CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a national phase filing, under 35 U.S.C. §371(c), of International Application No. PCT/EP2009/061560, filed Sep. 7, 2009, the disclosure of which is incorporated herein by reference in its entirety. 
     
    
     FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not Applicable 
       BACKGROUND 
       [0003]    The invention relates to an impregnation plant for impregnating a liner. 
         [0004]    Pipelines are commonly used to transport fluids over a long distance. Faulty pipeline systems may be renovated by introducing a lining tube into the pipeline. The lining tube, which further on will be referred to as a liner, may be placed inside the faulty pipeline such that the inner walls of the pipeline are completely covered by the liner. The liner may be used to repair faults such as leakage by sealing the interior of the pipeline to the walls of the pipeline. Leaking pipelines may constitute a hazard for the environment and for personal health, since contaminated and/or dangerous fluids may escape the pipeline into the surrounding outside environment. Alternatively, the liner may be used preventively to repair worn, damaged or badly maintained pipelines to prevent further damage, which may eventually lead to a leakage. 
         [0005]    The lining technology may be used on any pipeline system such as gas pipelines, water pipelines etc. The pipelines may have any orientation, such as e.g. vertical or horizontal. Further, the location of the pipeline may be e.g. either below ground or above ground, indoor or outdoor, in private buildings or in industrial environments. The liner may be installed by simply pulling it into place inside the pipeline, or by using eversion. By eversion is meant the technology of fastening one end of the liner onto a manhole and subsequently inverting the liner into the pipeline by the use of water, steam or pressurized gas. 
         [0006]    The major advantage of the above technology is achieved in connection with underground pipelines, such as sewer pipelines. The renovation may be performed quickly and trenchless with minimum inconvenience to the surroundings and considerably lower costs compared to a complete replacement of the pipeline. 
         [0007]    The liner is preferably made of a soft and flexible material, which is easy to package and transport to the installation site and which may be inserted into the pipeline system from the outside through e.g. a manhole or the like. When the liner is put in place inside the pipeline system it should be hardened for maximum stability. The liner is therefore preferably made from a fibre material. The fibre material may be a woven or non-woven material and may e.g. be of any of the following types: glass, carbon, aramid, polyester, polyacrylonitrile, mineral, viscose, polyamide, polyacrylic or natural fibres or a combination of the above. The fibre material is impregnated with a resin, such as styrene/polyester or styrene-free polyester, styrene/vinylester or styrene-free vinylester, vinylester urethane, furan, phenol, water glass, epoxy, methacrylate, isocyanate or the like. The resin should be curable, e.g. by application of heat or radiation, for an irreversible transition from a soft and flexible state into a hardened state. One example of such a liner may be found in EP 1 920 913, to which reference is made and which is hereby incorporated in the present specification by reference. The fibre material may be e.g. a glass fibre material or felt material, which is flexible and at the same time may hold a large quantity of resin. The material should exhibit affinity to the resin to allow the resin to soak the liner completely. 
         [0008]    The liner is typically impregnated by submerging the liner in a resin bath. When the liner is submerged, the resin will enter into the fibre material structure of the liner, such that the liner is soaked with resin. Thereafter the resin may be partially cured to achieve the soft and flexible state and avoid resin leaking from the liner. 
         [0009]    When impregnating the liner using the above technology, there is a need to ensure that no voids exist inside the liner. Such voids may be gas (air) bubbles trapped inside the fibre material after impregnation. Voids of any kind will constitute weak spots when the liner has been cured and may lead to premature degradation and damage to the liner. Voids may further lead to cracking of the liner and possibly to a leakage. 
       SUMMARY 
       [0010]    It is therefore an object according to the invention to provide a method and a system for impregnating a liner and at the same time reduce the risk of a void inside the liner after curing. 
         [0011]    The above need and the above object together with numerous other needs and objects which will be evident from the below detailed description are according to a first aspect of the present invention obtained by an impregnation plant for impregnating a liner with a resin, the liner being fibrous and flexible, the impregnation plant comprising:
       a vacuum lock comprising a housing having an inlet and an outlet and defining an ambient pressure space near the inlet and a low pressure space near the outlet, the ambient pressure space and the low pressure space being separated by a substantially gas-tight seal comprising a first sealing element and a second sealing element located juxtaposed the first sealing element, the first and second sealing elements being flexible for allowing the fibrous liner to be conveyed through the seal between the first sealing element and the second sealing element in a direction from the inlet towards the outlet, the liner being degassed by compressing the liner into a compressed state between the first and second sealing elements and subsequently relaxing the liner into a substantially uncompressed state inside the low pressure space,   a vacuum pump communicating with the low pressure space for reducing the pressure in the low pressure space in relation to the pressure in the ambient pressure space, and   an impregnation station being in gas-tight communication with the outlet of said vacuum lock, the impregnation station comprising a resin bath for accommodating the liner, a resin reservoir, a nozzle, a pipe system and a resin pump for propelling the resin from the resin reservoir via the pipe system and the nozzle into the resin bath in a direction towards the liner.       
