Abstract:
A pressure cylinder which is formed from two sections which are joined together to enclose a volume which is bounded by two spaced walls with a settable filler between the walls.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This invention relates to a pressure cylinder which can be used as a water heater or geyser for producing hot water for a domestic, industrial or other application, or as a gas container (cylinder) or in any other appropriate application which requires containment of a pressurised fluid (liquid or gas). 
         [0002]    A typical geyser or hot water tank is essentially a pressure vessel although, in order to avoid undue forces being exerted inside the vessel by water pressure, during use, it is known to make use of a pressure-reducing valve at an inlet connection to the tank. Nonetheless this type of vessel must be capable of withstanding a fair degree of internal pressure. 
         [0003]    It is known to fabricate an inner tank of a geyser from rolled or pressed copper sheeting or steel which is welded or otherwise sealed so that it is waterproof. Inlets and outlets are attached to the inner tank which thereafter is covered by an insulating material which, in turn, is encased in an outer protective skin e.g. of a light gauge metal. 
         [0004]    The fabrication of a geyser of the aforementioned kind is time consuming and laborious and requires a fair degree of technical skill. Another adverse factor is that although metallic components of the geyser are protected against corrosion they do have a limited life expectancy. The use of copper is expensive and generally has been discontinued. 
         [0005]    Similar considerations apply in respect of containers for use with a pressurised gas, for example liquid petroleum gas, propane, butane, natural gas etc. 
         [0006]    The invention is concerned with a pressurised cylinder which can be manufactured to a consistently high standard using a process which lends itself to automation and which is inherently resistant to corrosive or fluid (liquid or gas) leakage effects. 
       SUMMARY OF THE INVENTION 
       [0007]    The invention provides a pressure cylinder which includes a body which is formed from at least two sections, each section including an integrally formed inner wall and an outer wall which is spaced from the inner wall, and wherein the two sections are interconnected so that the inner walls enclose a fluid-containing volume inside the body. 
         [0008]    “Fluid” as used herein includes a liquid and a gas. 
         [0009]    Filler material may be located in a gap between the inner wall and the outer wall. 
         [0010]    The filler material may be of any appropriate kind and preferably is a rigid foam or similar settable material which may be injected into the gap to fill a void which is defined between opposing surfaces of the inner and outer walls and which bonds to these surfaces. For a water-heating application the filler material should have a good thermal insulating characteristic. The filler material acts to transfer pressure between the inner and outer walls and subsequently rigidifies the body due to the resultant “sandwich-type” construction. 
         [0011]    The inner wall may be of any appropriate shape and preferably includes a substantially cylindrical portion and an end piece at a first end of the cylindrical portion. The end piece is preferably domed so that its capability of withstanding force exerted by fluid pressure in the volume is increased. 
         [0012]    The outer wall is preferably substantially cylindrical. 
         [0013]    The section is preferably made in a moulding process and, to facilitate the moulding operation, the cylindrical inner wall portion and the cylindrical outer wall portion may be slightly tapered to enable the section to be released from a mould. 
         [0014]    The inner wall, at a second end which is remote from the first end, may be attached to the outer wall by means of an annular component which acts as a bridge between the inner and outer walls. The annular component may lie in a plane which is substantially at a right angle to a longitudinal axis of the body. 
         [0015]    The outer wall, on an external surface, may be formed with a recess which extends circumferentially around the outer wall adjacent the annular component. 
         [0016]    The end piece of the inner wall may be formed with at least one inlet or outlet aperture. Preferably such aperture is in the form of a spigot which projects from an outer surface of the end piece e.g. in a direction which is substantially parallel to a longitudinal axis of the body. 
         [0017]    Each spigot may be threaded to enable a screw coupling to be made to it. The spigot may be reinforced at a junction between the spigot and the end piece, for example by means of one or more webs or enlarged sections. The spigot or aperture may be provided with a metal or plastic insert which can be moulded into, or otherwise attached to, the section. 
         [0018]    The two sections may be substantially identical. 
