Patent Publication Number: US-2016223139-A1

Title: Cylinder for compressed fluids

Description:
This invention relates to a cylinder for compressed fluids. 
     More specifically, this invention relates to a cylinder for compressed fluids used in the sanitary and medical fields, as a storage component in civil and industrial firefighting plants and systems, for applications in the civil and transport sectors (in particular on trains, ships or aircraft) operating with compressed air or with different gaseous substances suitably mixed (for example, braking systems or air treatment systems “HVAC”). The cylinder for compressed fluids according to this invention is used, for example, also for propulsion systems for motor vehicles, in particular for systems equipped with mixed fuel supply (for example, petrol/methane) or fuel supply of the hybrid type (for example, hydrogen/electricity). 
     Moreover, this invention is advantageously used as a tank for storing high pressure compressed fluids used in the propulsion of space rockets and space vehicles in general. 
     In prior art solutions, the high pressure cylinders are made of steel or aluminium according to various production processes depending on the mechanical properties of the metal selected, the chemical-physical properties of the fluid contained and the pressures for storing the fluid itself, as well as the cost of the production process up to the end product. 
     In the prior art, the high pressure cylinder of a metallic type comprises a central cylindrical section closed at the ends by two hemispherical caps welded on the central cylindrical section. 
     This solution represents the more economical version but less efficient in terms of maximum pressure value which can be reached (usually approximately 30 bar) and, therefore, also in terms of volume of fluid which can be stored and used with a cylinder of this type. 
     According to the state of the art, welded high pressure cylinders are used to store fuel gas such as, for example, liquefied petroleum gas, better known as LPG, which is the by-product of refining crude oil. The above-mentioned cylinders are usually installed on board motor vehicles which have propulsion systems with mixed fuel supply of the petrol/LPG type. 
     Alternatively, there are prior art high pressure cylinders without welding. This version of the high pressure cylinder requires a production process involving a series of forming steps for drawing a metallic, plate-like, semi-finished product until reaching the predetermined shape, generally of a cylindrical type, with two hemispherical end portions for closing. 
     In this case, the production process of the pressurised cylinder, also called “seamless” cylinder, makes it possible to create a cylinder without welding, which generally represents a weak point of the structure. For this reason, the “seamless” cylinder version is generally safer and more efficient, whilst being more expensive than a traditional welded cylinder. 
     The cylinders made with the “seamless” technique already have on at least one end threaded connectors for fitting dispensers and/or opening valves, in exactly the same as on the welded metallic cylinders. The performance in terms of maximum pressure with the “seamless” cylinders is approximately 10 times greater compared with welded metallic cylinders, in other words this means that the maximum operating pressure value is, for example, approximately 200-300 bar. 
     The prior art high pressure cylinders have some drawbacks. 
     Mainly, the high pressure cylinders of a metallic type, in the welded or “seamless” embodiment, have a structural weight (meaning the empty weight of the cylinder) which represents a significant percentage of the total weight which comprises the weight of the compressed fluid and that of the storage cylinder. 
     The weight of the filled cylinder must be taken into consideration in every application, above all in installations or applications where the total weight requirements are included in the design specification. 
     In addition, prior art high pressure metallic cylinders are subject to serious corrosion problems, both outside and inside. Even the use of special metal alloys, for example a predetermined type of aluminium, does not avoid the effects of corrosion, which can even be serious, and there is therefore the actual risk of an explosion of the cylinder when it is seriously damaged by the corrosion. 
     For example, the compressing and storing of a gas such as pure oxygen subjects the inner walls of the high pressure cylinder to a corrosion which is five times faster than that with atmospheric air. 
     In addition to a possible chemical aggressiveness of the compressed fluid in the cylinder, it is also necessary to add the effect of steam condensation both on the inside and outside of the cylinder which there may be in the presence of significant changes in pressure (filling/emptying of the cylinder) and temperature (cyclical exposure between sun and shade or on account of the vicinity of direct sources of heat). 
     The prior art high pressure cylinders are subject to another drawback, in particular the metallic welded cylinders have large dimensions especially in proportion to the volume, in litres, of fluid included therein. 
