WO2008119932A1

WO2008119932A1 - Sewage pump blockage detection

Info

Publication number: WO2008119932A1
Application number: PCT/GB2008/000955
Authority: WO
Inventors: Laundon Andy
Original assignee: Retroflo Limited
Priority date: 2007-03-29
Filing date: 2008-03-18
Publication date: 2008-10-09
Also published as: AU2008234704A1; EP2137413A1; GB0706115D0; US20100166569A1; GB2447867A; GB2447867B

Abstract

A method of monitoring a pump which operates to pump sewage from a wet well in which the current drawn by the pump is detected along with the speed of operation of the pump and the wet well level. The detected values are compared with stored values in a look up table to determine whether the pump is blocked.

Description

Sewage Rump Blockage Detection

The present invention relates to improvements in sewage pumping and in particular to improvements in detecting whether a sewage pump is blocked.

In a usual arrangement waste water and sewage flows out of homes, businesses and surface water drains into a sewer system through which it is directed to a treatment works. In the treatment works the water is separated and purified for discharge into the water course. In a typical sewage system, the waste water and sewage flows primarily under gravity. This may not be possible throughout the whole network.. Accordingly, at some points, pumping stations are provided. The pumping stations are operable to raise waste water and sewage from the low end of one part of the system (the 'wet well') to the high end of an adjacent part of the system. Once in the adjacent part of the system, flow under gravity may resume. In certain systems smaller pumping stations may discharge into larger stations as so on until the flows reach the treatment works.

On occasions the pump may become blocked by the solid material in the waste water. When it is detected that the pump is blocked a self cleaning procedure is initiated, typically involving reversal of the pump. If, after the self cleaning procedure, a blockage is still detected, the pump is shut down and an engineer is despatched to inspect and repair the pump.

As the pumps used in sewage pumping stations do not differ significantly from water pumps used in other water pumping stations such as potable water booster stations, canal pumping stations, ground water pumping stations and drainage pumping stations, the same methods are used to determine whether a pump is blocked. This method involves monitoring the current drawn by the pump and deteπnining that a blockage has occurred when the monitored current exceeds a preset threshold. In such applications, as the amount of power required by the pump in normal operation does not vary appreciably this method works well. In sewage pumping however, the amount of solid material in the water can vary significantly which in turn significantly alters the power required by the pump to pump it out of the wet well. As such, many detected blockages in sewage pumping systems are false alarms resulting in unnecessary engineer call outs and unnecessary pump shut downs. A further problem is that whilst the pump is shut down, solid material has an opportunity to settle which increases the likelihood of a blockage occurring upon resumption of pumping.

It is therefore an object of the present invention to provide a method of detecting the blockage of a sewage pump that alleviates or overcomes the above problems.

According to a first aspect of the present invention there is provided a method of monitoring a pump operable to pump sewage from a wet well comprising the steps of: detecting the current drawn by the pump; detecting the speed of operation of the pump; detecting the wet well level; and comparing each of the detected values with stored values in a look up table to determine whether the pump is blocked.

This method, by looking at the values of three parameters, allows for greater flexibility in determining when a blockage has occurred than the known method of the prior art. This additional flexibility allows a correction for the presence of variable amounts of solid material in the waste water and thus reduces false alarms.

The look up table may be a standard look up table created for the pump. Alternatively, the look up table may be a look up table adapted to conform to the characteristics of a particular pumping station. The look up table may comprise upper and/or lower threshold values for each parameter. In order to determine that the pump is blocked, any two out of the three parameters or all three parameters may need to fall outside said threshold levels. The look up table may also comprise upper and/or lower super threshold levels wherein if the value of any one parameter falls outside the upper or lower super threshold, the pump is determined to be blocked. Additionally or alternatively, threshold levels and super threshold levels for one parameter may depend on the detected value of another parameter. For instance, pump speed threshold levels may be determined by the current drawn.

