NITROX-MIXTURES PRODUCTION MACHINE AND RELATED OPERATING METHOD

Abstract

Nitrox-mixtures production machine comprising: a molecular separator, which is structured so as to receive at inlet a flow of air and to provide at outlet an intermediate Nitrox mixture with high oxygen percentage; a low-pressure compressor, which is adapted to feed an airflow at inlet of the molecular separator; a mixing manifold, which communicates with the molecular separator so as to receive said intermediate Nitrox mixture, and is structured so as to mix the intermediate Nitrox mixture with fresh air coming from the outside, in order to provide at outlet a final Nitrox mixture with predefined composition; at least one oxygen sensor, which is adapted to measure the oxygen percentage present in said final Nitrox mixture; at least one pressure sensor, which is adapted to measure the air pressure in the molecular separator; and an electronic control device, which is connected to said at least one oxygen sensor and is adapted to regulate the flowrate of the airflow that is sucked in by the low-pressure compressor based on the signals coming from said at least one oxygen sensor and said at least one pressure sensor.

Claims

1. Nitrox-mixtures production machine (1) comprising: a molecular separator (2), which is structured so as to receive at inlet an airflow and to provide at outlet an intermediate Nitrox mixture with high oxygen percentage; a low-pressure compressor (3), which is adapted to supply an airflow at inlet of the molecular separator (2); a control valve (26) which is located upstream of the low-pressure compressor (3) and is adapted to regulate the flowrate of the airflow at inlet of the same low-pressure compressor (3); a mixing manifold (4), which communicates with the molecular separator (2) so as to receive said intermediate Nitrox mixture, and is structured so as to mix the intermediate Nitrox mixture with fresh air coming from the outside, in order to provide at outlet a final Nitrox mixture with predefined composition; and at least one oxygen sensor (5) that outputs a signal indicative of the percentage of oxygen present in said final Nitrox mixture; said Nitrox-mixtures production machine (1) being characterized by additionally comprising: at least one pressure sensor (7) that outputs a signal indicative of the pressure of the air in the molecular separator (2); an electronically-controlled driving device (28, 29, 34) which is adapted to move/shift, on command, the movable shutter of said control valve (26) so as to vary the flow rate of the airflow sucked by the low-pressure compressor (3); and an electronic control unit (25), which is connected to said at least one oxygen sensor (5) and to said at least one pressure sensor (7), and is configured so as to command said electronically-controlled driving device (28, 29, 34) as a function of the signals coming from said at least one oxygen sensor (5) and from said at least one pressure sensor (7).

2. Nitrox-mixtures production machine according to claim 1, wherein said electronic control unit (25) is programmed/configured so as to vary the position of the movable shutter of the control valve (26) implementing a feedback control based on the signals coming from said at least one oxygen sensor (5).

3. Nitrox-mixtures production machine according to claim 2, wherein said electronic control unit (25) is programmed/configured so as to actuate said feedback control based on the signals coming from said at least one oxygen sensor (5), when the trend of the air pressure inside the molecular separator (2) meets a given stable-pressure condition indicative of a trend stable over time of the air pressure inside said molecular separator (2).

4. Nitrox-mixtures production machine according to claim 3, wherein said stable-pressure condition is met when the variations over time of the value of the air pressure inside said molecular separator (2) remain within a predetermined tolerance range.

5. Nitrox-mixtures production machine according to claim 4, wherein said stable-pressure condition is met when the variations of the value of the air pressure inside the molecular separator (2) remain below a predetermined maximum threshold, for a monitoring time interval greater than 2 seconds.

6. Nitrox-mixtures production machine according to claim 5, wherein said preset maximum threshold is equal or lower 0.5 bar and/or said monitoring time interval is also lower than 20 or 30 seconds.

7. Nitrox-mixtures production machine according to claim 3, wherein said stable-pressure condition is met when the relative pressure of the air inside said molecular separator (2) is greater than a predetermined minimum threshold.

8. Nitrox-mixtures production machine according to claim 1, wherein the electronically-controlled driving device (28, 29, 34) comprises: a pneumatic actuator (28) which is adapted to vary the position of the movable shutter of the control valve (26) as a function of the value of the air pressure that the same actuator receives at inlet; and an electronically-controlled pressure reducer (29), which is interposed between the pneumatic actuator (28) and a pressurized gas source, and is adapted to regulate/vary, on command, the value of the pressure of the gas directed towards the inlet of the pneumatic actuator (28).

9. Nitrox-mixtures production machine according to claim 7, wherein said electronic control unit (25) commands said pressure reducer (29).

10. Nitrox-mixtures production machine according to claim 1, wherein said mixing manifold (4) is structured so as to be connected to the suction of a high-pressure compressor (101) in order to supply said final Nitrox mixture at inlet of the same high-pressure compressor (101).

11. Operating method of a Nitrox-mixtures production machine that comprises: a molecular separator (2), which is structured so as to receive at inlet an airflow and to provide at outlet an intermediate Nitrox mixture with high oxygen percentage; a low-pressure compressor (3), which is adapted to supply an airflow at inlet of the molecular separator (2); a mixing manifold (4), which communicates with the molecular separator (2) so as to receive said intermediate Nitrox mixture, and is structured so as to mix the intermediate Nitrox mixture with fresh air coming from the outside, in order to provide at outlet a final Nitrox mixture with predefined composition; at least one oxygen sensor (5) that outputs a signal indicative of the percentage of oxygen present in said final Nitrox mixture; and a control valve (26) which is located upstream of the low-pressure compressor (3) and is adapted to regulate the flow rate of the airflow at inlet of the same low-pressure compressor (3); the operating method being characterized by comprising: a step of pressure monitoring, wherein the pressure of the air inside said molecular separator (2) is monitored so as to determine when the trend of the air pressure in the molecular separator (2) meets a given stable-pressure condition that is indicative of a trend stable over time of the air pressure inside said molecular separator (2); and a subsequent step of feedback control, wherein the position of the movable shutter of the control valve (26) is corrected/varied as a function of the signals coming from said at least one oxygen sensor (5).

12. Operating method of a Nitrox-mixtures production machine according to claim 11, characterized by comprising, before said step of pressure monitoring, also the step of determining an optimal initial position of the movable shutter of the control valve (26).

13. Operating method of a Nitrox-mixtures production machine according to claim 12, wherein the step of determining the optimal initial position of the movable shutter of the control valve (26) includes estimating said optimal initial position based on a number of known sample positions.

14. Operating method of a Nitrox-mixtures production machine according to claim 11, characterized by comprising, after said step of feedback control, a further step of checking and, if necessary, updating said known sample position or positions.

