HOT WATER CLEANER WITH TEMPERATURE CONTROL

DESCRIPTION Field of the invention

The present invention relates to the field of the water cleaners, i.e. machines which supply a jet of hot water and high pressure for the removal of different types of material, in particular dirty and scaling, from solid surfaces.

The invention also relates to a method for adjusting the temperature of the water supplied by a water cleaner.

Background of the invention

As well known, the hand-actuated water cleaners are equipped with a jet lance, or gun, through which a high pressure cleaning liquid jet is supplied, generally water, or a mix of water and detergent, and, in case, a descaling agent for preserving the parts of the machine. The high pressure jet is produced by a pump unit that is hydraulically connected to a jet lance through a hydraulic circuit and that is able to provide, at the exit, a water flow at a pressure that can be higher than 300 bar.

More precisely, the pump unit, generally a piston pump operated by an electric motor, is connected at the delivery to the hydraulic circuit, which ends with the jet lance, and at the suction to a water source, for example the water supply. However, water cleaners are also known that are equipped with a self-priming pump.

The hydraulic circuit normally provides a first and a second pressure switches connected to a control unit. More in detail, the control unit combines the signals received from 2 pressure switches in order to monitoring the working status of the machine. In particular, the combination of the above described signals allows to verify how the machine works in the absence of feeding, the stand-by of the machine, if during the working there is a work stoppage, the stop of the boiler, if this has a pressure (equivalent flow rate) less than a minimum threshold value and any micro-leakage of the hydraulic circuit .

A particular type of water cleaners is the hot water cleaners. Thanks to the use high pressure and temperature water, the hot water cleaners allows to obtain, under the same pressure, a more effective cleaning action w.r.t. the water cleaners, which supply water at room temperature. According to the regulations in force at present, in the case of water cleaners with a maximum exit temperature of 110 °C, the highest pressure that can be used is 350 bar, as for those using cold water. If, instead, the maximum exit temperature raises to 155°C, the highest pressure that can be used cannot be higher than 32 bar.

In case of hot water cleaners, further to the above disclosed components, the hydraulic circuit is also provided with a boiler arranged to heat the high pressure water coming from the pump, up to a determined temperature. Also in this case, the high pressure and temperature water is delivered through a jet lance. The temperature at which the water is heated by means of boiler depends on the type of application to which the water cleaner is destined and is normally adjustable in such a way to have a machine with a certain versatility, i.e. that can be used for different purposes, e.g. car body washing, the washing of different surfaces, for example floors, hulls, etc.

Therefore, in these machines, the control unit adjusts also the temperature at which the water exits from the boiler. This is possible, because, these water cleaners are provided with a temperature sensor, which detects the water temperature and sends a corresponding signal of temperature to the control unit that consequently regulates the boiler turning it on, or off, i.e. opening, or closing, the valves that regulate the flow of fuel towards the boiler.

In the water cleaners of known type, the temperature sensor is positioned adjacent to the external wall of the boiler, and therefore, in this case, the sensor is not in contact with the water, or it is positioned directly into contact with the cleaning water.

In both the above described cases, the adjustment of the cleaning liquid temperature is not very precise.

In fact, in the first case, i.e. with the temperature sensor positioned adjacent to the external wall of the boiler, it is possible to prolong the average life of the sensor, but however, the temperature detection by the sensor is affected by a series of factors that compromise its accuracy. In particular, the temperature measurement is distorted by the presence of materials having different thermal conductivities. This causes, in fact, a temperature gradient, which distorts the measurement.

In the second case, instead, i.e. with the temperature sensor positioned, in operating conditions, in direct contact with the cleaning liquid, further to the thermal gradients generated for the use of different materials, generally different types of steels, or however for the use of materials having a low thermal conductivity, normally between 20 and 50-60 W/m-K, there are other aspects that compromise the temperature detection by the sensor. In particular, in this type of water cleaners, between the exit of the water from the boiler and the point where the temperature sensor is positioned, there are many changes of the liquid flow section. This causes turbulences in the water flowing through the circuit, that further distort the temperature detected by the sensor.

Examples of prior art water cleaners, which use a high pressure and temperature liquid, are described in EP0591660, WO00/45967 and US5607349.

In particular in EP0591660 a water cleaner is disclosed provided with a duct in which, in working conditions, a cleaning liquid at a determined pressure flows through. Furthermore, a boiler is provided fed with a determined fuel in order to cause the heating of the cleaning liquid. The apparatus is, furthermore, provided with a safety device in order to avoid that the temperature, or the pressure, of the cleaning liquid can exceed a determined threshold value.

