Abstract:
A device for regulating the delivery pressure of gases includes a valve unit having at least one valve seat and a respective closure element displaceable along an axis with respect to the valve seat which is controlled by a diaphragm. The device further includes a first spring which acts on the diaphragm in order to subject it to a preselected resilient load. A second spring is selectively activated to exert an additional resilient load on the diaphragm. The device includes a handle associated with the first and second springs in order to impose selectively the desired delivery pressure value, between a minimum value and a maximum value of pre-calibration, the pressure value being proportionally correlated with a predetermined resilient load exerted on the diaphragm.

Description:
This application is a U.S. National Phase Application of PCT International Application PCT/IT2005/000356 which is incorporated by reference herein. 
   TECHNICAL FIELD 
   The present invention relates to a device for regulating the delivery pressure of combustible gases. 
   BACKGROUND OF THE INVENTION 
   It is well known that such devices are used for regulating the pressure at which combustible gases are delivered to burners or similar equipment in order to keep substantially constant the value of the delivery pressure when the supply pressure varies. 
   The invention is applicable in particular to the specific technical field of pressure regulators that are arranged for use with combustible gases of various natures, such as, for example, natural gas and liquid gas, which have combustibility characteristics which differ from one another and which are such as to require corresponding separate operations for calibrating the regulator. 
   As is known, natural gas is normally supplied at a pressure lower than that of liquid gas and it is therefore preferable to provide in the distribution network, or in the equipment arranged for the alternative use of either of the two above-mentioned gases, pressure regulators in which a device capable of converting the regulator between two different calibration configurations is integrated. 
   An example of a regulating device having the above-mentioned features is known from U.S. Pat. No. 3,747,629. This document describes a pressure regulator which is provided with a first springing system which acts on the diaphragm of the regulator to determine a first pressure value, in the case of use with natural gas, and a second, additional, springing system which can be selectively activated to exert on the diaphragm a resilient load correlated with a second preselected pressure value, which is desired in the case of use with liquid gas. The passage from the first to the second calibration configuration is achieved by an auxiliary spacer means acting on the second springing system in the second configuration. The pre-setting of the two pressure values can in turn be regulated by screw means arranged to pre-load resiliently the respective springing systems. Thus, in order to use the device, the only requirement is the activation of the conversion spacer means in order to pass from one to the other of the configurations provided for, without requiring any other regulating intervention. 
   Also known in this field is the requirement to be able to keep the delivery pressure substantially constant when the flow rate varies, because the pressure tends to decrease as a function of the increase in the power required at the equipment. In applications in which the flow supplied can vary substantially (owing to the variation in the power required), a different and specific pre-setting is therefore desirable for each functioning condition and also for each of the gases provided for in the application. 
   SUMMARY OF THE INVENTION 
   A principal object of the present invention is to provide a pressure-regulating device which is structurally and functionally designed to satisfy the indicated requirements, at the same time overcoming the limits pointed out with reference to the mentioned prior art. 
   This and other objects which will emerge clearly hereinafter are achieved by a device for regulating the delivery pressure of combustible gases. 
   According to one aspect of the invention, a device for regulating the delivery pressure of gases of various natures is provided. The device comprises a valve unit having at least one valve seat and a respective closure element which is controlled by a diaphragm. The closure element is associated with the seat and is displaceable along a predetermined axis (X) during the movement of opening/closing the seat. A first resilient actuator means can be regulated and can act on the diaphragm in order to subject it to a preselected resilient load. A first means for regulating the resilient load is exerted on the diaphragm by the first resilient means. A second resilient means can be regulated and activated selectively to exert an additional resilient load on the diaphragm, in addition to the resilient load exerted by the first resilient means. A second means is provided for regulating the load exerted by the second resilient means. The second regulating means includes check means for the second resilient means. The check means may be associated selectively with the regulating device to convert it from a first operative configuration in which the second resilient means are inactive and are not exerting any resilient load on the diaphragm, to a second operative configuration in which the second resilient means are selectively activated to exert a preselected resilient load on the diaphragm. The first and second resilient actuator means comprise respective springing systems which act directly on the diaphragm and which are coaxial with the axis. The device comprises a handle-form operating means common to and associated with the first and second regulating means in order to impose selectively, in each of the operative configurations, the desired delivery pressure value between a minimum value and a maximum value of pre-calibration. The pressure value is proportionally correlated with a predetermined resilient load exerted on the diaphragm. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further characteristics and advantages of the invention will become clear from the following detailed description of some preferred examples of embodiment thereof, illustrated, for the purposes of guidance and without restrictive intent, with reference to the attached drawings, in which: 
       FIG. 1  is a view in axial section of a first example of a regulating device according to the invention in a first operative configuration, 
       FIG. 2  is a view in axial section of the regulating device of  FIG. 1  in a second distinct operative configuration; 
       FIGS. 3 and 4  are plan views from above of the device according to the invention shown in the preceding figures, 
       FIG. 5  is a view in axial section of a second example of a regulating device according to the invention in a first operative configuration, 
       FIG. 6  is a view in axial section of the regulating device of  FIG. 5  in a second distinct operative configuration; 
       FIGS. 7 and 8  are plan views from above of the device according to the invention shown in  FIGS. 5 and 6 , 
       FIG. 9  is a view in axial section of a third example of a regulating device according to the invention in a first operative configuration, 
       FIG. 10  is a view in axial section of the regulating device of  FIG. 9  in a second distinct operative configuration; 
       FIGS. 11 and 12  are plan views from above of the device according to the invention shown in  FIGS. 9 and 10 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   With initial reference to  FIGS. 1 and 2 , a first example of a device for regulating the delivery pressure of combustible gases which is produced in accordance with the present invention is generally indicated by  1 . 
