Patent Publication Number: US-2012039723-A1

Title: Controller for a liquid supply pump

Description:
TECHNICAL FIELD  
     The present invention relates to a controller for operating an electrically driven pump associated with a liquid supply system. It also relates to a method for pressurising a liquid supply in a liquid supply system. The invention is applicable for example to a water supply system in which water is drawn from a source of water, for example a holding tank, dam, reservoir or the like, and is supplied under pressure for household, farm, commercial or industrial use. The invention will be described with reference to its use in a water supply system, however it could also be used in other liquid supply systems. 
     BACKGROUND  
     A reference herein to a patent document or other matter which is given as prior art is not to be taken as an admission that that document or matter was, in Australia, known or that the information it contains was part of the common general knowledge as at the priority date of any of the claims. 
     Households that are not connected to a municipal (mains) water supply may rely upon water supplied from a storage tank and pressurised by a pump. The pump may be activated by a controller which uses detection of pressure to switch the pump on and off, for example two pressure thresholds may be set, that is an upper threshold at which the pump is switched off and a lower or “cut-in” threshold at which the pump is switched on. However if the difference between the two thresholds is relatively large, the pressure fluctuation in the water supply system may be unacceptable. 
     To alleviate this problem, a controller that automatically measures a pump&#39;s maximum output pressure when installed in a system (also known as its closed head pressure) and establishes a lower pressure threshold that is a certain percentage (say 80%) of this maximum output pressure has been proposed—see international publication WO 03/029656 A1 (PCT/AU02/01334). Although this can provide a relatively smaller pressure output variation (for example 20%) than with pre-set pressure thresholds, it may result in a higher “standby” pressure in the household&#39;s water supply system which increases the likelihood of leaks in pipe joints and taps etc. of the water supply system. The pressure drop occasioned by any such leaks with the higher cut-in pressure threshold (that is, the threshold value at which the pump is switched on) can lead to frequent switching on and off (that is, cycling) of the pump—which is undesirable. Thus, choosing the appropriate value of a cut-in (pump on) pressure is a compromise between the pump cycling when set too high and large pressure variation when set too low. 
     One proposal to avoid frequent cycling, such as when there is a slow leak in the water supply system, is to have two pre-set cut-in pressure thresholds, the higher one of which (say 80% of the pump&#39;s output pressure) is set when no leakage is detected, and the lower one of which (say 50% of the pump&#39;s output pressure) is set when leakage in the system is detected, that is when uniform pressure drops and repeat frequencies typical of slow leaks such as a dripping tap for example are detected. 
     Although a re-setting of the cut-in pressure threshold to a lower value may alleviate the slow leak, the householder will again experience a significant variation in supply pressure until the higher cut-in threshold is re-set. Also, the leakage response may be unnecessarily triggered by equipment with a slow but constant demand for water, for example an evaporative cooler. 
     The invention, according to one embodiment, seeks to provide a controller for the pump which alleviates the significant pressure variation problem yet still provides for effective detection of and response to leaks in the liquid supply system. 
     Other embodiments of the invention seek to satisfy other objects. Thus another embodiment seeks to provide a controller having parts that are relatively easily assembleable and may therefore save manufacturing costs. Yet another embodiment seeks to provide a controller through which the liquid flow is directed to allow for improved flow characteristic measurements. A further embodiment seeks to provide a pressure unit which allows an observer (for example a user of a water supply system) to ascertain the status of the pressure within the unit. 
     SUMMARY OF THE INVENTION 
     According to a first embodiment the invention provides a controller for operating a pump associated with a liquid supply system, the controller including: 
     a pressure unit including a housing having an inlet for connection to the liquid supply and an outlet for delivery of the liquid to a consumer, 
     a control circuit mounted on the housing and including a sensor, 
     wherein the pressure unit and the sensor are operatively associated such that the sensor generates signals related to pressures within the pressure unit, 
     and wherein the control circuit is operative to determine from the signals generated by the sensor a rate of pressure change within the pressure unit to vary, in dependence upon the rate of pressure change, a threshold pressure value at which the control circuit is operative to switch on the pump to pressurise the liquid supply for delivery to the consumer. 
     An aspect of the invention which may be associated with the above described first embodiment is the provision of a method for pressurising a liquid supply in a liquid supply system having a closed head pressure, the liquid supply system including a pump for pressurising the liquid supply wherein the pump is operated when the liquid supply pressure falls to a threshold value below the closed head pressure, the method including the steps of:
         (i) determining the closed head pressure of the liquid supply,   (ii) measuring changes in pressure of the liquid supply due to a flow of liquid from the liquid supply,   (iii) calculating a rate of pressure change from the measurements of step (ii),   (iv) varying the threshold pressure value for operating the pump in dependence upon the calculated rate of pressure change,       

     wherein the threshold pressure value is increased for relatively large rates of pressure change and is decreased for relatively low rates of pressure change. 
     The pressure unit may include a diaphragm within the housing and the diaphragm may have a permanent magnet associated therewith to which the sensor is responsive. Such a sensor may be a Hall effect device which generates a variable voltage signal related to pressures within the pressure unit in dependence upon the position of the diaphragm and thereby the permanent magnet. 
     The liquid supply system will have a closed head pressure, and preferably the variable threshold pressure at which the control circuit is operative to switch on the pump is a percentage of the closed head pressure (% cut-in ), and wherein the rate of pressure change 
     