As described in the document, the main purpose of that invention is to provide a safety device that is completely mechanical. In this regard, a temperature sensor is provided that is housed within a recess, which is orthogonal to said conduit. The temperature sensor has an internal section of a diameter less than the recess. Therefore, the cleaning liquid, which passes through the duct, floods the above disclosed recess, going in contact with the external wall of the temperature sensor body. Furthermore, coaxial to the sensor body, a piston is positioned that is able to slide axially to it. More in detail, when the cleaning liquid temperature exceeds a determined value, the piston starts to slide, opposed by a spring, and departing from the temperature sensor body, it moves in a position that causes the closure of the conduit, which feeds the fuel to the boiler. Therefore, the temperature of the cleaning liquid decreases.

In light of the above, the technical solution disclosed in EP0591660 does not allow to control the cleaning fluid temperature in a fast and precise way.

Summary of the invention

It is, therefore, a purpose of the present invention to provide a water cleaner that is able to overcome the above disclosed drawbacks of the prior art.

It is, in particular, a purpose of the present invention to provide a water cleaner that allows to adjust, in a very precise manner, the temperature of the cleaning liquid, which is delivered through a delivery device e.g. a jet lance, or a gun, in such a way to guarantee to a user of using the most suited temperature for the application to which the machine is destined.

These and other objects are achieved by a water cleaner comprising:

- a pump unit arranged to feed a determined flow of a cleaning liquid at a predetermined pressure in a hydraulic circuit;

- a boiler arranged to transfer to said cleaning liquid a predetermined thermal power in order to cause its heating up to a predetermined temperature, said boiler being provided with an outlet section of said liquid having a predetermined diameter;

- a delivery device hydraulically connected to said outlet section of said boiler and arranged to deliver said flow of said cleaning liquid at said predetermined pressure and at said predetermined temperature ;

whose main characteristic is to provide, furthermore:

- an adjusting unit arranged to adjust said thermal power supplied by said boiler to said cleaning liquid, said adjusting unit comprising:

- a temperature sensor, which is immersed, in use, in said high pressure cleaning liquid in such a way to detect its temperature and to generate a corresponding signal of temperature (Ti);

- a control unit operatively connected to said temperature sensor, said control unit comprising a microprocessor and being arranged to increase, or decrease, said thermal power supplied by said boiler to said cleaning liquid, depending on said signal of temperature (Ti) received by said temperature sensor;

- a measurement block provided with a housing arranged to house, in use, said temperature sensor, said measurement block having a main body provided with a passageway through which, in use, said cleaning liquid flows, said passageway being hydraulically connected to said housing and comprising an inlet mouth for the inlet inside the measurement block of said cleaning liquid and an outlet mouth for the exit of said cleaning liquid from the measurement block; and wherein said measurement block is configured in such a way that the temperature sensor is positioned, in use, at a distance from the outlet mouth of the boiler less than 20 mm.

The particular technical solution provided by the present invention allows, on the one hand, to eliminate the thermal jumps of the prior art solutions, at the connection walls of parts made of different materials and on the other hand, to carry out a temperature detection in a point of the hydraulic circuit that is very close to the boiler. As a consequence, it is possible to carry out a highly accurate temperature detection by the temperature sensor housed inside the measurement block, immediately downstream of the boiler.

In particular, the measurement block can be made of a single metallic material having a thermal conductivity higher than, or equal to, 150 W/m-K, in such a way to have a quick heat transfer and, therefore, to obtain a very accurate detection of the temperature by the temperature sensor .

Advantageously, the material in which the measurement block is made of, has a thermal conductivity higher than 200 W/m-K, in such a way to achieve an even faster heat transfer and, therefore, further increasing the precision of the temperature detection by the temperature sensor.

Advantageously, the flow passage section of the liquid between the outlet mouth of the boiler, the inlet mouth and the outlet mouth of the measurement block and the housing within which the temperature sensor is housed, is substantially constant. This allows to avoid thermal jumps due to turbulences produced by narrowings, or however, by changes in the flow section of the liquid as in the water cleaners of known type.

Preferably, the metallic material is aluminium, advantageously aluminium of high quality, or an aluminium alloy. In particular, the aluminium is, at the same time, a high thermal conductivity, about 200-240 W/(m-K), and is very light and, therefore, it has ideal properties for creating an environment in which the temperature sensor can carry out the detection.

