Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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STORM WATER FILTER ARRANGEMENT .
This invention relates to storm water filtration and in particular to the
filtering of
gross pollution from storm water at its entry or exit from the storm water,
underground and drainage systems.
BACKGROUND
Water quality degradation is a problem of growing proportions. One measure of
water quality is the amount of gross pollution that is carried from our roads
and
streets into our storm water system and eventually into the reservoirs that we
rely on
for potable water, our rivers and ultimately the ocean.
Gross pollution in the main (90%) comprises organic matter like branches,
twigs,
leaves, and soil, the remainder being non-organic matter like plastic
containers, bags,
wrappers; paper; cans; and cigarette butts.
In metropolitan and township areas storm water catchment consists of road
surfaces
and the entry points for storm water into the underground portion of a storm
water
drainage system consists of one or more gully traps located along the sides of
the
road surfaces. There exist different types of gullies, the side entry and the
surface
grate being the two most common.
Serious academic and practical studies of road surface, curb and channel
design
relating to road usage and safety are combined with gully trap configuration
(eg
depression, grate, deflector, etc) studies to provide the optimum means by
which to
trap storm water, and the inevitable gross pollution carried by it, and
directed into
the drains below the road surface.
Such traps are designed to operate effectively in a range of storm water run
off
conditions including low flow to very high flow which ideally captures 100% of
the
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flow but otherwise minimises the bypass of water and pollutants downstream of
the
trap.
Regardless though of the effectiveness of the traps, the problem identified by
the
inventors was how to effectively filter the full range of flows of water and
prevent
the .entry of gross pollution into the underground storm water drainage
systems
without affecting the efficiency of the traps.
One approach to the solution of this problem is disclosed in US specification
5232587
which describes the use of a two stage grate filter arrangement which in
theory is
meant to provide a path of least resistance to the storm water just internal
and
slightly below the entrance to the trap by providing a mufti aperture grate
and
beyond that a further grate with larger apertures located rearward and
internal of
the trap opening.
As gross pollution of a size unable to pass through the grates builds up, the
resistance to flow through the grates increases and it is soon found that the
efficiency
of the trap diminishes as is evidenced by the increasing amount of bypass
flow.
Eventually, the grates become covered with gross pollution and the trap is no
longer
useful. The volume of gross pollutants needed to produce this effect is quite
small
since the grates are located just below the road surface level which therefore
necessitates frequent cleaning to maintain trap efficiency.
Thus the invention is directed to overcoming the problems described above
while
also reducing the maintenance commitment.
BRIEF DESCRIPTION OF THE INVENTION
In a broad aspect of the invention a gross pollution filter apparatus for
placement
within a trap arrangement used in a storm water drainage system comprises a
filter
basket located below the entry level of the storm water into the trap
arrangement, the
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basket being adapted to prevent gross pollution passing into the i-~ap
arrangement,
and the basket also being located so as to provide a bypass channel to allow a
volume of storm water to pass through the trap arrangement, and a storm water
bypass being arranged to restrict entry of incoming storm water and gross
pollution
into said bypass channel while the combined pressure of storm water and gross
pollution inside the trap arrangement is such that storm water can pass
through the
filter basket but which is also arranged to allow storm water to pass into the
bypass
channel when the combined pressure of storm water and gross pollution inside
the
trap arrangement is such that the storm water is restricted from passing
through the
filter basket.
In a further aspect of the invention the trap arrangement comprises a side
entry pit
and the filter basket is located in the pit opposite the entry point of the
storm water
and the storm water bypass means is located across the top of the bypass
channel
which is located between the entry point of the storm water and the filter
basket.
In a yet further aspect of the invention the storm water bypass means is a one
way
valve means.
Specific embodiments of the invention will now be described in some further
detail
with reference to and as illustrated in the accompanying drawings. These
embodiments are illustrative, and are not meant to be restrictive of the scope
of the
invention.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig 1 depicts a side cross-sectional view of a gross pollution filter
apparatus
according to the invention located in a side entry trap arrangement;
Fig 2 depicts a cross-sectional view of a gross pollution filter apparatus;
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Fig 3 depicts a perspective view of a side entry trap arrangement and gross
pollution
filter in place;
Fig 4 depicts a storm water bypass means in the form of a pivotable flap shown
in a
closed (non-bypass) position;
Fig 5 depicts a storm water bypass means in the form of a pivotable flap in an
open
(bypass) position;
Fig 6 depicts a side cross-sectional view of a further embodiment of a gross
pollution
filter apparatus according to the invention having a substantially vertical
storm
water bypass means; and
Fig 7 depicts a side view of a gross pollution filter apparatus.
DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION
Road surfaces collect or are the primary collection area for storm water in
townships
and metropolitan areas. A plurality of storm water traps are located along the
sides
of roadways so as to facilitate the collection of storm water and the
redirection of that
storm water into underground storm water drainage systems which also
occasionally
use above ground water ways to communicate storm water to reservoirs and/or
the
ocean.
There exist as described previously a variety of trap arrangements and for the
purposes of describing this embodiment of the invention a side entry trap is
used. It
will be appreciated that the invention may be readily adapted to various other
trap
types. An example of a side entry trap is depicted in Figs 1 and 3.
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Fig 1 depicts a road surface 10 adjacent a trap arrangement 12 typically
constructed
of concrete which is moulded off site and transported for installation or
poured into
a suitable formwork in situ. The arrangement has a lid 14 which is typically
constructed of reinforced concrete. The upper surface of the lid is at
footpath level.
Storm water exits the trap arrangement via a passageway 16 which communicates
storm water into the underground storm water drainage system.
The storm water road surface run off entry aperture 18 is located on the side
of the
trap arrangement hence the use of the term side entry pit to describe this
particular
arrangement.
Fig 1 depicts a side view of the entry aperture 18 and the maximum possible
volume
of storm water that may enter the trap arrangement is determined not only by
the
depicted height but also the width of the trap. A typical proportion of width
to
height is depicted in Fig 3.
The gross pollution filter apparatus of this embodiment comprises a filter
basket 20
located below and on the opposite side of the entry aperture 18. The filter
basket is
sized or arranged so that a bypass channel 22 is provided. The bypass channel
is
sized so that the maximum possible volume of storm water that may enter the
pit is
capable of passing down the channel 22 in the event that the filter basket 20
is fully
occupied by gross pollution and unable to pass any incoming storm water.
The filter basket can be made of any suitable material however for robustness
and
longevity a stainless steel sheet having a plurality of circular apertures is
preferable.
The size and shape of the apertures may vary from trap to trap as the size and
type
of expected gross pollutants vary from trap site to trap site.
The basket is so called because it is used to collect gross pollution,
however, it may
be configured as a permanent fixture in the trap or it may be made removable
for
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ease of extraction of gross pollutants. Typically, the gross pollution is
vacuumed up
or removed by hand or with an implement via the entry aperture. Alternatively
the
lid 14 can be removed and the gross pollution may be extracted through the top
of
the trap.
It has been found that two monthly extractions of gross pollutants is
sufficient to
maintain the efficiency of the trap arrangement fitted with a gross pollution
filter of
the invention. Of course, this will vary dependent on the expected amount of
gross
pollution to be collected which may require that in certain seasons the traps
are
emptied more often or following special events when man-made gross pollution
levels are high.
The gap between the bottom level 24 of the entry aperture and the top of one
side 26
of the filter basket 20 is bridged in this embodiment by a bypass means 28. In
a
preferred embodiment of the bypass means a flat plate 30 lies substantially in
the
plane of the storm water when it flows from the road surface into the trap.
The
absence of apertures in the bypass means assists in preventing the movable
action of
the bypass means from being obstructed or hindered by gross pollutants.
The flat plate 30 is hinged along its width so as to be rotatably movable
downwards
and in the arrangement depicted in Figs 1 to 3 to lie adjacent the internal
wall of the
trap 12 and thereby allow storm water to access the bypass channel 22 from the
filter
basket side of the bypass means.
An elastomeric element 32, such as for example a spring, is anchored (not
shown) at
end 34 and attached to the flat plate 30 at 36, so as to bias the plate into a
closed
position so as not to allow access of storm water into the bypass channel
until
sufficient pressure builds up to overcome the bias force of the spring. A stop
(not
shown) restrains rotation of the plate towards the anchored end of the spring
and is
located so as to position the plate substantially in the plane of storm water
flow
between the entry aperture and the filter basket.
