U.S. patent application number 10/337098 was filed with the patent office on 2003-05-29 for pumps and filter assemblies.
Invention is credited to Hosford, James Peter.
Application Number | 20030099553 10/337098 |
Document ID | / |
Family ID | 10851052 |
Filed Date | 2003-05-29 |
United States Patent
Application |
20030099553 |
Kind Code |
A1 |
Hosford, James Peter |
May 29, 2003 |
Pumps and filter assemblies
Abstract
A combined pump and filter assembly having backwashing apparatus
for the filter assembly and apparatus for offsetting the tendency
for an increase in pump output flow resistance.
Inventors: |
Hosford, James Peter;
(Bridport, GB) |
Correspondence
Address: |
BROOKS & KUSHMAN
1000 TOWN CENTER 22ND FL
SOUTHFIELD
MI
48075
|
Family ID: |
10851052 |
Appl. No.: |
10/337098 |
Filed: |
January 6, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10337098 |
Jan 6, 2003 |
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09937947 |
Oct 2, 2001 |
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6520752 |
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Current U.S.
Class: |
417/313 ;
417/423.5 |
Current CPC
Class: |
B01D 29/682 20130101;
A01K 63/045 20130101; B01D 29/114 20130101; B01D 35/26 20130101;
A01K 63/047 20130101 |
Class at
Publication: |
417/313 ;
417/423.5 |
International
Class: |
F04B 039/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 8, 1999 |
GB |
9907880.0 |
Claims
1. A combined pump and filter assembly comprising in flow series:
a) an inlet in communication with a source of fluid and arranged in
use to admit a flow of fluid from said source, b) a filter assembly
which is adapted in use to filter the flow of fluid admitted
through said inlet and to obstruct any debris entrained within the
fluid c) a main pump which is connected to a main pump drive, d) a
main outlet which is connected to the main pump and through which
fluid admitted through the inlet and filter assembly is discharged
by operation of the main pump as a main output flow, the assembly
also including a backwashing means which is supplied with a flow of
backwashing fluid and which is arranged, in use, for backwashing
the filter to in use remove any debris from the filter;
characterised in that the pump and filter assemblies are combined
into a single unit, and that there is a backwashing pump which is
arranged, in use, to supply backwashing fluid to the backwashing
means, the backwashing pump and main pump are functionally
connected so that in use the tendency for an increase in pump
output flow resistance to cause an increase in fluid flow to the
backwashing assembly is offset.
2. A combined pump and filter assembly as claimed in claim 1 in
which the backwashing pump is drivingly connected to the main pump
and drive.
3. A combined pump and filter assembly as claimed in claim 1 in
which backwashing pump is drivingly connected to a backwashing
drive which is separate to the main pump drive, the backwashing
drive and main pump drive are connected to a control means which
maintains a relationship between the outputs of the main pump and
the backwashing pump and offsets the tendency for an increase in
the main pump output resistance to cause an increase in fluid flow
to the backwashing assembly
4. A combined pump and filter assembly as claimed in any preceding
claim in which an inlet to the backwashing pump is disposed on a
suction side of the main pump so that in use the backwashing flow
is drawn from the suction side of the main pump.
5. A combined pump and filter assembly comprising backwashing means
for the filter assembly and comprising means for offsetting the
tendency for an increase in pump output flow resistance to cause an
increase in fluid flow to the backwashing assembly.
6. A combined pump and filter assembly as claimed in claim 5 in
which the means for offsetting the tendency for increased flow to
the backwashing assembly to occur is provided by the use of dual
pump means for the main pump output and the backwashing
function.
7. A combined pump and filter assembly as claimed in claim 6 in
which the dual pump means are drivingly connected to a common
drive.
8. A combined pump and filter assembly as claimed in claim 7 in
which the dual pump means are coaxially disposed and a shaft
drivingly interconnects the dual pump means to a common drive
means.