Advantageously, the outlet section of the boiler and the inlet section of the measurement block are engaged by means of quickly releasable lock and unlock members.

Preferably, the measurement block is a monobloc, i.e. it is made of one single piece. In particular, the measurement block can be produced by a metal forming process .

Preferably, the predetermined distance is less than 10 mm.

In a particular embodiment of the invention, the distance at which the temperature sensor is positioned from the outlet section of the boiler, is less than 6 mm, for example about 4-5 mm.

In particular, the control unit is arranged to adjust the flow of fuel, e.g. oil, that is fed to the boiler, on the basis of the signal of temperature t(i) received by the temperature sensor.

According to another aspect of the invention, a method for adjusting the temperature of the cleaning liquid delivered by a water cleaner comprises the steps of: - pumping a flow of a cleaning liquid at a predetermined pressure into a hydraulic circuit of said water cleaner;

- heating, by means of a boiler, said cleaning liquid a said predetermined pressure up to reach a predetermined temperature, said boiler provided with an outlet section of said liquid having a flow section of predetermined diameter;

- detecting the temperature of the liquid flow exiting said boiler by means of a temperature sensor positioned downstream of said boiler, said temperature sensor being configured in such a way to provide a signal of temperature to a control unit, said sensor being housed within a housing made in said measurement block produced in a single metallic material and hydraulically connected to said outlet section of said boiler, said temperature sensor being positioned, in use, at a distance from said outlet mouth of said boiler that is less than 20 mm;

- adjusting by said control unit, the thermal power produced by said boiler to heat said cleaning liquid at said predetermined pressure up to said predetermined temperature;

- a delivery device hydraulically connected to said outlet section of said boiler and arranged to deliver said flow of said cleaning liquid at said predetermined pressure and at said predetermined temperature ;

- delivering of said liquid at said predetermined pressure and at said predetermined temperature by means of a device of delivering hydraulically connected to said measurement block. Brief description of the drawings

The invention will be illustrated in the following description of an exemplary embodiment thereof, exemplifying but not limitative, with reference to the attached drawings, in which:

Figure 1 shows a scheme of a possible embodiment of a water cleaner equipped with a temperature measurement block, according to the invention;

Figure 2 diagrammatically shows, in a longitudinal section view, a possible embodiment of a temperature measurement block for water cleaners, according to the invention;

Figure 3 shows the measurement block of figure 2 in a side perspective view;

Figure 4 shows an operation scheme in which the control unit, which processes the data detected by the temperature sensor, is shown, in order to adjust the operation of the boiler;

Figure 5 shows in a block scheme, the main components of the water cleaner, according to the invention;

Figures 6 shows in a block scheme, the main components of a first alternative embodiment of water cleaner of figure 5;

Figures 7 and 8 show in perspective views a particular embodiment of the measurement block provided by the present invention, i.e. provided with quickly releasable lock and unlock members;

Figures 9 shows in a block scheme the main components of another alternative embodiment of water cleaner of figure 5;

Figure 10 shows in a longitudinal section view a possible embodiment of the safety block provided by the embodiment of figure 9;

Figure 11 shows in a perspective view a possible embodiment of the safety block of figure 9;

Figure 12 diagrammatically shows, in a perspective view, the main components of the hydraulic circuit when both the safety block and the measurement block are present.

Description of some preferred exemplary embodiments

As diagrammatically shown in figure 1, a water cleaner 1, according to the present invention, comprises a pump unit 10 arranged to feed a flow of a cleaning liquid, for example water, at a predetermined high pressure, for example set between 25 and 32 bar, in a hydraulic circuit 100. This comprises a boiler 20 arranged to heat the high pressure cleaning liquid up to a predetermined temperature T .

In particular, as diagrammatically shown in figure 4, boiler 20 is provided with an outlet section 22 for the liquid having a predetermined diameter d. The water cleaner 1 is, furthermore, equipped with a control unit 300, in particular provided with a microprocessor, arranged to adjust the thermal power that the boiler 20 has to transfer to the cleaning liquid at the above disclosed predetermined high pressure, in order to heat it up to the predetermined temperature.

In order to verify that the liquid exiting the boiler 20 is actually at the desired temperature T*, the hydraulic circuit 100 is provided with a temperature sensor 30. This is configured in such a way to send a signal of temperature T(i) to the control unit 300. In particular, the control unit 300 is electrically connected to the temperature sensor 30 and is arranged to increase, or decrease, the thermal power transferred by the boiler 20 to the cleaning liquid, on the basis of the signal of temperature Ti received by the temperature sensor 30.