The method may include the step of determining a rate of change of any or all of: the current drawn by the pump; the speed of operation of the pump; and the wet well level. The determined rate of change values may be compared with rate of change values stored in the look up table to aid determination of whether the pump is blocked. As above, the look up table may comprise threshold levels and/or super threshold levels for the rates of change. To determine that the pump is blocked may require that two of the three or all threes rates of change fall outside the threshold levels or that at least one rate of change falls outside the super threshold levels.

Additionally or alternatively, the or each threshold level and/or super threshold level may be dependent on the determined rate of change of a different parameter. In response to a determination that the pump is blocked, a self cleaning procedure may be initiated. The self cleaning procedure may include reversing the operating direction of the pump. In a preferred self cleaning procedure, the pump is run in reverse at a specified speed for a specified time interval, then forward at a specified speed for a specified time interval, this procedure being repeated, say, three times. If, upon resumption of normal operation it is determined that the pump is still blocked, an alarm may be output.

The method may include the step of storing current, pump speed and wet well level values for future reference. The method may also include the step of storing details of occasions upon which the self cleaning procedure was initiated and/or occasions upon which alarms are output.

According to a second aspect of the present invention there is provided a control unit for a pump operable to pump sewage from a wet well, the control unit comprising: current detection means; pump speed detection means; wet well level detection means; memory means operable to store a look up table of current, pump speed and wet well level values; and a processor operable to compare each of the detected current, speed and level values with values stored in the look up table to determine whether the pump is blocked.

The control unit of the second aspect of the present invention may incorporate any or all of the features described in relation to the method of the first aspect of the invention as desired or as appropriate. The current, pump speed and wet well level can be monitored by any suitable means.

The processor may also be operable to determine a rate of change of any or all of: the current drawn by the pump; the speed of operation of the pump; and the wet well level. The processor may then be operable to compare the determined rate of change values with rate of change values stored in the look up table to determine whether the pump is blocked.

The control unit may be operable to initiate a self cleaning procedure if it is determined that the pump is blocked, hi the event that it is determined that the pump is still blocked after the self cleaning procedure, the processor may be operable to output an alarm signal.

The alarm signal may be received by an alarm means. The alarm means may be an integral alarm means. Additionally or alternatively, the alarm means may be an external unit with a suitable connection to the control unit. The external unit may be an external server or computer.

The memory means may be operable to store current, pump speed and wet well level values for future reference. The memory means may also be operable to store details of occasions upon which the self cleaning procedure was initiated and/or occasions upon which alarms are output.

The control unit may be provided with a user interface. The user interface may be operable to enable the cancellation of an alarm, the out put of an alarm, the initiation of the self cleaning procedure and the transmission of data stored in the memory means to an external unit.

According to a third aspect of the present invention there is provided a pump operable in accordance with the method of the first aspect of the present invention.

According to a fourth aspect of the present invention there is provided a pump incorporating a control unit operable in accordance with the second aspect of the present invention.

According to a fifth aspect of the present invention there is provided a sewage pumping station incorporating a pump according to the third or fourth aspects of the present invention.

According to a sixth aspect of the present invention there is provided a sewage network incorporating one or more pumping stations according to the fifth aspect of the present invention.

In order that the invention can be more clearly understood it is now described further below with reference to the accompanying drawings:

Figure Ia is a schematic diagram of part of a sewer network showing a pumping station;

Figure Ib is a schematic diagram of the pumping station of figure Ia; and

Figure 2 is a schematic block diagram of a pump control system for the pumping station of figure 1. Referring now to figure Ia, waste water flows under gravity in a first part 11 of a sewer network 10. At the low end of this part 11, the waste water is raised by a pumping station 100 to the high end of a second part 12 of the sewer network 10 where flow under gravity can resume. The sewer network 10 may be provided with a plurality of such pumping stations 100, as required.

Referring now to figure Ib, the pumping station 100 comprises a wet well 101 which waste water from the first sewer section 11 enters via an inlet 110. The waste water collects in the wet well 101 and is pumped out of the wet well 101 by a pump

102 into sewer section 12. The pump 102 is controlled by a pump control unit 200 in response to the water level in the wet well 101 and the pump 102 operation speed.