9. A combined pump and filter assembly as claimed in claim 6 in
which each of the pumps of the dual pump means are drivingly
connected to separate independent drive means, the independent
drive means being connected to a control means which maintains a
relationship between the outputs of the dual pump means and
provides the means for offsetting the tendency for an increase in
the main pump output resistance to cause an increase in fluid flow
to the backwashing assembly.
10. A combined pump and filter assembly as claimed in any preceding
claim in which the pump and filter assembly are combined into a
single unit.
11. A combined pump and filter assembly as claimed in any preceding
claim in which the filter assembly, and pump are arranged in flow
series, the assembly comprising a main pump to provide a main
outlet flow from a pressure side of the main pump, and the
backwashing means being arranged so that a supply of fluid for the
backwashing means is provided from a suction side of the main
pump.
12. A combined pump and filter assembly as claimed in any preceding
claim in which means are provided to increase the backwashing flow
in response to an increase in the pump output flow.
13. A method of operating a pump which is adapted to drive a filter
and backwashing assembly wherein dual output facilities are
provided by said pump, the method including the step of arranging
and operating the pump so that an increase in flow resistance in
one output of the pump causes a less than a proportionate increase
in fluid flow to the other output of the pump, the latter being the
output adapted for the connection to the backwashing assembly.
14. A method according to claim 11 wherein said method of operating
the pump comprises providing dual pumping means having at least a
degree of independence of operation whereby a reduction in flow
output from one portion of the pump due to flow resistance is
accompanied by less than a proportionate corresponding increase in
output of the other pump function.
15. A method of operating a combined pump and filter assembly
comprising a pump and filter assembly arranged in flow series and
backwashing means for backwashing the filter assembly, the method
including the step of arranging and operating the combined pump and
filter assembly so that in response to an increase in output flow
from the combined assembly a flow of fluid to the backwashing means
is maintained at at least substantially the same level.
16. A method as claimed in any one of claims 10 to 12 in which in
response to an increase in output flow from the pump a flow of
fluid to the backwashing means is increased.
Description
[0001] This invention relates to a method and apparatus related to
pumps and filter assemblies. A particular application of the
invention is to aquatic situations such as ponds and aquariums and
the like, but the method and apparatus is applicable outside this
field.
[0002] There is disclosed in our granted prior patent GB2 293 333B
a pump and filter assembly having great practical utility in which
provision is made for automatic backflushing of the filter by a
corresponding flow of the liquid medium being filtered.
[0003] We have discovered that the assembly disclosed in our prior
patent is susceptible of improvement in respect of the backflushing
function as explained below.
[0004] We have determined that there would be benefit in providing
an improved system for regulating the fluid pressure in the
supplies from the pump assembly to, respectively, the pump output
(typically a fountain or something of that sort in an aquatic
situation), and the supply of fluid to the filter backflushing
assembly itself.
[0005] Typically, what happens in normal usage with the prior
system disclosed in GB 2,293 333 is that when the back pressure on
the main output line is increased, the flow to the backflushing
system increases. This is because the backflushing supply is taken
from a T-connection on the output from the pump, the increase in
the resistance to the flow from the pump in the main output line
therefore causes an enhanced flow to the backflushing assembly. In
simple terms the pump output takes the line of lesser resistance,
which with increased resistance in the main output line will be, to
the backflush assembly. With increased resistance in the main
output line however the overall outlet flow from and through the
pump will decrease. This occurs particularly in the case of a
centrifugal pump, where the pump output increases as the resistance
in the pump output line decreases. Consequently there is less need
for the backflushing since less overall flow is entrained into the
assembly and so less blockage occurs. The increase in backflushing
flow in this situation is therefore not required. In fact this
increase in backflushing flow in this situation is undesirable
since it diverts flow and pump effort from the main output
line.
[0006] In the opposite situation when the resistance in the main
output line decreases the reverse occurs. Namely the flow in the
main output line increases and the backflushing flow will be
reduced. Overall though the flow through the pump will increase.