The water cleaner 1 is, then, provided with a delivery device 80 hydraulically connected to the boiler 20 and arranged to deliver the cleaning liquid flow 50 at the predetermined pressure and temperature.

In the embodiment of figure 1, the water cleaner 1 is, furthermore, provided with a reservoir 40 containing a detergent and descaling agent. More precisely, pump unit 10 can be arranged to suck the detergent and descaling agent from reservoir 40 and to add it to the cleaning liquid, in particular water, before feeding the resulting mix in the boiler 20. Furthermore, a reservoir 60 is provided containing a determined amount of fuel for boiler 20. More precisely, the fuel is sucked by a second pump unit 65, which provides to feed it to boiler 20. Between boiler 20 and the delivery device 80, a measurement block 70 is provided, which has a housing 75 arranged to house, in use, the temperature sensor 30. The measurement block 70 is provided, furthermore, with a passageway 170, in which, in use, the cleaning liquid flows, and that is hydraulically connected to the housing 75. Therefore, in operating conditions, temperature sensor 30 is dipped in the liquid at high pressure and predetermined temperature T.

In an embodiment diagrammatically shown in the block schemes of figures 5, 6 and 9, the adjusting unit comprises a feeding device of fuel 140 arranged to feed a determined flow of fuel to the boiler 20. In this case, the control unit 300 is arranged to command the feeding device 140 in order to feed, or decrease, the flow of fuel fed to the boiler 20, depending on the temperature detected by the temperature sensor 30. In this case, therefore, the thermal power transferred from boiler 20 to the cleaning liquid is adjusted increasing, or decreasing, the fuel flow that is fed to the boiler 20.

In the example shown in the block scheme of figure 6, the temperature sensor 30 is of electronic type and is, therefore, arranged to send the signal of temperature directly to the control unit 300. In particular, the temperature sensor 30 of electronic type can be a NTC thermistor, i.e. of Negative Temperature Coefficient type, or a Positive Temperature Coefficient thermistor.

In the alternative embodiment of the invention illustrated in the block scheme of figure 6, instead, temperature sensor 30 is the sensitive element of an electromechanical thermostat 32. In this case, therefore, the signal of temperature detected by the temperature sensor 30 is sent to the control unit 300 through the thermostat 32.

In a foreseen embodiment, the measurement block 70 can be made in a single metallic material having a high thermal conductivity. In this way, an ideal environment is created for detecting the liquid temperature exiting the boiler 20. In fact, unlike the solutions of prior art, which use different materials, in particular between the outlet section of boiler and the point of hydraulic circuit downstream of it where the temperature is detected, the use, in the present invention, of a single material having a high thermal conductivity, allows to avoid the drawback of the prior art solutions of having thermal discontinuity at the contact walls between the different parts made of different materials.

Therefore, the present invention is able to assure a measurement of the liquid temperature that is highly reliable and precise. As a consequence, it is possible also to regulate, very precisely and accurately, the boiler 20.

As shown in the block diagrams of figures 5, 6 and 9, depending on the temperature detected by temperature sensor 30, the control unit 300 is arranged to command an adjusting device 140, in particular comprising at least a pump and a valve that are not shown in figures for reasons of simplicity, per feed more, or less, fuel to boiler 20. For example, the control unit 300 can be configured in such a way to process the temperature data Ti detected by the temperature sensor 30 and to command the pump unit 65 of the adjusting device 140, in order to feed more, or less, fuel to the boiler 20, according to a predetermined function.

The solution provided by the present invention guarantees, therefore, the use of the most suited temperature for the specific application to which water cleaner 1 is intended for.

In particular, as shown in the block scheme of figure

6, an interface member 200, e.g. a touch-screen display, or a keypad, can be provided configured in such a way to allow a user to select a predetermined use among a predetermined plurality of uses that are provided and stored in the memory of water cleaner 100. More in detail, each selected use, e.g. the cleaning of a car body, or the removal of paint from a wall, or the sanitizing of an environment, corresponds to a predetermined threshold temperature, which is, therefore, communicated to the control unit 300.

In particular, the thermal conductivity of the metallic material having a high thermal conductivity, can be higher than, or equal to, 150 W/m-K. In this way, a quick heat transfer is obtained and, therefore, a very accurate detection is carried out.