15. Operating method of a Nitrox-mixtures production machine according to claim 11, wherein the position of the movable shutter of the control valve (26) is controlled by a pneumatic actuator (7), and the step of feedback control includes varying the pressure of the air supplied at inlet of said pneumatic actuator (7).

16. Operating method of a Nitrox-mixtures production machine according to claim 11, wherein said stable-pressure condition is met when the variations over time of the value of the air pressure inside said molecular separator (2) remain within a predetermined tolerance range.

17. Scuba-diving cylinders refilling equipment (100) comprising: a high-pressure compressor (101) which is structured for sucking in air or other gaseous mixture at ambient pressure and for providing at outlet a flow of high-pressure air or other gaseous mixture to be supplied at inlet of one or more scuba diving cylinders (200); and a Nitrox-mixtures production machine (1) which is located upstream of said high-pressure compressor (101) and is adapted to supply a Nitrox mixture with a predefined composition at inlet of the same high-pressure compressor (101); said Scuba-diving cylinders refilling equipment (100) being characterized in that said Nitrox-mixtures production machine (1) is realized according to claim 1.

18. Scuba-diving cylinders refilling equipment (100) comprising: a high-pressure compressor (101) which is structured for sucking in air or other gaseous mixture at ambient pressure and for providing at outlet a flow of high-pressure air or other gaseous mixture to be supplied at inlet of one or more scuba diving cylinders (200); and a Nitrox-mixtures production machine (1) which is located upstream of said high-pressure compressor (101) and is adapted to supply a Nitrox mixture with a predefined composition at inlet of the same high-pressure compressor (101); said Scuba-diving cylinders refilling equipment (100) being characterized in that said Nitrox-mixtures production machine (1) operates according to claim 11.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0035] The present invention will now be described with reference to the accompanying drawings, which show a non-limiting embodiment thereof, wherein:

[0036] FIG. 1 illustrates, schematically and with parts removed for clarity's sake, a scuba diving cylinder filling equipment equipped with a Nitrox-mixtures production machine realized according to the teachings of the present invention;

[0037] FIG. 2 is a schematic view of the Nitrox-mixtures production machine shown in FIG. 1;

[0038] FIG. 3 shows a block diagram concerning the operation of the Nitrox-mixtures production machine shown in FIG. 2; whereas

[0039] FIG. 4 is a schematic view of a different embodiment of Nitrox-mixtures production machine shown in FIG. 2.

DESCRIPTION OF SPECIFIC EMBODIMENTS OF THE INVENTION

[0040] With reference to FIG. 1, number 1 denotes as a whole a Nitrox-mixtures production machine, which capable of delivering a breathing gaseous mixture consisting mainly of oxygen and nitrogen, in which the oxygen percentage is greater than 21% and advantageously also less than 50%.

[0041] More specifically, the machine 1 is adapted to deliver a substantially binary nitrogen-oxygen gaseous mixture, in which the oxygen percentage is preferably less than 40% and advantageously equal to 32% or 36%.

[0042] The machine 1, in addition, is preferably adapted to be used in or incorporated into a scuba-diving cylinder refilling equipment 100, which is structured so as to fill up one or more scuba-diving cylinders 200 with a breathing gaseous mixture with a pressure preferably higher than 150 bar and advantageously also higher than 200 bar.

[0043] Scuba diving cylinders 200 are pressure vessels substantially cylindrical in shape, known and readily available on the market, so their structure won't be further described.

[0044] With reference to FIG. 1, on the other hand the scuba-diving cylinders refilling equipment 100 comprises at least one high-pressure compressor 101, which is specifically structured/dimensioned for sucking in air or any other gaseous mixture at ambient pressure, and for delivering at outlet a flow of high-pressure air or other gaseous mixture with a supply/delivery pressure preferably greater than 150 bar and advantageously also equal to or greater than 200 bar.

[0045] Preferably the high-pressure 101 compressor is moreover a positive displacement compressor.

[0046] The Nitrox-mixtures production machine 1, in turn, is preferably adapted to be placed upstream of the high-pressure compressor 101, so as to be able to feed, at inlet of the same high-pressure compressor 101, a Nitrox mixture with a predetermined composition.

[0047] In other words, the machine 1 is structured so as to be connected to the suction mouth of the high-pressure compressor 101, and is adapted to feed at inlet of the high-pressure compressor 101 a Nitrox gaseous mixture with a predetermined percentage of Oxygen and, consequently, of Nitrogen.

[0048] With reference to FIG. 1, in the example shown, the high-pressure compressor 101 is preferably a positive displacement reciprocating compressor with a multi-stage structure.

[0049] More in detail, the high-pressure compressor 101 preferably comprises: a piston pumping assembly 102 with a multistage structure, which has a series of variable-volume pumping chambers connected in cascade one after the other; an electric driving motor 103, which is mechanically coupled to the pumping assembly 102 so as to continuously cyclically vary the volume of the various variable-volume chambers; and preferably also a gas/liquid separator 104, which is located downstream of the piston pumping assembly 102 and is structured so as to retain within itself the droplets of oil and/or condensed water vapour present in the flow of high-pressure air or other gaseous mixture coming out of the pumping assembly 102.

[0050] Preferably the delivery of the high-pressure compressor 101 is therefore located downstream of the gas/liquid separator 104.

[0051] In addition, the pumping assembly 102 and the drive motor 103 are preferably arranged side by side to one another, advantageously resting on the same supporting platform or frame, so as to form an easily transportable single block. Also the gas/liquid separator 104 is preferably located on the same supporting platform or frame.

[0052] Preferably, the pumping assembly 102 and the drive motor 103 are moreover connected to each other by means of a drive belt, which is looped around two pulleys fixed one on the shaft of drive motor 103 and the other on the crankshaft of the pumping assembly 102.

[0053] Clearly, the drive motor 103 may be also an internal combustion engine.

[0054] Preferably, the high-pressure compressor 101 is moreover provided with a series of heat exchangers (not illustrated), which are located downstream of the various variable-volume chambers of the pumping assembly 102, and are structured so as to cool down the air or other gaseous mixture flowing from a corresponding variable-volume chamber to the next and/or leaving the pumping assembly 102.