     In other words, due to the maximum operating pressure, a prior art metallic welded cylinder can store a low quantity of compressed fluid. For this reason, if a metallic cylinder is used, for example, on a motor vehicle with a propulsion system using a mixed fuel supply of the petrol/LPG type, this raises the problem of the considerable space occupied by the cylinder, generally in the luggage compartment, compared with the relative low autonomy enjoyed by the driver of the vehicle in terms of distance which may be travelled. 
     In this context, the technical purpose which forms the basis of this invention is to provide a cylinder for compressed fluids that overcomes the above mentioned drawbacks of the prior art. 
     More specifically, the aim of this invention is to provide a cylinder for compressed fluids which is simultaneously light and sturdy, in particular which provides a good capacity for storage of a compressed fluid with a lightweight structure which is, therefore, easier to move by a user and/or installation technician. 
     Another aim of this invention is to provide a cylinder for compressed fluids which is free of the above-mentioned corrosion effects and is therefore safer and free from periodic control and maintenance activities. 
     The aim specified is substantially achieved by a cylinder for compressed fluids comprising the technical features stated in one or more of the appended claims. 
     The dependent claims correspond to possible embodiments of the invention. 
    
    
     
       Further features and advantages of the invention are more apparent in the detailed description below, with reference to a preferred, non-limiting, embodiment of a cylinder for compressed fluid as illustrated in the accompanying drawings, in which: 
         FIG. 1  is a cross section of a cylinder according to this invention; 
         FIG. 2  is a cross section of an enlarged detail of the cylinder of  FIG. 1 , 
         FIG. 3  shows an element used during a step of making the cylinder of  FIG. 1 ; 
         FIG. 4  schematically shows a machine used during a step of making the cylinder of  FIG. 1 ; 
         FIG. 5  schematically shows a different machine used during a step of making the cylinder of  FIG. 1 ; 
     
    
    
     With reference to the annexed  FIG. 1 , the numeral  1  denotes a cylinder for compressed fluids according to this invention. 
     The cylinder  1  for compressed fluids comprises a first hollow body  2  and at least one second hollow body  3  equipped with an opening  2   a  and  3   a , respectively, towards the outside  100 . 
     The first hollow body  2  forms with a respective inner cavity a first housing space  2   b  available for a compressed fluid; similarly the second hollow body  3  forms with a respective inner cavity a second housing space  3   b.    
     The first housing space  2   b  is distinct and different from the second housing space  3   b,  preferably the first housing space  2   b  has a capacity different to the capacity of the second housing space  3   b.    
     Preferably, the first hollow body  2  and the second hollow body  3  have an axially symmetrical shape, still more preferably they have the respective axes coincident in a single axis “X”, yet more preferably the hollow bodies  2 ,  3  are such as to extend along the above-mentioned axis “X” with a cylindrical in shape. 
     The first hollow body  2  and the second hollow body  3  extend along the axis “X” and are interposed between a head end  4  and a bottom end  5 , opposite the head end  4 . 
     Preferably, the first hollow body  2  has the relative opening  2   a  towards the outside  100  at the head end  4 . 
     Preferably, the second hollow body  3  has the relative opening  3   a  towards the outside  100  at the head end  4 . 
     Preferably, the first hollow body  2  and the second hollow body  3  at the relative openings  2   a,    3   a  have a head portion with an ogival shape, in particular hemispherical having in a central position an open connecting neck, respectively a first connecting collar  2   c  for the first hollow body  2  and a second connecting collar  3   c  for the second hollow body  3 . 
     The cylinder  1  for compressed fluids according to this invention comprises the second hollow body  3  housed inside the first hollow body  2  in such a way as to occupy at least partly the first housing space  2   b  with the relative external space. 
     Preferably, the second hollow body  3  is housed inside the first hollow body  2  in such a way as to define a first chamber  6  for housing the compressed fluids having as a space at least the first housing space  2   b  less at least the external space of the second hollow body  3  and a second chamber  7  for housing the compressed fluids having as a space at least the second housing space  3   b.    
     The first housing chamber  6  is insulated from the second housing chamber  7 , in other words, there is no fluid communication between the first housing chamber  6  and the second housing chamber  7  for compressed fluids due to the presence of the wall of the hollow bodies  2 ,  3 . 