         [0019]    The two sections may be interconnected in any appropriate way, for example by joining the annular components to each other. This may be done using any suitable mechanism or process. For example use may be made of an adhesive or, preferably, the sections are joined by friction or heat welding abutting and opposing surfaces of the annular components to each other. 
         [0020]    A ring or band may extend around the body and may be positioned in the recesses in the outer walls which are side-by-side once the sections are interconnected. The band may be provided for reinforcing or aesthetic or for both purposes. 
         [0021]    Each section may be made from any appropriate material such as PET or polyamide or polyolefin with performance enhancers. Such materials are known in the art. If the cylinder is to be used for containing gas, the material used must be resistant to gas permeation. 
         [0022]    In order to enhance the rigidity of the body at least one section may be formed with ribs or other formations which extend into the gap between the inner wall and the outer wall. These formations are preferably aligned with a longitudinal axis of each section to facilitate fabrication thereof during a moulding process. The formations are integrally formed with at least one of the walls. 
         [0023]    The pressure cylinder may include at least one end cap and preferably two end caps. Each end cap is engaged with a respective end of the body. Each end cap may be secured to the body by means of formations which engage with complementary formations in the respective sections e.g. in the inner wall or in the outer wall or both. 
         [0024]    The end cap is preferably formed with apertures through which the spigots in the associated end wall extend, preferably with a close fit which nonetheless permits a degree of relative movement, due for example to thermal effects which result in expansion or contraction, between the section and the end cap. The number of apertures may vary according to the intended application, for example for gas a single nozzle is provided for filling and dispensing, and for water (i.e. the cylinder is used as a geyser) multiple appropriate apertures are provided. 
         [0025]    Each end cap may be flat, domed or include formations which provide stable support for the body if the body is positioned in a vertical orientation i.e. with a longitudinal axis of the body extending vertically. Similarly each end cap or the outer wall of each section, or both, may include formations which provide stable support for the body when it is horizontally orientated. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0026]    The invention is further described by way of example with reference to the accompanying drawings in which: 
           [0027]      FIG. 1  is a perspective view of a pressure cylinder according to the invention in an exploded configuration, 
           [0028]      FIG. 2  is a perspective view of the pressure cylinder of  FIG. 1  fully assembled, 
           [0029]      FIG. 3  is a side view of the pressure cylinder, 
           [0030]      FIG. 4  shows, in cross section, on an enlarged scale, a section which is used with a similar section to make a body of the pressure cylinder, 
           [0031]      FIG. 5  shows the pressure cylinder in cross section, 
           [0032]      FIG. 6  is a plan view of an end cap used in the pressure cylinder, 
           [0033]      FIG. 7  is a side view of the end cap, and 
           [0034]      FIG. 8  illustrates a possible variation to the end cap. 
       
    
    
     DESCRIPTION OF PREFERRED EMBODIMENT 
       [0035]      FIGS. 1 and 2  of the accompanying drawings are perspective views of a pressure cylinder  10  according to the invention in an exploded configuration and in a fully assembled mode, respectively.  FIG. 3  is a side view of the pressure cylinder. 
         [0036]    The pressure cylinder includes a body  12  and end caps  14  and  16 . The body, in turn, consists of two sections  18  and  19  respectively which are substantially identical.  FIG. 4  illustrates the section  18  in cross section and on an enlarged scale. 
         [0037]    The following description relates to the section  18 . It is to be understood however that the section  19  is for all practical purposes the same as the section  18 . 
         [0038]    The section  18  includes an inner wall  20  with an end piece  22  and an outer wall  24 . An annular component  26  lies in a plane  28  which is at a right angle to a longitudinal axis  30  of the section. The component is integrally formed with the inner and outer walls and acts as a bridging member which interconnects a first end  32  of the inner wall to an adjacent first end  34  of the outer wall. The outer wall is tapered slightly towards the end piece. At a junction with the annular component the outer wall has a circumferentially extending recessed formation  36 . 
         [0039]    The inner wall  20  has a mouth  38  at the first end which opposes the end piece. Between the mouth and the end piece the inner wall is tapered slightly inwardly towards the end piece. 