[0055] With reference to FIG. 1, preferably the scuba-diving cylinders refilling equipment 100 furthermore comprises: a high-pressure gas distribution assembly 105, which communicates with the delivery of the high-pressure compressor 101 so to receive at inlet the flow of high-pressure air or other gaseous mixture produced by the high-pressure compressor 101, and is selectively connectable to one or more scuba diving cylinders 200 so as to be able to channel said flow of high-pressure air or other gaseous mixture to said cylinder (s) 200; and filtering assembly 106 preferably of the activated carbon type, which is located between the distribution assembly 105 and the delivery mouth of the high-pressure compressor 101, and more in detail between the gas/liquid separator 104 and the distribution assembly 105, and is structured so as to retain impurities and other physical and/or biological contaminants present in the flow of high-pressure air or other gaseous mixture flowing towards the distribution assembly 105.

[0056] Preferably, the scuba diving cylinders refilling equipment 100 moreover comprises a drying device 107 which is capable of retaining at least part of the water vapour present in the flow of high-pressure air or other gaseous mixture that flows towards the distribution assembly 105.

[0057] In the example shown, in particular, the drying device 107 is preferably an absorption dryer structured so as to reduce the amount of water vapour in the air leaving the high-pressure compressor 101 to a value less than or equal to 15 mg/m.sup.3.

[0058] In addition, the distribution assembly 105 and/or the filtering assembly 106 and/or the dryer device 107 is/are preferably also located/fixed on the supporting platform or frame that supports the pumping assembly 102 and the drive motor 103.

[0059] Preferably, the high-pressure gas distribution assembly 105 in turn comprises: a distribution manifold 108, which communicates with the delivery of the high-pressure compressor 101 so as to receive the flow of high-pressure air or other gaseous mixture produced by the high-pressure compressor 101, and is provided with one or more manually-operated shut-off valves, separate and independent from each other, each of which is capable of regulating/controlling the exit of the high-pressure air or other gaseous mixture from the same manifold 108; and advantageously also one or more flexible connecting hoses 109, each of which is connected to the distribution manifold 108 so as to communicate with a single, respective shut-off valve of the distribution manifold 108, and is provided with a coupling connector specifically structured to be removably coupled to the valve of any scuba diving cylinder 200.

[0060] Preferably, the scuba-diving cylinders refilling equipment 100 moreover comprises: a pressure sensor 110, which is located immediately upstream of the distribution assembly 105, or rather upstream of the distribution manifold 108, and is structured to provide as output a (electrical) signal indicative of the pressure value of the high-pressure air or other gaseous mixture arriving in the distribution assembly 105; and an electronic control unit 111, which is connected to the pressure sensor 110 and is programmed/configured to switch off the high-pressure compressor 101, or rather switch off the drive motor 103, when the pressure value of the high-pressure air or other gaseous mixture arriving in the distribution assembly 105 reaches or exceeds a given limit value advantageously comprised between 200 and 300 bar.

[0061] Preferably, the scuba-diving cylinders refilling equipment 100 is finally also equipped with a normally-closed discharge valve 112, which is located immediately upstream of the distribution assembly 105, and more in detail between the dryer device 107 and the distribution assembly 105, and is structured so as to selectively divert/discharge directly outside the flow of high-pressure air or other gaseous mixture arriving from the high-pressure compressor 101, before it may reach the high-pressure gas distribution assembly 105.

[0062] With reference to FIGS. 1 and 2, the Nitrox-mixtures production machine 1 in turn comprises: a molecular separator 2, which is structured so as to receive at inlet a flow of air and supply at outlet an intermediate Nitrox mixture with a high percentage of oxygen; a low-pressure compressor 3, which is adapted to feed at inlet of the molecular separator 2 a flow of air with a predetermined nominal pressure preferably higher than 3 bar and/or lower than 20 bar; and a mixing manifold 4, which communicates with the molecular separator 2 so as to receive said intermediate Nitrox mixture, and is structured so as to mix the intermediate Nitrox mixture with fresh air from the outside, in order to provide at outlet a final Nitrox mixture having a predetermined composition.

[0063] Clearly, the oxygen percentage of the final Nitrox mixture is lower than or equal to the oxygen percentage of the intermediate Nitrox mixture.

[0064] Preferably, the outlet of the mixing manifold 4 is moreover structured so as to be connected or connectable directly to the suction mouth of the high-pressure compressor 101, in order to feed said final Nitrox mixture at inlet of the same high-pressure compressor 101.

[0065] Molecular Separator 2, on the other hand, is preferably a semi-permeable membrane molecular separator.

[0066] In addition, the Nitrox-mixtures production machine 1 moreover comprises: at least one oxygen sensor 5, which is capable of measuring the percentage of oxygen present in the Nitrox mixture exiting the mixing manifold 4, i.e. the oxygen percentage present in the Nitrox mixture; and an electronic control device 6, which is connected to the oxygen sensor (s) 5, and is adapted to regulate the flowrate of the air flow that the low-pressure compressor 3 feeds at inlet of the molecular separator 2, depending on the signals arriving from the oxygen sensor (s) 5.

[0067] More specifically, the or at least one of the oxygen sensors 5 is preferably located at the outlet of the mixing manifold 4 or immediately downstream of the mixing manifold 4, and is structured so as to provide as output a signal indicating the percentage of oxygen present in the Nitrox mixture directed towards the suction mouth of the high-pressure compressor 101.

[0068] The electronic control device 6, on the other hand, is adapted to regulate the flowrate of the airflow that the low-pressure compressor 3 feeds at inlet of the molecular separator 2, so as to automatically maintain at a predetermined target value, hereinafter referred to as the target percentage O %.sub.0, the oxygen percentage of the Nitrox mixture that comes out of the mixing manifold 4 and advantageously enters the suction mouth of the high-pressure compressor 101.

[0069] Preferably said target percentage O %.sub.0 is moreover manually selectable by the user among a predetermined range of values. With particular reference to FIG. 2, furthermore the Nitrox-mixtures production machine 1 comprises also at least one pressure sensor 7, which is located in the molecular separator 2 and is structured so as to provide at output a (electrical) signal indicative of the value of the pressure of the air contained within the molecular separator 2.

[0070] The electronic control device 6, in turn, is connected also to the pressure sensor (s) 7, and is adapted to regulate the flowrate of the airflow that the low-pressure compressor 3 feeds at inlet of the molecular separator 2 also based on the signals coming from the pressure sensor or sensor 7.

[0071] In addition, the Nitrox-mixtures production machine 1 preferably also includes a preferably electrically-powered, heating device 8, which is interposed between the low-pressure compressor 3 and the molecular separator 2, and is adapted to heat up the airflow that the low-pressure compressor 3 feeds at inlet of the molecular separator 2.

