamber through
the reverse flow channel.
Simultaneously, filtered water flows from chamber 48
through filter 12 to the peripheral opening 56 of toroidal
channel 54, cleaning that particular part of the filter.
This reverse flow water flows through channel piece 50 to
chamber 49 and then flows through reverse flow outlet
channel 39 which is under atmospheric pressure. Channel
piece 50 is closed at the top and thus forms a piston unto
whose effective piston surface a downward force is exerted
by the difference in pressure between inlet 24 and the
pressure in chamber 49 when shut-off 42 is open. Channel
piece 50 moves slowly downward until sealing ring 64 seals
chamber 49 ~rom chamber 44. The downward force on the
piston surface then increases due to an increased pressure
difference, since chamber 49 is then onLy opened to atmos-
pheric pressure and no more water flows through gap 68.
This causes channel piece 50 to move downward at a higher
speed until its lower end position is reached. At this time
the whole inlet suxface of the filter 12 has been passed over
by opening 56 of toroidal channel 54 and thereby has been
cleaned by reverse flow water.
The speed of movement of channel piece 50 is equal-
ized and slowed up by a damper 74 consisting of a damping
cylinder 70 and a damping piston 72. Dampiny cylinder 70 is
coaxial to channel pice 50 and has a bottom opening, while
piston 72 is fixed to the end of a piston rod 76 centrally
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mo~nted within hollow cylinder 30 and pointing upwards. The
inside of cyLinder 72 is connected to chamber 48 (Fig L) or
chamber 49 (Figs. 2 and 3) through a bore 78 in piston 72
and a bore 80 or line 82 in piston rod 76. During the
reverse flow or cleaning phase, water from the inLet side
still can pass through the free portion of filter 12
the filtered water side. The filtering operation is thus
maintained during the cleaning process.
When, at the end of the cleaning process, shut-
off 42 is closed, the pressure in chamber 49 again becomes
the operating pressure, so that channel piece 50 will reach
its initiaL position in the manner described below.
For the embodiment illustrated in Fig. l, the
movement back to the original position of channel piece 50
is accomplished by means of a helical spring (reset spring) 83
whose one end is fastened to a abutment of channel piece 50
and whose other end is supported by the bottom of hollow
cylinder 30. The spring power available for resetting must
be overcome by the pressure exerted on the pis~on surface of
channel piece 50 during the cleaning process, so that reliable
operation takes place only when the operating pressure exceeds
a predetermined minimum pressure.
For the embodiments shown in Figs. 2 and 3, the
resetting takes pLace independently of the then present
operating pressure. Here, resetting of channel piece 50 is
accomplished by water from chamber 49 which is under operating
pressure and which passes through line 82 and opening 78 to
the inside of cylinder 70. In addition, a bore 86 is pro-
1~ 36
vided to allow a toroidal space 84 of cylinder 70 defined by
the lower side of piston 72 and pistGn rod 76 to be constant-
Ly under atmospheric pressure.
While shut-off 42 is closed, channel piece 50 is
held in its upper position through the pressure difference
between the operating pressure in chamber 49 and atmospheric
pressure in toroidal space 84. As soon as the cleaning pro-
cess or phase is initiated by opening of shut-off 42, water
flows out of cylinder 70 through opening 78 because of the
pressure difference between inlet 24 and chamber 49. It
flows through line 82 which opens into the reverse flow out-
let channel, so that the channel piece moves downwards in a
slow and uniform manner. The actual speed of movement is
determined by the dimensions of the cross section of opening 78.
When shut-off 42 is again closed, the pressure inside of the
cylinder 70 again equalizes to the operating pressure, while
a~mospheric pressure is still present in toroidal space 84.
This causes channel piece S0 to return slowly to its initial,
upper position.
In the embodiment illustrated in Fig. 3, a second
toroidal channel 90 having a peripheral openinq 92 is pro-
vided at a predetermined distance below the upper toroidal
channel 54. This allows a greater part of the surface of the
filter to be cleaned for any one position of channel piece 50,
thus allowing a decrease in the total travel of the Latter
without requiring an increase in the overall size of the
apparatus .
In the embodiment illustrated in Fig 4, a plurality
of filters 12, each with a channel piece 50, is arranged
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side by side to one another. Each is constructed in accordance
with the embodiment illustrated in Fig. 3. A separate reverse
flow channel 38 with a shut-off 42 is provided for each filter.