   The device  1  comprises a valve unit located in a duct  3  (shown schematically) and including a closure element  4  capable of shutting off a valve seat  5  by way of which a stream of gas is delivered to a consumer, such as a burner or similar equipment not illustrated in the drawings. The closure element  4  is displaceable during the movement of opening/closing the seat  5  in a direction identified in the drawings by the axis X. 
   The device  1  also comprises a diaphragm  6  which controls the closure element  4  and which is connected rigidly thereto by a connecting element  7 . 
   On the element  7  is a cylindrical blind seat  8  which is coaxial with the axis X and in which a rod  9  of a spring-carrying disc  10  is supported rotatably about said axis. A first and a second spring, which are coaxial with each other and with the axis X and which are indicated  11  and  12 , respectively, act directly on the disc  10 . In more detail, the corresponding axial ends of the springs  11 ,  12  are fitted on respective protuberances  11   a ,  12   a  which extend from the spring-carrying disc  10  and which are suitable for holding and guiding the springs on the disc. 
   At its opposite axial end, the spring  11  abuts a corresponding end  13   a  of a tubular formation (or first checker)  13  which is centrally hollow and which extends axially along the axis X. Said tubular formation  13  is guided axially and rotatably inside a sleeve  14  which is connected rigidly to a stationary structure of the valve unit and which extends coaxially with the axis X. 
     15  indicates sealing rings interposed between the surfaces of the sleeve  14  and of the tubular casing  13  which are coupled slidingly to one another. A male thread/female thread coupling is also provided between those surfaces, in particular between an externally threaded portion  16  of the tubular formation  13  and a female thread  17  formed by internal threading of the sleeve  14 . 
     18  indicates an axially hollow ring capable of being fitted on the tubular formation  13 . The ring has a head  18   a  from which extends a cylindrical shell  18   b  which is threaded externally at the location of its free axial end  18   c  so that it can be screwed into the female thread  17  of the sleeve  14  (with the shell  18   b  interposed between the sleeve  14  and the tubular formation  13 ). 
   The ring  18  is used, among other things, to cancel out the clearance of the male thread/female thread coupling  16 ,  17 . The ring is also fixed for rotation and axial translation with the tubular formation  13 . 
   It should be noted that, by rotating the tubular formation  13  about the axis X, the formation is subjected to an axial translation movement owing to the male thread/female thread coupling  16 ,  17 , and consequently the resilient pre-loading of the spring  11  can be varied between a minimum value and a maximum value which are predetermined during the stage of calibrating the device. Advantageously, the resilient load is selected in such a manner that, in the case of use with combustible natural gas, the above-mentioned pre-setting guarantees the desired values of the gas delivery pressure downstream of the closure element  4 . 
   In order to set the tubular formation  13  in rotation, the device  1  is provided with a substantially bell-shaped handle-form operating means  19  which extends from a centrally hollow head  19   a  and which is fitted on the tubular formation  13  and is also fixedly joined thereto by a screw means, such as a locking grub screw  20 . The handle  19  is also locked on the ring  18 , for example by means of a coupling having a grooved axial profile. 
   At the end opposite that fitted on the protuberance  12   a , the second spring  12  abuts a guide element  21  which is in turn connected to the free end of a rod-shaped stem  22  which extends coaxially with the axis X and which is guided axially inside the axial cavity of the tubular formation  13 . In this connection, a first shoulder  23  is provided in the tubular formation  13  and is capable of holding and guiding a corresponding portion  22   a  of the stem. 
   A shoulder surface  24 , which is advantageously produced in the form of a resilient ring, is also provided on the stem portion  22   a . A spring  25  whose function will emerge clearly in the course of the description is active between the facing surfaces formed by the shoulders  23  and  24 . 
   The stem portion  22   a  is also held and guided axially by an element in the form of a centrally hollow bush  26  having an external cylindrical profile threaded in such a manner that it can be screwed into a female thread  27  formed by the internal threading of part of the axial cavity formed at the end  13   b  of the tubular formation  13 , which is axially opposite the end  13   a.    