[0072] The electronic control device 6, moreover, is preferably also adapted to command the heating device 8 advantageously so as to bring and maintain the temperature of the airflow entering the molecular separator 2 to a predetermined target value, hereinafter referred to as the target temperature T.sub.0, which is advantageously comprised between +35? C. and +45? C. More in detail, the Nitrox-mixtures production machine 1 is preferably also provided with at least one temperature sensor 9, which is located between the molecular separator 2 and the heating device 8, and is structured so as to provide as outlet a (electrical) signal indicative of the temperature of the air directed towards the molecular separator 2.

[0073] The electronic control device 6, in turn, is preferably connected to the temperature sensor (s) 9, and is preferably adapted to command the heating device 8 according to the signals arriving from the temperature sensor (s) 9, so as to bring the temperature of the airflow entering the molecular separator 2 to said target temperature T.sub.0.

[0074] In addition, the electronic control device 6 is preferably also adapted to command the heating device 8 according to the signals arriving from the oxygen sensor (s) 5 and/or according to the signals arriving from the pressure sensor (s) 7.

[0075] More specifically, the electronic control device 6 is preferably also adapted to vary/modify the value of said target temperature T.sub.0 according to the signals arriving from the oxygen sensor (s) 5 and/or according to the signals arriving from the pressure sensor (s) 7.

[0076] With reference to FIG. 2, in the example shown, in particular, the semi-permeable membrane molecular separator 2 is preferably structured so as to provide at outlet a Nitrox mixture with an oxygen percentage lower than 50% and advantageously ranging between 38% and 45%.

[0077] In addition, the molecular separator 2 preferably comprises: a pressure vessel 10 advantageously oblong in shape, which is preferably made of a metal or composite material, and is provided with an inlet and two outlets separate and distinct from each other; an automatic discharge valve 11, which is located at a first outlet of the pressure vessel 10 and is adapted to maintain the pressure of the gas inside the pressure vessel 10 more or less constant at a predetermined value advantageously lower than 20 bar; and a bundle of hollow fibres with a semi-permeable wall (not visible in the figures), which are arranged inside the pressure vessel 10 so as to connect the inlet of the vessel directly with the outlet of the vessel where the discharge valve 11 is located, and are made of a polymeric or composite material having a structure permeable to molecules of oxygen, water vapour, carbon dioxide and, more generally, to molecules with dimensions smaller than those of nitrogen molecules.

[0078] The pressure sensor (s) 7 is/are preferably mounted on the pressure vessel 10 so as to measure/detect the air pressure within the bundle of hollow fibres of the molecular separator 2.

[0079] The semi-permeable membrane molecular separator 2 and the pressure sensor (s) 7 are components readily available on the market, so they won't be further described.

[0080] The semi-permeable membrane molecular separator 2 operates as follows: while the air flow produced by the low-pressure compressor 3 enters the pressure vessel 10 and flows within the hollow fibres towards the discharge valve 11, most of the molecules of oxygen, carbon dioxide and/or water vapour contained in the air succeed in freely passing through the wall of the hollow fibres, and heads towards the second outlet of the pressure vessel 10. Instead, almost all of the nitrogen molecules contained in the air flowing within the hollow fibres remain confined within the hollow fibres and reach the first outlet of pressure vessel 10, from where they exit the pressure vessel 10 through the discharge valve 11.

[0081] From the first outlet of pressure vessel 10, therefore, a gaseous mixture is discharged into the atmosphere with a very high nitrogen percentage advantageously high than 90%.

[0082] From the second outlet of pressure vessel 10, instead, it comes out a Nitrox mixture with a high oxygen percentage, with the addition of a small percentage of water vapour and/or carbon dioxide.

[0083] More specifically, a Nitrox mixture with an oxygen percentage preferably ranging between 38% and 45% comes out of the second outlet of pressure vessel 10.

[0084] Mixing manifold 4, in turn, is preferably connected to the second outlet of pressure vessel 10 in order to receive said Nitrox mixture with the high oxygen percentage.

[0085] With particular reference to FIG. 2, the mixing manifold 4 preferably comprises: an oblong and advantageously also substantially rectilinear, tubular body 13, which is provided with an additional mouth spaced apart from the two main mouths located at the two opposite ends of the same tubular body 13; and advantageously also a series of deflecting fins or appendages 14, which are spread within the tubular body 13 and are adapted to create a strong turbulence in the gaseous mixture flowing within the tubular body 13.

[0086] The first end/mouth of the tubular body 13 communicates directly with the outside. The second end/mouth of the tubular body 13 is structured so as to be connected directly to the suction mouth of the high-pressure compressor 101, preferably by means of a removable connecting pipe 15.

[0087] The additional mouth of tubular body 13, on the other hand, communicates directly with the outlet of the molecular separator 2, or rather with the second outlet of the pressure vessel 10, so as to allow the Nitrox mixture with the high oxygen percentage to freely enter inside the same tubular body 13.

[0088] Preferably, the mixing manifold 4 additionally includes a filtering assembly 16, which is located at first end/mouth of tubular body 13, and is adapted to retain the dust suspended in the air entering the tubular body 13.

[0089] With particular reference to FIG. 2, in addition, the or at least one of the oxygen sensors 5 is preferably fixed on the tubular body 13 at or near the second end/mouth of tubular body 13.

[0090] Preferably, the or each oxygen sensor 5 moreover consists of an electrochemical oxygen cell of a known type, that provides at output an electrical signal indicative of the value of the oxygen percentage present in the gaseous mixture grazing the cell.

[0091] The heating device 8, on the other hand, preferably comprises: an oblong tubular body 17, which is preferably substantially rectilinear and/or made of metallic material, and is adapted to be crossed by the airflow directed towards the molecular separator 2; and a resistor 18, which is located within the tubular body 17 so as to be lapped and cooled by the airflow passing through the same oblong tubular body 17.

[0092] Preferably, the or at least one of the temperature sensors 9 is also located/mounted on tubular body 17, at the end/mouth from where the airflow exits the tubular body 17, directed towards the molecular separator 2.

[0093] With reference to FIGS. 1 and 2, on the other hand, the low-pressure compressor 3 is preferably structured so as to suck air at ambient pressure and feed the molecular separator 2 with an airflow with a pressure advantageously ranging between 8 and 15 bar.

[0094] In addition, the low-pressure compressor 3 is preferably a rotary volumetric compressor.

[0095] More specifically, the low-pressure compressor 3 is preferably a volumetric screw compressor.