 
         [0015]    In the impregnation plant according to the first aspect of the present invention the liner is impregnated while being conveyed through a vacuum lock and a resin bath. The liner is made of a soft and porous fibre material, such as a woven or non-woven material or fabrics or combination comprising glass fibre, polyester or felt or a combination of the above. The material should preferably have a high resin affinity. The porous structure of the fibre material will contain a large volume of air. The air volumes may be encapsulated in resin during impregnation and constitute voids after curing. To avoid the above the liner is first of all compressed between two sealing elements to remove a substantial amount of the air located inside the liner. It must however be ensured that the liner is not crushed or damaged when compressing the liner. Therefore, the pressure applied to the liner by the sealing elements is limited. Consequently, some amount of residual air will remain inside the liner after degassing. The sealing element may comprise sealing lips or rollers or the like. The sealing element should be soft to allow it to deform and correspond to the compressed shape of the liner such that any air leakage is minimized. 
         [0016]    To remove the residual air in the liner it is subsequently allowed to expand inside a low pressure space, which may define a low pressure chamber. The low pressure chamber is connected to a constantly running vacuum pump such that the low pressure chamber may define a partial vacuum. The residual air in the liner will expand in the low pressure chamber and the vacuum pump will suck away any residual air from the low pressure chamber. The liner will thereby become substantially degassed. 
         [0017]    The liner subsequently enters the resin bath. Resin bath should in the present context be understood to mean any volume or body of liquid resin without specifying any particular shape. To ensure that the liner is completely soaked and all cavities in the liner are filled with resin in the resin bath, a resin jet is propelled against the liner. The resin jet will allow resin to penetrate deep into the liner by applying a resin pressure and a velocity at the liner. The flow jet is propelled from a nozzle connected to a pipe system and a pump is used to pump resin from the reservoir towards the liner. The flow jet will allow the resin to penetrate deeper into the liner and fill out the cavities better than by e.g. submerging the liner. The word “nozzle” should be understood to mean any form of fluid outlet having either a constant or a varying shape, e.g. a straight shape, a converging shape or a diverging shape. The ambient pressure space is understood to encompass any space having atmospheric pressure. 
         [0018]    In a further embodiment according to the first aspect of the present invention the resin reservoir may constitute a resin receptacle for receiving excess resin. By excess resin is meant any resin exiting the resin bath while not being accommodated inside the liner. Excess resin is a result of a pressure in the resin bath/nozzle and is preferred since it shows that resin has penetrated the liner and impregnated it sufficiently. The excess resin is collected in the resin receptacle and may be re-used by re-circulating it to the resin bath via the nozzle. A filter may be employed in the resin receptacle to remove any contamination such as fibres from the liner in the excess resin to avoid clogging the nozzle or pipe system. 
         [0019]    In a further embodiment according to the first aspect of the present invention the impregnation station may have a first end being in gas-tight communication with said outlet of said vacuum lock and a second end being in gas-tight communication with a further vacuum lock, said further vacuum lock comprising a further housing having a further inlet and a further outlet and defining a further ambient pressure space near said further outlet and a further low pressure space near said further inlet, said further ambient pressure space and said further low pressure space being separated by a substantially gas-tight further seal comprising a further first sealing element and a further second sealing element located juxtaposed said further first sealing element, said further first and second sealing elements being flexible for allowing said fibrous liner to be conveyed through said further seal between said further first sealing element and said further second sealing element in a direction from said further inlet towards said further outlet. The working principle of the further vacuum lock is reversed compared to the original vacuum lock. The further vacuum lock should apply a very limited force on the liner to avoid pressing out any resin accommodated inside the liner. It should be noted that the two vacuum locks may have different working principles, i.e. one may employ sealing lips while the other may employ rollers. 
         [0020]    In a further embodiment, according to the first aspect of the present invention the impregnation station has a first end being in gas-tight communication with said outlet of said vacuum lock and a second end being open to the outside ambient pressure, said first end and said second end being separated gas-tightly by said resin. The resin will thus act as a further vacuum lock comprising a liquid vacuum lock between the low pressure space and the ambient air pressure. A liquid vacuum lock will have the additional advantage of substantially zero leakage. The ambient air pressure acting on the resin at the second end will act as a pressure force to push the resin towards the first end. This pressure may be balanced by the pressure inside the resin bath generated by the supply of resin from the nozzle and pipe system. Alternatively, the pressure force may be balanced by the gravity force from the resin such that the gravity force of the pile of resin located near the first end and above the resin level of the second end compensates the pressure force of the ambient air pressure. Thus, the resin level at the first end of the receptacle will be higher than the resin level at the second end. 
         [0021]    In a further embodiment according to the first aspect of the present invention the resin bath is formed between said first and second end by the continuous supply of resin by said nozzle. This way, the resin bath must not comprise a reservoir suitable for permanently storing the resin, but may simply comprise a defined space where resin and liner may interact. This means the continuously supplied resin may either be accommodated inside the liner or exit the resin bath as excess resin. The resin bath may thus comprise e.g. a partially enclosed volume or alternatively a single surface or the resin bath may be entirely defined by the continuous supply of resin. 
         [0022]    In a further embodiment according to the first aspect of the invention the impregnation plant may comprise a system for monitoring the level of resin in said resin reservoir. Such system may range from a simple floatation device inside the resin reservoir to more advanced radar detectors for detecting the surface of the resin in the resin reservoir. 
