CONTROL SYSTEM FOR A PUMP, IN PARTICULAR OF A HOUSEHOLD APPLIANCE

Abstract

 The control system (1) comprises a first sensor (12) intended for being crossed by a flow of liquid directed towards the inlet of the pump (100) and configured to output a first signal (S1) indicative of the flow of liquid. There is a second sensor (14) intended for being crossed by the flow of liquid and configured to output a second signal (S2) indicative of the flow of liquid. A control unit (16) is configured to receive the signals (S1, S2) and command the execution of at least one predefined operation as a function of the signals (S1, S2).

Description

Technical field

[0001] The present invention relates to a control system for a pump, in particular of a household appliance such as a beverage-making machine.

Technical background

[0002] Pumps are commonly used for delivering fluids, particularly in household appliances. A typical application of such pumps concerns the supply of water intended for alimentary use, e.g. for beverage-making machines, such as coffee-making machines. Some examples of such pumps are described in patent publications WO 2019/166954 A1, WO 2019/166955 A1 and WO 2019/166956 A1, all by the same Applicant. In such patent publications, the pumps are, advantageously, of the vibration type.

[0003] Household appliances generally include a tank from which the pump draws water. Typically, during the operation of such pumps, it is important to reliably and accurately monitor the water flow entering the vibration pump and, accordingly, to suitably and safely control said vibration pump and/or the household appliance it is associated with.

Summary of the invention

[0004] It is one object of the present invention to provide a control system capable of effectively monitoring the flow of water directed towards the pump, so that the pump and/or the household appliance it is associated with can be controlled in an improved and safer manner compared with the prior art. In particular, according to a further object of the present invention, it is advantageously possible to prevent the pump from operating "dry", i.e. in a condition in which there is no liquid that can be drawn from the tank. First and foremost, this aspect is important to prevent the internal mechanisms of the pump from suffering damage due to the absence of water. This aspect is particularly important for vibration pumps. In fact, when a vibration pump operates in a dry condition, the coil of the electromagnetic actuator that controls the vibration pump will overheat, also because the generated heat will not be dissipated by the (inexistent) water flow. For this reason, a thermal protection device is generally associated with the coil, which will prevent the pump from operating in such an abnormal condition. Moreover, excessive overheating (e.g. ca. 180°C) may mechanically damage the walls within which the ferromagnetic core of the vibration pump is configured to slide. The high reliability of the system made in accordance with this preferred and advantageous aspect of the present invention makes it unnecessary to employ a thermal protection device in order to protect the system from abnormal operation.

[0005] According to the present invention, these and other objects are achieved through a control system having the technical features set out in the appended independent claim.

[0006] It is understood that the appended claims are an integral part of the technical teachings provided in the following detailed description of the present invention. In particular, the appended dependent claims define some preferred embodiments of the present invention that include some optional technical features.

[0007] Further features and advantages of the present invention will become apparent in light of the following detailed description, provided herein merely as a non-limiting example and referring, in particular, to the annexed drawings as summarized below.

Brief description of the drawings

[0008] 

Figure 1 is a block diagram of a control system for a pump, in particular a vibration pump, made in accordance with an exemplary embodiment of the present invention.

Figure 2 is a perspective view of a detection device made in accordance with an exemplary embodiment of the present invention. The illustrated detection device is included in the control system shown in Figure 1.

Figures 3 and 4 are perspective views of the detection device shown in Figure 2, wherein such detection device is viewed from the rear and from the front, and wherein at least part of the casing has been removed to show internal elements and components.

Figure 5 is a side elevation sectional view of the detection device of the preceding figures; the section runs along the sectional lines V-V shown in Figures 2 and 6.

Figures 6 and 7 are front and rear elevation sectional views of the detection device shown in the preceding figures, wherein the sections run along the lines VI-VI and VII-VII, respectively, shown in Figure 5.

Figures 8 and 9 are partial elevation sectional views of the detection device shown in the preceding figures, wherein such sections run diametrically with respect to an axis of rotation of an impeller of the system.

Detailed description of the invention

[0009] With particular reference to Figure 1, numeral 1 designates as a whole a control system made in accordance with an exemplary embodiment of the present invention.

[0010] Furthermore, with particular reference to Figures 2 to 9, numeral 10 designates as a whole a detection device made in accordance with an exemplary embodiment of the present invention. In the illustrated embodiment, device 10 can advantageously, but not necessarily, be combined with control system 1.