Opening and closing of the associated shut-off 4~ thus allows
each filter to be cleaned independently of the others.
It is of course also possible to modify the embodi-
ment of Fig. 4 so that all filters are connected to a common
reverse flow outlet channel which, of course, must then have
a correspondingly increased cross section. A single shut-off
will then be required. For this embodiment, opening of the
shut-off will cause all filters to be cleaned at the same
time.
In the embodiments shown in Figs. 6 to 9, filter 12
is fastened only to headpiece 18 in a kind of bayonet locking
mechanism 102 and is additionally centered in a central open-
ing 100 of the headpiece. Filter cup 10 is inserted in a
thxeaded bore 104 of headpiece 18 which is also concentric to
the other two openings.
Headpiece 18 further has a central opening 105 to
which is fastened control apparatus 106 which initiates the
sliding movement of channel piece 50.
In the embodiment illustrated in Figs. 6 and 7,
filter 12 carries a sealing ring 110 which presses against the
inner surface of filter cup 10. Pipe 52 of channel piece 50
points downward and passes through a central opening 108
of filter element 12. The lower end of the pipe carries a
shut-off member 114 which may be introduced into a water-tight
13~i;
seat 112. Reverse flow chamber 49 is formed by the lower
part of filter cup 10. Filter cup 10 has a reverse flow water
outlet 116 which may be shut by shut-off member 114 and which
leads to a nipple 118 which i5 screwed to the filter cup 10
from below. Nipple 18 is subjected to atmospheric pressure
through a radial toroidal opening 120, thereby preventing the
drawing in of dirty water into the filtering apparatus from
a channel connected thereto.
Pipe 52, which enters into chamber 49, has slot
shaped openings 122, 124 in its upper and lower parts. Coarser
dirt particles can pass from chamber 44 into chamber 49 and
thence to opening 116 through these slots, both when the
shut-off is closed as illustrated in the figure, or when
channel piece 50 is moved to its topmost position. In the
intermediate region 123 between the upper and lower slots 122,
124, the pipe is sealed relative to central opening 108 of the
filter. In its upper region, channel piece 50 has an axiaLly
projecting hollow piston 126, which projects into a control
cylinder 128 of the hydraulic control apparatus 106. Control
cylinder 128 is open towards the bottom.
As illustrated in Fig. 7, hydraulic control
- apparatus 106 consists of a 3/2 port valve 130 which is oper-
able from the outside through a valve lifter 132. In the
so called operating position of valve 130, which is illustrated
in Fig. 7, control cylinder 128 is connected to chamber 44
through channels 134, thereby causing channel piece 50 to be
retained with shut-off member 114 in water-tight seat 112 by
the operating pressure existing in chamber 44. Seat 112 is
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in reverse flow water outlet lL6.
Movement of valve lifter 132 from the operating
position to the lower, so-called reverse flow position,
causes the passage from chamber 44 to control cylinder 128
to be blocked in the region of valve seat 136, while an open-
ing in the region of valve seat 138 creates a connection be-
tween control cylinder 128 and a centrally located, downward
pointing pipe 140. Central pipe 140 passes in a water-tight
manner throu~h a central axial bore 142 in channel piece 50
and is open at its end 144 to nipple 118. In the reverse
flow position, control cylinder 128 is thus discharged to
atmospheric pressure.
Thus when valve 130 is moved from its operating
position into the reverse flow position, channel piece 50 is
moved upwards because of the pressure difference between
chamber 49 and control cylinder 128, water being driven from
control cylinder 128 through central pipe 140.
This causes shut-off lL4 to move from seat 112,
thereby opening outlet 116. In the first part of the clean-
ing phase, the coarse dirt which has accumulated in the lower
part ofthe reverse fLow chamber is flushed out. As channel
piece 50 moves further upward, recesses 122 move out of the
region of opening 108 so that pressure equalization can no
longer take place between chamber 44 and chamber 49. In these
intermediate positions, the places on filter element 12 which
are opposite the toroidal openings are flushed from the out-
side towards the inside with clean water, the water flowing
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.
through axial bore 146 in pipe 52 to nipple 118. Simul-
taneously, the coarser dirt particles are scraped off
the smooth filter surface by wipers L48 which contain
toroidal channel 54. Wipers 148 are arranged in a diagonally
upward position. The particles which are scrapped off the
filter pass through openings 60 into the chamber below,
namely chamber 150 of filter 12. In the upper end position,
the lower recesses 124 are aligned with central opening 108,
so that the particles which have gathered in chamber 150 are
swept up by the downward flowing impure water and passed to
outlet 116. ~hannel piece 50 moves towards an upper stop
only as long as an operating member 152 which is connected
to value lifter 132 is held down.