       
         
           
             
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     and the % cut-in  are linearly, logarithmically or exponentially related. 
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     are linearly related between a maximum % cut-in  (for example 90% of the closed head pressure) and a minimum % cut-in  (for example 30% of the closed head pressure) and wherein for pressures above and below, respectively, the maximum and minimum % cut-in  values, the respective % cut-in  value is constant. 
     The water supply system may include an external accumulator, and in this case the % cut-in  may be a function of 
     
       
         
           
             
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     According to a second embodiment, the invention provides a controller for operating a pump associated with a liquid supply system for the pump to pressurise the liquid supply, the liquid supply system having a closed head pressure, the controller including: 
     a pressure unit including a housing having an inlet and an outlet, 
     a diaphragm within the housing which is biased to act against the pressure of the liquid supply between the inlet and the outlet when a liquid supply is connected to the inlet, 
     wherein the bias on the diaphragm is such that the diaphragm remains in substantially one position whilst the liquid supply pressure within the housing is at the closed head pressure, (wherein said one position depends upon the closed head pressure and may differ for the controller in different liquid supply systems), 
     a circuit structure carrying a control circuit for operating the pump for supplying liquid to and through the housing, 
     the control circuit including a sensor which is mounted on the circuit structure such that it is operatively associated with the diaphragm for sensing positions of the diaphragm as the diaphragm moves away from said one position in response to liquid pressures within the housing below the closed head pressure, 
     wherein the sensor provides signals to the control circuit indicative of liquid pressures within the housing for the control circuit, whilst there is a liquid flow through the housing, to operate the pump when the sensor provides a signal indicative of a liquid pressure within the housing that is a predetermined value below the closed head pressure, such that the liquid supply pressure is maintained within a predetermined range from the closed head pressure. 
     The closed head position of the diaphragm (that is, the said “one position”)has a direct relationship with the supply pressure. This allows the controller to automatically adapt to a large range of different pumps and pressures. 
     The sensor may be a Hall effect device which is responsive to a permanent magnet that is associated with the diaphragm, as is described above for the first embodiment. 
     In the first and second embodiments, the circuit structure may include a liquid flow sensor as part of the control circuit, in which case the housing includes an aperture and the circuit structure is mounted on the housing such that the liquid flow sensor is exposed to a liquid flow through the housing from the inlet to the outlet. 
     When the liquid pressure within the housing is the predetermined value below the closed head pressure, the control circuit will operate the pump. The liquid flow sensor provides a flow signal to the control circuit to recognise when there is a liquid flow through the housing and if this signal is present, operation of the pump is continued. However if the flow signal is not present, operation of the pump is stopped after a short time in the order of seconds (e.g. 5 seconds). When liquid flow is present, operation of the pump is continued until the flow stops. Thus primarily the flow signal is used by the control circuit to determine a no-flow condition through the housing at which time the control circuit will turn the pump off. In some circumstances the flow sensor may also be used to turn the pump on when there is sufficient flow through the housing but no detectable pressure change (for example, if there is no water in a system, and hence zero pressure, and then water is returned to the system by, say, rain). 
     Also in both embodiments, the inlet of the housing may include a valve for preventing reverse liquid flow into the inlet. Such a valve may include a moveable closure member which contacts a valve seat when the valve is closed and the moveable closure member may be shaped such that a flow of liquid into the housing when the valve is open is directed towards the liquid flow sensor. 
     According to a third embodiment the invention provides a controller for operating a pump associated with a liquid supply system, the controller including: 
     a pressure unit including a housing having an inlet for connection to the liquid supply and an outlet for delivery of the liquid to a consumer, 
     a circuit structure carrying a control circuit for operating the pump for supplying liquid to and through the housing, the control circuit including a liquid flow sensor, 
     wherein the housing includes an aperture and the circuit structure is mounted on the housing such that the liquid flow sensor is exposed to liquid within the housing, 
     wherein the inlet of the housing includes a valve for allowing a flow of liquid into the housing from the inlet and preventing a reverse flow of the liquid from the housing into the inlet, 
     wherein the valve is shaped such that a flow of the liquid into the housing is directed towards the liquid flow sensor, 
     wherein the liquid flow sensor provides a flow signal to the control circuit to recognise there is a liquid flow through the housing. 
     The above described third embodiment of the invention may include one or more of the additional features associated with either the first or second embodiments of the invention. 