Preferably, the metallic material in which the measurement block 70 is made of is aluminium, in particular aluminium of high quality. More in detail, the aluminium is able to assure, at the same time, a high thermal conductivity, for example comprises between 200 and 240 W/(m-K), and is very light, ideal properties for the walls 76 of the measurement block 70, within which the temperature detection is carried out by the sensor 30.

As diagrammatically shown in the partially sectioned view of figure 4, between the outlet mouth 24 of the outlet section 22 of boiler 20 and the housing 75, in which the sensor 30 is housed, a substantially constant ha a flow passage section of liquid 50, is provided. In this way, unlike the prior art solutions, abrupt thermal jumps are avoided due to changes in the flow section, in particular narrowings of the ducts that lead the liquid from the boiler 20 to the detection zone of the temperature. In fact, as well known, changes in the flow sections of the ducts cause localized turbulences and, therefore, distortions in the temperature detection by sensor 30.

In particular, as diagrammatically shown in the figures 2 and 3, the measurement block 70 has an inlet section 71 having an inlet mouth 72 through which the cleaning liquid flows into it. The measurement block 70 is, furthermore, provided with an outlet section 73 provided with an outlet mouth 74 hydraulically connected to the inlet mouth 72 and from which the cleaning liquid exit the body of the measurement block 70. between the inlet mouth 72 and the outlet mouth 74 a passageway 170 is defined, through which the cleaning liquid flows through the measurement block 70 (figure 2) . As it is diagrammatically shown in figure 4, the section Φ of passageway 170 where the cleaning liquid 50 reaches the temperature sensor 30, has a surface higher than 100 mm ² , in particular set between 100 mm ² and 150 mm ² . This is possible because of the combination of the fact that the temperature sensor 30 is positioned very close to the outlet mouth 24 of boiler 20, and the section of passageway 170 of the measurement block 70 between the outlet mouth 24 and the detection zone, is substantially constant. The possibility to have a so high contacting surface and to avoid turbulences, almost completely, allows to have a large detection surface, and, therefore, to obtain an extremely accurate temperature detection.

In a possible embodiment of the invention, inlet section 71 of measurement block 70 can be directly connected to the outlet section 22 of boiler 20. In particular, quickly releasable lock and unlock members can be provided arranged to engage in a releasable manner the outlet section 22 of boiler 20 and the inlet section 71 of the measurement block 70. For example, as diagrammatically shown in the figures 7 and 8, the quickly releasable lock and unlock members can comprise at least a locking pin 90, in particular "U" shaped, arranged to engage, in use, in through holes 77 provided at the inlet section 71 and in respective through holes 27 provided at the outlet section 22 of boiler 20. In this way, it is possible to engage, or disengage, in a quick and precise manner, the boiler 20 and the measurement block 70 acting on the quickly releasable lock and unlock members. For example, in the case shown in the figures 8 and 9, at the moment of disassembling the measurement block 70 from the outlet section 22 of boiler 20, will be sufficient to unthread the locking pin 90 from the holes 77 and 27, action that a user can carry out easily and quickly by hand, or using a tool, e.g. a screwdriver.

Analogously to what described above for the engagement between the outlet section 22 of boiler 20 and the inlet section 71 of measurement block 70, also the temperature sensor 30 can be engaged to the measurement block at the housing 75 by means of quickly releasable lock and unlock members .

In particular, again as diagrammatically shown in the figures 7 and 8, the temperature sensor 30 can comprise a enlarged portion 31 arranged to position, in use, at a engagement portion 78 of measurement block 70. The engagement portion 78, at the wall 76 of the measurement block 70, is provided with an aperture 79, for example at the opposite side of the outlet mouth 74. Through the apertures 79, it is possible to introduce, or extract, the temperature sensor 30. More precisely, the enlarged portion 31 of temperature sensor 30 can be provided with holes 37 in which, in use, a second locking pin 95, in particular "U"-shaped, is introduced. This latter, in use, is introduced in the holes 77 of the outlet section 73 of measurement block 70, and in the above disclosed holes 37 of the enlarged portion 31 of temperature sensor 30, in such a way to maintain them in position. At the moment to extract the temperature sensor 30, it is sufficient to remove, also in this case, the locking pin 95 and extract the temperature sensor 30 by hand, or using a tool.