However with the overall flow increasing there is more likelihood
of the filter being blocked and so what would ideally; be required
is an increase in the backflushing flow in such a situation.
[0007] It can therefore be seen that with the arrangement disclosed
in GB 2,293,333 the changes in backflushing flow in response to
changes in the main output line resistance and overall flow are the
opposite of what would desirably be required.
[0008] Having discovered this Latter factor, we have invented a
solution to the problem whereby the tendency for the backflushing
supply to increase when the main pump output resistance increases
and the main output flow decreases, is at least partially offset
and/or which provides improvements generally to pump and filter
assemblies.
[0009] According to a first aspect of the present invention there
is provided a combined pump and filter assembly as described in the
appended claims 1 to 12.
[0010] According to a second aspect of the present invention there
is provided a method of operating a combined pump and filter
assembly as described in appended claims 13 to 16.
[0011] Accordingly, in its broadest aspect, the present invention
seeks to provide a means whereby the tendency for the backflushing
supply to increase when the main output is subjected to increased
flow resistance, is offset at least in part.
[0012] In one embodiment, this offsetting effect is achieved by the
provision of dual pumping means. In the embodiment, the increased
flow resistance in the output from one of the pumping means (the
main pumping means) reduces its output flow, but does not reduce to
the same extent the output flow in the other pumping means. Where
the dual pump means are entirely separate, there is effectively
little or no output effect on the second pumping means, except if
they have a common drive and the increased load on the main pump
slows down the second pump.
[0013] The present invention will now be described by way of
example only with reference to the following figures in which:
[0014] FIG. 1 is a schematic cross section of a pump and filter
assembly according to the present invention;
[0015] FIG. 2 is a schematic section along section X-X of the
filter and pump assembly of FIG. 1;
[0016] FIG. 3 is a schematic cross section similar to that of FIG.
1 of a second embodiment of the pump and filter assembly according
to the present invention;
[0017] FIGS. 4 and 5 are schematic cross sections of further
embodiments of pump and filter assemblies according to the present
invention;
[0018] FIG. 6 is an axial view of the radial flow backwashing
impellor of the embodiments shown in FIGS. 4 and 5.
[0019] Referring to FIG. 1 there is shown a combined pump and
filter assembly 7 comprising a filter section 10 and a pump section
12 all housed within a generally cylindrical housing 2. The pump
and filter assembly 7 is disposed about a central axis 1 with the
filter section 10 towards one axial end and the pump section 12
towards the other. Within the housing 2 an internal partition 9
divides the pump section 12 from the filter section 10. A central
passageway 16 is defined within the partition 9 interconnecting the
filter section 10 with the pump section 12.
[0020] The pump section 12 is of, a centrifugal, type and comprises
a rotary impellor 14 mounted inside the housing 2 and within a pump
chamber 3 defined by the housing 2 and partition 9. The impellor 14
is arranged to rotate about the central axis 1, as shown by, arrow
36, A shaft 15 extends from the impellor 14, through the housing 2,
and drivingly connects the impellor 14 to a motor 18. The central
passageway 16 provides the inlet to the pump section 12, whilst in
a portion of the housing 2 radially outward of the impellor 14
there is an outlet 8.
[0021] The portion of the housing 2 of the filter section 10 and
the partition 9 define an internal filter chamber 20. A portion of
the housing 2 of the filter section 10 comprises a filter screen
assembly 4. Typically this filter screen assembly 4 extends around
a significant if not the entire circumference of the housing 2. The
filter screen assembly 4 is of a conventional configuration and
comprises a mesh or filter. The filter assembly 4 is arranged so
that working fluid from a surrounding region 6 outside of the
housing 2 can flow through the filter assembly 4 into the internal
chamber 20, whilst any entrained solids, or particles above a
certain size, within the working fluid are obstructed by the filter
assembly 4 and are prevented from entering the internal chamber 20.