     Preferably the design of the valve and its positioning within and size relative to the housing is such as to minimally affect pressure loss within the housing. 
     In all embodiments, the aperture of the housing may be adjacent the valve, and thus adjacent the inlet, allowing any arrangement and number of outlets. In one embodiment, the inlet and the outlet of the pressure unit may be in-line and the aperture may be laterally located between the inlet and the outlet for the directed liquid flow to pass over the liquid flow sensor. 
     In all embodiments, the circuit structure is preferably a printed circuit board on which the pressure sensor (for example a Hall effect device) and the flow sensor (for example a structure based on thermal techniques) are mounted. 
     According to a fourth embodiment of the invention, there is provided a pressure unit for a liquid supply system for delivery of the liquid to a consumer, the liquid supply system having a closed head pressure, the pressure unit including: 
     a housing having an inlet and an outlet, a diaphragm within the housing which is biased to act against the pressure of the liquid supply between the inlet and the outlet when a liquid supply is connected to the inlet, 
     wherein the bias on the diaphragm is such that the diaphragm remains in substantially one position whilst the liquid supply pressure within the housing is at the closed head pressure (wherein said one position depends upon the closed head pressure and may differ for the controller in different liquid supply systems) and the diaphragm moves away from said one position when the liquid supply pressure within the housing decreases, 
     wherein the diaphragm is associated, on its side that is not exposed to the liquid supply, with a moveable member having pressure indicia, 
     wherein the housing includes a window and the window and moveable member are such that for the diaphragm in said one position a pressure indicium indicating the closed head pressure is exposed through the window and for movement of the diaphragm away from said one position, a pressure indicium indicating a decreased pressure is exposed through the window. 
     The indicia that are viewable through the window advantageously provide a relatively simple means for several pieces of information as to the liquid supply pressure condition within the pressure unit to be conveyed to a consumer without providing a quantitative pressure measurement. Thus it shows whether liquid is available—for example, if there is no liquid, the pressure will be zero and this could be indicated by red indicia being exposed in the window. For normal pressures, the exposed indicia could be green and if, for example, there is a leaking tap, and thereby reducing pressure within the pressure unit, the associated movement of the diaphragm may be indicated by green to red indicia being exposed. Use of quantitative pressure measurements is deliberately avoided because there may be a range of “normal” operating pressures which may not be realised by consumers. 
     For a better understanding of the various embodiments of the invention and to show how they may be performed, a preferred embodiment will now be described, by way of non-limiting example only, with reference to the accompanying drawings. It is to be understood that various of the features of the preferred embodiment may be omitted to realise exemplifications of the first to fourth embodiments of the invention as broadly described above. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a liquid supply system with which the preferred embodiment is useable. 
         FIG. 2  is an isometric view of a controller according to the preferred embodiment. 
         FIG. 3  is an exploded view of the controller of  FIG. 2  viewed from one direction. 
         FIG. 4  is an exploded view of the controller of  FIG. 2  viewed from another direction to that of  FIG. 4 . 
         FIGS. 5 and 6  are longitudinal cross-sections of the controller of  FIG. 2  illustrating its diaphragm in two different locations. 
         FIGS. 7 and 8  are transverse cross-sectional views through a pressure chamber of the controller of  FIG. 2 , illustrating the inlet and outlet and a valve arrangement therewith,  FIG. 7  illustrating the valve in a closed position and  FIG. 8  illustrating the valve in an open position. 
         FIGS. 9 and 10  are isometric views of a portion of the controller of  FIG. 2  illustrating the valve arrangement in two positions, similarly to  FIGS. 7 and 8 . 
         FIG. 11  is a block diagram illustrating functions of an electronic control circuit of the controller of  FIG. 2 . 
         FIG. 12  is a circuit diagram of the control circuit. 
         FIGS. 13 and 14  are graphs illustrating operational regimes for a controller of  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  illustrates a simple liquid supply system  20  with which the embodiment of a controller to be described below may be associated. The liquid supply system is a water supply system and the preferred embodiment will hereinafter be described with reference to its use in such a system. 
     The water supply system  20  includes a reservoir  22  for a supply for the water  23 , for example a household rainwater tank, having a pump  24  driven by an electric motor  26  in an outlet for pumping the water to various consuming outlets  28 , for example a tap, toilet, shower and/or laundry. The electric motor  26  of the pump  24  is controlled via a controller  30  which controls the operation of the pump  24  based upon water pressure and water flow parameters that are determined via the controller  30 . 