         [0023]    In a further embodiment according to the first aspect of the invention the impregnation plant may comprise a resin supply tank and a resin supply pump for delivering resin from said resin supply tank to said resin reservoir. When the liner is constantly impregnated the resin level in the resin reservoir will sink. To compensate for this and to keep the resin level constant, resin must be injected into the resin reservoir. This may be done by delivering resin to the resin reservoir from a nearby resin supply tank via a pump. 
         [0024]    In a further embodiment according to the first aspect of the invention the impregnation plant may comprise two nozzles mounted in a juxtaposed position for applying the resin on both sides of said liner. The nozzles are preferably mounted such that the resin flow jet is applied perpendicular to the liner surface. Since the resin can penetrate the liner from two opposite directions, the resin needs to penetrate only half the distance compared to when the resin jet is only applied from one direction. This way the resin need not penetrate the entire liner, and the risk of voids will be additionally reduced. The impregnation plant may further comprise a plurality of nozzles, such as 2-1000, preferably 100-800, more preferably 400-600, most preferably 400, or alternatively 200-400, or alternatively 400-600. The nozzles should be equally distributed such that the whole surface of the liner is subjected to the resin flow jet, and preferably equally distributed on each side of the liner. If some areas of the liner are not subjected to the resin jet, they may not be completely impregnated and consequently a void may arise there. 
         [0025]    In a further embodiment according to the first aspect of the invention the impregnation plant may comprise a low pressure space having an absolute pressure lower than 100 kPa, preferably 10−90 kPa, more preferably 50−70 kPa, most preferably 60 kPa, or alternatively 50−60 kPa, or alternatively 60−70 kPa. Lower pressure will reduce the amount of voids in the liner. High vacuum is costly to achieve and maintain and will in most cases not be necessary to achieve the intended void-free result. 
         [0026]    In a further embodiment according to the first aspect of the invention the impregnation plant may comprise a system for monitoring the pressure in said low pressure chamber. Such a system may comprise a pressure sensor in the low pressure space. The pressure in the low pressure space should be controlled since it influences the amount and severity of any voids in the liner and may additionally influence the resin level. 
         [0027]    In a further embodiment according to the first aspect of the invention the sealing element may comprise a roller seal or alternatively a lip seal or yet alternatively a roller and lip seal. A roller has the advantage of being able to provide a gas-tight seal with low wear compared to the alternative lip seals. The roller may in turn preferably be sealed by lip seals in relation to the housing. 
         [0028]    In a further embodiment according to the first aspect of the invention the roller may comprise rubber foam. Rubber foam is a soft and air-tight material which may preferably be used for the rollers. By having soft rollers the airtight properties may be realized without any need of compressing the liner excessively. 
         [0029]    In a further embodiment according to the first aspect of the invention the liner may be guided through said device by one or more guiding rollers. The guiding rollers as well as the rollers in the vacuum lock may be driven by a motor, such as a pneumatic motor or an electric motor. In this way the liner may be conveyed inside the impregnation plant. 
         [0030]    In a further embodiment according to the first aspect of the invention the vacuum lock may be having more than 2 rollers, such as e.g. 3-10 rollers, or preferably 6 rollers. Having a series of rollers will improve the sealing quality by providing additional compartments having a pressure between the pressure of the low pressure compartment and the ambient pressure. In this configuration the pressure difference across a pair of rollers will be lower and consequently the amount of gas leaking through the seal will be lower. The rollers may be configured in juxtaposed pairs in a row, or alternatively form a sequence where each roller, except the first and the last, is juxtaposed to 2 other rollers. The compartments formed between the rollers may optionally be connected to a vacuum pump. 
         [0031]    In a further embodiment according to the first aspect of the invention the impregnation plant may comprise a control unit. A control unit may be used to control the different features of the invention, such as the pressure in the low pressure space, the pressure of the resin jet, the level of resin, the velocity of the liner and many other features, which will be evident from the description. 
         [0032]    In a further embodiment according to the first aspect of the invention the liner may be submerged in the resin reservoir. The submersion of the liner may be used in addition to the flow jet for impregnating the liner. The submersion may be performed either before, during or after applying the flow jet. 
         [0033]    In a further embodiment according to the first aspect of the invention the resin-filled receptacle comprises a first vessel having an elongated and substantially vertical orientation and defining an upper inlet and a lower outlet, a second vessel having an elongated and substantially vertical orientation and defining a lower inlet and an upper outlet, and a third vessel connecting the lower outlet and the lower inlet. Upper and lower should in this context be understood in relation to the earth gravity. The shape described above has been proved to be the most efficient concerning material use. If vacuum is applied to the upper inlet, the resin level will rise in the first vessel and fall in the second vessel if it is assumed that ambient pressure is applied to the second opening. The earth gravity and ambient pressure determine the resin levels as discussed above. Assuming earth conditions, typical vacuum pumps/seals and typical resin density, the resin-filled receptacle and/or said second vessel of said resin-filled receptacle should have/has an elongation of 1-10 meters, preferably 2-6 meters, more preferably 3-5 meters, and most preferably 4 meters, or alternatively 2-4 meters, or alternatively 4-6 meters. 