   The first axial portion  26   a  which is extended by a second portion  26   b  of smaller diameter is formed in the axial through-hole of the bush  26 . The first portion  26   a  constitutes a cylindrical guide means for a corresponding cylindrical portion  22   b  of the stem  22  having a diameter larger than that of the portion  22   a . The second portion  26   b , on the other hand, constitutes an axial guide for the portion  22   a , while the shoulder surface formed between the portions  26   a  and  26   b  acts as an abutment check element for the portion  22   b , with the function of limiting the axial travel of the stem  22 . It should be noted that the position of this travel stop abutment can be regulated axially by means of the male thread/female thread coupling between the bush  26  and the tubular formation  13 . 
   A terminal stem portion  22   c  on which an end portion  28   a  of a spring  28  having an opposite free end indicated  28   b  is fitted, is provided at the free end of the stem  22 , which end is opposite that connected to the element  21 . 
   As shown in the configuration of the device of  FIG. 1 , the end  28   b  of the spring  28  is kept spaced from a check surface  29  which faces it and which is formed in a screw element  30 . This spaced position is achieved by the interposition of a bush  31  between the screw  30  and the tubular formation  13 . To be more precise, the bush  31  has an axial hole and is provided with a head  31   a  from which extends a cylindrical shell portion  31   b  which is in turn axially extended by an externally threaded end portion  31   c . The end portion  31   c  can be screwed into the female thread  27  of the tubular formation  13  while the cylindrical portion  31   b  is guided in the through-hole through the handle  19 . The head  31   a  is advantageously provided with a polygonal external profile in order to permit the engagement of a control key. 
   At the location of the head  31   a , the axial through-hole in the bush  31  has an internally threaded portion  32  into which a corresponding externally threaded shank portion  30   a  of the screw  30  can be screwed. 
   The surface  29  is formed in the screw at the base of a blind cavity  29   a  formed axially in the shank  30   a  at the end opposite a head portion  30   b  of the screw. The head  30   b  is provided with a notch  29   c  for the engagement of a screwdriver. 
   In the configuration of  FIG. 2 , it is provided that the bush  31  is removed beforehand from the device  1  and the screw  30  is screwed directly into the tubular formation  13 , by mutual screwing engagement between the threaded portion  30   a  and the female thread  27 . In this configuration, the end  28   b  of the spring  28  is actively checked by the base surface (or second checker)  29  of the screw  30 , with consequent compression of the spring  28  (and of the other springing systems axially associated therewith along the stem  22 ) and generation of a corresponding resilient load on the diaphragm  6 . It should be noted that the resilient load is added, in the configuration of  FIG. 2 , to the resilient load generated by the spring  11 . 
   As shown in  FIGS. 3 and 4 , the handle  19  is also provided with a pair of check surfaces  33   a ,  33   b  which can interfere with a corresponding abutment surface  34  in the stationary structure of the device  1 . These surfaces  33   a ,  33   b , by interfering with the abutment  34 , act as elements limiting the angular regulating travel (with rotation about the axis X) of the handle  19 . 
   In operation, the configuration of  FIG. 1  is that typically provided when the regulating device is used with combustible natural gas. In this configuration the diaphragm  6  is acted upon by the resilient load generated exclusively by the compression of the spring  11 , which is achieved by regulating the axial position of the tubular formation  13 . Before the calibration stage, the ring  18  is locked on the tubular formation  13  so as to remain fixedly joined thereto for rotation (about the axis X) and for translation (along the axis X). 
   At the stage of calibrating the device  1 , the axial position of the end  13   a  of the tubular formation  13  (and of the ring  18 ) corresponding to the minimum resilient load, which is correlated with the minimum delivery pressure desired, is determined. Once this position has been defined, the handle  19  is inserted and locked in such a manner that a condition of abutment of the check surface  33   a  of the handle on the abutment  34  corresponds to the above-mentioned position. 
   The axial position corresponding to the maximum resilient load, which is correlated with the maximum delivery pressure obtainable, is determined in a similar manner. Once this position has been defined, it is combined with the operative regulating condition in which the check surface  33   b  of the handle interferes with the abutment  34 . A rotation of the handle of approximately 210° is advantageously provided in order to pass from the minimum to the maximum delivery pressure in the configuration of  FIG. 1 . In addition, in the configuration of  FIG. 1 , the spring  25  is used to cancel out the pre-loading of the spring  12  and also to oppose the weight of the stem  22  and of the other masses associated therewith. 
   On the other hand, the configuration of  FIG. 2  is that typically provided when the regulating device is used with combustible liquid gas, having different combustibility characteristics from those of natural gas. 
   In this configuration, after the bush  31  has been removed, the screw  30  is screwed directly into the tubular formation  13  in order to generate on the spring  28  a resilient pre-load capable of moving the stem  22  as far as the condition in which the stem portion  22   b  abuts the shoulder formed between the portions  26   a  and  26   b  of the bush  26 . At the calibration stage, regulation of the axial position of the bush  26  (which determines a travel limit of the stem  22  in the direction of the axis X) and suitable dimensioning of the spring  28 , and also of the springs  12  and  25 , pre-set the delivery pressure values desired at the location of the maximum and minimum handle positions  19  (shown in  FIGS. 3 and 4 ). 