Accordingly the flow of working fluid from the surrounding region 6
through into the internal chamber 20 is filtered by the filter
assembly 4.
[0022] A backwash assembly 29 is rotatably mounted about the
central axis 1 within the filter chamber 20. The backwash assembly
29 comprises pair of arm members 22 which extend radially from a
central hub. At the distil end of each of the arms 22 there is an
axially extending rail member 24a,24b. The backwash assembly 29 is
mounted and configured such that the rail members 24a,24b are in
close proximity to the inside of the filter screen assembly 4 with
the rail members 24a,24b extending axially substantially over thee
axial length of the filter screen assembly 4. Conduits 32 for, in
use, the passage of backwashing fluid are defined within the
backwash assembly and extend from an inlet 30 in the central hub of
the backwash assembly, through the arms 22 and along the rail
members 24a,24b. Along the length of each of the rail members
24a,24b there are a series of nozzles 26 which are interconnected
with the conduits 32. Whilst the nozzles 26 are directed radially
outwardly towards the filter assembly 4, they are also angled
relative to the radial direction and directed backward relative to
the direction of rotation of the backwash assembly 29. By this
arrangement, in use, backwashing fluid supplied to the conduit 32
will issue from the nozzles 32 and will be directed against the
filter screen assembly 4. Furthermore this flow of backwashing
fluid from the nozzles 26 will also provide a driving moment to
rotate the backwashing assembly 29 about the central axis 1. As a
result, as the backwashing assembly 29 rotates a stream of
backwashing fluid will be directed via the nozzles 26 against the
radially inside of the entire circumference of the filter assembly
4.
[0023] In fluid communication with the backwash assembly inlet 30
and filter chamber 20 there is a backwash supply pump means 31
which is distinct from the main pump 12. The backwash supply pump
means 31 comprises a backwash impellor 28 which is rotatably
mounted about the central axis 1, coaxially with and within the
circular inlet 30 to the conduit 32 of the backwash assembly 29.
The backwash impellor 28 is of an axial flow type. In this
embodiment a backwash impellor shaft 34 drivingly interconnects the
backwash impellor 28 to the main pump impellor 14 and so to the
motor 18. Accordingly, in use, the backwash impellor 28 is rotated
about the central axis 1, drawing in working fluid from the filter
chamber 20, which is then directed into the backwash conduit 32 to
provide a supply flow of backwashing fluid to the nozzles 26.
[0024] In operation the motor 18 drives and rotates the main pump
impellor 14 and the backwash supply impellor 28 working fluid,
which may include entrained particles and debris, from the region 6
surrounding the assembly is then drawn into the filter section 10
through the filter screen assembly 4, as shown generally by arrows
A. Working fluid passes through the filter screen assembly 4 whilst
the debris and particles within the working fluid will be trapped
by the filter assembly 4. The majority of the fluid passing through
the filter screen assembly 4 and into the filter chamber 20 is then
drawn into the suction side of pump section 12 through the central
passageway 16 and inlet to the main pump as shown by arrow B. The
main pump impellor 14 works on this fluid and the fluid is then
discharged and pumped through the outlet 8, as shown by arrow C. A
smaller proportion of the fluid within the filter chamber 20
however is entrained by the backwash impellor 28 into the
backwashing assembly 29, as shown by arrow D to be used as
backwashing fluid. This backwashing fluid is then driven and
propelled by the backwash impellor through the conduits 32 in the
backwash assembly 29 and out through the nozzles 26 in the rail
assemblies, as indicated by arrows E and F. This flow of fluid out
of the nozzles 26 rotates the backwashing assembly 29 and
backwashes the filter screen assembly 4. Backwashing occurring by
virtue of the flow of fluid F from the nozzles 26 being directed in
the reverse direction to the general flow direction through the
filter assembly 4. Accordingly any particles and debris trapped in
the filter assembly screen 4 will be dislodged and forced radially
outwards, away from the filter screen assembly 4 by the nozzle flow
F. The filter screen assembly 4 is thereby substantially kept clear
and unobstructed.