[0096] In other words, the low-pressure compressor 3 preferably comprises: a screw pumping assembly 20; an electric drive motor 21, which is mechanically connected to the screw pumping unit 15 so as to drive into rotation the two rotors of the screw pumping assembly 20, advantageously with a predetermined and substantially constant rotation speed; and preferably also a gas/liquid separator 22, which is located downstream of the screw pumping assembly 20, and is structured to retain within itself the droplets of oil and/or condensed water vapour present in the airflow coming out from the pumping assembly 20.

[0097] In addition, the low-pressure compressor 3 is preferably also provided with a filtering assembly 23, which is located upstream of the screw pumping assembly 20, and is adapted to retain the dust suspended in the air being sucked in by the low-pressure compressor 3.

[0098] Preferably, the pumping assembly 20 and the drive motor 21 are moreover arranged side by side to each other, advantageously resting on the same supporting platform or frame, so as to form an easily transportable single block. Also the gas/liquid separator 22 and/or the filtering assembly 23 is/are advantageously located on the supporting platform or frame that hosts the pumping assembly 20 and the drive motor 21.

[0099] In addition, the screw pumping assembly 20 and the drive motor 21 are preferably connected to each other by means of a drive belt, which is looped around two pulleys fixed one to the shaft of the drive motor 21 and the other to the shaft of the screw pumping assembly 20.

[0100] Clearly, the drive motor 21 may drive into rotation the shaft of pumping assembly 20 without the use of belts and/or other intermediate motion transmission parts.

[0101] Preferably also the molecular separator 2 and/or the mixing manifold 4 and/or the electronic control device 6 and/or the heating device 8 is/are located on the supporting platform or frame that hosts the pumping assembly 20 and the drive motor 21, so as to form an easily transportable single block.

[0102] With particular reference to FIG. 2, the electronic control device 6, in turn, is adapted to regulate/vay the flowrate of the airflow that is sucked in by the low-pressure compressor 3, or rather by the screw pumping assembly 20, based on both the signals coming from the oxygen sensor (s) 5 and the signals coming from the pressure sensor (s) 7.

[0103] The electronic control device 6 in particular comprises: an electronically-controlled valve assembly 24, which is located upstream of the suction of the low-pressure compressor 3, or rather upstream of the suction mouth of the screw pumping assembly 20, so as to regulate/vary the flowrate of the airflow that is sucked in by the low-pressure compressor 3; and an electronic control unit 25, which is connected to the oxygen sensor (s) 5 and advantageously also to the pressure sensor (s) 7, and is adapted to command the valve assembly 24 based on the signals arriving from both the oxygen sensor (s) 5 and the pressure sensor (s) 7.

[0104] More in detail, the valve assembly 24 comprises: a control valve 26, which is located upstream of the suction of low-pressure compressor 3, or rather upstream of the suction mouth of the screw pumping assembly 20, and has a movable shutter that regulates, according to its position inside the valve, the flowrate of the airflow that flows towards the suction mouth of the low-pressure compressor 3, advantageously between a maximum and a minimum value; and an electronically-controlled driving device 27, which is adapted to move/shift, on command, the movable shutter of the same control valve 26.

[0105] The electronic control unit 25, in turn, is adapted to command the electronically-controlled driving device 27, so as to control, advantageously in real time, the position of the movable shutter of control valve 26.

[0106] The electronic control unit 25, in addition, is program-med/configured so as to maintain the oxygen percentage in the Nitrox mixture flowing out of outlet of mixing manifold 4, or rather flowing out of the second end/mouth of tubular body 13, and is advantageously directed towards the suction of high-pressure compressor 101, substantially constant over time and substantially equal to said target percentage O %.sub.0.

[0107] More in detail, the electronic control unit 25 is programmed/configured so as to continuously vary/correct the position of the movable shutter of control valve 26 based on signals coming from the oxygen sensor (s) 5, so as to implement a feedback control of the valve assembly 24.

[0108] In other words, the electronic control unit 25 is programmed/configured to implement a feedback control of the position of the movable shutter of the control valve 26 based on signals coming from the oxygen sensor (s) 5.

[0109] In addition, the electronic control unit 25 is programmed/configured to implement a feedback control of the position of the movable shutter of command valve 26 when the air pressure inside the molecular separator 2 meets certain conditions.

[0110] Clearly, the air pressure inside the molecular separator 2 is measured with the aid of the pressure sensor (s) 7.

[0111] With reference to FIG. 2, in particular, the driving device 27 preferably comprises: a pneumatic actuator 28, which is adapted to varying the position of the movable shutter of the control valve 26 according to the value of the air pressure that the same actuator receives at its inlet; and an electronically-controlled pressure reducer 29, which is interposed between the pneumatic actuator 28 and the delivery of the low-pressure compressor 3, and is adapted to adjust/vary, on command, the value of the air pressure directed towards the inlet of the pneumatic actuator 28.

[0112] In other words, the pneumatic actuator 28 is coupled to, or incorporated into, the control valve 26 so as to freely move/displace the movable shutter of the control valve 26, and the pressure of the air that the pneumatic actuator 28 receives at inlet determines the position assumed by the movable shutter of the valve.

[0113] Thus, the pressure of the air that the pressure reducer 29 feeds at inlet of the pneumatic actuator 28 determines the position of the movable shutter of the control valve 26.

[0114] The electronic control unit 25, in turn, is preferably adapted to control the pressure reducer 29 so as to feed, at inlet to the pneumatic actuator 28, a flow of pressurised air having a pressure set by the same electronic control unit 25.

[0115] In the example shown, in particular, the control valve 26 is preferably a butterfly valve or gate valve, and is preferably interposed between the filtering assembly 23 and the suction mouth of the screw pumping assembly 20.

[0116] The control valve 26, in addition, is advantageously structured so as to regulate/vary the flowrate of the airflow entering the low-pressure compressor 3 between zero and a predetermined maximum value.

[0117] The pneumatic actuator 28, in turn, is preferably a single-acting pneumatic cylinder, which is advantageously incorporated within the control valve 26, and is adapted to move the movable shutter of the control valve 26 preferably by overcoming the force of a counter spring that instead tends to bring and maintain the movable shutter in a closed position.

[0118] With reference to FIG. 2, the electronic control device 6 is moreover provided with an external control panel 30 or other type of user interface, via which the user can communicate to the electronic control unit 25 the oxygen percentage of the Nitrox mixture that has to come out from the mixing manifold 4 and advantageously reach the suction of the high-pressure compressor 101; and preferably also with a display or other external visualising device 31, which is commanded by the electronic control unit 25 and is capable of displaying the oxygen percentage momentarily set as target percentage O %.sub.0 by the user.