   From this it advantageously follows that, in operation, the conversion of the device from one to the other of the above-mentioned configurations, owing to the change in the gas delivered, requires only the insertion or removal of the spacer bush  31 , without the necessity for any other regulating intervention, because the delivery pressure values obtainable have been imposed beforehand at the calibration stage by means of the regulation measures discussed above. When the device is used, all that is required, in the first configuration (use with natural gas), is that the bush  31  should be screwed in until the head  31   a  abuts the corresponding surface of the handle head, while, in the second configuration (use with liquid gas), all that is required is that, after the bush  31  has been removed, the screw  30  should be screwed in until the head  30   b  of the screw abuts the tubular formation  13  axially, at the location of its end  13   b.    
   With reference to  FIGS. 5 to 8 ,  100  indicates the whole of a second example of a device for regulating the delivery pressure of combustible gases, made in accordance with the present invention, in which, where considered appropriate, details similar to those of the preceding example have been identified by the same reference numerals. 
   The device  100  comprises a valve unit located in a duct  3  (shown schematically) and including a closure element  4  capable of shutting off a valve seat  5  by way of which a stream of gas is delivered to a consumer, such as a burner or similar equipment not illustrated in the drawings. The closure element  4  is displaceable during the movement of opening/closing the seat  5  in a direction identified in the drawings by the axis X. 
   The device  100  also comprises a diaphragm  6  which controls the closure element  4  and which is connected rigidly thereto by a connecting element  7 . 
   On the element  7  is a cylindrical blind seat  8  which is coaxial with the axis X and in which a rod  9  of a spring-carrying disc  10  is supported rotatably about said axis. A first and a second spring, which are coaxial with each other and with the axis X and which are indicated  11  and  12 , respectively, act directly on the disc  10 . In more detail, the corresponding axial ends of the springs  11 ,  12  are fitted on respective protuberances  11   a ,  12   a  which extend from the spring-carrying disc  10  and which are suitable for holding and guiding the springs on the disc. 
   At its opposite axial end, the spring  11  abuts a corresponding end  13   a  of a tubular formation (or first checker)  13  which is centrally hollow and which extends axially along the axis X. Said tubular formation  13  is guided axially and rotatably inside a sleeve  14  which is connected rigidly to a stationary structure of the valve unit and which extends coaxially with the axis X. 
     15  indicates sealing rings interposed between the surfaces of the sleeve  14  and of the tubular casing  13  which are coupled slidingly to one another. A male thread/female thread coupling is also provided between those surfaces, in particular between an externally threaded portion  16  of the tubular formation  13  and a female thread  17  formed by internal threading of the sleeve  14 . 
     18  indicates an axially hollow ring capable of being fitted on the tubular formation  13 . The ring has a head  18   a  from which extends a cylindrical shell  18   b  which is threaded externally at the location of its free axial end  18   c  so that it can be screwed into the female thread  17  of the sleeve  14  (with the shell  18   b  interposed between the sleeve  14  and the tubular formation  13 ). 
   The ring  18  is used, among other things, to cancel out the clearance of the male thread/female thread coupling  16 ,  17 . The ring is also fixed for rotation and axial translation with the tubular formation  13 . 
   It should be noted that, by rotating the tubular formation  13  about the axis X, the formation is subjected to an axial translation movement owing to the male thread/female thread coupling  16 ,  17 , and consequently the resilient pre-loading of the spring  11  can be varied between a minimum value and a maximum value which are predetermined during the stage of calibrating the device. Advantageously, the resilient load is selected in such a manner that, in the case of use with combustible natural gas, the above-mentioned pre-setting guarantees the desired values of the gas delivery pressure downstream of the closure element  4 . 
   In order to set the tubular formation  13  in rotation, the device  100  is provided with a substantially bell-shaped handle-form operating means  19  which extends from a centrally hollow head  19   a  and which is fitted on the tubular formation  13  and is also fixedly joined thereto by a screw means, such as a locking grub screw  20 , which is only shown schematically in the drawings. The handle  19  is also locked on the ring  18 , for example by means of a coupling having a grooved axial profile. 
   At the end opposite that fitted on the protuberance  12   a , the second spring  12  abuts a guide element  21  which is in turn connected to the free end of a rod-shaped stem  122  which extends coaxially with the axis X and which is guided axially inside the axial cavity of the tubular formation  13 . In this connection, a first shoulder  123  is provided in the tubular formation  13  and is capable of holding and guiding a corresponding portion  122   a  of the stem. 
   A shoulder surface  124 , which is advantageously produced in the form of a resilient ring, is also provided on the stem portion  122   a . A spring  125  whose function will emerge clearly in the course of the description is active between the facing surfaces formed by the shoulders  123  and  124 . 