When operating member 152 is released, control
valve 130 is again moved into its operating position by the
force of reset spring 154 and the water pressure exerted
against valve surface 156. In the operating
position, control cylinder 128 is subjected to operating
pressure from chamber 44. Channels 134 in control valve 130
exert a damping effect which prevents a sudden pressure equal-
ization and causes channel piece 50 to return slowly to its
lower end position. During this movement, the inner filter
surface is again swept over and is cleaned of any remaining
dirt. As o~tlet 116 closes, a slow decrease in the cross
sectional area takes place in the region of conical throttle
element 158, preventing the generation of fluid shocks during
the closing process.
Shut-off member 114 has a sealing element consist-
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ing of a ring 160 which has an upward openir,g grove which
allows the water pressure in chamber 49 to reinforce
the sealing effect.
The valve in Fig. 6 is operated manually. It is of
course possible to operate the valve automatically, for ex-
ample by use of a solenoid.
In the preferred embodiment illustrated in Figs. 8
and 9, central pipe 52 of channel piece 50 has two rings each
with six openings 200 into which the ends of individual wiper
~0 elements 202 are inserted, forming a water-tight seal. Wiper
elements 202 together form a toroidal wiper 148. Flexing of
the wiper element is facilitated by len~thw se slots 206. The edges
of slot-shaped openings 56 of wiper elements 202 are pressed
against the smooth inner surface of filter 212. Filter 212
in turn is stretched smoothly over the inside surface of a support-
ing member 210 which has through openings 208. Elements 202
have grooves 214 facing towards the inside and together form-
ing an annular groove into which, if necessary, an expanding
ring (not shown) may be inserted to increase the pressure ex-
erted by wiper elements 202 against filter 212. Wiper
elements 202 of each wiper 48 are spaced by small distances 216
from one another in the peripheral direction, thereby provid-
ing space for radial flexing. This compensates for manufactur-
ing tolerances and for any uneveness on the surface of
filter 212 resulting from dirt deposits.
Filter 212 is stretched between notched front
faces 222, 224 of supporting member 210 by rings 218, 220 at
its ends
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In this embodiment filter 212 is a webbed tube
Rings 218, 220 are provided at its ends and retain filter 212
in a stretched state between faces 222, 224 of supporting
member 210. Contact with the filter is made by a helical
supporting rib 226, so that wiper 14~ contacts the filter
with approximately the same pressure and therefore the same
sliding fiction throughout its whole axial displacement, allow-
ing a continuous movement. Rib 226 even extends into
regions 228, 230, 232 of supporting member 210, namely the
regions in which there are no through openings. These '-egions
are designed to receive wipers 148 in their end position. The
same sliding friction therefore exists in these regions also.
A plurality of radial openings 234 spaced at pre-
determined distances in the peripheral direction from one
another are provided at the lower end of channel piece 50.
In the position illustrated in Fig. 8, these are closed by
a ring 236 on filter 12, thereby preventing the entrance of
impure water. Downward through slots 238 are provided in
channel piece 50 between openings 234. During filtering,
dirt can pass through these from chamber 44 into chamber 49.
As channel piece 50 moves downward during the reverse flow
- process, slots 238 are closed by a cylindrical surface 240
which extends into ring 236, while, at the same time, open-
ings 234 leading to chamber 49 are opened. An actuating
rod 242 is provided which extends in the upward direction over
the filter housing. Rod 242 is connected to channel piece 50
to permit relative rotation, but not translation. A shut-
off element 240 is mounted for axial movement relative to
rod 242 by means of a peg 250 which extends into a hollow
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space 246 of rod 242. A pin 252 is provided to prevent re-
lative rotation between shut-o~f element 244 and rod 242.
Shut-of~ element 244 further has a threaded spindle which
engages a threaded bushing 256, the latter being mounted in
a metal pipe 262. Metal pipe 262 is non-rotatably mounted in
an opening 258 in filter cup 10 and provides a water-tight
seat 260 for shut-off element 244. This allows any shut-off
. foraes which are applied to seat 260 to be completely ab-
sorbed by pipe 262 and therefore prevents their transmission
to filter cup 10 which is made of a synthetic material.