[0011] System 1 is intended for installation on a pump, which is, advantageously but not necessarily, a vibration pump 100. In particular, vibration pump 100 is configured to deliver water into a household appliance. More in particular, vibration pump 100 is configured to deliver water into a beverage-making machine, such as a hot-beverage infusion machine. Typically, the household appliance includes a tank intended to contain an amount of water that vibration pump 100 is configured to deliver in a controlled manner.

[0012] By way of non-limiting example, vibration pump 100 may be of the type described in patent publications WO 2019/166954 A1, WO 2019/166955 A1 and WO 2019/166956 A1 by the present Applicant. For brevity's sake, vibration pump 100 will not be described in detail herein.

[0013] As an alternative, the pump may be different from vibration pump 100 described and illustrated herein; for example, it may be a gear-type pump.

[0014] As aforementioned, system 1 may comprise, for example, detection device 10 shown in Figures 2 to 9. Nevertheless, as will become apparent from the present description, system 1 may use detection devices or means other than device 10 that will be described in detail herein.

[0015] System 1 comprises a first sensor intended for being crossed by a flow of water directed towards the inlet of vibration pump 100. Preferably, the first sensor is a flow meter 12.

[0016] System 1 comprises also a second sensor intended for being crossed by the above-mentioned flow of water directed towards the inlet of vibration pump 100. Preferably, the second sensor is a conductivity sensor 14.

[0017] A control unit 16 is also provided, which co-operates with flow meter 12 and conductivity sensor 14, as will be described hereinafter.

[0018] Flow meter 12 is configured to output a first signal indicative of a flow of water. Preferably, the first signal is a flow signal S1 indicative of the rate of the flow of water. In particular, the water may come from the tank to which vibration pump 100 is connected.

[0019] Conductivity sensor 14 is configured to output a second signal indicative of the presence of water (and/or of a flow of water).

[0020] Preferably, the second signal is a conductivity signal S2 indicative of the electric conductivity of the flow of water.

[0021] Control unit 16 is configured to receive flow signal S1 and conductivity signal S2 and command the execution of one or more predefined operations as a function of signals S1, S2. According to one embodiment of the present invention, control unit 16 may be, for example, integrated into system 1. According to an alternative embodiment, control unit 16 may belong to a motherboard of the household appliance in which vibration pump 100 is installed. According to yet another embodiment of the present invention, control unit 16 may be functionally distributed among a plurality of control modules, e.g. including a first control module integrated into system 10 and a second control module integrated into the motherboard of the household appliance in which vibration pump 100 is installed; in this latter case, the first control module may contribute, together with sensors 12, 14, to processing signals S1, S2 and transmitting them to the second control module, while the second control module may contribute to controlling vibration pump 100 according to signals S1, S2 received from the first control module.

[0022] By exploiting the information carried by signals S1 and S2, it is possible to reliably and redundantly monitor the flow of water directed towards vibration pump 100 and to suitably control the operation of the latter. In fact, the simultaneous monitoring of both a first parameter, preferably referring to the water flow rate, and a second parameter, preferably referring to the electric conductivity of the water flow, makes it possible to control vibration pump 100 and/or the household appliance it is associated with in a safer, more redundant and more effective manner, particularly also in accordance with the information that follows.

[0023] As mentioned above, in further embodiments of the present invention the first and second sensors must not necessarily be flow meter 12 and conductivity sensors 14, but may be sensors of different types and/or differently combined than described and illustrated herein. For example, the first sensor and the second sensor may also be two flow meters situated in distinct positions and anyway co-operating with control unit 16. In general, each one of the first and second sensors is configured to output a signal indicative of a flow of liquid and/or of the presence of the liquid.

[0024] Preferably, the predefined operation commanded by control unit 16 comprises a deactivation of vibration pump 100.

[0025] In the embodiment illustrated herein, the deactivation of vibration pump 100 is triggered by control unit 16 when said control unit 16 detects at least one of the following conditions:

a) flow signal S1 is representative of substantially no flow of water (in particular, it is representative of a water flow rate below a predefined flow rate threshold value), and

b) conductivity signal S2 is representative of substantially no flow of water (in particular, it is representative of an electric conductivity below and/or above a predefined conductivity threshold value).