   The stem portion  122   a  is also held and guided axially by an element in the form of a centrally hollow bush  126  having an external cylindrical profile threaded in such a manner that it can be screwed into a female thread  127  formed by the internal threading of part of the axial cavity formed at the end  13   b  of the tubular formation  13 , which is axially opposite the end  13   a.    
   A first axial portion  126   a  which is extended by a second portion  26   b  of smaller diameter is formed in the axial through-hole of the bush  126 . The first portion  126   a  can constitute a cylindrical guide means for a corresponding cylindrical portion  122   b  of the stem  122  having a diameter larger than that of the portion  122   a . The second portion  126   b , on the other hand, constitutes an axial guide for the portion  122   a , while the shoulder surface formed between the portions  126   a  and  126   b  acts as an abutment check element for the portion  122   b , with the function of limiting the axial travel of the stem  122 . It should be noted that the position of that travel stop abutment can be regulated axially by means of the male thread/female thread coupling between the bush  126  and the tubular formation  13 . 
     131  indicates a screw element, acted on by a blind axial cavity  132 , which can engage by screwing the female thread  127  of the tubular formation  13 , at the location of the free end  13   b.    
   In more detail, the screw element  131  has, extending from its axial end  131   a  towards the opposite end  131   b , a first externally threaded shell portion  133 , a shoulder  134  and a second externally threaded shell portion  135  (the portions  133  and  135  have the same thread pitch and diameter). The shell portions extending at the locations of the corresponding ends  131   a  and  131   b  are shaped with polygonal profiles (hexagonal, for example) for the engagement of corresponding operating keys, to enable the screw element  131  to be screwed in and out. Alternatively, transverse notches can be provided for the engagement of screwdrivers. 
   The blind cavity  132  is delimited, at one end, by a base surface  132   a , and forms a seat for housing a pressure pin  136 , whose function will become clearer from the following text. The pin  136  has opposite tapered radial ends, between which a shoulder  137  is also formed. A spring  138 , fitted axially on the corresponding pin portion, is also active between the shoulder  137  and the base (or second checker)  132  of the seat. In order to retain the pin  136  in the seat of the blind cavity  132 , the latter is provided with a rim  139  (produced by chamfering, for example) extending at the location of the opening of the cavity in the proximity of the end  131   b . The said annular rim  139  has a size such that it does not interfere with the shoulder  137  to prevent the pin  136  from moving completely out of the seat  132 . 
   In the configuration of the device of  FIG. 5 , the threaded portion  135  of the screw element  131  is screwed into the tubular formation  13  (with the shoulder  134  abutting against the end  13   b  of the tubular formation), so that the end  131   b  faces and is spaced apart from the free end of the stem  122 . In this configuration the pin  136  is housed in the seat  132 . Advantageously, a cover element  140  is provided for closing at least partially the axial through-hole in the handle  19  and consequently keeping the pin  136  housed in the seat  132 , in opposition to any resilient action of the spring  138 . The cover  140  can be removably fixed to the body of the handle  19 , for example with appendages  140   a  of the cover snap-fitted into corresponding projections  119   b  of the handle, or can be fixed to the screw element  131 , for example by a screwed engagement in the threaded portions  133  or  135 . 
   In the configuration of  FIG. 6 , the screw element  131  is made to be rotatable through 180° about an axis perpendicularly incident on the axis X with respect to the configuration of  FIG. 5 , and to be screwed into the tubular formation  13  with its threaded portion  133 . In this configuration, the pressure pin  136  acts on the stem  122 , by means of the resilient action of the spring  138 , so as to displace the stem  122  to abut the shoulder surface formed between the portions  126   a  and  126   b  of the bush  126 . Consequently, the resilient load generated by the compression of the spring  12  (and of the other springing systems associated with it along the stem  122 ) is added to the resilient load exerted on the diaphragm  6  by the spring  11 . 
   As shown in  FIGS. 7 and 8 , the handle  19  is also provided with a pair of check surfaces  143   a ,  143   b  which can interfere with a corresponding abutment surface  144  in the stationary structure of the device  100 . These surfaces  143   a ,  143   b , by interfering with the abutment  144 , act as elements limiting the angular regulating travel (with rotation about the axis X) of the handle  19 . 
   In operation, the configuration of  FIG. 5  is that typically provided when the regulating device is used with combustible natural gas. In this configuration the diaphragm  6  is acted upon by the resilient load generated exclusively by the compression of the spring  11 , which is achieved by regulating the axial position of the tubular formation  13 . Before the calibration stage, the ring  18  is locked on the tubular formation  13  so as to remain fixedly joined thereto for rotation (about the axis X) and for translation (along the axis X). 
   At the stage of calibrating the device  100 , the axial position of the end  13   a  of the tubular formation  13  (and of the ring  18 ) corresponding to the minimum resilient load, which is correlated with the minimum delivery pressure desired, is determined. Once this position has been defined, the handle  19  is inserted and locked in such a manner that a condition of abutment of the check surface  143   a  of the handle on the abutment  144  corresponds to the above-mentioned position. 