     As shown in  FIGS. 2 to 6  the controller  30  includes a pressure unit  32 , which is made up of a housing  34  having an inlet  36  for connection to the water supply from the pump  24  and an outlet  38  for delivery of the water to the consumer devices  28 . The figures show a priming cap  128  screwed onto the outlet  38 . In use, the outlet  38  would be connected to a pipe leading to the consuming outlets  28 . The housing  34  may also include additional outlets for supply of water to additional consumers, for example a second outlet  130  is illustrated. If only one outlet  38  is to be used, the additional outlets would be blocked, for example by priming caps  128 . The housing  34  is composed of three portions, that is, an end portion  34   a  which principally contains a helical compression spring  42 , an intermediate portion  34   b  which principally defines a pressure chamber  44  and a cover portion  34   c.    
     The housing  34  contains a diaphragm  40  which is biased via the helical compression spring  42  to act against the pressure of the water within the pressure chamber  44  between the inlet  36  and the outlet  38  when a water supply is connected to the inlet  36 . Thus the portion  34   b  of the housing  34  and the diaphragm  40  define the pressure chamber  44  with which the inlet  36  and the outlet  38  (which are formed in the intermediate portion  34   b  of housing  34 ) are in communication. The end portion  34   a  of the housing  34  and the diaphragm  40  define another chamber  46  within which the spring  42  is located. A still further chamber  48 , which is adjacent to the pressure chamber  44  and opposite the diaphragm  40 , is defined by the intermediate portion  34   b  and the cover portion  34   c  of the housing  34 . A circuit structure  50  carrying a control circuit  140  (to be described in detail below with reference to  FIGS. 11 and 12 ) is mounted within the chamber  48 . 
     The end portion  34   a  of housing  34  includes an inwardly extending tubular part  52  (see  FIGS. 5 and 6 ) over which the spring  42  locates. A guide member  54  for operative association with the housing  34  end portion  34   a,  the spring  42  and the diaphragm  40  comprises a central stem  56  which extends through a cylindrical part  58  having an end cap  60 . One end of the spring  42  locates over the inwardly extending tubular part  52  of the housing end portion  34   a  and the other end locates within the annular space between the rearward portion of the stem  56  and the cylindrical part  58  of the guide member  54 , with part of the rearward portion of the stem  56  fitting inside the inwardly extending tubular part  52  and able to slide therein. The outside diameter of the cylindrical part  58  of the guide member  54  is sized such that it also is a sliding fit within an internal diameter defined by ribs  62  in the housing  34  end portion  34   a  that surround the inwardly extending tubular part  52 . The guide member  54  furthermore includes an outermost cylindrical skirt  59  which is shorter than the cylindrical part  58  and provides an end rim  61  which serves a purpose to be described below. 
     The end cap  60  of the guide member  54  provides a solid supporting seat for a raised central area  64  of the diaphragm  40 . The diaphragm  40  has an outwardly flared wall  66  (best seen in  FIG. 5 ) which extends from the periphery of its central area  64  and which joins with a curved outer wall  68  having a circumferential flange  70 . The flange  70  formation seats within a complementary shaped recess  72  defined by the housing  34  end portion  34   a  and is clamped in position by a complementary shaped facing end  74  of a rib  76  on the housing  34  intermediate portion  34   b  when the housing  34  is assembled. The contact regions between the flange  70  of the diaphragm  40  and the complementary recess  72  of the end portion  34   a  and the end  74  of rib  76  of the intermediate portion  34   b  are such that when the pressure chamber  44  contains water under pressure, the junctures are sealed to prevent the pressurised water from leaking into the spring chamber  46 . 
     The diaphragm  40  also includes, protruding centrally from its central area  64 , a blind cylindrical extension  78 , within which fits the forward portion of the stem  56  of the guide member  54 . A permanent magnet  80  is mounted within the stem  56  at its forward end. 
     The inlet  36  and the outlet  38  of the pressure chamber  44  include there between a valve arrangement  82  for allowing water to flow into the pressure chamber  44  of the housing  34  from the inlet  36  and preventing a reverse flow of the water from the pressure chamber  44  into the inlet  36 . The valve  82  includes a closure member  84  which is held captured within a tubular part  85  which fits through and screws into an internal thread of the outlet  38 . The tubular part  85  includes legs  86  having a smaller diameter ring  87  at their ends which captures the closure member  84  whilst allowing it to reciprocate towards and away from the inlet  36 . The closure member  84  includes a shaped end  88  (which is generally conical with a rounded apex—best seen in  FIG. 8 ) which has a peripheral groove that retains an O ring  91 . The O ring  91  seals onto a valve seat  90  on the inlet  36 . A helical compression spring  92  (see FIGS.  7  and  8 —the spring  92  has been omitted from the other figures for clarity) surrounds the smaller diameter ring  87  of the tubular part  85  and acts between the ends of the legs  86  and a rear surface  89  of the shaped end  88  of the closure member  84  to bias the closure member  84  towards the inlet  36  into engagement with the valve seat  90 . 
     The inlet  36  comprises a conduit  94  which extends into the pressure chamber  44  and is moulded as part of the intermediate portion  34   b  of the housing  34 . A connector fitting  96  (see  FIGS. 3 and 4 ), which includes at one end a screw thread  98  and a nut formation  100  and at the other end the valve seat  90  below which is a groove  102 , is fitted through the conduit  94  and held captive therein by a circlip  104  which sits within the groove  102  and bears upon an end rim of the conduit  94  within the pressure chamber  44 . Thus the connector fitting  96  is rotatable within the conduit  94  which allows ready attachment of piping from the pump  24  onto the threaded end  98 . 