         [0034]    In a further embodiment according to the first aspect of the invention the impregnation plant may comprise a pre-curing device for applying radiant energy onto said liner after impregnation. Such pre-curing may be achieved by applying radiant energy directly after impregnation of the liner. This way the resin will attach better to the liner. 
         [0035]    The above need and the above object together with numerous other needs and objects which will be evident from the below detailed description are according to a second aspect of the present invention obtained by a vacuum lock comprising a housing having an inlet and an outlet and defining an ambient pressure space near said inlet and a low pressure space near said outlet, said ambient pressure space and said low pressure space being separated by a substantially gas-tight seal comprising a first sealing element and a second sealing element located juxtaposed said first sealing element, said first and second sealing elements being flexible for allowing a fibrous liner to be conveyed through said seal between said first sealing element and said second sealing element in a direction from said inlet towards said outlet, said liner being degassed by compressing said liner into a compressed state between said first and second sealing elements and subsequently relaxing said liner into a substantially uncompressed state inside said low pressure space. From the above it is evident that the vacuum lock from the first aspect of the present invention may be used as a stand-alone unit. The above vacuum lock will allow a liner to enter from an ambient pressure space into a low pressure space with a low leakage. At the same time the liner is compressed and drained from gas located inside the liner. The rollers are preferably connected to a motor such that the liner is driven and guided through the vacuum lock. It is further evident that the vacuum lock may be used in the opposite direction, i.e. for conveying a liner from a low pressure space to an ambient pressure space or alternatively from a high-pressure space to a low pressure space or vice versa. 
         [0036]    From GB 1080562, a labyrinth gland is known, allowing a glass fibre mat to be introduced into a vacuum chamber. The reference, however, fails to describe the essential feature of degassing the mat by compressing the mat in the labyrinth gland. 
         [0037]    From JPA 61051312 a further degassing vacuum chamber is known, in which a labyrinth gland similar to the above described structure known from GB 1080562 is described. Similar to the GB reference, the Japanese reference fails to describe the essential feature of degassing the material by compressing the material in the labyrinth gland. 
         [0038]    From U.S. Pat. No. 3,730,678, a technique of treating textile fibres is known. The reference, however, includes no vacuum lock. On the contrary, the technique involves the pressurizing of the treatment chamber by injection of steam or suitable reaction vapour or air into the reaction chamber. 
         [0039]    The above need and the above object together with numerous other needs and objects which will be evident from the below detailed description are according to a third aspect of the present invention obtained by a impregnation station comprising a resin bath for accommodating said liner, a resin reservoir, a nozzle, a pipe system and a resin pump for propelling said resin from said resin reservoir via said pipe system and said nozzle into said resin bath in a direction towards said liner. From the above it is evident that the impregnation station from the first aspect of the invention may be used as a stand-alone unit. The above impregnation station may preferably be made substantially flat and compact. 
         [0040]    From JPA 04193506, a technique of impregnating fibre bundles by the use of melted resin is known. The reference, however, describes no technique in relation to the impregnation of a fibrous liner, i.e. a structure including fibres orientated in a multiplicity of direction or in any arbitrary direction and constituting a structure similar to a mat. The impregnation of the fibre bundles by use of a melted resin is according to the teachings of the Japanese reference performed under an elevated pressure or high pressure as distinct from the technique according to the present invention, according to which technique the impregnation is performed in a degassed or low pressure chamber. 
         [0041]    The above need and the above object together with numerous other needs and objects which will be evident from the below detailed description are according to a fourth aspect of the present invention obtained by a method of impregnating a liner by providing an impregnation plant, said liner being fibrous and flexible, said impregnation plant comprising:
       a vacuum lock comprising a housing having an inlet and an outlet and defining an ambient pressure space near said inlet and a low pressure space near said outlet, said ambient pressure space and said low pressure space being separated by a substantially gas-tight seal comprising a first sealing element and a second sealing element located juxtaposed one another, said first and second sealing element being flexible,   a vacuum pump communicating with said low pressure space, and   an impregnation station being in gas-tight communication with said outlet of said vacuum lock, said impregnation station comprising a resin bath, a resin reservoir, a nozzle, a pipe system and a resin pump, and by performing the following steps:   reducing the pressure in said low pressure space in relation to the pressure in said ambient pressure space,   degassing said liner by conveying said liner through said seal between said first sealing element and said second sealing element in a direction from said ambient pressure space to said low pressure space, and   impregnating said liner by conveying said liner through said impregnation station and by using said pump propelling said resin from said resin reservoir via said pipe system and said nozzle into said resin bath in a direction towards said liner. It has been shown that by impregnating a liner according to the above method the amount of voids caused by air/gas bubbles inside the liner will be considerably reduced. The method may be applied as a continuous process where a liner of infinite length is impregnated and afterwards cut into suitable lengths. Alternatively, the liner is cut into suitable lengths before entering the impregnation plant. Yet alternatively, the method may be applied in a mobile impregnation plant, e.g. where the impregnation plant is mounted on a truck for on-site impregnation and installation.       