   The axial position corresponding to the maximum resilient load, which is correlated with the maximum delivery pressure obtainable, is determined in a similar manner. Once this position has been defined, it is combined with the operative regulating condition in which the check surface  143   b  of the handle interferes with the abutment  144 . A rotation of the handle of approximately 210° is advantageously provided in order to pass from the minimum to the maximum delivery pressure in the configuration of  FIG. 5 . In addition, in the configuration of  FIG. 5 , the spring  125  is used to cancel out the pre-loading of the spring  12  and also to oppose the weight of the stem  122  and of the other masses associated therewith. 
   On the other hand, the configuration of  FIG. 6  is that typically provided when the regulating device is used with combustible liquid gas, having different combustibility characteristics from those of natural gas. 
   To obtain this configuration, the cover  140  is first disengaged and the threaded portion  135  is unscrewed from the corresponding female thread of the tubular formation  13 . Once the screw  131  has been disengaged, it is rotated through 180° (in the plane of the drawings) with respect to a direction perpendicular to the axis X and is screwed into the female thread  127  of the tubular formation  13  by means of the threaded portion  133 , until the shoulder  134  abuts the end  13   b . The cover  140  is then refitted on the handle  19 . 
   In this configuration, the pin  136 , which is resiliently loaded by the spring  138 , interferes with the stem  122 , pushing the latter into the position shown in  FIG. 6 , in which the stem portion  122   b  abuts the shoulder formed between the portions  126   a  and  126   b  of the bush  126 . At the calibration stage, regulation of the axial position of the bush  126  (which determines a travel limit of the stem  122  in the direction of the axis X) and suitable dimensioning of the spring  138 , and also of the springs  12  and  125 , pre-set the delivery pressure values desired at the location of the maximum and minimum handle positions  19  (shown in  FIGS. 7 and 8 ). 
   From that it advantageously follows that, in operation, the conversion of the device from one to the other of the above-mentioned configurations, owing to the change in the gas delivered, requires only the fitting of the screw element  131 , in one or other of the positions described above, without the necessity for any other regulating intervention, because the delivery pressure values obtainable have been imposed beforehand at the calibration stage by means of the regulation measures discussed above. 
   Advantageously, the externally visible part of the surface of the base portion of the cavity  132  can be made to have a colour (red, for example) which is different from the colour provided in the end area of the pressure pin  136  (blue, for example) opposite the end  132 . Making the cover  140  from at least partially transparent material will thus make the areas with different colours visible from the outside, allowing fast and easy identification of the configuration present in the pressure regulator. 
   With reference to  FIGS. 9 to 12 ,  200  indicates the whole of a third example of a device for regulating the delivery pressure of combustible gases, made in accordance with the present invention, in which, where considered appropriate, details similar to those of the preceding examples have been identified by the same reference numerals. 
   The device  200  comprises a valve unit located in a duct  3  (shown schematically) and including a closure element  4  capable of shutting off a valve seat  5  by way of which a stream of gas is delivered to a consumer, such as a burner or similar equipment not illustrated in the drawings. The closure element  4  is displaceable during the movement of opening/closing the seat  5  in a direction identified in the drawings by the axis X. 
   The device  200  also comprises a diaphragm  6  which controls the closure element  4  and which is connected rigidly thereto by a connecting element  7 . 
   On the element  7  is a cylindrical blind seat  8  which is coaxial with the axis X and in which a rod  9  of a spring-carrying disc  10  is supported rotatably about said axis. A first and a second spring, which are coaxial with each other and with the axis X and which are indicated  11  and  12 , respectively, act directly on the disc  10 . In more detail, the corresponding axial ends of the springs  11 ,  12  are fitted on respective protuberances  11   a ,  12   a  which extend from the spring-carrying disc  10  and which are suitable for holding and guiding the springs on the disc. 
   At its opposite axial end, the spring  11  abuts a corresponding end  13   a  of a tubular formation (or first checker)  13  which is centrally hollow and which extends axially along the axis X. Said tubular formation  13  is guided axially and rotatably inside a sleeve  14  which is connected rigidly to a stationary structure of the valve unit and which extends coaxially with the axis X. 
     15  indicates sealing rings interposed between the surfaces of the sleeve  14  and of the tubular casing  13  which are coupled slidingly to one another. A male thread/female thread coupling is also provided between those surfaces, in particular between an externally threaded portion  16  of the tubular formation  13  and a female thread  17  formed by internal threading of the sleeve  14 . 
     18  indicates an axially hollow ring capable of being fitted on the tubular formation  13 . The ring has a head  18   a  from which extends a cylindrical shell  18   b  which is threaded externally at the location of its free axial end  18   c  so that it can be screwed into the female thread  17  of the sleeve  14  (with the shell  18   b  interposed between the sleeve  14  and the tubular formation  13 ). 
