The invention applies to the steam generating machines to be associated with various appliances such as flairons, cleaning devices, air humidifiers, etc., and is directed to obtain a controlled and precise filling of the boiler in order to ensure that the functioning of the steam generator is always in condition of best efficiency.

Steam generators are known incorporating a boiler constituted by an hermetically closed container tank, provided with heating resistors having the function of transforming the water into steam.

The known boilers normally have a level sensor which provides to disconnect the resistors as soon as the level of the water reaches a predetermined minimum level, as well as to signal to the user such condition so that he can provide for the manual filling of the boiler.

The addition of new water is possible only when said boilers have cooled down or when the steam within them has lost its pressure.

Presently it has been proposed to use, in co-operation with said boilers and within a single casing, auxiliary water tanks which, through pumps started by an input from said level sensor, automatically supply the boiler as soon as the water goes below the said minimum level.

This allows to avoid the waiting times for the cooling of the boiler and/or the waiting times for the lowering of the steam pressure, to reduce the time required to bring the water in the boiler to evaporation temperature,

to ensure more safety for the user and to spare the manual filling operations.

Such an automatic refilling or supply of additional water does not provide to fill the boiler for the whole or for the most part of its capacity, as it normally happens by the manual filling, but provides for the introduction of a little quantity of water to ensure that the temperature in the boiler does not drop substantially because of the introduction of a great quantity of cool water.

For this reason the operation of the pump is very frequent and fractioned.

Such a solution has the advantage, as said before, to spare the waiting times between the fillings of the boiler and to avoid the manual filling, but has the disadvantage that just a part of the power of the resistor is used to generate steam, since part of said power is used to heat the new cool water which, even if in little quantities, is each time introduced by the pump.

That means that, by the same power of the resistor, the generator using such an automatic refilling system is able to generate less steam than a generator with a manual refilling in which, once the water has reached the evaporation temperature, the whole power is used to generate steam.

On the other hand, as above said, a generator equipped with a manual refilling system has the disadvantage of the waiting times necessary to make said refilling.

According to Italian patent application No. UD 96 A 000 224 in the name of the same applicant as in the present invention, there has been proposed a steam generator capable to maintain the advantages of the automatic refilling, combined with the capability to generate steam typical of

the manual refilling generators.

This is obtained by providing a machine capable to be set for operating with two functions depending upon the desire of the user: a first function operation with fractioned and frequent automatic restoration of the water and a second function operation with the restoration of the water through the same pump substantially for the total useful capacity of the boiler, which is normally at about 2/3 of its inner volume.

Nevertheless it has occurred a problem with the filling of the boiler in the second function operation. It is, in fact, known that the pump flow rate is a function of the pressure in the container to which the water is fed.

In such a situation, a control based on the pump operation time to effect the filling has resulted to be inaccurate since the water quantity introduced through the pump, in a same period of time, changes depending from the pressure inside the boiler.

This causes operating problems due to the fact that if the boiler is filled too much or to little, with respect to the pre-established maximum level, the working conditions of the appliance connected to the steam generator are not optimal, since there can be produced steam which results to be excessively humid, or scarcely humid, for an effective use.

Object of the present invention is therefore to provide for a process for the restoring the level of water in boilers of steam generating machines which consents to control the operation of the pump and to guarantee with extreme precision, and under any circumstance, the reaching of the desired level of water within the boiler.

The invention foresees the use of an auxiliary tank through which the boiler is filled by controlled operation of the restoration pump.

According to the invention, the functioning of the pump is operatively

connected with a pressure measuring device arranged at the interior of the boiler; said measuring device is normally a component with which the boiler is usually provided.

The signal of the instantaneous pressure in the boiler controls the functioning of the pump, which changes its flow rate features according to said pressure and according to the typology of the pressure flow rate curve typical of the kind of pump used.