 
         [0048]    The above need and the above object together with numerous other needs and objects which will be evident from the below detailed description are according to a fifth aspect of the present invention obtained by a method of degassing a liner by providing a vacuum lock comprising a housing having an inlet and an outlet and defining an ambient pressure space near said inlet and a low pressure space near said outlet, said ambient pressure space and said low pressure space being separated by a substantially gas-tight seal comprising a first sealing element and a second sealing element located juxtaposed said first sealing element, said first and second sealing elements being flexible for allowing a fibrous liner to be conveyed through said seal between said first sealing element and said second sealing element in a direction from said inlet towards said outlet, and by performing the following steps:
       reducing the pressure in the low pressure space in relation to the pressure in the ambient pressure space,   conveying said liner through said seal between said first sealing element and said second sealing element in a direction from said ambient pressure space to said low pressure space, and   degassing said liner by compressing said liner into a compressed state between said first and second sealing elements and subsequently relaxing said liner into a substantially uncompressed state inside said low pressure space. The above method may be applied for degassing a liner before further treatment. The method is preferably applied together with the previously described vacuum lock.       
 
         [0052]    The above need and the above object together with numerous other needs and objects which will be evident from the below detailed description are according to a sixth aspect of the present invention obtained by a method of impregnating a fibrous liner by providing an impregnation station, said impregnation station comprising:
       a resin bath, a resin reservoir, a nozzle, a pipe system and a resin pump, and by performing the following steps:   impregnating said fibrous liner by accommodating and conveying said liner through said resin bath and propelling said resin from said resin reservoir via said pipe system and said nozzle into said resin bath in a direction towards said liner.       
 
         [0055]    It is further evident that numerous variations of the systems and methods described above are possible, in particular by combining some of the features of the aspects and embodiments described above. A detailed description of the figures of five specific and currently preferred embodiments of the invention follows below. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0056]    The invention will now be further described by reference to the drawings, in which 
           [0057]      FIG. 1  shows a side cut-out view of a first and currently preferred embodiment of an impregnation plant; 
           [0058]      FIG. 2  shows a further embodiment of a compact impregnation plant, which may be suitable for a mobile impregnation plant; 
           [0059]      FIGS. 3A and 3B  show two different embodiments of a vacuum lock for use with an impregnation plant; and 
           [0060]      FIG. 4  shows an impregnation station for use in an impregnation plant. 
       
    
    
     DETAILED DESCRIPTION 
       [0061]      FIG. 1  shows an impregnation plant  10  for impregnating a liner  12  with a resin. The resin is indicated in  FIG. 1  by hatching. The liner  12  is used for lining and re-lining pipelines such as sewer pipelines. The liner  12  is made of a glass fibre material or alternatively a felt material or a combination. The liner  12  has a flat shape with an indefinite length and a predefined width, which is determined according to the circumference of the pipeline, which is going to be lined. The width of the liner  12  may typically range from a few centimetres up to a few meters. The liner  12  is conveyed in a travelling direction according to the arrow A and enters the impregnation plant  10  at an opening  14 . The liner  12  is transported and directed via a first guiding roller  18  through the opening  14  into an ambient pressure chamber  15 . The ambient pressure chamber  15  and a low pressure space  24  together form parts of a vacuum lock  16 . The vacuum lock  16  is divided into the ambient pressure chamber  15  and the low pressure space  24  by three vacuum seals  20  mounted in a row. Each vacuum seal  20  comprises two juxtaposed mounted sealing rollers  22 ,  23 . The sealing roller  22  has a circular shape and has a flexible surface. The sealing roller  22  may preferably be made of a flexible and pressure-tight material such as e.g. rubber to achieve a good sealing effect. The sealing roller  22  is mounted such that it seals the space between the wall of the vacuum lock  16  and the juxtaposed mounted sealing roller  23  substantially gas-tight. The sealing roller  22  is preferably made to apply a force to the wall of the vacuum lock  16  as well as to the juxtaposed mounted sealing roller  23 . The force may deform the sealing rollers  22 ,  23  slightly. Optionally, a separate gasket (not shown) may be used to improve the sealing and/or reduce the friction between the wall of the vacuum lock  16  and the sealing roller  22 . Such a gasket should be made of low friction material. The sealing rollers  22 ,  23  rotate in opposite rotational directions such that the liner  12  may be transported in the travelling direction between the rollers  22 ,  23 . 
         [0062]    The liner  12  is compressed between the sealing rollers  22 ,  23  such that no substantial amount of air may leak into the low pressure space  24  between the rollers  22 ,  23 . The sealing rollers  22 ,  23  should be made significantly less flexible than the liner  12 , such that the liner  12  is compressed to a fully compressed state. The fully compressed state should be understood to mean the state where the liner  12  is compressed by the rollers  22 ,  23  to its maximum flexibility, but still may resume an uncompressed state, i.e., substantially the initial state, when relaxed, i.e., when the compression force from the rollers  22 ,  23  is removed. During the compression the force from the rollers  22 ,  23  must not permanently deform the shape of the liner  12  or substantially damage the material, such that the uncompressed state is not reached when removing the compression force. The sealing rollers  22 ,  23  may optionally be spring-loaded in direction towards each other for the rollers  22 ,  23  to be able to apply a higher pressure onto the liner and at the same time to be able to adapt to any unevenness of the liner  12 . 