   The ring  18  is used, among other things, to cancel out the clearance of the male thread/female thread coupling  16 ,  17 . The ring is also fixed for rotation and axial translation with the tubular formation  13 . 
   It should be noted that, by rotating the tubular formation  13  about the axis X, the formation is subjected to an axial translation movement owing to the male thread/female thread coupling  16 - 17 , and consequently the resilient pre-loading of the spring  11  can be varied between a minimum value and a maximum value which are predetermined during the stage of calibrating the device. Advantageously, the resilient load is selected in such a manner that, in the case of use with combustible natural gas, the above-mentioned pre-setting guarantees the desired values of the gas delivery pressure downstream of the closure element  4 . 
   In order to set the tubular formation  13  in rotation, the device  200  is provided with a substantially bell-shaped handle-form operating means  19  which extends from a centrally hollow head  19   a  and which is fitted on the tubular formation  13  and is also fixedly joined thereto by a screw means, such as a locking grub screw  20 , which is only shown schematically in the drawings. The handle  19  is also locked on the ring  18 , for example by means of a coupling having a grooved axial profile. 
   At the end opposite that fitted on the protuberance  12   a , the second spring  12  abuts a guide element  21  which is in turn connected to the free end of a rod-shaped stem  222  which extends coaxially with the axis X and which is guided axially inside the axial cavity of the tubular formation  13 . In this connection, a first shoulder  223  is provided in the tubular formation  13  and is capable of holding and guiding a corresponding portion  222   a  of the stem. 
   A shoulder surface  224 , which is advantageously produced in the form of a resilient ring, is also provided on the stem portion  222   a . A spring  225  whose function will emerge clearly in the course of the description is active between the facing surfaces formed by the shoulders  223  and  224 . 
   The stem portion  222   a  is also held and guided axially by an element in the form of a centrally hollow bush  226  having an external cylindrical profile threaded in such a manner that it can be screwed into a female thread  227  formed by the internal threading of part of the axial cavity formed at the end  13   b  of the tubular formation  13 , which is axially opposite the end  13   a.    
   A first axial portion  226   a  which is extended by a second portion  226   b  of smaller diameter is formed in the axial through-hole of the bush  226 . The first portion  226   a  constitutes a cylindrical guide means for a corresponding cylindrical portion  222   b  of the stem  222  having a diameter larger than that of the portion  222   a . The second portion  226   b , on the other hand, constitutes an axial guide for the portion  222   a , while the shoulder surface formed between the portions  226   a  and  226   b  acts as an abutment check element for the portion  222   b , with the function of limiting the axial travel of the stem  222 . It should be noted that the position of this travel stop abutment can be regulated axially by means of the male thread/female thread coupling between the bush  226  and the tubular formation  13 . 
   A terminal stem portion  222   c , on which an end portion  228   a  of a spring  228  having an opposite free end is fitted, is provided at the free end of the stem  222 , which end is opposite that connected to the element  21 . 
     231  indicates a screw element affected by a pair of blind axial cavities, indicated  232  and  233 , respectively, which are coaxial with each other and separated by a wall. The wall  234  defines, on opposite sides, respective base surfaces (or second checker)  232   a ,  233   a  of the corresponding cavities  232 ,  233 . The cavity  232  also has a greater axial length than has the cavity  233 . Each cavity  232 ,  233  is also provided, at the end axially opposite its base surface, with a respective polygonal internal profile  232   b ,  233   b , which is expediently selected for engagement with a hexagonal wrench. 
   The screw element  231  is capable of being screwed into the female thread  227  of the tubular formation  13 , at the location of the free end  13   b . In more detail, a first externally threaded shell portion  235 , a shoulder  236  and a second externally threaded shell portion  237  (the portions  235  and  237  having the same thread diameter and pitch) are formed on the screw element  231 , starting from an axial end  231   a  thereof in the direction towards the opposite end  231   b.    
     238  indicates a circumferential groove provided at the location of the end  231   b , which groove is contiguous with the portion  237  and is also capable of accommodating a ring  239 , preferably an O-ring. 
   In the configuration of the device of  FIG. 9 , the screw element  231  is screwed by means of its threaded portion  237  into the tubular formation  13  (with the shoulder abutting the end  13   b  of the tubular formation  13 ). In that configuration, the end of the spring  228  is maintained at a distance from the base surface  232   a  of the cavity  232 , which surface faces it.  240  indicates a cover element arranged to close the opening of the axial cavity ( 232  or  233 ) which remains visible from outside the handle in each of the respective operative conditions. It is provided that the closure element  240  is equipped with a profile for coupling, for example snap-type coupling, to the corresponding profile of each of the ends  231   a ,  231   b  of the screw element  231 . 