Opening and closing of shut-off element 244 is accomplished
by turning of rod 242 and is therefore independent of the
sliding motion of the actuating rod during the reverse
flow process. In the closed condition, the shut-off force
o~ shut-off element 244 is increased by the pressure within
- the filter housing, while opening of the element is facilitated
by a channel 264 which reverses the flow of the cleaning
water, and deflects it upward toward element 244. The end
of actuating rod 242 projecting over the filter housing is
designated by reference numeral 266. It extends into an
extension 26~ of the housing and is provided with an actuating
knob 272 whose downward movement is opposed by the for.ce of
a spring 270. Actuating knob 272 allows actuating rod 242 to
be rotated, thereby effecting opening and closing of shut-off
element 242,and to be moved in the axial direction, thereby
causing axial translation of channel piece 50. Knob 272 has
a shaft 274 with two lengthwise slots 278 each having an
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upper and a lower locking recess 276. A guide and locking
pin 280 projects radially on both sides from the actuating
rod and engages sLots 278. This constitutes the mechanism
allowing lowering of knob 272.
Damper apparatus 282 is provided to cause the move-
ment of channel piece 50 and wiper 148 to be a slow, even
movement during the reverse flow process. The damper apparatus
consists of a damping cylinder 264 fixedly arranged within
chamber 44. Rod 242 passes through cylinder 284. A damping
piston 288 having an opening 286 is arranged on rod 242 with-
in cylinder 284. Cylinder 284 has an increased cross
section 290 in its upper region, thereby preventing the in-
troduction of additional friction at the start of movement,
since at that time the static friction between wiper 148 and
filter 12 must be overcome.
Piston 288 is provided with a downward facing annular
water~tight lip 292 which increases the throttling effect
when pushed down Further, the lower through opening in the
cylinder provided for actuating rod 242 is bounded by a
water-tight lip 294 which prevents an exchange of water with
that in chamber 44 while actuating rod 242 is pushed down-
wards, but not while the rod is being raised.
In the embodiment illustrated in Fig. 9, the outlet
from channel piece 50 is constituted by an axially downward
facing ring-shaped opening 234' arranged in a doubLe walled
extension 300 of channel piece 50. An inner pipe 302, attached
to actuating rod 242, extends through and downwardly below
extension 300. Inner pipe 302 carries a shut-off member 308
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having a toroidal shut-off element 306 for axial movement
therewith.
~s long as only a small or no pressure difference
exists between chamber 49 and the inside of channel piece 50,
shut-off element 306 i.s pushed against the rim of opening 234'
by the force exerted by reset spring 310. This prevents the
entry of unfiltered water, and thus of dirt particles, from
chamber 44 or 49 into channel piece 50 On the other hand,
chamber 44 is connected to chamber 49 through annular
opening 238', so that the coarser dirt particles can fall
down into chamber 49 during the filtering operation. When,
at the start of the reverse flow phase, activating rod 242
is rotated, lifting shut-off element 244 from its seat 260,
the unfiltered water and the accumulated coarse dirt particles
are rinsed out of chamber 49 by unfiltered water streaming
through opening 238'. As long as opening 238' remains open,
opening 234' remains closed. When, subsequently, actuating
rod 242 with channel piece 50 is pushed downward so that the
outer pipe 312 of extension 300 enters into opening 238' and
blocks this against further entry of water from chamber 44, a
pressure difference builds up between the inside of channel
piece 500 and chamber 49. This pressure difference acts
opposite the force exerted by reset spring 310 to lift shut-
off element 306 from opening 234' and allows the reverse flow
water carrying the finer dirt removed from the filter element
to flow from channel piece 50 through chamber 49 to outlet
nipple 118. In this phase, the dirt removed from the
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surface of filter 212 by wiper elements 202 is collected in
a conical annular space 314 of filter element 12 until such
time as opening 238' is again freed by l.ifting of actuating
rod 242. Immediately thereafter, shut-off element 306 is re-
turned to its upper closed position by the force of reset
spring 310. Thus the dirt that has been collected in a
space 314 during the reverse flow process is carried away
to the outlet nipple by unfiltered water streaming into
chamber 49. This takes place without entry of any dirt
particles into channel piece 50.
While the invention has been illustrated in pre-
ferred embodiments, it is not to be limited to the circuits
and structures shown, since many variations thereof will be
evident to one skilled in the art and are intended to be
encompassed in the present invention as set forth in the
following claims.