[0025] As the main pump impellor 14 rotational speed increases,
possibly as a result reduced resistance at the pump outlet 8, the
overall flow of working fluid through the assembly 7 will increase.
This increases the likelihood of the filter screen assembly 4
becoming blocked since more entrained particles and debris will be
drawn into the filter assembly 4. With this arrangement and system
7 however a relationship is maintained between the rotational speed
of the main pump impellor 14 and the backwashing impellor 28. This
relationship is provided by linking the main pump impellor 14 and
backwashing impellor 28 via shaft 34. Consequently as the main pump
impellor 14 speed increases, the flow of backwashing fluid and
backwashing of the filter screen assembly 4 will also be increased.
This increased backwashing will offset the increased amount of
entrained particles and debris drawn into the filter assembly 4 as
a result of the increased flow. The required degree of backwashing
and clearance of debris and entrained particles from the filter
screen assembly 4 to keep the filter screen assembly 4 clear and
unobstructed, is therefore provided automatically by this system 7.
Furthermore by this arrangement since changes in the flow
resistance at the pump output 8 will cause the pump impellor 14 to
slow down, the backwashing impellor 28 will also slow and the
backwashing flow will be reduced. Consequently the configuration of
the system provides a means for offsetting the tendency for an
increase in the output resistance at the pump outlet 8 to cause an
increase in fluid flow to the backwashing assembly 29. Accordingly
this addresses the above mentioned problem with the current prior
art type of arrangements discussed above.
[0026] The problems of the backwashing flow and main pump output 8
flow effecting each other, which are present with the conventional
arrangements are also mitigated and reduced in the present
invention by the backwashing flow being drawn and provided from the
suction, inlet, side of the pump section 12. This can be contrasted
with the previous conventional arrangement, described in GB
2,234,168, in which the backwashing flow is drawn from the pressure
side and outlet of the main pump. Further advantages of the
arrangement according to present invention are that it is a simple,
combined pump and filter unit which utilises the filtered working
fluid to provide the backwashing and automatically keep the filter
clear. Debris is also kept out of the pump section 14 with the pump
being protected being jammed by debris and entrained particles in
the fluid. Furthermore the close proximity of the pump section 12
and filter section 10 within a combined unit and housing 2 reduces
the possibility of additional particles being entrained within the
fluid as the fluid flows from the filter section 10 to the pump
section 12.
[0027] In this embodiment a main pump 14 and a separate backwashing
pump 28 which is disposed with the backwashing pump inlet 30 on the
suction side of the main pump 14 is provided, with the main pump 14
and backwashing pump 28 drivingly connecting the backwashing pump
28 to the main pump 14. In this way the main pump 14 and
backwashing pump 28 are functionally connected so that in use the
tendency for an increase in main pump 14 output 8 flow C to cause
an increase in fluid flow to the backwashing assembly 29 is offset.
Accordingly by this functional connection in this way according to
the invention, an decrease in main pump 8 output 8 flow C (due for
example to an increase in main pump output 8 resistance) does not
lead to an increase in backwashing flow F. On the contrary, and
preferably such an decrease in main output 8 flow C causes an
decrease in backwashing flow F. Similarly in the reverse situation,
the functional connection according to the invention ensures that
when an increase in main output 8 flow C occurs the backwashing
flow F is at least maintained and preferably is increased.