         [0063]    The compartments between the seals  20  may have a pressure between the pressure of the low pressure space  24  and the ambient pressure. This reduces the pressure force and sealing requirement of each separate vacuum seal  20 . Optionally, the compartments between the vacuum seals  20  may be connected to a vacuum pump (not shown) for achieving a lower pressure inside the low pressure space. Alternatively, a pressure regulator may be used to define a specific pressure inside each of the compartments between the vacuum seals  20 . 
         [0064]    After the vacuum seals  20  the liner enters the low pressure space  24 . The rollers will have removed the most of the air inside the liner  12 . Inside the low pressure space  24  the liner  12  will resume an uncompressed state. The low pressure space  24  is connected to a vacuum pump (not shown), which preferably is constantly acting to reduce the pressure inside the low pressure space  24 . The pressure in the low pressure space  24  should be considerably lower than the ambient (atmospheric) pressure. The vacuum pump may e.g. be of the piston type to achieve a suitable pressure in the low pressure space  24  of around 50% to 70% of the atmospheric pressure. The low pressure inside the low pressure space  24  will allow any residual gas bubbles inside the liner  12  to expand and exit the liner  12 . The vacuum pump (not shown) should preferably run continuously to allow a constant low pressure, since a leakage may quickly result in an unsuitably high pressure inside the low pressure space  24 . 
         [0065]    The liner  12  is directed within the low pressure space  24  by a second guiding roller  26 . The vacuum efficiently acts on any gas volumes still present within the liner. Any gas volume inside the liner  12  will expand due to the vacuum and the gas will be sucked away by the vacuum pump (not shown). Consequently, the liner  12  will be degassed of any substantial amount of air left within the liner after the compression by the sealing rollers  22 ,  23 . Any air left within the liner  12  will constitute voids after impregnation. Such voids may compromise the material properties of the impregnated liner and may lead to a rupture of the liner  12 . 
         [0066]    The liner subsequently enters a resin bath  28 . The resin bath  28  is filled with a resin. The resin is preferably a polymeric resin and more preferably a light curable polymeric resin. On each side of the walls of the resin bath  28  a set of nozzles  32  is located. The nozzles  32  constitute a reduced flow area for achieving a flow velocity of the resin through the nozzles  32 . The nozzles  32  inject resin into the resin bath  28  towards the liner  12  with a flow velocity such that a jet is formed. The jet is directed towards the liner  12  and interacts with the liner  12 . When the jet is interacting with the liner  12  the flow velocity will be reduced and the pressure will be increased. The locally increased pressure at the point of interaction between the flow jet and the liner  12  will allow the resin to enter further into the liner  12 . The flow velocity additionally will cause the resin to reach even further into the liner  12 . Preferably, a large number of nozzles is used, such as 300 to 500, to ensure that the whole liner  12  is subjected to a flow jet. The nozzles may be placed on both sides of the liner  12  and preferably spread out on the wall of the resin bath  28 . 
         [0067]    The resin is guided through the resin bath  28  via the bottom  34  of the resin bath  28  via a pump  36  and a pipe system  38  into the nozzles  32 , forming a closed circuit. The resin will circulate according to the arrows E indicated in the resin. The liner  12  is further guided by a third guiding roller  40  near the bottom  34  of the resin bath  28 . The liner  12  will then exit the resin bath  28  into an ambient pressure space  42 . The fourth guiding roller  44  directs the liner  12  out of the resin bath  28  to the outside as shown by arrow B. The space may optionally be used for pre-curing the resin-impregnated liner  12 . 
         [0068]    The ambient pressure space  42  may be used for applying pre-curing to the resin. Pre-curing may be applied by a heat or radiation source and has the objective of turning the liquid resin into a semi-solid state. The pre-curing acts to partially cure the resin to achieve a highly viscous liquid for avoiding any resin leaking from the liner  12  and for gaining simplified handling of the liner  12 . In subsequent stages the impregnated liner  12  may be wrapped in one or more layers of plastic foil, cut into suitable lengths, folded into transportable packages and loaded on a truck for transportation to an installation site. 
         [0069]    It should be noted that there is a difference in resin level inside the resin bath. This is due to the different pressures inside the resin bath  28 . The pressure along the direction of the liner from level C to level D will first rise until the lowest point near the bottom  34  is reached. The pressure will fall until the level D is reached. Local pressure deviations may result from the flow jet. In the present embodiment the resin bath  28  constitutes a second vacuum lock. The resin bath takes the shape of a U. The resin level at the end of the resin bath  28  communicating with the low pressure space  24  will be higher than the resin level at the second end communicating with the ambient pressure space, assuming a standard pressure and gravity. The ambient air pressure acting on the resin at the second end will act as a pressure force to push the resin towards the low pressure space. The gravity force from the resin may balance the pressure force such that the gravity force of the pile of resin located near the low pressure space and above the resin level D will compensate the pressure force of the ambient air pressure. 