     The first housing chamber  6  and the second housing chamber  7  have respective openings  2   a  and  3   a  towards the outside  100 . 
     Preferably, in accordance with the preferred, non-limiting embodiment of this invention, the first housing chamber  6  and the second housing chamber  7  have the openings  2   a,    3   a  towards the outside  100  at the same head end  4 . 
     At the bottom end  5  the first hollow body  2  has a closing portion with an ogival shape, in particular hemispherical, on which preferably there is a bottom opening “C” such as to place in fluid communication the first housing space  2   b  with the outside  100 . Preferably, the bottom opening “C” of the first hollow body  2  at least in a condition of use of the cylinder  1  is normally closed. 
     At the bottom end  5  the second hollow body  3  has a closing portion with an ogival shape, in particular hemispherical, preferably without any type of opening. 
     In a different embodiment of the cylinder  1  according to this invention, not illustrated in the accompanying drawings, the second hollow body  3  has a bottom opening at the bottom end  5  such as to place in fluid communication the second housing space  3   b  with the first housing space  2   b,  or in a different embodiment of this invention, the second hollow body  3  has a bottom opening at the bottom end  5  such as to place in fluid communication the second housing space  3   b  with the outside  100 . Preferably, the wall which delimits the inner cavity respectively of the hollow body  2  and of the hollow body  3  has a wall thickness “S” which is uniform and equal at all points of the extension of the first hollow body  2  and the second hollow body  3 . 
     In a different embodiment of the cylinder  1  and fully covered in the scope of the invention, not illustrated in the accompanying drawings, the first hollow body  2  and the second hollow body  3  may have, for example, a spherical shape or another shape and a thickness of the wall which is, for example, not uniform, that is, variable along the extension of the wall. 
     Preferably, the first housing chamber  6  and the second housing chamber  7  are placed in fluid communication with the outside  100  with the respective openings  2   a  and  3   a  of the first hollow body  2  and the second hollow body  3 . 
     Preferably, the first hollow body  2  and the second hollow body  3  are connected to a single connecting body  8 , at the respective openings  2   a  and  3   a.    
     With reference to the detail shown in  FIG. 2 , the connecting body  8  comprises a coupling portion  8   a  designed for connecting with the hollow bodies  2 ,  3  and the opposite shaped portion  8   b.    
     Preferably, the coupling portion  8   a  of the connecting body  8  has at least one threaded end  8   c  for fixing the connecting body  8  to the second hollow body  3  at the opening  3   a  and at least a sleeve portion  8   d  on which is fixed the connecting collar  2   c  of the first hollow body  2  at the opening  2   a.    
     Thus, the connecting body  8  is such that, once the connecting bodies  2 ,  3  have been fixed on it, respectively by means of the connecting collar  2   c  and the threaded end  8   c,  it keeps in position the first hollow body  2  and the second hollow body  3  with the respective axes of symmetry coinciding with the above-mentioned axis “X”. The connecting body  8  is preferably aligned along the axis “X” in a condition of use of the cylinder  1 . 
     Preferably, the shaped portion  8   b  comprises at least two connecting seats: a first connecting seat  8   e  and a second connecting seat  8   f  for dispensing at least one pressurised fluid from the cylinder  1 . 
     More specifically, the connecting body  8  has inside it at least a first dispensing conduit  82  and a second dispensing conduit  83  which extend, respectively, between a coupling portion  8   a  of the connecting body  8  up to the respective first connecting seat  8   e  and second connecting seat  8   f , preferably positioned opposite one another. 
     Preferably, the first dispensing conduit  82  extends from a lateral surface of the sleeve portion  8   d  facing the first housing chamber  6  to the shaped portion  8   b,  towards the outside  100 . 
     Preferably, the second dispensing conduit  83  extends from the threaded end  8   c  of the connecting body and facing the second housing chamber  7  to the shaped portion  8   b,  towards the outside  100 . 
     Preferably, the first dispensing conduit  82  faces the outside  100  at a bottom wall of the first connecting seat  8   e  whilst the second dispensing conduit  83  faces the outside  100  at a bottom wall of the second connecting seat  8   f.    
     Advantageously, the first dispensing conduit  82  is such as to place in fluid connection the first housing chamber  6  with the outside environment  100  and the dispensing conduit  83  is such as to place in fluid connection the first housing chamber  7  with the outside environment  100 . 