The pump control unit 200 is illustrated schematically in figure 2. The pump control unit comprises a processor 210 which receives signals from a pump speed monitor 202, a wet well level monitor 203 and a pump current monitor 204. The processor is operable to compare the signals received from monitors 202-204 with values for pump speed, wet well level and current in a look up table stored in memory means 205 to determine whether the pump 102 is blocked. This is achieved by comparing the detected values for each parameter with upper and lower threshold levels. If two or more of the detected values fall outside the respective threshold levels, then the pump is determined to be blocked.

hi more complex implementations, all three of the detected values may need to fall outside the respective threshold levels, for a determination that the pump is blocked. Additionally, or alternatively, the threshold levels for some of the parameters may be dependent on the detected values of one or more of the other parameters. One of more of the parameters may have an upper and/or lower super threshold level, which if the detected value falls outside, is sufficient to determine that the pump is blocked. In some embodiments, the processor may additionally or alternatively be operable to calculate the rate of change of the pump speed, wet well level and current and compare these with values stored in the look up table, as described above, to determine whether the pump 102 is blocked.

The threshold levels may be standard threshold levels for the particular pump. Alternatively, the threshold levels may be optimised for the particular pumping station in which the pump is provided. Optimised levels may be input via an input/output interface 206. The input/output interface 206 may also be operable in some embodiments to output the threshold level information stored in the memory means 205.

If the processor determines that the pump 102 is blocked, it is operable to control the pump to operate a self cleaning procedure. The details of the initiation of the self cleaning procedure may also be stored in the memory means 205. In the present invention the self cleaning procedure comprises the steps of running the pump in reverse at a relatively high speed for a relatively short period, then running the pump forwards at a relatively high speed for a relatively short period and repeating twice more. After this, normal operation is resumed. If the processor 210 determines that the pump is still blocked, the pump 102 is shut down and an alarm signal is output. The alarm signal is passed to an alarm means 207 via the input/output interface 206. In the embodiment shown both the alarm means 207 and input/output interface 206 are separate components. It is of course possible that either or both may be implemented as part of the control unit 200. Similarly, it is possible that the alarm means 207 may be connected directly to the processor 210 rather than via the input/output interface 206.

The input/output interface 206 may be used to retrieve data stored in the memory means 205, update data stored in the memory means 205, such as data stored in the look up table and/or override the processor 201 to issue/cancel an alarm or initiate/cancel a self cleaning procedure.

The processor 201 may also be operable, when the pump is not determined to be blocked to operate any suitable pumping regime such as a batched pumping regime wherein once the level in the wet well 101 exceeds a predetermined pump start level, the pump 102 is started and runs at constant speed until the level in the wet well 101 drops below a predetermined stop level; or a constant level pumping regime wherein the pump 102 is run at a variable speed to transfer flows entering the wet well 101 directly to the adjacent part of the system 12.

It is of course to be understood that the invention is not to be restricted to the details of the above embodiments which have been described by way of example only.

Claims

1. A method of monitoring a pump operable to pump sewage from a wet well comprising the steps of: detecting the current drawn by the pump; detecting the speed of operation of the pump; detecting the wet well level; and , comparing each of the detected values with stored values in a look up table to determine whether the pump is blocked.

2. A method as claimed in any preceding claim wherein the look up table is a standard look up table created for the pump.

3. A method as claimed in claim 1 or claim 2 wherein the look up table is a look up table adapted to conform to the characteristics of a particular pumping station.

4. A method as claimed in any preceding claim wherein the look up table comprises upper and/or lower threshold values for each parameter.

5. A method as claimed in any preceding claim wherein in order to determine that the pump is blocked, any two out of the three parameters or all three parameters may need to fall outside said threshold levels.

6. A method as claimed in claim 4 or claim 5 wherein the look up table also comprises upper and/or lower super threshold levels wherein if the value of any one parameter falls outside the upper or lower super threshold, the pump is determined to be blocked.