         [0040]    The end piece  22 , which is integrally formed with the inner wall  20 , is domed. As illustrated the pressure cylinder is intended to be used as a water heater (geyser) and for this application, which is exemplary only, a number of spigots  40  are integrally formed with the end piece and project in an axial direction, i.e. substantially parallel to the longitudinal axis  30 , from the end piece. If the cylinder is to be used as a gas cylinder then a single spigot or moulded-in nozzle (not shown) would be formed to act as a filling and dispensing aperture, in place of the spigots  40 . 
         [0041]    The spigots are externally or internally threaded, to standard thread gauges, according to requirement. To achieve this in a cost-effective and robust manner each spigot may be formed by means of a moulded-in metal insert. Each spigot is tubular and projects from a corresponding aperture  42  formed through the end piece. Each spigot can be stiffened or reinforced by means of a rib or web  44  which is formed between a base of the spigot and an adjacent surface of the end piece. 
         [0042]    A small double rim  46  on an outer surface of the end piece extends along a circular path around the spigots. 
         [0043]    The outer wall  24  is formed with a number of holes  50  at spaced locations opposing the end piece  22 —see  FIG. 1 . 
         [0044]    The section  18  is formed in a suitable moulding process. The taper on the inner wall  30  facilitates release of the section from a suitable tool, not shown. Similarly the spigots are aligned with the longitudinal axis  30  so that such spigots can be integrally formed with the end piece. 
         [0045]    It is also possible during the moulding process, to form ribs or other reinforcing formations, not shown, in a substantially cylindrical annular gap  52  between opposing surfaces of the inner and outer walls. 
         [0046]    The end caps  14  and  16  are also substantially identical. Each end cap has a substantially circular, slightly domed, cover  60 , see  FIG. 6 , with four projecting feet  62 ,  64 ,  66  and  68  respectively which are spaced from each other and which impart a castellated appearance to the end cap. Apertures  70  are formed in a circular central section  72  of each end cap, at spaced locations from each other, corresponding to the position and shape of the respective spigots. The section  72  is surrounded by a circular wall  73 —see  FIGS. 1 and 7 . 
         [0047]    Flexible lugs  74  with hook-shaped formations  76  at their extremities extend from an outer rim  78  of the cover  60 —see  FIG. 7 . Alternatively the hook-shaped lugs can be on an inner wall surface of the end cap, allowing the end cap to fit over the holes  50 . 
         [0048]    Alternatively, as is shown in  FIG. 8 , a central circular section  72 A (of a modified end cap  14 A) is substantially flat, with a central aperture  70 A. This would be an appropriate construction for a gas cylinder. The hook-shaped lugs are dispensed with for the cap  14 A is attached to a body section by passing suitable fasteners (not shown) through holes  79  in a rim  78 A of the cover which are brought into register with the respective holes  50  in the body section. 
         [0049]    The end caps are manufactured in a suitable moulding process. The various formations on each end cap are positioned to facilitate fabrication thereof in a direct manner without resorting to complex moulding techniques. 
         [0050]    The body sections  18  and  19 , which for practical purposes are identical, are moulded independently of each other. Use is made of any appropriate plastics material such as a polyamide or polyolefin or PET with suitable enhancers. These materials are suitable for a water-heating application but, for a gas-containment application, might require modification or replacement to ensure that the sections are resistant to gas permeation. The thickness of the inner wall and of the outer wall can be varied according to requirement and structural characteristics, but typically lies in the range of from 4 mm to 6 mm. 
         [0051]    When each end cap  14 ,  16  is clipped into position, the apertures  70  in each cover are aligned with the corresponding spigots  40  and the covers are then pushed home so that the hook-shaped lugs are deflected and can then engage with a spring action with the holes  50  in the outer wall  24 . 
         [0052]    The cover is located in position not only by the hook-shaped lugs but also by means of the rim  46  which engages with the wall  73  on the inner surface of the cover. 
         [0053]    Optional fixing holes  82  are provided in the cover for fasteners which are used to fix the cover mechanically to the corresponding body section. 