   In the configuration of  FIG. 10 , the screw element  231  is made to be rotatable through 180° about an axis perpendicularly incident on the axis X with respect to the configuration of  FIG. 9 , and to be screwed into the tubular formation  13  with its threaded portion  235 . In this configuration, the end of the spring  228  is actively checked by the base surface  233   a  of the cavity  233 , with consequent compression of the spring  228  (and of the other springing systems axially associated therewith along the stem  222 ) and generation of a corresponding resilient load on the diaphragm  6 . It should be noted that the resilient load is added, in the configuration of  FIG. 10 , to the resilient load generated by the spring  11 . 
   In a similar way to what is provided in the device  100  described above and also shown in  FIGS. 11 and 12 , the handle  19  of the device  200  is also provided with a pair of check surfaces  143   a ,  143   b  which can interfere with a corresponding abutment surface  144  formed in the stationary structure of the device  200 . These surfaces  143   a ,  143   b , by interfering with the abutment  144 , act as elements limiting the angular regulating travel (with rotation about the axis X) of the handle  19 . 
   In operation, the configuration of  FIG. 9  is that typically provided when the regulating device is used with combustible natural gas. In this configuration the diaphragm  6  is acted upon by the resilient load generated exclusively by the compression of the spring  11 , which is achieved by regulating the axial position of the tubular formation  13 . Before the calibration stage, the ring  18  is locked on the tubular formation  13  so as to remain fixedly joined thereto for rotation (about the axis X) and for translation (along the axis X). 
   At the stage of calibrating the device  200 , the axial position of the end  13   a  of the tubular formation  13  (and of the ring  18 ) corresponding to the minimum resilient load, which is correlated with the minimum delivery pressure desired, is determined. Once this position has been defined, the handle  19  is inserted and locked in such a manner that a condition of abutment of the check surface  143   a  of the handle on the abutment  144  corresponds to the above-mentioned position. 
   The axial position corresponding to the maximum resilient load, which is correlated with the maximum delivery pressure obtainable, is determined in a similar manner. Once this position has been defined, it is combined with the operative regulating condition in which the check surface  143   b  of the handle interferes with the abutment  144 . A rotation of the handle of approximately 210° is advantageously provided in order to pass from the minimum to the maximum delivery pressure in the configuration of  FIG. 9 . In addition, in the configuration of  FIG. 9 , the spring  225  is used to cancel out the pre-loading of the spring  12  and also to oppose the weight of the stem  222  and of the other masses associated therewith. 
   On the other hand, the configuration of  FIG. 10  is that typically provided when the regulating device is used with combustible liquid gas, having different combustibility characteristics from those of natural gas. 
   To obtain this configuration, the cover  240  is first disengaged and the threaded portion  237  is unscrewed from the corresponding female thread of the tubular formation  13 . Once the screw  231  has been disengaged, it is rotated through 180° (in the plane of the drawings) with respect to a direction perpendicular to the axis X and is screwed into the female thread  227  of the tubular formation  13  by means of the threaded portion  235 , until the shoulder  236  abuts the end  13   b . The cover  240  is then refitted on the handle  19 . 
   In this configuration, the screw  231 , with the base surface  233   a , interferes with the spring  228  in order to generate on the spring  228  a resilient pre-load capable of moving the stem  222  into the condition in which the stem portion  222   b  abuts the shoulder formed between the portions  226   a  and  226   b  of the bush  226 . 
   At the calibration stage, regulation of the axial position of the bush  226  (which determines a travel limit of the stem  22  in the direction of the axis X) and suitable dimensioning of the spring  228 , and also of the springs  12  and  225 , pre-set the delivery pressure values desired at the location of the maximum and minimum handle positions  19  (shown in  FIGS. 11 and 12 ). 
   It should be noted that, in the configuration of  FIG. 10 , the ring  239  remains visible outside the handle, thus constituting a means for indicating the configuration selected for using the regulator with combustible liquid gas. 
   From this it advantageously follows that, in operation, the conversion of the device from one to the other of the above-mentioned configurations, owing to the change in the gas delivered, requires only the fitting of the screw element  231 , in one or other of the positions described above, without the necessity for any other regulating intervention, because the delivery pressure values obtainable have been imposed beforehand at the calibration stage by means of the regulation measures discussed above. 
   Thus the invention achieves the proposed objects while yielding the indicated advantages by comparison with the known solutions. 
   Attention should be drawn in particular to the improved ease with which the regulating device can be used with combustible gases of various natures in equipment in which regulation of the delivery pressure between at least two minimum and maximum pressure values is required, as a function of the variation in flow required at the burner. 
   It should also be pointed out that the entire predetermined angular rotation of the handle is used in the modulation between the minimum and maximum delivery pressures, for each of the configurations provided for as a function of the type of gas used. 
   While exemplary embodiments of the invention have been shown and described herein, it will be understood that such embodiments are provided by way of example only. Numerous variations, changes and substitutions will occur to those skilled in the art without departing from the spirit of the invention. Accordingly, it is intended that the appended claims cover all such variations as fall within the spirit and scope of the invention.