     In normal operation of the pressure unit  32  with pressurised water within the pressure chamber  44  and the pump  24  not operating and water present at the inlet  36 , the closure member  84  of the valve arrangement  82  is held in sealing engagement against the valve seat  90  of the inlet  36  by the pressure of the water acting on the rear surface  89  of the closure member  84  assisted by the spring  92 , thus preventing flow of the water from the pressure chamber  44  into the inlet  36 . When the pump  24  is operated, water is pumped into the inlet  36  until its pressure increases sufficiently to force the shaped end  88  of the closure member  84  to unseat from the valve seat  90  and thus open the valve arrangement  82  for the water to be pumped through the pressure chamber  44  from the inlet  36  into the outlet  38 . 
     The design of the valve arrangement  82  and more particularly the shaped end  88  of the closure member  84  within the pressure chamber  44  (which is relatively large compared to the valve arrangement  82 ) is such that there is minimal loss of head through the pressure chamber  44 . 
     The wall  105  of the intermediate portion  34   b  of the housing  34  opposite to the diaphragm  40  includes an aperture  106  for a purpose to be described below. 
     The circuit structure  50  mounted within the chamber  48  is a printed circuit board  108  which includes a liquid flow sensor. The flow sensor is of the type that operates based on thermal techniques and includes sources of heat such as resistive heater elements and temperature sensors, such as thermistors. Examples of such sensors are disclosed in International Publications WO 91/19170 (PCT/AU91/00239) and WO 03/029656 (PCT/AU02/01334). 
     The electronic circuitry of the flow sensor of the present embodiment is described in detail below with reference to  FIGS. 11 and 12 . Structurally, the flow sensor comprises a metal plate  110  (see  FIGS. 3 and 4 ) onto an insulating layer on a rear surface of which the heater elements and thermistors are mounted. The printed circuit board  108  includes an aperture  112  and the metal plate  110  is attached to the printed circuit board  108  over the aperture  112  such that its uninsulated front surface, when the printed circuit board  108  is mounted within the chamber  48  via posts  109  and the cover portion  34   c,  is exposed to water flow within the pressure chamber  44  via the aperture  106 . A ring seal  114  is located within the chamber  48  between the periphery of the aperture  106  and the metal plate  110  of the printed circuit board  108  to prevent leakage of water from the pressure chamber  44  into the chamber  48  within which the circuit structure  50 , that is the printed circuit board  108  is mounted. 
     The purpose of the shaped end  88  of the closure member  84  of the valve arrangement  82  is to direct water flow entering the pressure chamber  44  from the inlet  36  towards the flow sensor, that is towards and over the surface of the metal plate  110  which is exposed through the aperture  106 . The flow sensor provides a flow signal to the control circuit  140  (to be described below with reference to  FIGS. 11 and 12 ) to recognise there is a water flow through the pressure chamber  44  of the housing  34  for the control circuit  140  to continue to operate the electric motor  26  of the pump  24 . 
     As shown in  FIG. 11  the control circuit  140  also includes water pressure detection circuitry  146  which includes a Hall effect device  116  as a sensor (see  FIGS. 3 ,  5  and  6 ). The Hall effect device  116  is mounted on the printed circuit board  108  such that when the printed circuit board  108  is mounted within the chamber  48 , the device  116  is located closely adjacent to wall  105  of the housing  34  intermediate portion  34   b  and is positioned to lie on the central axis of the diaphragm  40 /guide member  54  arrangement, such that it is influenced by the magnetic field of the permanent magnet  80  that is mounted at the forward end of the stem  56  of the guide member  54  as the diaphragm  40  moves. Thus, as the water pressure within the pressure chamber  44  decreases, the permanent magnet  80  moves towards the Hall effect device  116  and as the liquid pressure increases, the permanent magnet  80  moves away from the Hall effect device  116 . When a current is flowing through the Hall effect device  116 , the movement of the permanent magnet  80  and thereby its magnetic field relative to it generates voltage signals which, as will be described below, are utilised to determine rates of pressure change within the pressure chamber  44  of the pressure unit  32 . 
     Two limits are defined for the movement of the diaphragm  40 /guide member  54  arrangement. One limit, for high pressure within the pressure chamber  44 , is set by the end rim  61  of the outer most cylindrical skirt  59  of the guide member  54  bearing upon a step  118  inside the end portion  34   a  of the housing  34  (see  FIG. 6 ). The other limit, for low pressure within the pressure chamber  44 , is set by a laterally extending head  122  of a screw  120  in the rearward end of the stem  56  of the guide member  54  bearing against a shoulder  124  formed within the bore of the inwardly extending tubular part  52  of the end portion  34   a  of the housing  34  (see  FIG. 5 ). A protective cap  126  is fitted to the end portion  34   a  to close the bore of the tubular part  52 . 
     As shown in the exploded views of  FIGS. 3 and 4 , a sealing ring  132  is interposed between the intermediate portion  34   b  and the cover portion  34   c  of the housing  34  to ensure that the circuit structure  50  is sealed within the chamber  48 . 
     The control circuit  140  comprises several sections that serve different functions, as shown by the functional blocks in  FIG. 11 . Thus there is a microcontroller and its support circuitry  142 , and power supply circuitry  144  for operating the various functions via the microcontroller. There is water pressure detector circuitry  146 , of which the Hall effect device  116  is a component, and water flow detector circuitry  148  of which the metal plate  110  is a part. The microcontroller and support circuitry  142  determines the operation of pump driver circuitry  152  for operating the pump  24  via its electric motor  26 . Additionally there is LED and LED driver circuitry  154  for indicating various control conditions. 
     With reference to  FIG. 12 , the water flow detector circuitry  148  is made up of resistors (H 1 , H 2 , H 3 , R 12 , R 15 , R 19 , R 22  and R 23 ), thermistors (TH 1 , TH 2  and TH 3 ), capacitors (C 10 , C 11  and C 12 ) and transistor Q 3 . 
     The resistors H 1 , H 2  and H 3  are mounted on the rear surface of the metal plate  110  over an insulating layer and are connected in series and form the basis of the primary heat source. The power dissipated by these three resistors is regulated by the microcontroller IC 1 , through pulse width modulation on the switching of the transistor Q 3 . The three thermistors, TH 1 , TH 2  and TH 3 , are strategically located on the metal plate  110  of the printed circuit board  108 , also over the insulating layer, and are designed to measure the temperature at the surface on which they are mounted. As the insulating layer of the metal plate  110  is a poor thermal conductor, the power dissipated by the resistors, H 1 , H 2  and H 3 , will be distributed unevenly along the surface of the metal plate  110 , hence the three thermistors, TH 1 , TH 2  and TH 3  will register slightly different temperature measurements. The microcontroller IC 1  continuously monitors the temperature differential between the thermistors TH 1  and TH 2 . The metal plate  110  of the printed circuit board  108  is in constant contact with water, hence water flow will improve the thermal conduction along the surface of the metal plate  110  and a reduction in the temperature differential between TH 1  and TH 2 . The microcontroller IC 1  will use this information in an algorithm to determine whether water is flowing or not. The thermistor TH 3  is used to compensate for an additional temperature effect due to the Triac Q 1  while the pump is in operation. 
     The water pressure detector circuitry  146  comprises the integrated circuit IC 2  and capacitor C 13 . The integrated circuit IC 2  is a Hall effect device that translates the magnetic field it senses from the permanent magnet  80  into an analogue voltage that is presented to pin  2  of the microcontroller IC 1 . 
     The pump driver circuitry  152  comprises resistors (R 4 , R 6 , R 7 , R 8 , R 9  and R 10 ), transistor Q 2 , Triac Q 1  and integrated circuit IC 6 . When a logic high level signal is outputted at pin  7  of IC 1 , transistor Q 2  will switch on and cause current to flow through the LED of the optocoupler IC 6 . This forward current that flows through the LED will generate infrared radiation that triggers the detector. Once triggered, the detector stays latched in the “on state” until the current through the detector drops below the specified holding current. The detector&#39;s “on state” will cause sufficient current to flow into the gate of the Triac Q 1  and cause it to switch on and start conducting, hence operating the pump motor. A logic low level signal outputted at pin  7  of IC 1  will switch off transistor Q 2  and subsequently the pump motor. 
     The microcontroller and support circuitry comprises the integrated circuit IC 1 , resistors (R 5 , R 11 , R 24 ) and capacitor (C 1 ). The integrated circuit IC 1  is an  8 -bit microcontroller with flash memory. With the firmware loaded into its flash memory, IC 1  will perform the control algorithm. 
     The power supply circuitry  144  comprises the Varistor (VDR 1 ), capacitors (C 2 , C 3 , C 4 , C 5 , C 6 , C 7 , C 8 , C 14 , C 15 , C 17  and C 18 ), resistors (R 1 , R 16 , R 25 , R 26 , R 27 , R 28 , R 29  and R 30 ), diodes (D 1 , D 2 , D 3 , D 4 , D 5 , D 6 , D 7 , D 8 , D 9  and D 10 ), inductors (L 1  and L 2 ), transformer (T 1 ) and integrated circuits (IC 3 , IC 4  and IC 5 ). VDR 1  and C 1  provide protection against electrical noise spikes at the mains supply input. Diodes D 1 , D 2 , D 3  and D 4  form a full bridge rectifier which rectifies the input mains supply voltage to a full-wave rectified DC voltage. Components C 2 , L 1  and C 3  form a pi-filter network that provides filtering to the rectified DC voltage from the bridge rectifier a well as differential mode EMI filtering. 
     A flyback power supply is formed by the integrated circuit (IC 3 ), resistors R 16 , R 25 , R 26 , R 27  and R 28 , diodes D 5 , D 6  and D 10 , capacitors C 4 , C 18  and C 19  and transformer T 1 . Diode D 5 , capacitors C 3 , C 5 , and resistors R 26  and R 27  form a clamp circuit limiting the leakage inductance turn-off voltage spike on pin  4  of IC 3  to a safe value. The rectified and filtered input voltage is applied to the primary winding, pin  1 , of the transformer T 1 . The other side of the transformer primary, pin  2 , is driven by the integrated circuit IC 3 . 
     The AC voltage at the secondary winding of the transformer T 1  is half-wave rectified by the diode D 9  and converted into a filtered DC voltage by a pi-filter comprised of L 2 , C 15  and C 14 . The filtered DC voltage is regulated by the zener diode D 7 . When the filtered DC voltage exceeds the sum of the zener diode&#39;s voltage and optocoupler LED forward voltage, current will flow in the coupler LED and will cause the transistor of the optocoupler to sink current. When this current exceeds the threshold level at pin  1  of IC 3 , IC 3  will inhibit the next switching cycle. When the filtered DC voltage falls below the threshold, IC 3  will initiate a conduction cycle and by adjusting the number of enabled cycles, output regulation is maintained. 
     Components D 6 , R 28 , R 16 , C 4 , D 10  and C 18  provide over-voltage protection to the power supply. When an over-voltage condition occurs and the bias voltage exceeds the sum of the zener diode&#39;s voltage, D 10 , and the threshold voltage level at pin  2  of IC 3 , current begins to flow into pin  2  of IC 3 . When this current exceeds the threshold of IC 3 , IC 3  will shut down until the voltage level at pin  2  of IC 3  drops below a pre-determined level. 
     The AC voltage across the pins  10  and  8  of the transformer T 1  is half-wave rectified by the diode D 8  and converted into a filtered DC voltage level by capacitors C 6  and C 7 . The integrated circuit IC 5  is a voltage regulator that converts the filtered 
     DC voltage at its input pin  3  into a regulated lower voltage level, say 5 Vdc, suitable for the rest of the electronics to operate in. The capacitor C 8  provides further filtering at the output of IC 5  to eliminate any voltage level fluctuations. 
     The resistors (R 13 , R 14  and R 17 ) and LEDs (LD 1 , LD 2  and LD 3 ) form the LED and LED driver circuitry  154 . A high logic level at pin  3 , pin  9  and pin  15  of IC 1  will turn on the LED LD 1 , LD 2  and LD 3  respectively. Resistor R 24  and push button S 1  form the user input circuit. Pressing S 1  will present a logic level low signal at pin  11  of IC 1 . 
     Upon installation of a controller  30  in a water supply system  20 , the pump  24  is operated to establish a closed head pressure for the system, that is the maximum water pressure within the pressure unit  32  that is established with all of the consuming outlets  28  closed. The pump  24  is then turned off and the pressure unit reverts to a normal standby condition wherein, as illustrated by  FIG. 6 , the diaphragm maintains a first position against the bias of the spring  42  whereat the magnet  80  is maximally spaced from the Hall effect device  116  and, as illustrated by  FIG. 7 , the valve arrangement  82  is closed. When a consuming outlet  28  is open, the pressure within the pressure chamber  44  reduces and the diaphragm  40  (and thus the magnet  80 ) is moved by the bias of spring  42  towards the Hall effect device  116  (see  FIG. 5 ) and thus the pressure drop is detected. So long as there is prime at the inlet  36 , the valve arrangement  82  will open (see  FIG. 8 ) and water will flow over the metal plate  110 , thus a water flow will be detected by circuitry  148 . When the pressure within the pressure chamber  44  reduces to some predetermined level of pressure below the closed head (called the cut-in pressure) the pump driver circuitry  152  of the control circuit  140  will switch on, via the Triac Q 1 , the electric motor  26  and thus the pump  24 , provided the water flow detector circuitry  148  detects water flow over the metal plate  110  and the water level detector circuitry  150  detects that there is a supply of the water. The switching on of the pump  24  ensures that the water supply pressure in the water supply system  20  is maintained within a predetermined range from the closed head pressure. When the consuming outlet or outlets  28  is/are closed, the flow signal ceases and the controller  30  reverts to the normal standby condition. 
     In the fault situation of a loss of prime at the inlet  36 , the bias of the diaphragm registers zero pressure, no water flow will occur over the metal plate  110  and thus there will be no detection of flow by the water flow detector  148  and the pump will be switched off after possibly being on for a very short period. 
     In another fault situation of a leak in the water supply system  20 , for example a dripping tap  28 , then from the standby condition of the controller  30 , there will occur a slow loss of pressure within the pressure chamber  44  which will result in movement of the diaphragm  40  (and thus its associated magnet  80 ) towards the Hall effect device  116  and thus detection of the reducing pressure via the circuitry  146 . According to an embodiment of the present invention, such detection of the reducing pressure is operative to vary the cut-in pressure, that is, generally to reduce it to avoid frequent switching on and off of the pump  26 . 
     The LED and LED driver circuitry  154  is operative for the LEDs to indicate different conditions, for example green for “on”, red for “standby” and yellow for “fault”. The push button  51  is a manual start button for priming the pump. 
     In the preferred embodiment of the present invention, the control circuit  140  is operative to determine from the signals generated by the Hall effect device  116 , a rate of pressure change within the pressure unit  32  (specifically within the pressure chamber  44 ) to thereby vary the threshold pressure value at which the control circuit  140  is operative to switch on, via the Triac Q 1 , the electric motor  26  of the pump  24  to pressurize the water supply  23  for delivery to the consumer. The rate of pressure change may be determined by the microprocessor from, for example, five voltage readings from the Hall effect device  116  per second. Thus, if the demand from consuming outlets  28  is high, there will be a large rate of pressure change and the cut-in pressure threshold can be high, whereas if the consumer demand is such as to create a slow rate of pressure change, such as for example may be caused by a leaking tap  28 , then the cut-in pressure threshold can be low. Thus a cut-in pressure can be determined as a percentage of the closed head pressure (% cut-in ) dependent upon a rate of change of pressure ( 
     
       
         
           
             
               
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     where P is pressure and t is time). 
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     can be linear, for example as shown by line  160  of the graph of  FIG. 12 . Alternatively it may for example be logarithmic (see curve  162  of  FIG. 12 ) or exponential (see curve  164  of  FIG. 12 ). 
     Also the relationship need not be a continuous function, for example a maximum and/or a minimum % cut-in  (for example 90% and 30% respectively as illustrated by the graph of  FIG. 13 ) may be provided where values respectively above and below these % cut-in&#39;s  are set to a constant value. The relationship  116  illustrated by  FIG. 13  is linear between the maximum and minimum % cut-in  values. 
     A water supply system  20  may include a relatively large external accumulator tank (not shown). If such an accumulator tank is present in the system  20 , the rate of pressure change will be slower for any given flow rate than in a system without such a tank. The controller  30  may be adapted for such a system by making the % cut-in  a function of not only the rate of change of pressure but also the water flow rate, for example: 
     
       
         
           
             
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     where Q is the volumetric flow 
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     With this regime, the higher the flow rate Q or the rate of change of pressure, the higher the cut-in percentage and vice versa. Of course, how the two parameters of flow rate Q and the rate of change of pressure 
     
       
         
           
             
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     are combined and weighted would be tailored to suit the target water supply system. 
     The controller  30  may include indicia viewable by a consumer to give an indication as to the water supply pressure condition within the pressure chamber  44 . Thus, as shown in  FIG. 2 , the housing portion  34   a  may include a window  170  and the guide member  54  may include, on its outermost cylindrical skirt  59 , indicia  172  that are viewable through the window  170 . The visible indicia may be green for the diaphragm  40 /drive member  54  arrangement positioned as illustrated in  FIG. 6  (that is for normal pressure within the pressure chamber  44 ) and may show red for pressures that are reduced, for example for the diaphragm  40 /guide member  54  arrangement positioned as illustrated in  FIG. 5 . 
     It is envisaged that a controller  30  according to embodiments of the invention may be used for “mains boosting”, that is, for example with a mains supply system to a household where the mains pressure is low or unacceptably variable. Using the control regime described above and with the mains pressure applied to the pressure chamber  44 , so long as the mains pressure is above a threshold cut-in value, the pump will not start. However should the pressure fall below the cut-in pressure, then according to the rate of pressure change, the pump will be started at some lower threshold ready to boost the supply pressure. 
     The preferred embodiment described above is illustrative of the various embodiments of the invention as initially summarised. These generally described embodiments, and the specifically described preferred embodiment, are susceptible to variations, modifications and/or additions other than those specifically described and it is to be understood that the invention in all its various embodiments includes all such variations, modifications and/or additions which fall within the scope of the following claims.