     In other words, the connecting body  8  allows the escape of a fluid contained in the first housing chamber  6  and/or of a fluid contained in the second housing chamber  7  towards the outside environment  100  independently. 
     For this reason, the first  6  and second  7  housing chambers are separate and insulated from each other, and such as to house fluids under pressure of different chemical-physical types which can be dispensed independently and in conditions of use of the cylinder  1  which are different and/or independent from each other. 
     More in detail, the wall thickness “s” of the cylinder  1  in particular of the second hollow body  3  has values such that there is no interference and/or collision between the outer wall of the second hollow body  3  with the inner cavity of the first hollow body  2 . 
     For example, in a condition of use of the cylinder  1  there may be dispensing of a pressurised fluid contained in the first housing chamber  6  through the first dispensing conduit  82  up to the complete emptying of the first chamber  6 , whilst the fluid housed in the second chamber  7  is dispensed through the second dispensing conduit  83  only afterwards. 
     In a different use condition of the cylinder  1  according to this invention, the cylinder  1  for compressed fluids may be connected to a propulsion unit, for example, a rocket engine, which requires simultaneous feeding a fuel fluid (hydrogen) and a comburent fluid (oxygen) to create the combustion reaction also in empty space. 
     In effect, both the fuel and the comburent are stored in suitable tanks (at least two and different from each) which are particularly spacious and installed together on a single propulsion unit equipped with a special combustion chamber followed by an expansion nozzle. 
     For this reason, the dispensing of the comburent and fuel occurs through the first  82  and second  83  dispensing conduits with specific pressure and flow rate values for the type of combustion characterising the propulsion unit. 
     Preferably, the different capacity between the first housing chamber  6  and the second chamber housing  7  makes it possible to manage, for example, the storage of the two fluids in the cylinder  1  as a function of the quantity required for each fluid in the chemical reaction in question, in such a way that it is balanced in an optimum fashion. 
     Preferably, the first connecting seat  8   e  and second connecting seat  8   f  comprise a thread for connecting to a conduit of a system or to a coupling of a dispenser of fluids under pressure. 
     Preferably, the threaded end  8   c  of the connecting body  8  has a size of the outside diameter which is less than the size of the outside diameter of the sleeved portion  8   d.    
     Preferably, the dimension of the connecting body along the extension of the axis “X” at least includes the length of extension of the connecting collar  2   c  and of the connecting collar  3   c,  respectively, of the two hollow bodies  2 ,  3  and of the dimension of the first connecting seat  8   e  and second connecting seat  8   f.    
     Preferably, the connecting body  8  is made of a resistant material such as, for example, a metal, preferably stainless steel, titanium or a lightweight alloy for high pressures. 
     Preferably, at least the second hollow body  3  has at the opening  3   a  a connecting collar  9 , having a through hole  9   a  at least partly threaded. The connecting collar  9  is included in the housing space  3   b  of the second hollow body  3  in such a way that the through hole  9   a  allows the above-mentioned fluid communication to be made. 
     More specifically, the connection between the second hollow body  3  and the connecting body  8  is possible by screwing between the thread of the through hole  9   a  with the thread of the threaded end  8   c,  such a coupling also guaranteeing a tight seal of the fluids under pressure. 
     Preferably, the connecting collar  9  is made of a metallic material, for example stainless steel, titanium or a lightweight alloy for high pressures. 
     Preferably, the first hollow body  2  and the second hollow body  3  are made of a composite material, that is to say, of a material comprising a fibrous material impregnated with a resin. 
     In a different embodiment not described, but in any case covered in the scope of the invention, the first hollow body  2  and the second hollow body  3  are made of a metallic material or plastic, for example obtained by moulding or die casting or mechanical processing. 
     Preferably, the reinforcement of the composite material is a thread made of carbon, or a mixed textile thread made of carbon and Kevlar. 
     Still more preferably, depending on the particular constructional requirements of the cylinder  1 , which are described in more detail below, the reinforcement thread may be of the type comprising a carbon-Kevlar fibre and/or the type comprising glass fibre. In other different embodiments, not illustrated and described but falling within the scope of the invention, the reinforcement thread may be made of another material, for example it may be a thread based on aramid fibre or based only on carbon fibre or other fibre. 
