Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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A method and pump unit for a pressure sewerage system
Field of the invention
The present invention relates to pump units in pressure sewerage systems and
methods of operation.
Background of the invention
Pressure sewerage systems are used in areas where the cost of tanks, pumps,
pressure pipelines and pumping of sewage is less than the cost of the larger,
deeper
sewers required for conventional gravity sewerage systems. Individual pump
systems
are provided for each property, with each system pumping into a common
pressure
pipeline. They are particularly suitable where conventional gravity systems
are
prejudiced by localised topography, geology and/or environmental and social
conditions.
Current pump systems include an underground upright tank in which a pump is
mounted. The tank located in each property receives sewage from that property
and
when the tank fills to an 'on' level, the pump is activated to pump the sewage
from the
tank to a common pressure pipeline to which each of the properties along a
street is
connected. The pump remains active until the level of sewage in the tank goes
down to
an 'off level within the tank.
The spacing of the 'on' and 'off levels is traditionally- determined as a
function of a
maximum number of pump starts per hour. A typical .i'.ousehold produces about
600
litres per day of sewage. For a tank of maximum volume of 667 litres, the
spacing would
typically align to 189 litres between the 'on' and 'off' levels. These pumps
typically pump
about 0.5 litres per second and can include an over-pressure cut-out feature,
which
stops the pump if the pressure at its outlet exceeds c certain threshold. This
feature
protects the pump motors in the advent of pipeline blockage or hydraulic
overloading of
the pressure system when too many pumps attempt to start simultaneously in
peak flow
periods and particularly after an extended power failure.
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The volume in the tank above the 'on' level is provided for emergency storage
in the
advent of extended power failure as well as temporarily storing abnormal peak
flows of
sewage such as when water is released from a full spa bath. The amount of
water
below the 'off level is typically a simple function of the geometry of the
pump and the
tank, as most pumps are placed in the bottom of standard tanks without
specific
consideration to the use of the tank. The amount below the 'off level can be
65 litres,
which can lead to deposits on the base of the tank.
There are inherent conflicting design requirements for sizing of the street
pressure main
pipelines. On one hand these pipelines must be as large as possible to
minimise
pumping costs and overflow risks, allow simultaneous operation of as many
pumps as
possible during peak flow periods and post power outage recovery. On the other
hand
they must be as small as possible to minimise cost and sewage age. Compromises
invariably do not favour sewage age considerations.
A key problem with current pressure sewerage systems include significant
hydrogen
sulphide generating with resultant odour (a rotten egg odour), causing OH&S
and pipe
corrosion risks in the pump unit itself, and also in the pressure pipeline and
in the
downstream receiving sewerage system. This arises because the average age of
the
sewage leaving a property is commonly more than 12 hours. Age dependent
septicity
onset is dependent on many factors including climate, nature of the sewage,
sewage
temperature, trade wastes, groundwater and topography. In Victoria, Australia,
for
example, septicity onset of sewage commonly occurs at an age of around 6 to 9
hours.
Compromised street pressure pipelines invariably add sewage age to the point
where
septic discharges to the downstream sewerage system are unavoidable. Septic
sediments that accumulate in a tank cause acceleration in the septicity of
fresh sewage.
Another key problem with current pressure sewerage systems is that during a
power
failure, the tanks of all of the properties in a street can fill up, or even
overflow during
extended power failures, such as those over 24 hours. When the power supply
reactivates, all of the pumps would attempt to commence operation
simultaneously.
This results in the pressure within the common pipeline along the street
exceeding the
pump cut-out threshold, so that the pumps of the upstream properties remain
inactive
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for an extended period of time until the pumps of the downstream properties
have
emptied their tanks to their respective 'off' levels and stopped pumping. This
in turn
means that the downstream units return to normal operation relatively quickly,
whilst the
upstream units might remain inactive for up to 36 hours or so leading to
increased
overflow risks from those tanks, as well as increased localised odour risks
from
increased sewage age.