[0028] A further advantage of this arrangement 7 is that the
arrangement 7 is significantly more efficient than the prior
arrangement and in particular than the arrangement described in GB
2,293,333. With the prior arrangement, of which that described GB
2,293,333 is typical, the fluid for backwashing is taken from a Tee
junction in the output of the pump. Such a Tee connection
introduces friction resistance and inefficiencies in the flow of
backwashing fluid. Furthermore the arrangement of conduits to
supply the upstream backwashing assembly also introduces further
losses. Typically with units similar to that described in GB
2,393,333, using various different pumps of both centrifugal and
positive displacements types, 20 to 25% of the pump output may be
required to supply the backwashing assembly. This represents 20-25%
of the overall power requirement, in order to provide sufficient
flow to the backwashing nozzles. Using the arrangement 7 of the
present invention incorporating a separate backwashing pump and
impellor 28 it has been found that only 7-10% of the total power is
required to provide an equivalent backwashing flow F. Accordingly
the arrangement 7 of the present invention provides a significant
reduction in the total power required and an improvement in
efficiency.
[0029] A second embodiment of the present invention is shown in
FIG. 3. This embodiment is generally similar to that described with
reference to FIGS. 1 and 2 and consequently only the differences
will be described. In addition like reference numerals have been
used for like features.
[0030] In this embodiment the backwash supply pump means and
specifically the backwash impellor 28' are not connected to the
main pump 12 and impellor 14. Instead a separate motor 40 is
drivingly connected to the backwash supply impellor 28' via a shaft
44'. In this way the main pump and backwash pump are not drivingly
interconnected and are entirely separate.
[0031] A controller 42 is connected to the main pump motor 18 and
also to backwash motor 40. Preferably the controller 42 maintains a
relationship between the rotational speed of the two motors 18,40
such that as the main motor 18 increases speed, the backwashing
motor 40 speed is also increased. In this way as the main pump
impellor 14 rotational speed increases, possibly as a result
reduced resistance at the pump outlet 8, the overall flow of
working fluid through the assembly 7' will increase. This increases
the likelihood of the filter screen assembly 4 becoming blocked
since more entrained particles and debris will be drawn into the
filter assembly 4. However since the back wash motor 40 speed will
also be increased by the controller 42, the flow of backwashing
fluid and backwashing of the filter screen assembly 4 will also be
increased. This increased backwashing will offset the increased
amount of entrained particles and debris drawn into the filter as a
result of the increased flow.
[0032] The controller 42 in this embodiment provides in this
arrangement a functional connection between the main pump and
backwashing assembly 29. This functional connection arranged and
providing the means so that in use the tendency for an increase in
main pump output 8 flow resistance, and so decrease in main pump
output flow C, to cause an increase in fluid flow to the
backwashing assembly 29 is offset. The functional connection and
arrangement furthermore preferably providing that in response to a
decrease in main pump output 8 flow C there is a decrease in
backwashing flow F and similarly that in response to an increase in
main pump output 8 flow C there is an increase in backwashing flow
F.
[0033] By fine tuning the relationship between the motor 18,40
provided by the controller 42 the system can be optimised and the
required degree of backwashing and clearance of debris and
entrained particles from the filter screen assembly 4 can be
maintained under varied operating conditions to keep the filter
screen assembly 4 clear and unobstructed.
[0034] Although this embodiment is slightly more complicated than
that of FIG. 1, and requires a further motor 18, it has the further
advantage that within the combined pump and filter unit and system
7' the backwashing and pump sections are entirely separate and
unconnected. Therefore whilst the backwashing will vary with
changes in the pumping section 12 as required, both the pumping
section 12 and backwashing will have no effect on each other. With
the previous embodiment since the main pump impellor 14 and
backwashing pump impellor 28 have a common drive, increased load on
the main pump impellor 14 will slow down the backwashing pump
impellor 28.
[0035] This second embodiment also has the advantage that the
variation of the backwashing in response to changes in the
operation of the main pump can be better optimised and adjusted
with more control via the controller 42. In particular different
relationships between the amount of backwashing for an the main
pump speed can be used for different parts of the operating range.
In other words a non-constant and/or non-linear relationship can be
used using the controller 42 and separate motors 18,40. Furthermore
further transducers monitoring the operation of the assembly 7' and
pressures could be incorporated with the controller 42 to provide
yet further control.