     Preferably, the above-mentioned resin may be a thermoplastic or thermosetting polymer resin, still more preferably, the resin is thermosetting of the epoxy type. 
     The fibrous component of the composite material, that is, the thread, represents the reinforcement whilst the resin component represents the matrix of the composite material. 
     Preferably, the process for making the cylinder  1  comprises a step of impregnating the fibrous material made of carbon-Kevlar and/or glass fibre with the epoxy resin before its installation on a die  10 , shown in detail in  FIG. 3 . The die  10  is preferably metallic, still more preferably tin-based. 
     Preferably, the metal die  10  is assembled in separate pieces which reproduce the shape of the inner cavity of the first hollow body  2  and the second hollow body  3 , with different geometries and measurements suitable for the housing capacity provided for the first housing space  2   b  and for the second housing space  3   b.    
     The metal die  10  is fixed on a supporting shaft  11  as shown in  FIG. 3  and which is used in the production process to move the cylinder  1  during the various production steps. 
     Preferably, the wall thickness “S” is proportional to the maximum operating pressure of the cylinder for compressed fluids  1  as well as to the strength characteristics of the composite material from which the walls are made. 
     The making of the first hollow body  2  and the second hollow body  3  from composite material mentioned above comprises the use of a spinning machine  200 . 
     The spinning machine  200  illustrated in the accompanying drawings is shown schematically with a schematic view of non-limiting embodiment according to this invention. 
     In other words, the spinning machine  200  may comprise further accessory elements not illustrated and described which do not limit the inventive concept of the invention. 
     With reference to  FIGS. 4 and 5 , the spinning machine  200  comprises:
         a spindle  201  for pulling a metal die  10  using a shaft  11  along an axis of rotation “Y” of the spindle; Preferably, during the rotation of the metal die  10  on the spindle  201 , the axis “X” of symmetry of the cylinder  1  coincides with the axis of rotation “Y” of the spindle  201 ;   at least one spinner  202  of a thread  300  of fibrous material such as to move at least one relative portion with guide passages  203  of the thread alternately along at least one direction parallel to the axis of rotation “Y” for spinning the thread about the metal die  10 ;   at least one spool  204  of the thread  300  of fibrous material such as to cross the guide passages  203  of the spinner  202 ;       

     Preferably, with reference to  FIG. 5 , the spinning machine  200  also comprises an apparatus  205  for impregnating the thread  300  of fibrous material with a resin  400  in such a way as to make a composite material for the spinning about the metal die  10 . 
     Preferably, the movable parts of the spinning machine  200 , for example the spindle  201  and the spinner  202 , are managed by an electronic system which comprises motors of the brushless type connected to drives controlled by an industrial controller of the PLC type. 
     The software program for controlling the PLC controller can be adapted each time on the basis of production specifications for the cylinder  1 , that is to say, dimensions, capacity, wall thickness, structural rigidity of finished composite material, and so on. 