         [0070]    The pressure force acting on the resin is permitting a higher resin pillar on the vacuum side than on the ambient side. The difference in length is calculated according to the specific density of the resin. An ambient pressure of 100 kPa absolute is assumed. The direction of gravity is assumed to be in the direction towards the lower end of the figure. The value of the gravitational constant is assumed to be 9.81 N/kg. Having a resin density of around 1.1 kg/cm 3  will yield a resin pillar and minimum height of the resin bath  28  of 9 meters when assuming a perfect vacuum. Assuming less than a perfect vacuum will lower the minimum height of the resin bath  28 . Assuming a typical pressure of 60% of the atmospheric pressure inside the low pressure space will yield a minimum height of the resin bath of 4 m. To avoid any leakage of resin due to local pressure fluctuations a safety margin should be applied when dimensioning the resin bath  28 . 
         [0071]    The resin level C and D should be continuously monitored and additional resin should continuously be delivered to the resin bath  28  to keep the resin levels C and D substantially constant within a certain margin. Resin will continuously exit the resin bath by being impregnated into the liner  12 . Preferably, a resin supply tank is connected to the resin bath  28  via a supply pump (not shown), which is controlled by a control system (not shown). 
         [0072]    The pressure in the low pressure space  24  should as well be monitored and controlled, since any pressure fluctuation in the low pressure space  24  results in a deviation in the resin levels C and D. A pressure rise in the low pressure space  24  will make the level C drop. To avoid any leakage of resin if the pressure in the low pressure space  24  rises the ambient pressure space  42  should be properly sealed up to the fourth guiding roller  44 , located at substantially the same elevation as the vacuum lock  16 . 
         [0073]      FIG. 2  shows a compact impregnation plant  10 ′ for impregnating a liner  12 ′. The liner  12 ′ is fed by a first guiding roller  18 ′ from an ambient pressure chamber  15 ′ to a low pressure space  24 ′ via a primary vacuum lock  16 ′ comprising a series of three vacuum seals  20 ′. Each vacuum seal  20 ′ comprises sealing rollers  22 ′ and 23′. The functional principle of the vacuum seal  20 ′ is analogous to the description in  FIG. 1 . The liner is then guided by a second guiding roller  26 ′ into a resin bath  28 ′ filled with a resin. The resin is indicated in  FIG. 2  by hatching. The resin bath  28 ′ comprises a set of nozzles  32 ′ directing a resin flow jet onto the liner  12 ′. 
         [0074]    The nozzles  32 ′ are fed with pressurized resin from a pipe system  38 ′ connected to a pump  36 ′. The pump  36 ′ sucks resin from the bottom of the resin bath  28 ′ forming a closed circuit. The liner  12 ′ is fed through the resin bath  28 ′ and back into the low pressure space  24 ′ by a third guiding roller  40 ′, which in the present embodiment constitutes a pair of rollers. The liner  12 ′ is subsequently guided in an opposite direction in relation to the primary vacuum seals  20 ′ by a fourth guiding roller  44 ′ and exits the low pressure space via a secondary vacuum lock  16 ″. The functional principle of the secondary vacuum lock  16 ″ is analogous to the primary vacuum lock  16 ′, except for the conveying direction being reversed, i.e from the low pressure space  24 ′ into the ambient pressure space  42 ′. 
         [0075]    The above embodiment has the drawback of needing a secondary vacuum lock  16 ″, in which rollers may cause some resin to leak from the liner  12 ′. This may be partially prevented by a pre-curing before the liner  12 ′ exits the low pressure space  24 ′. The advantage of the above embodiment is the compact shape, making it a preferred alternative for a mobile impregnation plant. 
         [0076]      FIG. 3A  shows a close up view of a vacuum lock  16 ′″ having lip seals according to the present invention. The vacuum lock  16 ′″ is located between a low pressure space  24 ′″ and an ambient pressure space  42 ′″. The vacuum lock  16 ′″ comprises 3 vacuum seals  20 ′″, each comprising two juxtaposed lip seals  21 ′. A liner  12 ′″ is propagated through the vacuum seals  20 ′″ between the lip seals  21 ′. The lip seals  21 ′ seal the area between the wall of the vacuum lock  16 ′″ and the liner  12 ′″ pressure-tightly. The lip seals  21 ′ are preferably made of rubber or any similar soft material. The compartments between the vacuum seals  20 ′″ will have reduced pressure as well. They may optionally be connected to a vacuum pump or pressure regulator. 
         [0077]      FIG. 3B  shows a close up view of an alternative embodiment of a vacuum lock  16 ″ between a low pressure space  24 ″ and an ambient pressure space  42 ″. In the alternative embodiment the vacuum seals  20 ″ additionally comprise two juxtaposed rollers  22 ″,  23 ″. A liner  12 ″ is propagated through the seal between the rollers  22 ″,  23 ″. The rollers  22 ″,  23 ″ are made of soft material, such as rubber foam, to achieve good sealing properties and at the same time avoid damage to the liner  12 ″. The rollers  22 ″,  23 ″ are sealed towards the wall of the vacuum lock by lip seals  21 ′, preferably made of flexible material such as rubber. Using rollers  22 ″,  23 ″ will reduce the resistance caused by friction when the liner is passing through the vacuum seals  20 ″. High resistance may cause damage to the liner  12 ″ since a high force is then needed to drive the liner  12 ″ through the vacuum seals  20 ″. The rollers  22 ″,  23 ″ may optionally be motorized for additional reduction of the resistance. 