It is therefore a desired object of the invention to provide an alternate pump
unit for
pressure sewerage systems that overcomes, or at least minimises, at least one
of the
problems associated with current systems, or at least provides an alternative
solution.
Reference to any prior art in the specification is not, and should not be
taken as, an
acknowledgment or any form of suggestion that this prior art forms part of the
common
general knowledge in Australia or any other jurisdiction or that this prior
art could
reasonably be expected to be ascertained, understood and regarded as relevant
by a
person skilled in the art.
Summary of the invention
The present invention provides a timer unit for controlling a pump for a
pressure
sewerage system, the timer unit enabling activation of the pump for a first
predetermined time period and preventing activation of the pump for a second
predetermined time period directly following the first time period.
According to a first aspect, the present invention provides a pump unit for a
pressure
sewerage system, including:
a pump for insertion in a sewage holding tank, the pump being capable of
operation in response to the sewage level in the tank attaining a first
predetermined level to pump sewage out of the holding tank to an external
pipeline of a sewerage system;
a timer unit programmed to allow the pump to operate during a first
predetermined time period and to prevent the pump from operating during a
second predetermined time period directly following the first predeteremined
time
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period, whereby the first predeteremined time period and second predetermined
time period are continuously repeated in turn,
wherein the pump includes an over-pressure cut-out device or control
arrangement, which prevents the pump from operating if the pressure at the
outlet
exceeds a set threshold.
Preferably, the pump unit is provided as a kit. The timer unit may be provided
as part of
a controller unit. The timer unit is preferably programmed to send start and
stop signals
to the pump controller.
According to a second aspect, the present invention provides an arrangement
for a
pressure sewage system, including:
a holding tank for receiving and temporarily holding sewage from a building;
and a pump unit according to the first aspect of the invention.
According to a third aspect, the present invention provides a pressure
sewerage
system, including:
a plurality of holding tanks at spaced locations connected to a common sewage
pipeline; and
each holding tank including a pump unit according to the first aspect of the
present invention.
Preferably, the pump unit includes a switch that prevents the pump operating
until the
sewage in the tank reaches a first predetermined level. The pump unit may be
configured whereby the pump is stopped when the sewage in the tank reaches a
second predetermined level below said first level, or when the first
predetermined time
period ends, whichever occurs earlier. Once the second predetermined time
period
ends, if the activation switch is still triggered, the pump will be activated.
The first
predetermined time period may be, for example, 30 seconds and the second
predetermined time period may be 9 minutes and 30 seconds, whereby each
individual
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sewage pump arrangement is capable of pumping sewage into the common pipeline
for
30 seconds every 10 minutes.
The switch may be a level control device, such as a float switch, multi-trode,
ultrasonic
switch or other.
Advantageously, the timer unit is independently powered.
Preferably, the internal diameter of the bottom section of the tank is less
than the upper
section of the tank. The bottom section of the tank may be stepped into a
smaller
diameter or may be downwardly tapered. The volume of sewage held between the
pump activation level and the pump deactivation level is preferably less than
20 litres,
more preferably being 10 litres. Alternatively, a conical insert can be
provided, that is
inserted into the base of a standard shaped tank, lessening the volume of the
base of
the tank, therefore shortening the duration between activations of the pump.
Preferably, each pump includes an over-pressure cut-out device, such as a
pressure
switch or thermal overload, which stops the pump from activating if the
pressure at the
outlet exceeds a set threshold or is near pump shut-off head.
According to a fourth aspect, the present invention provide a method of
controlling a
pressure sewerage system, including:
providing each of a plurality of spaced buildings with:
a holding tank for receiving and temporarily holding sewage from a
building;
a pump housed in the tank, the pump being capable of operation in
response to the sewage level in the tank attaining a first predetermined
level to pump sewage out of the holding tank to an external pipeline;
a timer unit in communication with the pump;
an over-pressure cut-out device for preventing operating of the pump
when the pressure at the outlet exceeds a set threshold;
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wherein each timer unit independently allows operation of a respective pump
for
a first predetermined time period and prevents operation of the respective
pump
for a second predetermined time period directly following the first time
period,
whereby the over-pressure cut-out device prevents simultaneous operation
activation of a predetermined number of pumps, and the timer units allow for
the
random operation of the plurality of pumps.
According to an embodiment, the controller units of the plurality of spaced
holding tanks
could be in communication with a central monitoring system, whereby an over-
riding
shut off message could be sent to individual pump units or a plurality of pump
units.
Brief description of the drawings
The invention will now be described, by way of example only, with reference to
the
accompanying drawings, in which:
Figure 1 is a diagrammatic representation of a common sewage pipeline system
for
several properties in a street, each having a holding tank for sewage;
Figure 2 is a perspective view of a holding tank according to a first
embodiment of the
present invention;
Figure 3 is a cross-sectional side view of a sewage pump arrangement including
the
holding tank of Figure 2; and
Figure 4 is a cross-sectional side view of a sewage pump arrangement according
to a
second embodiment of the present invention.
Detailed description of the embodiments
As shown in Figure 1, a pressure sewage system 10 includes a common pipeline
12 to
which a nurnter of properties 14 are connected. The buildings 16 on each
property 14
feed sewage via conventional gravity house drains via conduits 18 into holding
tanks
20, which are typically at least partially buried below ground surface. The
holding tanks
20 are connected to the common pipeline 12 via small diameter pressure
conduits 22.
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20, which are typically at least partially buried below ground surface. The
holding tanks
20 are connected to the common pipeline 12 via small diameter pressure
conduits 22.
Holding tanks 20 (Figure 2) are generally cylindrical with an upright wall 24.
The tank 20
has an upper opening 28, which provides access to the inside of the tank and
would be
closed by a manhole cover (not shown). The bottom section 30 of the tank 20
includes
an insert 35 providing a step at 34 such that the diameter is less in the
bottom section
30 than in the upper section 32, whereby the bottom section 30 holds a
relatively small
volume of fluid, being less than 50 litres, but preferably 15 litres, below
the step 34. Step
34 is inclined at about 1:1 slope (a 45 degree angle) so as to prevent
sediment
retention. The conical insert 35 is inserted into a standard shaped tank 20.
This
provides a high structural integrity for the base. The cavity 37 formed
beneath the
conical insert can be filled with concrete to weigh down the base. This would
prevent
floatation of the tank, which readily occurs during extremely wet weather
periods. As
shown in Figure 4, rather than a conical insert, the bottom of the tank 21
could be
stepped at 34.
The tank 20 includes a number of inlets 36, being an opening positioned just
above the
step 34. The inlet 36 connects to conduit 18. A flat base 38 is provided on
which sits a
pump 40, which can be activated to pump sewage from the bottom of the tank
through
pipe 42 to outlet 44 positioned near the top of wall 24, to connect up with
conduit 22
which connects to the common pipeline 12.
A controller unit 48 with various sensing arrangements within the tank, such
as float
switch 46, controls the activation and deactivation of the pump. An override
timer unit 50
is provided within the pump that is programmed to send start and stop signals
to the
controller unit 48, which controls the duration of the pump activation, only
allowing the
pump to operate periodically. The timer unit in the embodiment shown is
integrated into
the controller unit. The timer unit allows the activation of the pump for a
first
predetermined time period, such as 30 seconds, and then sends a stop signal to
prevent activation of the pump for a second predetermined time period, such as
9
minutes and 30 seconds, directly following the first time period. At the end
of the second
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time period a start signal is sent, with the stop signal only being sent once
the pump has
activated again for a period of 30 seconds.
The activation of the pump 40 is by float switch 46 that is located in the
bottom section
30 of the tank. As the tank 20 fills with sewage, the float switch 46 is
raised to the top of
the bottom section, generally aligning with the step 34. Once it reaches an
upper
predetermined 'on' level 50, the pump is triggered to activate. If the timer
unit is not
within the second predetermined time period, then the pump will be allowed to
activate
to pump the sewage out of the pump. The pump will then stop when either the
float
switch 46 reaches a lower predetermined `off level 52, or when the first
predetermined
time period has ended, whichever occurs first. If the float switch 46 is
raised to the
upper predetermined 'on' level 50, whilst the timer unit is within the second
predetermined time period, then the pump will be prevented from activating
until the
second predetermined time period has ended and the timer unit has sent a start
signal
to the controller.
The reduced volume in the bottom section 30 means that the volume of fluid
between
the upper 'on' level 50 and lower 'off' level 52 is reduced from around 190
litres to 10
litres (one toilet flush), thus the tank operates for shorter periods more
frequently. This
can result in sewage being held in the tank for up to 3 hours, as opposed to
10 hours in
current systems. Sewage can turn septic after 6 to 9 hours. The combination of
minimising retained sewage below the lower 'off' level 52 and the flat sloping
surface of
the step 34 avoids or at least minimises "dead" pockets which can accumulate
sediment. Whilst the temporary storage volume has decreased, the overall
storage
volume of the tank is not reduced greatly, such that it is still able to hold
sufficient
amounts as required during a power failure or extreme weather conditions. The
configuration of the system provides additional buffer storage of around 200
litres above
the upper 'on' level 50, at step 34, and the inlet pipe 36. An alarm system
can be
provided that indicates when the tank has reached a level near the top of the
tank; this
can also occur when the pump fails.
Each pump includes an over-pressure cut-out, which additionally stops the pump
from
activating if the pressure at the outlet exceeds a set threshold.
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The pump 40 is only allowed to pump sewage out of the tank 20 when the level
of
sewage is at or above a certain height, being the upper 'on' level 50, and
when the timer
is in the first predetermined time period. In effect the timer unit is an over-
riding two way
switch.
According to this approach, after a power failure the reactivation of the
pumps of system
is not correlated in the traditional way, as the starting of the pumps is
randomised so
that the upstream pump units return to operational state at a similar time to
the
downstream units. As the pump units are each allowed to run for shorter
periods, each
would in effect take it in turns to empty part of their tanks, rather than the
upstream
10 tanks having to wait until the downstream tanks were fully emptied. By
controlling the
pumping periods and discharges for each pump unit, the amount of time that
pumps
operate simultaneously is reduced, leading to a reduction in peak flows and
sewage age
throughout the common system.
The timer unit 50 is powered independently, such that the timer units are not
reset by a
power failure. Random pump operation is maintained in the advent of a power
failure as
timer settings are frozen and upon power resumption, settings resume and are
not reset
to zero. This means that after a power failure all of the pumps in a system do
not
commence operation simultaneously.
The timer unit 50 and the pump 40, which would include the controller unit,
could be
provided as a kit for insertion into an existing tank 20. Alternatively, a
sewage pump
arrangement could be provided, where the timer unit and pump are provided with
a
tank.
The present invention thereby reduces the likelihood of tanks turning septic.
The
present invention also attenuates peak flows which allows smaller street
pressure
mains; it is thought that the advantages are sufficient such that a smaller
common
pipeline down the street, about half the size of conventional, can be used
thus leading
to a significant cost saving, whilst also significantly reducing the problems
associated
with sulphides. This greatly reduces the impact on the downstream sewerage
system
and means that existing sewerage systems can be expanded to include new areas,
as
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the existing sewerage system could be adapted to accommodate, rather than
having to
create all new sewerage systems for new areas, as is currently required when a
sewerage system is at maximum capacity.
It will also be appreciated that the systems could be configured to
communicate with the
5 Smart Meters, which are being introduced to properties to measure the flow
rate of
individual properties. The Smart Meters could be used to communicate back to a
centralised monitoring point, where individual pump units or a number of
properties
could be shut down through their timer unit, when there was an overload on the
downstream sewerage system, or when repair work was required on the sewerage
10 system of common pipeline.
It will be understood that the invention disclosed and defined in this
specification
extends to all alternative combinations of two or more of the individual
features
mentioned or evident from the text or drawings. All of these different
combinations
constitute various alternative aspects of the invention. -