[0119] Preferably, the visualising device 31 is moreover capable of displaying, advantageously in real time, the value detected by the oxygen sensor (s) 5 and/or the value detected by the pressure sensor (s) 7.

[0120] In the example shown, in particular, the electronic control unit 25 and/or the control panel 30 and/or the visualising device 31 are advantageously located within a rigid boxlike enclosure of known type.

[0121] Preferably, the electronic control unit 25 is moreover connected also to the temperature sensor (s) 9, and is advantageously also adapted to command the heating device 8 based on the signals arriving from the temperature sensor (s) 9 and optionally also based on the signals arriving from the oxygen sensor (s) 5.

[0122] More in detail, the electronic control unit 25 is preferably programmed/configured so as to independently establishes the target temperature T.sub.0 that the airflow entering the molecular separator 2 must have advantageously choosing it among a predetermined range of values, and then it is adapted to activate and deactivate the heating device 8 so as to heat the airflow directed towards the molecular separator 2 up to this target temperature T.sub.0.

[0123] In other words, the electronic control unit 25 is preferably programmed/configured to command the electric current circulating in the resistor 18 of heating device 8.

[0124] Preferably, the visualising device 31 is moreover capable of displaying, advantageously in real time, the value measured by said temperature sensor (s) 9.

[0125] In a less sophisticated embodiment, however, the electronic control unit 25 may be programmed/configured to activate and deactivate the heating device 8 in order to heat the airflow headed towards the molecular separator 2 up to a preset and non-adjustable target temperature T.sub.0, advantageously ranging between +35? C. and +45? C.

[0126] Preferably, the electronic control unit 25 of the electronic control device 6 is finally also adapted to open the discharge valve 112 if the composition of the Nitrox mixture coming out of mixing manifold 4 does not correspond to the set composition. With reference to FIGS. 1 and 2, preferably the Nitrox-mixtures production machine 1 additionally comprises, upstream of the molecular separator 2 or the heating device 8, a drying device 32 and/or a filtering assembly 33.

[0127] The drying device 32 is adapted to retain at least part of the water vapour present in the airflow coming out of the low-pressure compressor 3, or rather coming out of the screw pumping assembly 20, and is preferably located immediately downstream of the gas/liquid separator 22 or the screw pumping assembly 20.

[0128] In the example shown, the drying device 32 is preferably an absorption dryer structured to reduce the amount of water vapour in the air leaving the low-pressure compressor 3 to a value less than or equal to 15 mg/m.sup.3.

[0129] The filtering assembly 33, on the other hand, is preferably located between the drying device 32 and the molecular separator 2, or the heating device 8, and is structured so as to retain impurities and other physical and/or biological contaminants present in the airflow directed towards the molecular separator 2.

[0130] In the example shown, the filtering assembly 33 is preferably made up of a series of activated carbon filters arranged in cascade one to the other.

[0131] Preferably also the drying device 32 and/or a filtering assembly 33 is/are located on the supporting platform or frame that hosts the pumping assembly 20 and the drive motor 21, so as to form an easily transportable single block.

[0132] General operation of the scuba-diving cylinders refilling equipment 100 and of its high-pressure compressor 101 are already known in the market and therefore need no further explanation.

[0133] As regard instead the Nitrox-mixtures production machine 1, the electronic control unit 25 of electronic control device 6 is programmed/configured so as to carry out a feedback control of the valve assembly 24, or rather of the position of the movable shutter of the control valve 26 of valve assembly 24, based on the signals arriving from the oxygen sensor (s) 5.

[0134] Clearly, the electronic control unit 25 varies/modifies the position of the movable shutter of control valve 26 suitably commanding the electronically-controlled driving device 27 of valve assembly 24, or rather the pressure regulator 29.

[0135] In other words, the electronic control unit 25 is programmed/configured to continuously modify/adjust the position of the movable shutter of control valve 26 based on the signals from the oxygen sensor (s) 5, so as to bring and maintain the oxygen percentage of the Nitrox mixture coming out of mixing manifold 4 to a value substantially equal to the target percentage O %.sub.0 set by the user.

[0136] By varying the flowrate of the airflow entering the low-pressure compressor 3, in fact, the electronic control unit 25 also varies the flowrate of the airflow entering the molecular separator 2 and, consequently, the flowrate of the flow of intermediate Nitrox mixture entering the mixing manifold 4. Each change in the flowrate of the Nitrox mixture entering into the mixing manifold 4, in turn, results in a change of the oxygen percentage of the Nitrox mixture that comes out of mixing manifold 4 and is sucked in by the high-pressure compressor 101.

[0137] In addition, the electronic control unit 25 is moreover programmed/configured so as to carry out the feedback control of the valve assembly 24 when the trend over time of the pressure of the air inside the molecular separator 2 has substantially stabilized over time.

[0138] In other words, the electronic control unit 25 is programmed/configured to monitor the air pressure inside the molecular separator 2, and to implement the feedback control of the valve assembly 24, or rather of the pressure reducer 29, when the trend over time of the air pressure inside the molecular separator 2 meets a stable-pressure condition, which is indicative of the fact that the air pressure inside the molecular separator 2 has substantially stabilised over time.

[0139] More in detail, the electronic control unit 25 is preferably programmed/configured to start the feedback control of the valve assembly 24, when the variations over time of the air-pressure value inside the molecular separator 2 remain within a predetermined tolerance range.

[0140] Preferably, the electronic control unit 25 is moreover programmed/configured to start the feedback control of the valve assembly 24, when the relative pressure (difference between the absolute pressure and the ambient pressure) of the air inside the molecular separator 2 has exceeded a predetermined minimum threshold.

[0141] Advantageously, this minimum threshold is furthermore greater than or equal to 0.8 bar.

[0142] More specifically, the electronic control unit 25 is preferably programmed/configured so as to start the feedback control of valve assembly 24, when variations (in absolute value) in the value of the air pressure inside the molecular separator 2 remain below a predetermined maximum threshold advantageously equal to or less than 0.5 bar, for a monitoring time interval greater than 2 s (seconds) and advantageously also lower than 60 s (seconds).

[0143] In other words, the stable-pressure condition is met when the variations (in absolute value) of the air-pressure value inside the molecular separator 2 remain below a predetermined maximum threshold advantageously equal to or less than 0.5 bar, for a monitoring time interval of more than 2 s (seconds) and advantageously also less than 60 s (seconds). In addition, the stable-pressure condition is preferably met when the relative air pressure inside the molecular separator 2 is greater than or equal to 0.8 bar.