The correction of the pump flow rate features according to the pressure can occur with the desired frequency according to the continuous changing of the pressure itself as the restoring stage (refilling with water) goes on.

In this way, the water quantity fed into the boiler is constantly and substantially continuously checked, assuring with extreme precision the reaching of the desired level and so ensuring working conditions always optimal of the appliance connected to the steam generating machine.

This is moreover obtained without adding any component to the machine with the exception of the connection between the pressure measuring device which is in the boiler and the pump control system.

According to a modified embodiment, on the feeding line connecting the pump to the boiler there is inserted a flow rate reader connected in feedback to the pump control system.

According to this latter solution, the real flow rate of the pump is continuously checked and the changes in said flow rate due to the pressure unstable conditions within the boiler are corrected in feedback by acting on the pump control system to constantly obtain controlled filling conditions.

According to a further variation, the pump is operatively connected to a maximum level sensor providing for its disconnection as soon as said

maximum level is reached.

Further features of the invention will be apparent form the following detailed description of some preferred embodiments made, by way of non- limiting example, with reference to the figures of the attached drawing, in which: Figure 1 schematically shows the means for carrying out the process for restoring the level of water in boilers of steam generating machines according to the invention; Figure 2 shows a modified embodiment of the invention.

In the figures, reference numeral 10 indicates generically a detail of a steam generating machine using the process for restoring the level of water in the boiler 11, according to the invention.

Said machine 10 includes a water containing auxiliary tank 12 connected to a pump 13 connected to the boiler 11 through an inlet 14. The water of the tank 12 is introduced, at command, through the pump 13 to fill the boiler 11, where it is progressively heated and then led to evaporation by the electric heating resistor 15 to generate steam which is supplie to the appliance (not shown) through the delivery outlet 16.

The pump 13 is automatically operated, by a starting and control device 17, any time the water in the boiler 11 reaches a predetermined minimum level LO which is calculated in such a manner to maintain the electric resistor 15 always submerged.

In the specific case, the reaching of said minimum level LO is detected by the same inlet conduit 14 which acts as conduction probe as the water level reaches its lower edge 18.

In the embodiment according to Figure 1, whenever the said level LO is reached the pump 13 is started and operated for the time, checked by the

timer 20, which is necessary for reaching the level L1 corresponding to a desired filling maximum level.

In the specific case, the operation of the pump 13 is operatively controlled by the pressure measuring device 19 which, by utilising the continuously detected value of the pressure inside the boiler 11, controls the pump 13, through said starting and control device, to cause the said pump to modify its flow rate according to the value of said pressure.

The flow rate of the pump 13 is in fact variable depending upon the variation of the pressure in the boiler 11 and changes continuously, during the refilling operations, according to the variation of the quantity of water contained in the boiler 11.

The control of the flow rate of the pump 13 according to the pressure in the boiler 11 allows to ensure under any circumstance and at any time the control of the filling conditions, by modifying the time of operation of the pump 13 to ensure the exact reaching of the maximum level L1.

Such control and consequent variation of the flow rate, which is based on the characteristic pressure/flow rate curve of the specific pump 13 used, according to a first solution occurs in a substantially continuous way.

According to another solution, said variation occurs with a desired frequency, for instance every second, also depending upon the mechanical features of the pump 13.

According to a modified embodiment, shown in Figure 2, on the feeding duct connecting the pump 13 to the boiler 11 there is arranged an instantaneous flow rate reader 21.

Said reader 21 continuously detects the real instantaneous flow rate of the pump 13, as it changes according to the pressure within the boiler 11, and controls in feedback the starting and control device 17 in such a

manner that it modifies the delivery features of the pump 13 in order to obtain the desired and precise filling under any operating condition.

According to still another modification, alternatively or together with either one of the above-mentioned solutions, at the level L1 of maximum filling there is provided a level sensor 22, connected in feedback to the control and activation system 17, which provides to stop the pump 13 as soon the level L1 is reached.