         [0054]    A rigid foam material  84  is injected into the annular gap  52  of each section—see  FIG. 5 . This can be done before the end caps are fixed in position but preferably is done after the end caps are fixed in position. The foam completely fills the void and to a substantial extent is bonded in position. The bonding action can be enhanced by forming keying formations in the surfaces of the inner and outer walls which face into the gap  52 . The foam substantially rigidifies the walls and imparts hoop strength to the section. As each end piece  22  is domed outwardly it is inherently capable of withstanding substantial fluid pressure which arises in the volume inside the body. This capability is however enhanced by the use of the foam, if it is used. The foam, in a water-heating application, must have a good thermal insulating characteristic, a factor which is of lesser importance in a gas containment application. 
         [0055]    Each domed end piece can be reinforced, as necessary, by moulding a network of honeycombed or radial ribs  46 A on an outer surface  22 A integrally with the end piece. These ribs, shown in dotted outline only in  FIG. 4 , typically would extend over the surface  22 A and for example merge and terminate with various webs  44  adjacent the spigots  40 . The spigots, in themselves, extend in the axial direction of the body and thus also inherently act to stiffen the domed end piece. 
         [0056]    The two sections  18  and  19  are joined to each other by means of a heat or other welding process which bonds the outer surfaces of the annular components  26  to each other. Thereafter a band  86  is placed around the outer walls, located in the abutting recesses  36 . The band provides an aesthetic function in that it covers the joint line between the two sections but also acts to some extent as a reinforcing component for it increases the hoop strength of the body  12  at a central location of the body. 
         [0057]    Each spigot passes with a tight fit through the corresponding aperture but in a manner which allows for a limited degree of relative movement to take place between the body section and each end cap arising, for example, from thermal expansive or contractive actions. The tight fit also reduces the likelihood of fluid, from any source, passing through the interface between the cover and the spigot and then entering the rigidifying foam inside the gap  52 . 
         [0058]    The number of spigots in each end piece varies according to requirement. Typically, if the cylinder is to be used as a geyser, provision is made for a cold water inlet, a hot water outlet, the mounting of an electric element, the mounting of a control thermostat, a pressure or thermal release valve and an outlet for water drainage. 
         [0059]    The pressure cylinder of the invention offers a number of advantages. It is made from two halves which are welded together to provide a smooth external cylindrical appearance. Reinforcement features and other constructional formations are hidden from external view. The cylinder thus has a smooth, aesthetically pleasing, appearance. Of significance is the fact that the annular components  26  constitute flanges, which may be about 50 mm wide, which are radially aligned relatively to the central axis  30 . These flanges are bonded together in the assembly process and, inherently, provide reinforcing at the centre of the body. The flanges, in turn, are stiffened by the inner and outer side walls and the intervening foam material which act, collectively, to brace the flanges against deflection in a sideways direction i.e. in a direction which is lateral to the width of each flange. This allows the resulting body, which is formed from components made by conventional injection moulding techniques, to withstand the high forces which are generated by fluid (water or gas) pressure inside the body. 
         [0060]    The threaded spigots are integrally moulded in the end pieces optionally using pre-formed inserts. The likelihood of leakages occurring between a separately formed spigot and an end piece to which the spigot is attached, as is the case in prior art pressure cylinders, is thus eliminated. 
         [0061]    The end caps close off the foam material in the gap  52 , and the projecting feet  68  to a substantial extent protect pipe connections which are made to these spigots. On the other hand, access to the spigots is permitted inter alia by means of the gaps between adjacent feet. 
         [0062]    The feet  62  to  68  can be used to support the body  12  in a vertical orientation, if required. If the cylinder is to be used in a horizontal orientation the shape of the feet can be altered to provide a stable, ground-engaging support. Another possibility is to form appropriate formations on the outer walls of the body sections so that the body can be supported horizontally, when required. It is also possible to attach a respective band to the outer wall of each body section and for the band to carry ground-engaging members with flat surfaces which stabilise the cylinder when it is placed on a horizontal surface. 
         [0063]    The rigid foam between the inner and outer walls creates a beam effect which distributes forces which arise from internal pressure in the volume inside the body, during use. 
         [0064]    As the body is made from a thermoplastic material it is inert and corrosion resistant and thus has substantial life expectancy.