7. A method as claimed in claim 6 wherein threshold levels and super threshold levels for one parameter depend on the detected value of another parameter.

8. A method as claimed in any preceding claim wherein the method includes the step of determining a rate of change of any or all of: the current drawn by the pump; the speed of operation of the pump; and the wet well level.

9. A method as claimed in claim 8 wherein the look up table comprises threshold levels and/or super threshold levels for the rates of change.

10. A method as claimed in claim 9 wherein the determined rate of change values are compared with rate of change values stored in the look up table to aid determination of whether the pump is blocked.

11. A method as claimed in claim 10 wherein to determine that the pump is blocked requires that two of the three or all three rates of change fall outside the threshold levels or that at least one rate of change falls outside the super threshold levels.

12. A method as claimed in claim 11 wherein the or each threshold level and/or super threshold level is dependent on the determined rate of change of a different parameter.

13. A method as claimed in any preceding claim wherein in response to a determination that the pump is blocked, a self cleaning procedure is initiated.

14. A method as claimed in claim 13 wherein the self cleaning procedure includes reversing the operating direction of the pump.

15. A method as claimed in claim 14 wherein in the self cleaning procedure, the pump is run in reverse at a specified speed for a specified time interval, then forward at a specified speed for a specified time interval, this procedure being repeated three times.

16. A method as claimed in any one of claims 13 to 15 wherein if, upon resumption of normal operation it is determined that the pump is still blocked, an alarm is output.

17. A method as claimed in any preceding claim wherein the method includes the step of storing current, pump speed and wet well level values for future reference.

18. A method as claimed in any one of claims 13 to 17 wherein the method also includes the step of storing details of occasions upon which the self cleaning procedure was initiated and/or occasions upon which alarms are output.

19. A control unit for a pump operable to pump sewage from a wet well, the control unit comprising: current detection means; pump speed detection means; wet well level detection means; memory means operable to store a look up table of current, pump speed and wet well level values; and a processor operable to compare each of the detected current, speed and level values with values stored in the look up table to determine whether the pump is blocked.

20. A control unit as claimed in claim 19 wherein the control unit is operable in accordance with the method of any one of claims 1 to 18.

21. A control unit as claimed in any one of claims 19 to 20 wherein the processor is operable to determine a rate of change of any or all of: the current drawn by the pump; the speed of operation of the pump; and the wet well level.

22. A control unit as claimed in claim 21 wherein the processor is then operable to compare the determined rate of change values with rate of change values stored in the look up table to determine whether the pump is blocked.

23. A control unit as claimed in claims 22 wherein the control unit is operable to initiate a self cleaning procedure if it is determined that the pump is blocked.

24. A control unit as claimed in claim 23 wherein if it is determined that the pump is still blocked after the self cleaning procedure, the processor is operable to output an alarm signal.

25. A control unit as claimed in claim 24 wherein the alarm signal is received by an alarm means

26. A control unit as claimed in claim 25 wherein the alarm means is an integral alarm means.

27. A control unit as claimed in claim 25 wherein the alarm means is an external unit with a suitable connection to the control unit.

28. A control unit as claimed in claim 27 wherein the external unit is an external server or computer.

29. A control unit as claimed in claim 28 wherein the memory means is operable to store current, pump speed and wet well level values for future reference.

30. A control unit as claimed in claim 29 wherein the memory means is also operable to store details of occasions upon which the self cleaning procedure was initiated and/or occasions upon which alarms are output.

31. A control unit as claimed in claim 30 wherein the control unit is provided with a user interface.

32. A control unit as claimed in claim 31 wherein the user interface is operable to enable the cancellation of an alarm, the out put of an alarm, the initiation of the self cleaning procedure and the transmission of data stored in the memory means to an external unit.

33. A pump operable in accordance with the method claimed in any one of claims l to 18

34. A pump incorporating a control unit as claimed in any one of claims 19 to 32.

35. A sewage pumping station incorporating a pump as claimed in claim 33 or claim 34.

36. A sewage network incorporating one or more pumping stations as claimed in claim 35.