         [0078]    The above embodiments may also be combined as a lip and roller seal. From the above it is evident to any person skilled in the art that the above vacuum locks may be employed to bridge not only a low pressure space and an ambient pressure space, but also a low pressure space and a high pressure space, or an ambient pressure space and a high pressure space. It is further evident to the skilled person that the conveying direction of the liner may be reversed without any further changes to the vacuum lock. The arrow in  FIGS. 3A and 3B  shows only a preferred conveying direction. 
         [0079]      FIG. 4  shows an alternative embodiment of an impregnation plant  10 ″ according to the present invention. The alternative embodiment  10 ″ features an impregnation station  11 , which may be used in connection with the above vacuum lock  16 . The impregnation station  11  comprises two parallel plates  13  located close to each other and defining a resin bath  28 ″ between them. The plates  13  and thereby the resin bath  28 ″ extend between a low pressure space  24  and an ambient pressure space  42 . The distance between the plates is approximately equal to the thickness of the liner  12 , such that the liner  12  may be accommodated between the plates  13 . The liner  12  is conveyed through the resin bath  28 ″ between the plates  13  from the low pressure space  24  to the ambient pressure space  42  in the direction of the arrow A. 
         [0080]    Each plate  13  comprises a set of nozzles  32 ″ connected to a pipe system  38 ″. A pump  36 ″ propels the resin, which is indicated in  FIG. 4  by hatching, from a resin reservoir  29  via the nozzles  32 ″ towards the liner  12 . The liner  12  is thereby subjected to a pressurized resin jet from both sides. The continuous flow of resin will fill the resin bath  28 ″ with resin. Due to the pressure of the resin, a large amount of resin will penetrate deep into the liner and fill all the cavities of the liner with resin. Some resin will, however, not enter the liner  12 , but exit the resin bath  28 ″ outside the liner as excess resin. The excess resin will, due to the pressure, propagate towards the low pressure space  24 , and in the opposite direction towards the ambient pressure space  42 . The viscosity of the resin will cause the excess resin to propagate slowly outside the resin bath  28 ″. A continuous supply of pressurized and viscous resin will completely fill the resin bath  28 ″ and thus act as a liquid pressure seal between the low pressure space  24  and the ambient pressure space  42 . It should be noted the resin bath  28 ″ is not completely encapsulated and a continuous flow of resin is required for impregnation and good sealing quality. 
         [0081]    The excess resin is allowed to slowly drip off the resin bath  28 ″ and may preferably be collected into the resin reservoir  29  outside the resin bath at both sides. The excess resin may thus be re-used by re-circulating it according to the arrows E from the resin bath via the pump  36 ″ and nozzles  32 ″ into the resin bath  28 ″ towards the liner  12  and possibly again into the resin reservoir  29 . A filter or the like may be applied in the resin reservoir  29  to remove any contamination from the used resin. Such contamination may be fibres of fibre particles released from the liner  12  during impregnation. Such contamination may possibly clog the nozzles  32 ″, the pipe system  38 ″ or the pump  36 ″. 
       LIST OF PARTS 
       [0000]    
       
           10 . Impregnation plant 
           11 . Impregnation station 
           12 . Liner 
           13 . Plate 
           14 . Opening 
           15 . Ambient pressure chamber 
           16 . Vacuum lock 
           18 . First guiding roller 
           20 . Vacuum seal 
           21 . Lip seal 
           22 . Sealing roller 
           23 . Sealing roller 
           24 . Low pressure space 
           26 . Second guiding roller 
           28 . Resin bath 
           29 . Resin reservoir 
           32 . Nozzle 
           34 . Bottom 
           36 . Pump 
           38 . Pipe system 
           40 . Third guiding roller 
           42 . Ambient pressure space 
           44 . Fourth guiding roller 
         A &amp; B. Liner-conveying direction 
         C &amp; D. Resin level 
         E. Resin circulation direction 
       
     
         [0108]    It should be further noted that a prime symbol in the description and in the figures denotes an alternative realization of the same part.
The object of the invention is to provide a method and system for impregnating a liner, simultaneously reducing the risk of a void inside the liner after curing. This object is achieved by an impregnation plant ( 10) comprising a vacuum lock ( 16) comprising a housing having an inlet ( 14) and an outlet and defining an ambient pressure space ( 15) near the inlet and low pressure space ( 24) near the outlet. The pressure spaces are separated by a seal ( 20) comprising a first and a second sealing element ( 22, 23), allowing the fibrous liner ( 12) to be conveyed there between from the inlet ( 14) towards the outlet. The liner is degassed by compressing it between the first and second sealing elements ( 22, 23) and is subsequently relaxed in an uncompressed state inside the low pressure space ( 24). The plant further comprises a vacuum pump communicating with the low pressure space, and an impregnation station in gas-tight communication with the outlet or the vacuum lock ( 16) and comprising a resin bath ( 28) for accommodating the liner, a resin reservoir, a nozzle ( 32), a pipe system ( 38) and a resin pump ( 36) for propelling the resin from the resin reservoir via the pipe system ( 38) and the nozzle ( 32) into the resin bath ( 28) in a direction towards the liner.