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An embodiment of a bypass means is provided in greater detail in Figs 4 and 5.
Fig 2 depicts in greater detail an embodiment of the filter basket 22
comprising a
stainless steel sheet 38 having a plurality of circular apertures therein (not
shown).
The sheet is adapted to rest upon a support member 40 and affixed thereto by
fixing
means, for example a pin 42, which stops the sheet sliding off the member but
is
arranged so that the pin can be extracted from a complementary set of
apertures in
the sheet and support member so that the basket can be taken from the trap for
emptying.
The support member 40 is fixed to the side of the trap as depicted in Figs 1
and 3, by
fixing means 42, for example a dyna-bolt.
The opposite side of the basket 20 is supported by a second support member 44
which, as does support member 40, extends the width of the trap. The sheet 38
is
adapted to rest upon the support member 44 and is fixed thereto by bracket 46.
The depth of the basket into the trap is determined largely by the amount of
gross
pollutants which are desired to be trapped. As depicted in Fig 1, the basket
is
approximately two thirds of the depth of the trap below the road surface
level.
Conveniently the bottom of the basket is approximately level with the top of
the exit
aperture of the trap arrangement.
An additional shape supporting bar 48 is located approximately three fifths
down the
side of the basket adjacent the bypass channel and held at this location by
bar 50
which depends from support member 44. This arrangement reduces the deformation
of the filter basket into the bypass channel as gross pollution accumulates in
the filter
basket.
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Fig 3 depicts a perspective view of an in situ entry trap arrangement with a
gross
pollution filter according to the invention.
Fig 4 depicts a perspective view of an embodiment of a bypass means 28
comprising
a flat plate 30 and a hinge member 52 which may be preferably a nylon tape
which is
rugged enough to maintain an adequate hinge function in the harsh
environmental
conditions of its use. An elastomeric element 32 is provided in this
embodiment by a
spring fixed at one end to the flat plate 30 and at its other end to a
framework
member 54 which itself is attached adjacent to the entry aperture 18 of the
trap
arrangement.
The spring biases the flat plate upwards and against stop 36 which in this
embodiment is formed by a triangular shaped sheet of metal projecting from the
framework member 54.
The bypass means depicted in Figs 1 to 5 is of the form described above,
however, it
is possible for a unitary sheet of plastic having a memory characteristic of
its
preferred shape to provide a functionally similar arrangement. Such an
arrangement
is provided by any form of one way valve which closes off the entry to the
bypass
channel while the filter basket is adequately passing storm water but which
opens to
allow excess storm water to enter the bypass channel as required.
Fig 4 depicts the bypass means in a closed position and Fig 5 depicts a bypass
means
in an open position. Like elements in the foregoing Figs are identified with
like
numerals.
Fig 6 depicts a side cross-sectional view of a top entry trap having a grating
58
located at the entry level and aperture of the trap. In most arrangements the
grating
will act as a primary filter to gross pollutants which results in only a
certain size of
pollutants being carried into the trap. A diverter member 60 is located under
a
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portion of the grate to direct storm water and any water borne pollutants into
the
filter basket.
The bypass channel 22 is preferably sized so as to communicate the maximum or
a
reasonable proportion of the expected volume of storm water collected by the
trap.
In this embodiment the bypass means 28 has a vertical orientation and operates
in
the same manner as that described previously. The flat plate 30 of the bypass
means
28 is biased in a closed position until the pressure of storm water on the
filter basket
side of the bypass means is sufficient to overcome the bias force. The
pressure of the
storm water moves the flat plate and allows the flow of storm water into the
bypass
channel 22.
Fig 7 depicts like elements of Fig 6 with like numerals and the dotted outline
30'
shows the flat plate in a position to allow overflow of storm water into the
bypass
channel 22.
The two types of traps described in the specification are merely examples of
traps to
which the filter apparatus of this invention may be adapted. However, the
filter
apparatus can be made to suit many other types of traps.
It will be appreciated by those skilled in the art, that the invention is not
restricted in
its use to the particular application described, nor is it restricted to the
feature of the
preferred embodiments described herein. It will be appreciated that various
modifications can be made without departing from the principles of the
invention,
therefore, the invention should be understood to include all such
modifications
within its scope.