[0144] More conveniently, this maximum threshold is preferably equal to 0.3 bar or, more advantageously, equal to 0.2 bar. The monitoring time interval, on the other hand, is preferably greater than or equal to 5 s (seconds) and/or less than or equal to 30 s (seconds) or, more advantageously, less than or equal to 20 s (seconds).

[0145] Even more conveniently, the stable-pressure condition is preferably met if variations (in absolute value) of the air-pressure value inside the molecular separator 2 remain below a maximum threshold of approximately 0.1-0.15 bar, at either end of a monitor time interval of approximately 10-15 s (seconds). In addition, the stable-pressure condition is preferably met when the relative air pressure inside the molecular separator 2 is greater than or equal to 1 bar.

[0146] Preferably, the electronic control unit 25 is moreover programmed/configured so as to end the feedback control of the valve assembly 24, or rather of the pressure reducer 29, and advantageously also to close the valve assembly 24, upon the occurrence of one or more predetermined operational events.

[0147] More in detail, the electronic control unit 25 is preferably programmed/configured so as to end the feedback control of the valve assembly 24, and advantageously also to close the valve assembly 24, when a new and different value of the target percentage O %.sub.0 is set via the control panel 30, and/or when a stop signal is received advantageously coming from the control panel 30 (stop of machine 1 decided unilaterally by the user) and/or from the electronic control unit 111 (shutdown of the high-pressure compressor 101).

[0148] Assuming that the user has already selected the oxygen percentage of the Nitrox mixture that has to come out of the mixing manifold 4, i.e. has already selected the desired target O %.sub.0, the operation of the electronic control device 6 firstly entails: [0149] a step of pressure monitoring, in which the air pressure inside the molecular separator 2 is monitored, so as to determine when the trend over time of the air pressure in the molecular separator 2 has stabilised over time, i.e. meets said stable-pressure condition; and [0150] a subsequent step of feedback control, in which the position of the movable shutter of control valve 26 is continuously adjusted/varied based on the signals coming from the oxygen sensor (s) 5, so as to bring and maintain the oxygen percentage of the Nitrox mixture coming out of the mixing manifold 4 at a value substantially equal to the target percentage O %.sub.0 set by the user.

[0151] Preferably, the feedback-control step starts after the trend over time of the air pressure in molecular separator 2 has stabilised over time, i.e. after said stable-pressure condition has been met.

[0152] In addition, beforehand the pressure-monitoring step, operation of the electronic control device 6 preferably also includes the step of determining an optimal initial position of the movable shutter of control valve 26.

[0153] The optimal initial position is the position that the movable shutter of control valve 26 should likely assume, on the basis of previous operating cycles, such that the machine 1 can deliver a Nitrox mixture having an oxygen percentage substantially equal to the target percentage O %.sub.0 set by the user.

[0154] Preferably, the step of determining the optimal initial position of the movable shutter of control valve 26 in particular involves estimating, advantageously by means of linear interpolation, said optimal initial position on the basis of a plurality of already known sample positions, which are advantageously associated to Nitrox mixtures with specific oxygen percentages.

[0155] Finally, operation of electronic control device 6 preferably includes, at the end of the feedback-control step, a step of verification and possible updating of the sample position or positions based on the parameters used in the feedback-control step that has just ended.

[0156] With reference to FIG. 3, in particular, the electronic control unit 25 preferably starts by determining (block 300) the optimal initial position that the movable shutter of the control valve 26 should assume, so that the machine 1 can likely provided at outlet a Nitrox mixture having an oxygen percentage substantially equal to the target O %.sub.0 set by the user.

[0157] More in detail, the electronic control unit 25 is preferably programmed/configured to estimate the optimal initial position of the movable shutter of valve assembly 26 by interpolating this initial optimum position from a series of already known sample positions.

[0158] In other words, the electronic control unit 25 preferably has a non-volatile memory in which are stored the sample positions that the movable shutter of control valve 26 should assume in order to obtain at least two different values of target percentage O %.sub.0, and is preferably programmed/configured so as to determine the new optimal initial position of the movable shutter of control valve 26 via interpolation based on said sample positions.

[0159] For example, the sample positions could be the position of the mobile shutter of control valve 26 associated to a Nitrox gaseous mixture with an oxygen percentage equal to 28% (EAN-28), and the position of the mobile shutter of control valve 26 associated to a Nitrox gaseous mixture with an oxygen percentage equal to 36% (EAN-36).

[0160] After having determined the optimal initial position of the movable shutter of control valve 26, the electronic control unit 25 drives (block 310) the valve assembly 24, or rather the electronically-controlled driving device 27, so as to place the movable shutter of control valve 26 in said optimal initial position.

[0161] After having placed the movable shutter of control valve 26 in said optimal initial position, the electronic control unit 25 monitors (block 320) the value of the air pressure inside the molecular separator 2, and checks (block 330) whether the trend over time of the air pressure inside the molecular separator 2 has stabilised over time, i.e. whether it meets said set of stable-pressure conditions.

[0162] Clearly, the monitoring of the air pressure inside the molecular separator 2 is carried out with the aid of the pressure sensor (s) 7.

[0163] When the pressure of the air inside the molecular separator 2 has stabilised, the electronic control unit 25 starts the feedback control (block 340) of the valve assembly 24 based on signals coming from the oxygen sensor (s) 5.

[0164] In other words, when the pressure of the air inside the molecular separator 2 has stabilised, the electronic control unit 25 continuously modifies/adjusts the position of the movable shutter of control valve 26 based on the signals coming from the oxygen sensor (s) 5, so as to bring and maintain the oxygen percentage of the Nitrox mixture coming out of mixing manifold 4 at a value substantially equal to the target percentage O %.sub.0 set by the user.

[0165] In addition, the electronic control unit 25 preferably ends (block 350) the feedback control of the valve assembly 24 when a predefined stop condition occurs.

[0166] Preferably, this stop condition includes the setting of a new and different value of the target percentage O %.sub.0 via the control panel 30, and/or the reception by the electronic control unit 25 of a stop signal that advantageously comes from the control panel 30 and/or the electronic control unit 111.

[0167] Preferably, after having ended the feedback-control step of valve assembly 24, the electronic control unit 25 finally compares (block 360) the sample position stored internally with the actual position assumed by the movable shutter of control valve 26 during, or at the end of, the feedback operation cycle just completed and, if necessary, takes this actual position as a new sample position.