In light of the above, the locking system, which provides the locking pins 90 and 95, allows to easily and quickly disassemble the measurement block 70, for example when ordinary or extraordinary maintenance interventions has to be carried out, without the need of disassemble other parts of the water cleaner.

In a preferred embodiment of the invention, the measurement block 70 is made of one single piece, for example produced by a metal forming process.

More in detail, the measurement block 70 is configured in such a way that the temperature sensor 30 is positioned, in use, at a very short distance d from the outlet mouth 24 of boiler 20. More precisely, the above indicated distance d is less than 20 mm, advantageously less than 10 mm, preferably less than 6 mm. In a preferred embodiment of the invention, the distance d at which the temperature sensor 30 is positioned from the outlet mouth 24 of boiler 20, is set between 4 and 5 mm, i.e. 4<d≤5. In particular, the very short distance existing between the outlet mouth 24 of boiler 20 and the sensor 30 and the fact to have a substantially constant flow section between the outlet mouth 24 of boiler 20 and the sensor 30, contribute to avoid to have narrowings, and therefore turbulences, in this portion of hydraulic circuit. The solution above described allows, furthermore, to obtain a high thermal exchange surface. This, together with the other advantages above disclosed, makes sure that, the temperature sensor 30, of which the measurement block 70, according to the invention, is equipped, is able to detect with high precision only the cleaning liquid temperature changes, and that is not affected, instead, by thermal flywheels .

As diagrammatically shown in the block diagram of figure 7, the water cleaner, according to the invention, can be provided with a safety block 110 positioned between the pump unit 10 and the inlet section 21 of boiler 20. More in detail, the safety block 110 is provided with an inlet section 111 through which the high pressure cleaning liquid coming from the pump unit 10 enters the safety block 110 and an outlet section 112 through which the cleaning liquid exits the safety block 110 in order to be fed to boiler 20.

According to the invention, what above described concerning the measurement block 70, in particular that it is made in a single piece of metallic material having a high thermal conductivity, to be produced in a single piece, and the possibility to use quickly releasable lock and unlock members to engage it to the hydraulic circuit 100 and to sensor 30, can be advantageously applied also to the safety block 110.

In particular, the safety block 110 is provided with a pressure relief valve 120 arranged to prevent that the feeding line of the cleaning liquid exiting the pump unit 10 exceed a predetermined threshold pressure. For example, the pressure relief valve 120 can comprise a main body 121, which is housed, in use, within a housing 115, and that can move between a closed position, when the pressure inside the safety block 110 is less than the threshold value, to a discharge position, when the pressure inside the safety block 110 exceeds the above indicated threshold pressure. For example, an elastic member 125 can be provided arranged to elastically oppose the movement of the main body 121 from the closing position to the discharge position. More in detail, the measurement of the elastic member 125 is carried out in such a way that, when the predetermined threshold pressure is exceeded, the elastic member elastically withdraws, thus causing the main body 121 to move in the discharge position. When the pressure inside the safety block 110 decreases, the force exerted by the elastic member 125, which is higher than the pressure exerted by the cleaning liquid, brings the main body 121 back in closing position. In order to guarantee a hermetic sealing and, therefore, to avoid that the cleaning liquid can come out, when the pressure relief valve is in closing position, sealing members 116 are provided (see figure 10) .

The particular pressure relief valve 120 is only one possible technical solution that can be used, and analogous solutions can be also used with the same purpose . In a further embodiment, the safety block 110 can, furthermore, comprise a temperature sensor 130 housed, in use, within a chamber, for example provided at a side portion 118 of the safety block 110, as shown in figure 11. More in detail, the temperature sensor 130 is arranged to detect the temperature upstream the boiler 20, and to send a signal of temperature to the control unit 300, that, if the cleaning liquid temperature is higher than a predetermined threshold value, commands the pump unit 10 to stop.

In figure 12 the main components of the hydraulic circuit are diagrammatically shown when both the safety block 110, which is connected to the inlet section 21 of boiler 20, or more precisely to coil 25, through which, in use, the cleaning liquid flows, and the measurement block 70 connected to the outlet section 22 of the coil 25 same.

The foregoing description of a specific embodiment will so fully reveal the invention according to the conceptual point of view, so that others, by applying current knowledge, will be able to modify and/or adapt for various applications such an embodiment without further research and without parting from the invention, and it is therefore to be understood that such adaptations and modifications will have to be considered as equivalent to the specific embodiment. The means and the materials to carry out the different functions described herein could have a different nature without, for this reason, departing from the field of the invention. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation .