Method and pump unit for a pressure sewerage system   

Abstract: A pump unit for a pressure sewage system, including a pump for insertion in a sewage holding tank, the pump being capable of activation for pumping sewage out of the holding tank to an external pipeline, and a 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.

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 household 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 a 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.

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 sewage 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 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

The present invention provides a timer unit for controlling a pump for a pressure sewage 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 sewage system, including: a pump for insertion in a sewage holding tank, the pump being capable of activation for pumping sewage out of the holding tank to an external pipeline; a 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.

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 a sewage pump arrangement for a pressure sewage system, including: a holding tank for receiving and temporarily holding sewage from a building; a pump housed in the tank, the pump being capable of activation for pumping sewage out of the holding tank to an external pipeline; a 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 third aspect, the present invention provides a pressure sewage 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 is activated by a switch triggered when the sewage in the tank reaches a first predetermined level. The pump is deactivated by either a switch triggered 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 sewage pump arrangement is capable of pumping sewage into the common pipeline for 30 seconds every 10 minutes.

The activation and deactivation switches 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 provides a method of controlling a pressure sewage 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 activation for pumping sewage out of the holding tank to an external pipeline; a timer unit in communication with a pump controller; an over-pressure cut-out device for preventing activation of the pump when the pressure at the outlet exceed a set threshold; wherein the timer units enable activation of the respective pumps for a first predetermined time period and prevent activation of the respective pumps for a second predetermined time period directly following the first time period, whereby the over-pressure cut-out device prevents simultaneous activation of a predetermined number of pumps, and the timer units allow for the random activation 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:

FIG. 1 is a diagrammatic representation of a common sewage pipeline system for several properties in a street, each having a holding tank for sewage;

FIG. 2 is a perspective view of a holding tank according to a first embodiment of the present invention;

FIG. 3 is a cross-sectional side view of a sewage pump arrangement including the holding tank of FIG. 2; and

FIG. 4 is a cross-sectional side view of a sewage pump arrangement according to a second embodiment of the present invention.

DETAILED DESCRIPTION

As shown in FIG. 1, a pressure sewage system 10 includes a common pipeline 12 to which a number 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.

Holding tanks 20 (FIG. 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 FIG. 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 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.

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 10 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 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 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 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 centralized 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 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.