[0168] More in detail, the electronic control unit 25 preferably updates the sample position when the difference between the sample position stored internally and the actual position assumed by the movable shutter of control valve 26 during, or at the end of, the last feedback operation cycle exceeds a preset maximum threshold which is advantageously equal to 10-15%. In the example shown, in particular, since the position of the movable shutter of control valve 26 is preferably controlled by the pneumatic actuator 28 on the basis of the pressure of the that the pressure reducer 29 feeds at inlet of pneumatic actuator 28, the electronic control unit 25 operates as follows.

[0169] Firstly, the electronic control unit 25 is preferably programmed/configured to determine (block 300) the value of the optimal initial pressure Pi that should be sent to the pneumatic actuator 28 of valve assembly 24, so that the machine 1 can reasonably provide at outlet of a Nitrox mixture having an oxygen percentage substantially equal to the target percentage O %.sub.0 set by the user.

[0170] More specifically, the electronic control unit 25 is preferably programmed/configured to estimate the value of said optimal initial pressure Pi on the basis of a plurality of sample pressures, advantageously stored within the same electronic control unit 25.

[0171] More specifically, the electronic control unit 25 is preferably programmed/configured to calculate/find the value of the optimal initial pressure Pi by interpolation, based on said plurality of already known sample pressures.

[0172] In other words, within the non-volatile memory of electronic control unit 25 there are advantageously stored the nominal pressure values (sample pressures), which the air at inlet of pneumatic actuator 28 must have in order to obtain at least two different values of target percentage O %.sub.0, and the electronic control unit 25 is preferably programmed/configured to determine said optimal initial pressure Pi by advantageously linear interpolation, based on said nominal pressure values (sample pressures).

[0173] In the example shown, in particular, within the non-volatile memory of electronic control unit 25 there are preferably stored the nominal value of the air pressure (sample pressure) to be fed at inlet of pneumatic actuator 28 for obtaining a Nitrox gaseous mixture with oxygen percentage equal to 28% (EAN-28), for example 1, 25 bar; and the nominal value of the air pressure (sample pressure) to be fed at inlet of pneumatic actuator 28 for obtaining a Nitrox gaseous mixture with oxygen percentage equal to 36% (EAN-36), for example 1.1 bar.

[0174] After having determined the value of the optimal initial pressure Pi that the air at inlet of the pneumatic actuator 28 must the electronic control unit 25 is preferably programmed/configured to drive (block 310) the pressure reducer 29 so that the pneumatic actuator 28 receives at its inlet an airflow having a pressure value equal to said optimal initial pressure Pi.

[0175] After having driven the pressure reducer 29 so that the pneumatic actuator 28 receives at inlet a flow of air with a pressure equal to said optimal initial pressure Pi, the electronic control unit 25 is preferably programmed/configured to determine (block 320) the momentary pressure of the air inside the molecular separator 2, advantageously based on the signals coming from the pressure sensor (s) 7.

[0176] After having determined the air pressure inside the molecular separator 2, the electronic control unit 25 is preferably programmed/configured to analyse (block 330) the trend over time of the air pressure in the molecular separator 2, so as to determine whether the trend of the air pressure in the molecular separator 2 has stabilised over time.

[0177] In other words, the electronic control unit 25 is preferably programmed/configured to check (block 330) when the trend over time of the air pressure inside the molecular separator 2 meets said stable-pressure condition.

[0178] After having determined that the trend over time of the air pressure present inside the molecular separator 2 has stabilized, i.e. meets said stable-pressure condition, the electronic control unit 25 is preferably programmed/configured so as to continuously modify/adjust (block 340) the pressure of the air that the pressure reducer 29 feeds at inlet of pneumatic actuator 28 based on the signals coming from the oxygen sensor (s) 5, i.e. carries out the feedback control, so as to bring and maintain the oxygen percentage of the Nitrox mixture coming out of mixing manifold 4 to a value substantially equal to the target percentage O %.sub.0 set by the user.

[0179] Preferably, the electronic control unit 25 is moreover programmed/configured to reset (block 350) the value of the air pressure that the pressure reducer 29 feed at inlet of pneumatic actuator 28 and to end the feedback control of the pressure reducer 29, when said stop condition occurs.

[0180] Finally, once the feedback control of the pressure reducer 29 of valve assembly 24 is ended, the electronic control unit 25 is preferably also programmed/configured so as to update (block 360) the sample pressure stored internally when the difference between the sample pressure stored internally and the air pressure fed to the pneumatic actuator 28 during the last feedback operation cycle is advantageously equal to or greater than 20%.

[0181] The advantages connected to the new Nitrox-mixtures production machine 1 and to its operating method are remarkable. The Nitrox-mixtures production machine 1 does not require continuous supervision by the user and, in addition, is also capable of discharging externally the produced Nitrox mixture if its composition does not correspond to that set by the user.

[0182] In addition, the particular operating method implemented by the electronic control unit 25, which carries out the feedback control of valve assembly 24 only when the air pressure inside the molecular separator 2 has stabilised, makes it possible to minimise the duration of the transients in which the oxygen percentage of the Nitrox mixture coming out of mixing manifold 4 does not correspond to that set by the user, thus reducing the amount of Nitrox mixture that is discharged externally from the scuba-diving cylinders refilling equipment 100.

[0183] Finally, it is clear that modifications and variations may be made to the Nitrox-mixtures production machine 1 and/or the scuba diving cylinder refilling equipment 100 without however departing from the scope of the present invention.

[0184] For example, the low-pressure compressor 3 may be a lobe-type volumetric compressor.

[0185] In addition, the automatic discharge valve 11 of molecular separator 2 may be replaced by a simple pressure reducer and/or flow reducer.

[0186] The pneumatic actuator 28 of electronically-controlled valve assembly 24, moreover, could also be supplied with pressurised air coming from a source of pressurised air or other pressurised gas other than the low-pressure compressor 3.

[0187] In this case, the pressure reducer 29 would be interposed between the pneumatic actuator 28 and said pressurised-air source.

[0188] With reference to FIG. 4, finally, in a more sophisticated embodiment, the electronically-controlled driving device 27 of valve assembly 24 comprises, in place of the pneumatic actuator 28 and the pressure reducer 29, an electronically-controlled electric or electromechanical actuator 34, which is advantageously provided with a position transducer, and is coupled to the control valve 26 so as to move/displace, on command, the movable shutter of the same valve.

[0189] In this case, the electronic control unit 25 directly controls the electric or electromechanical actuator 34.

[0190] Clearly, also in this embodiment the electronic control unit 25 implements the feedback control of the valve assembly 24, or rather the feedback control of the electric or electromechanical actuator 34, when the air pressure inside the molecular separator 2 has stabilised.