[0026] In other words, the deactivation of vibration pump 100 is triggered by control unit 16 when flow signal S1 is indicative of the absence of flow (i.e. a substantially null flow) of water through flow meter 12 and/or when conductivity signal S2 is indicative of the absence of water in proximity to conductivity sensor 14.

[0027] The deactivation of vibration pump 100 can be obtained by control unit 16, for example, by interrupting the supply of current to the solenoid of an electromagnetic actuator controlling the reciprocating motion of a plunger containing ferromagnetic material of vibration pump 100. In particular, the interruption of the current supply may occur in a per se known manner through the activation, by control unit 16, of a relay co-operating with a triac. Also, the current supply interruption occurs at the end of a normal beverage preparation cycle.

[0028] As already partly mentioned above, in the embodiment described herein the predefined flow rate threshold value and/or the predefined conductivity threshold value are indicative of a reduced or substantially null flow of water directed towards said vibration pump 100. In particular, both threshold values are indicative of a substantially null flow of water, i.e. a substantially "dry" operation of the vibration pump.

[0029] It is thus advantageously possible to prevent vibration pump 100 from operating in the absence of water, which would otherwise result in the above-mentioned problems. This dual monitoring of both signals S1, S2 makes it possible to turn off vibration pump 100 even should any one of flow meter 12 and conductivity sensor 14 be inoperative and/or malfunctioning. Moreover, this measure makes it unnecessary to install a thermal protector typically associated with vibration pump 100 (e.g. with the solenoid of the electromagnetic actuator), since system 1 ensures sufficient intrinsic safety.

[0030] Optionally, the predefined operation further comprises outputting a fault indication. In particular, the fault indication is triggered by control unit 16 when said control unit 16 detects only one of the above-described condition a) and condition b).

[0031] In fact, in case of "dry" operation of the pump, control unit 16 should detect both conditions a) and b) from both signals S1 and S2. More in detail, if condition a) occurs without the simultaneous occurrence of condition b), this probably means that either one of flow meter 12 and conductivity sensor 14 is malfunctioning or that there is a problem concerning the hydraulic continuity between flow meter 12 and conductivity sensor 14. The same is also true if condition b) occurs without the simultaneous occurrence of condition a).

[0032] As known from the scientific article entitled: "Tap water hardness estimated by conductivity measurement to reduce detergent dosing" by Geert R. Langereis, Wouter Olthuis and Piet Bergveld of the MESA Research Institute, University of Twente, for example, electric conductivity is correlated with water hardness. Therefore, conductivity signal S2 is indicative of the hardness of the water flowing through conductivity sensor 14. In this regard, document "Guidelines for drinking-water quality, 2nd ed. Vol. 2. Health criteria and other supporting information" by the World Health Organization, published in Geneva in 1996, discloses also a correlation between electric conductivity and total dissolved solids (TDS) in water. Therefore, conductivity signal S2 is also, advantageously, indicative of the amount of dissolved solids in the water flowing through conductivity sensor 14. In light of the above, the predefined operation may optionally comprise a water hardness indication and/or a filter malfunction indication indicative of the need for replacing/servicing a water filter installed upstream of vibration pump 100 and/or of sensors 12, 14. The water hardness and/or filter malfunction indications are triggered by control unit 16, for example, when said control unit 16 detects that conductivity signal S2 is representative of an electric conductivity above and/or below a further predefined conductivity threshold value. In fact, the further predefined conductivity threshold value may be indicative of a high hardness and/or a high content of total dissolved solids in the flow of water directed towards vibration pump 100.

[0033] With particular reference to Figures 2 to 9, the following will describe in detail some preferred technical and structural features of detection device 10.

[0034] The following description will first tackle the technical features of the structure of flow meter 12.

[0035] In the embodiment illustrated herein, flow meter 12 comprises a hollow casing 18 having a cavity 20 configured to be crossed by a flow of water, in particular coming from a tank. Hollow casing 18 comprises an inlet 22, intended for receiving the flow of water directed towards cavity 20, and an outlet 24, intended for letting the water flow out of cavity 20. In the illustrated embodiment, outlet 24 opens in the vicinity of conductivity sensor 14.

[0036] In the embodiment illustrated herein there are a single inlet 22 and a single outlet 24. However, in further implementation variants a plurality of inlets and/or a plurality of outlets may be provided.

[0037] Flow meter 12 comprises an impeller 25 situated in cavity 20 and rotatably supported by hollow body 18 around an axis of rotation X-X. Impeller 25 is configured to be rotatably driven by the flow of water entering through inlet 22 and exiting through outlet 24.