[0036] In either of the systems 7,7' shown in the figures the
backwashing assembly 29 could be connected to the backwashing
impellor 28 and/or to the main pump impellor and/or to the motors
18, 40. By such connection a more direct and reliable rotation of
the backwashing assembly 29 could be provided than is the case with
relying on the discharge from the nozzles to rotate the assembly
29.
[0037] It will also be appreciated that although these systems are
shown and described as simply drawing in fluid from a region 6
surrounding the system 7,7' in alternative embodiments further
conduit means could be arranged to duct the fluid to the filter
screen assembly 4.
[0038] In the above embodiments the backwashing pump means 31 has
been described as being of an axial flow type. It will be
appreciated though that in other embodiments the backwashing pump
and backwashing impellor 28 could be of a radial flow, centrifugal
type.
[0039] The backwashing assembly 29 has also been described as
including a number of nozzles 26 for directing the backwashing flow
F to clear the filter screen assembly 4. It will be appreciated
that these nozzles 26 could be of any known conventional type used
in backwashing assemblies. Preferably however the nozzles 26 are
made from an elastomer which defines an orifice through which a jet
of fluid is discharged. In this way due to the resilience of the
elastomer material the orifice can open to allow any remaining
debris particles to pass through and so prevent blocking of the
nozzles 26. Such a nozzle 26 made from an elastomer is described in
GB 2,293,333. The number of individual nozzles 26 could also be
amalgamated and replaced with one large nozzle in the form
essentially of a slit to provide a single wide but thin jet. Such a
slit like nozzle is simpler to manufacture than a series of nozzles
26 and ensures that a more uniform jet and flow F of backwashing
fluid is directed at the backwashing screen assembly 4.
[0040] Two further embodiments corresponding to those shown in
FIGS. 1 and 3, but incorporating such alternatives as are described
above are shown in FIGS. 4 and 5.
[0041] In FIGS. 4 and 5 like reference numerals have been used for
the like features shown in FIGS. 1 and 3 and the arrangements, are
generally the same as the previous embodiments. The arrangement 7"
of FIG. 4 corresponds generally to the embodiment of FIG. 2, whilst
the arrangement 7'" of FIG. 5 corresponds generally to the
embodiment of FIG. 3 and includes a separate backwashing motor 40.
The backwashing means 31' and backwashing impellor 28" however are
of a radial flow type comprising radial vanes 50 which are arranged
to draw in backwashing fluid from the internal filter chamber 20
through an inlet 52 and propels the backwashing fluid radially
outwardly to backwashing nozzles 28". The backwashing impellor 28"
including the vanes 50 is shown in more detail FIG. 6, and is
generally similar to the centrifugal radial flow main pump impellor
14. Such radial flow pumps are generally well known in the art.
Furthermore the filter nozzles 28" comprise a single axially
extending thin slot which extends along the axial length of the
rail members 24a,24b. Such a slit nozzle 28" provides in use a jet
of backwashing fluid flow in the form of a wide sheet like jet F'
which is directed at and over the axial length of the filter screen
assembly 4.
[0042] The illustrated embodiments shown in the figures and
described above show dual pump arrangements having dual pump rotors
which achieve the offsetting advantage discussed above.
[0043] Other ways of achieving a related offset may be devised in
terms of flow control means providing a relationship between the
output flows of the pump assembly to its main output and to its
subsidiary backwashing function.
[0044] Amongst other modifications which could be made in the above
embodiments are the following:
[0045] a) The use of various different kind of pumps including
positive displacement as well as centrifugal pumps;
[0046] b) The use of entirely separate pump units or separate pump
units having a common drive;
[0047] c) The use of the invention in relation to gas filtration as
well as for liquid filtration; and the use of alternative
arrangements for backwashing and indeed alternative systems for
filter clearing or cleaning other than backwashing itself, whether
in combination with backwashing or not.
* * * * *