     According to this invention, the method for making a cylinder  1  for high pressure compressed fluids as described above comprises:
         preparing at least two metal dies  10 , respectively a first metal die for the first hollow body  2  and a second metal for the second hollow body  3 . The metal die has dimensions greater than the second metal die;   preparing a spinning machine  200  preferably as described above;   if necessary covering the outer surface of the second metal die  10  of the second hollow body  3  with a covering material such as to define the inner wall of the cavity of the second housing chamber  7 ;   making with a composite material, preferably as described above, the second hollow body  3  by spinning the thread  300  of fibrous material about the second metal die  10  and if necessary including in the structure at the opening  3   a  a connecting collar  9 ;   removing from the spindle  201  of the spinning machine  200  the second metal die  10  covered by the second finished hollow body  3 ;   preparing a step of treating the assembly of the second metal die  10  and second hollow body  3  preferably in an autoclave at a temperature such as to exceed the melting point of the material of the second metal die  10  and for a predetermined time sufficient for polymerising the resin  400  and with a pressure such as to compress every layer of thread  300  of fibrous material soaked with the resin  400 ;   extracting the second metal die  10  from the inner cavity of the second hollow body  3  through the relative opening  3   a  towards the outside  100  when the second metal die  10  has adopted the liquid state as a result of the temperature in the autoclave;   if necessary covering the outer surface of the second hollow body  3  with a covering material such as to define the outer wall of the second hollow body  3 ;   if necessary mounting on the second hollow body  3  a connecting body  8  at the opening  3   a  towards the outside  100 ;   preparing a larger first metal die  10  preferably fixed axially on the connecting body  8  and outside the second hollow body; In other words the first metal die  10  is larger and includes in its internal hollow space the second hollow body  3  previously made;   preparing again the spinning machine  200  preferably as previously illustrated;   if necessary covering the outer surface of the first metal die  10  with a covering material such as to define the inner wall of the cavity of the first housing chamber  6 ;   making with a composite material, preferably as described above, the first hollow body  2  by spinning the thread  300  of fibrous material about the first metal die  10 ;   removing from the spindle  201  of the spinning machine  200  the first metal die  10  covered by the first hollow body  2 ;   preparing a step of treating the assembly of the first metal die  10 , second hollow body  3  and first hollow body  2  preferably in an autoclave at a temperature such as to exceed the melting point of the material of the first metal die  10  and for a predetermined time sufficient for polymerising the resin  400  and with a pressure such as to compress every layer of thread  300  of fibrous material soaked with the resin  400 ;   extracting the first metal die  10  from the inner cavity of the first hollow body  2  through a bottom opening “C” towards the outside  100  when the first metal die  10  has adopted the liquid state;   if necessary covering the outer surface of the first hollow body  2  with a covering material such as to define the outer wall of a cylinder  1  for compressed fluids;   if necessary applying on the outer surface of the cylinder  1  for compressed fluids identification elements which are visible and/or traceable using electronic devices showing the nameplate data of the cylinder  1 ;   if necessary covering the outer surface of the cylinder  1  for compressed fluids with a covering material such as to define the outer wall of the cylinder  1  for compressed fluids.       

     Preferably, the above-mentioned covering material is a gel-coat sensitive to UV rays for being treated in an efficient fashion during the hardening and drying step and also having high level properties such as moisture barrier. 
     In a different embodiment not illustrated, the cylinder  1  for compressed fluids may comprise what is indicated above except for the following elements: the second hollow body  3  and relative connecting collar  9 , the second dispensing conduit  83  and the respective second connecting seat  8   f.    
     For this reason, during production there is no step for making the second hollow body  3  and the process starts with the preparation of the spinning machine  200  for making the first hollow body  2 . 
     Advantageously, the cylinder  1  according to this invention has the capacity of storing in a single structural body at least two different compressed fluids. 
     Advantageously, the structure of the cylinder  1  has a very reduced weight when empty allowing an easy movement during installation and/or storage and transport. 
     Advantageously, thanks to a simple and effective production process, the number of components assembled at a later stage are also reduced to a minimum, after the hollow bodies  2 ,  3  have been made. 
     The possibility of fitting the connecting body  8  during the production process of the cylinder  1  directly on the connecting collar  3   c  of the second hollow body  3  allows the time for production of the cylinder  1  to be considerably reduced and especially avoids the need to insert seals (“O-Ring” and the like) which are generally subject to regular maintenance and replacement as they are easily perishable. 
     Preferably, during the steps of making the cylinder  1  a separation material may be inserted between a layer of thread  300  and a succession of the first hollow body  2  and/or the second hollow body  3 . More specifically, the above-mentioned separating material may be a plastic material or a material of another nature and may be inserted preferably in the cylindrical portion of the cylinder  1  to increase the insulation of the inner space external humidity. 
     Advantageously, the optimisation of the housing spaces  2   b,    3   b  where the second is contained in the first gives the cylinder  1  outside dimensions and geometry which can be better used in the case of transport, installation and handling. 
     Advantageously, the cylinder  1  according to this invention is not subject to corrosion (inside and outside) and the cylinder  1  is thus free of regular checks and maintenance. In other words, the cylinder  1  made of composite material does not require checks and tests of the seals (apart from those planned close to the connecting seats  8   e,    8   f ) and inspections of the welding or zones most stressed mechanically during use of the cylinder  1  for pressurised fluids.