[0038] In addition, flow meter 12 comprises sensing means 26 configured to sense the rotation of impeller 25 and output a flow signal S1 dependent on the revolution speed of impeller 25. Outlet 24 is radially spaced apart from the axis of rotation X-X of impeller 25. Such structure and location of outlet 24 make it possible to dampen the pulsating water flow generated during the operation of vibration pump 100.

[0039] According to the present invention, inlet 22 may be located anywhere upstream of impeller 25, and outlet 24 may be located anywhere downstream of impeller 25.

[0040] Preferably, outlet 24 is oriented parallel to the axis of rotation X-X. Alternatively, outlet 24 may also be oriented perpendicular to the axis of rotation X-X.

[0041] In the embodiment illustrated herein merely by way of non-limiting example, inlet 22 and outlet 24 have respective circular-section ports for the water flow. According to such an embodiment, the ratio between the diameter defined by outlet 24 (in particular, its inside diameter) and the diameter defined by inlet 22 (in particular, its inside diameter) is preferably in the range of 0.6 to 1.4. In other words, the diameter of the hole defined by outlet 24 may be comprised within an interval ranging from a minimum value, equal to the diameter of inlet hole 22 reduced by 40%, and a maximum value, equal to the diameter of the outlet hole increased by 40%.

[0042] The following will provide more general indications, compared with the above diameter ratio recommendations, concerning a preferred range of values for the ratio between the areas of inlet 24 and outlet 26 available for the water flow, regardless of the shape and total number of inlets and outlets. In this respect, the ratio between:

• the total area of the cross-section of outlet 24 relative to the axial direction of the water flow out of cavity 20, and
• the total area of the cross-section of inlet 22 relative to the axial direction of the water flow into cavity 20

is in the range of 0.36 to 1.96.

[0043] Moreover, still according to a preferable solution, the ratio between the diameter of impeller 25, expressed in millimeters, and the number of blades is comprised between 2 and 3 (e.g. if the diameter of impeller 25 is 20mm, the blades may be 9, since the above-mentioned ratio will be 2,2).).

[0044] Impeller 25 further comprises a permanent magnet 28, and detection means 26 are configured to detect the variation occurring in the magnetic field generated by permanent magnet 28, so as to measure the rate of the flow of water through cavity 20 and output flow signal S1. In the illustrated embodiment, the magnetic poles of magnet 28 are oriented radially relative to the axis of rotation X-X, in particular being situated at diametrically opposite positions relative to the latter.

[0045] In particular, inlet 22 is oriented tangentially relative to the axis of rotation X-X of impeller 25. Preferably, the inlet 22 essentially consists of a tube entering supporting half-shell 34.

[0046] In addition, impeller 25 comprises a central hub 30 from which a plurality of radial blades 32 extend, which are configured to intercept the water flow coming from inlet 22, being thus made to rotate. Magnet 28 is mounted to the impeller at an axial end of central hub 30.

[0047] In the illustrated embodiment, hollow casing 18 comprises a supporting half-shell 34 and a closing element 36 sealingly coupled together and defining cavity 20.

[0048] In the illustrated embodiment, supporting half-shell 34 is shaped substantially as a tray or cup. Preferably, supporting half-shell 34 has a substantially circular section. In particular, supporting half-shell 34 is situated at the top of hollow casing 18.

[0049] In the illustrated embodiment, closing element 36 is thin, being substantially shaped as a foil. Preferably, such closing element 36 consists of a disk. In particular, closing element 36 is situated in an intermediate portion of casing 18.

[0050] Together, supporting half-shell 34 and closing element 36 define cavity 20. Moreover, supporting half-shell 34 carries inlet 22, whereas closing element 36 carries outlet 24 at a radially offset position relative to the axis of rotation X-X of the impeller.

[0051] Supporting half-shell 34 rotatably supports impeller 25. In particular, supporting half-shell 34 rotatably supports an axial end of central hub 30.

[0052] The following will describe the technical features of the structure of conductivity sensor 14.

[0053] In the illustrated embodiment, conductivity sensor 14 is advantageously situated downstream of flow meter 12. However, in further implementation variants of the present invention, conductivity sensor 14 may be situated upstream of flow meter 12.

[0054] As will be further described in detail hereinafter, conductivity sensor 14 is integrated with flow meter 12.

[0055] In particular, hollow casing 18 has also a chamber 40 in which conductivity sensor 14 is situated.
In the illustrated embodiment, chamber 40 has, for example, a substantially annular shape, and is intended to receive the flow of liquid directed towards vibration pump 100, advantageously exiting flow meter 12.

[0056] More in detail, as will be further described more specifically hereinafter, chamber 40 is formed by advantageously using a further portion 38 of hollow casing 18, in addition to the previously described supporting half-shell 34 and closing element 36.

[0057] In the illustrated embodiment, conductivity sensor 14 is advantageously made in accordance with patent publication WO 2016/174569 A1 in the name of the present Applicant. Said patent publication describes the application of a conductivity sensor in order to sense the electric conductivity of the washing bath of a washing machine. Nevertheless, as will be apparent to a person skilled in the art, the same conductivity sensor may also be used for sensing the electric conductivity of the water exiting flow meter 12.

[0058] Preferably, hollow casing 18 further comprises an additional supporting half-shell 48, and chamber 40 is defined by the additional supporting half-shell 48 and by closing element 36. In particular, the additional supporting half-shell 48 is situated at the bottom of hollow casing 18.

[0059] Conductivity sensor 14 comprises a pair of electrodes 42, 44 mounted to the additional supporting half-shell 48 in chamber 40 and configured to stay in contact with the water flow. Moreover, conductivity sensor 14 preferably comprises an electrically insulating supporting covering 46 through which electrodes 42, 44 extend. Furthermore, in the implementation example described herein, conductivity sensor 14 comprises circuit means configured to supply electric energy to electrodes 42, 44 and output conductivity signal S2 as a function of the potential difference assumed by electrodes 42, 44, in a per se known manner.

[0060] Electrodes 42, 44 are situated in the additional supporting half-shell 48 in order to sense the conductivity within the additional chamber 40. In particular, supporting covering 46 that carries electrodes 42, 44 is constrained in the additional supporting half-shell 48.

[0061] As an alternative to the above, a single electrode may be employed instead of the pair of electrodes 42, 44, wherein the potential difference is calculated between the voltage at the single electrode and the ground voltage.

[0062] In the illustrated embodiment, flow meter 12 and conductivity sensor 14 are, advantageously, mutually integrated.

[0063] In more detail, advantageously, supporting half-shell 38, closing element 36 and supporting half-shell 48 are assembled together to form a single enclosure structure (i.e. hollow casing 18) that encloses the components of flow meter 12 and those of conductivity sensor 14.

[0064] In particular, additional supporting half-shell 48 is shaped substantially like a tray or cup, and is configured to be sealingly coupled to supporting half-shell 34 to define chamber 40. Preferably, the additional supporting half-shell 48 is inserted in supporting half-shell 34, thereby defining a substantially annular shape of chamber 40. In the illustrated embodiment, the coupling between supporting half-shell 34 and bottom half-shell 48 is of the snap type, e.g. through the interposition of an annular sealing gasket 49.

[0065] In the illustrated embodiment, closing element 36 is mechanically locked between supporting half-shell 34 and additional supporting half-shell 48, particularly at its periphery. Preferably, closing element 36 is in abutment with a supporting wall 50 of the additional bottom half-shell 48, in particular being housed in a recess 52 formed on supporting part 50. In particular, closing element 36 has a plurality of supporting feet 54 protruding into and resting on recess 52.

[0066] Furthermore, supporting wall 50 is provided with a tip 56 projecting towards cavity 20 and acting as a support for the rotation of impeller 25 about the axis of rotation X-X. In particular, hub 30 of impeller 25 is fitted onto tip 56.

[0067] Furthermore, outlet 24 of flow meter 12 opens into chamber 40 in an axial direction relative to the axis of rotation X-X. In particular, outlet 24 opens into chamber 40 in a region that is radially offset or spaced apart from the axis of rotation X-X. More particularly, outlet 24 opens into additional cavity 40 through a passage 58 formed in supporting wall 50.

[0068] The additional supporting half-shell 48 comprises a central outlet portion 60 that allows water to flow out of annular chamber 40 annularly situated around central outlet portion 60. Outlet portion 60 has a lateral aperture 62 through which the water can exit chamber 40. Moreover, outlet portion 60 is configured to be sealingly connected, by means of a connector 64, to the inlet of vibration pump 100, in particular even without the interposition of any flexible tubes.

[0069] Preferably, control unit 16 is integrated with flow meter 12 and conductivity sensor 14.

[0070] Control unit 16 comprises a printed circuit board 64 which carries detection means 26 and electrodes 42, 44. Printed circuit board 64 is mounted to hollow casing 18, in particular to half-shells 34, 48. In particular, printed circuit board 64 is partially inserted in a sealed manner in the additional cavity 40, transversally thereto, through the additional supporting half-shell 48. Also, printed circuit board 64 is arranged outside supporting half-shell 34 in a position laterally facing permanent magnet 28.

[0071] In particular, the time trend of conductivity signal S2 is substantially harmonic in accordance with the pulsation of the flow of liquid, similarly to the time trend of flow signal S1. This provides substantial redundancy between the time trend of flow signal S1 and the time trend of conductivity signal S2.

[0072] Of course, without prejudice to the principle of the invention, the forms of embodiment and the implementation details may be extensively varied from those described and illustrated herein by way of non-limiting example, without however departing from the scope of the invention as set out in the appended claims.

Claims

1. Control system (1) for a pump (100), in particular of a household appliance; said system comprising:

- a first sensor (12) intended for being crossed by a flow of liquid directed towards the inlet of said pump (100) and configured to output a first signal (S1) indicative of said flow of liquid and/or presence of said liquid;

- a second sensor (14) intended for being crossed by said flow of liquid and configured to output a second signal (S2) indicative of said flow of liquid and/or presence of said liquid; and

- a control unit (16) configured to receive said signals (S1, S2) and command the execution of at least one predefined operation as a function of the signals (S1, S2).

2. System according to claim 1, wherein said at least one predefined operation comprises a deactivation of said pump (100) .

3. System according to claim 2, wherein said deactivation is triggered by the control unit (16) when said control unit (16) detects at least one of the following conditions:

a) the first signal (S1) is representative of substantially no flow of liquid and/or substantial absence of said liquid, and/or

b) the second signal (S2) is representative of substantially no flow of liquid and/or substantial absence of said liquid.

4. System according to any one of the preceding claims, wherein said at least one predefined operation further comprises a fault indication.

5. System according to claim 4, wherein said fault indication is triggered by the control unit (16) when said control unit (16) detects only one of said condition a) and said condition b).

6. System according to any one of the preceding claims, wherein said first sensor is a flow meter (12) intended for being crossed by a flow of liquid directed towards the inlet of said pump (100) and configured to output a flow signal (S1) indicative of the rate of said flow of liquid.

7. System according to claim 6, wherein said condition a) is given by the fact that said flow signal (S1) is representative of a rate of flow of liquid below a predefined flow rate threshold value.

8. System according to claim 7, wherein said predefined flow rate threshold value is indicative of a reduced or substantially null flow of liquid directed towards said vibration pump (100).

9. System according to any one of the preceding claims, wherein said second sensor is a conductivity sensor (14) intended for being crossed by said flow of liquid and configured to output a conductivity signal (S2) indicative of the electric conductivity of said flow of liquid.

10. System according to claim 9, wherein said condition b) is given by the fact that the conductivity signal (S2) is representative of an electric conductivity below and/or above a predefined conductivity threshold value.

11. System according to claim 10, wherein said predefined conductivity threshold value is indicative of a reduced or substantially null flow of liquid directed towards said vibration pump (100).

12. System according to any one of the preceding claims, wherein said at least one predefined operation comprises the provision of a liquid hardness indication and/or a filter malfunction indication indicative of the need for replacing/servicing a liquid filter installed upstream of said sensors (12, 14).

13. System according to claim 12 when dependent on claim 2, wherein said hardness indication and/or said filter malfunction indication are triggered by the control unit (16) when said control unit (16) detects that the conductivity signal (S2) is representative of an electric conductivity above and/or below a further predefined conductivity threshold value.

14. System according to claim 13, wherein said further predefined conductivity threshold value is indicative of a high hardness and/or a high content of total dissolved solids in the flow of liquid directed towards said vibration pump (100).

15. System according to claim 6 and claim 9, wherein said flow meter (12) and said conductivity sensor (14) are mutually integrated into a single detection device (10).

16. System according to any one of the preceding claims when dependent on claim 9, wherein the trend of said conductivity signal (S2) is substantially harmonic in accordance with the pulsation of said flow of liquid.

Drawing