Abstract:
A hydraulic coupling for sub sea applications comprises inter-engageable male and female connectors. The male connector defines a male member for receipt in a chamber defined by the female connector. Each connector has a respective check valve for controlling the flow of fluid through internal bores in the connectors. The check valves are actuable by an actuator between an open position in which hydraulic fluid may flow through the respective internal bore and a closed position in which such flow is interrupted, depending on the distance between the first and second check valves. The male and female connectors are moveable between an uncoupled position in which the check valves are in the closed position and a coupled position in which the male and female connectors are engaged and extend along a longitudinal axis with the male member occupying the chamber of the female connector in a sealed relationship. A pair of seals are provided one on the male member and the other on the in the chamber. The seals are arranged so that they seal the chamber at opposite ends by sealing against respective sealing surfaces in the coupled position. The distance between the first and second check valves in the sealing position is such that the actuator urges them to their open positions. The arrangement ensures that seawater between the connectors is allowed to escape before the sealing relationship is established and, upon coupling, the check valves are opened to allow fluid to flow.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a national phase application of PCT Application No. PCT/GB2009/002841, filed Dec. 8, 2009, which claims priority to United Kingdom Patent Application No. 0822375.2, filed Dec. 9, 2008, the entire contents of which are both hereby incorporated by reference herein. 
     
    
     BACKGROUND 
       [0002]    The present invention relates to a hydraulic coupling and more particularly, but not exclusively, to such a coupling of the kind that is used to interconnect hydraulic fluid flow lines in sub sea applications. 
         [0003]    Hydraulic couplings are used, for example, to interconnect hydraulic fluid lines associated with sub sea wellheads and/or the assembly of valves, spools and other fittings known in the drilling industry as the “christmas tree”. The hydraulic fluid, which may be, for example, control fluid or an injected chemical for cleaning or otherwise treating the pipeline, the well, or christmas tree components, may be supplied under pressure from a floating vessel or a shore location. The couplings generally comprise male and female connectors having seals that are disposed at the junction between them when the coupling is complete. In many applications multiple hydraulic lines are bundled together into an umbilical string and multiple couplings are required to interconnect the respective lines. In such an arrangement the connectors are supported on respective manifold plates (often referred to in the art as “stab plates”) that are brought together to couple the connectors, and therefore the lines, together. The stab plates are typically transported and brought into register either manually by sub sea divers or by using a remote operated vehicle (ROV). 
         [0004]    In one typical hydraulic coupling the male and female connectors are in the form of cylindrical bodies with internal bores. At a mating end of each connector the bore is of a relatively large diameter for sealed engagement with the mating end of the other connector and at the other end the bore has a relatively small diameter where it is connected to the hydraulic line via a check valve. The male connector is inserted axially into the relatively large diameter bore of the female connector and sealed thereto by a seal located in the bore. When the connectors are sealed, further axial movement causes actuators associated with the respective check valves to be displaced such that they are open and allow hydraulic fluid to flow through the sealed coupling. The seals prevent ingress of seawater into the hydraulic fluid line and the egress of hydraulic fluid out of the coupling. When the male and female connectors are disconnected the check valves are biased to a closed position so that hydraulic fluid cannot leak out into the environment. 
         [0005]    One of the problems associated with such couplings is the large force required to connect or disconnect them, when the coupling is filled with hydraulic fluid. When the male and female connectors are engaged and moved axially towards each other to complete the connection, a force has to overcome the resistance provided by a small volume of incompressible seawater trapped in the internal bores by the seals. The forces acting on the seals serve to resist connection or disconnection, particularly under the hydrostatic head of seawater. Disconnection can be a problem as a low pressure or partial vacuum is created within bores that serves to resists disengagement of the male and female connectors. The forces required to connect and disconnect are multiplied when a plurality of such couplings are used on a pair of stab plates. 
         [0006]    The check valves in hydraulic couplings of the kind described above are generally in the form of poppet valves with a conical or frusto-conical valve member whose outer face is designed to seal against a corresponding valve seat surface defined in the internal bore. The effective sealing of such valves can be problematic as it is important to manufacture the respective surfaces to a fine tolerance to ensure a good seal. In some instances the valve seat is defined at a significant axial distance along the inside of the connector and it can be difficult to achieve the required quality of finish in the machining process. 
         [0007]    In the event that a check valve does not perform to the requisite standard the coupling is generally removed and replaced in its entirety. 
       SUMMARY 
       [0008]    It is one object of the present invention to obviate or mitigate the aforementioned disadvantages. It is another object of the present invention to provide for an alternative, or improved, hydraulic coupling. 
         [0009]    According to a first aspect of the present invention there is provided a hydraulic coupling a male connector having a body defining a male member, an internal bore in the body and a first check valve for controlling fluid flow through the internal bore; a female connector having a body defining an internal bore with a chamber for receipt of the male member and a second check valve for controlling fluid flow through the internal bore; the male and female connectors each having a respective mating end; an actuator disposed between the first and second check valves for moving the first and second check valves between an open position in which hydraulic fluid may flow through the respective internal bore and a closed position in which the flow is interrupted, depending on the distance between the first and second check valves; the male and female connectors being movable between an uncoupled position in which the mating ends are separated and the first and second check valves are in the closed position and a coupled position in which the male and female connectors are engaged at their mating ends and extend along a longitudinal axis; wherein the first and second check valves are each removable from the respective mating ends of the male and female connectors. 
         [0010]    The ability to remove of the check valves from the mating ends enables the valves to be replaced, service or repaired in-situ without having to remove the whole coupling. This is much quicker and easier than compared to prior art hydraulic couplings. 
         [0011]    The first and second check valves preferably form part of a removable check valve assembly that may comprise a valve member and a valve seat. It may further comprise a valve cage that supports the valve member. The first and second check valves may be ball check valves. Each ball check valve may comprise a ball valve member biased against a valve seat by a biasing member such as a spring. The spring may be supported on a member such as a spigot that limits travel of the ball valve member away from the valve seat. The valve seat may comprise a principal seat which may, for example, be made of PEEK and a back-up seat, that may for example, comprise an annulus of metal. 
         [0012]    The male and female connectors may each comprise an outer body with a removable insert. The first or second check valve may be removable once the respective removable insert has been removed. The outer body of the female and the male connectors may be substantially identical. 
         [0013]    The removable insert of the male connector may define the male member and the removable insert of the female connector may define the chamber. The removable inserts may be threadedly connected in the respective outer bodies and they may abut or receive a respective one of the first and second check valves. 
         [0014]    The outer bodies may each define a port for connection to a hydraulic line. The connection may be provided, for example, by a thread defined on a surface that defines the port. 
         [0015]    The first and second check valves may be movable by the actuator to interrupt or permit flow through the respective port to the hydraulic line. 
         [0016]    According to a second aspect of the present invention there is provided a hydraulic coupling comprising: a male connector having a body defining a male member, an internal bore in the body and a first check valve for controlling fluid flow through the internal bore; a female connector having a body defining an internal bore with a chamber for receipt of the male member and a second check valve for controlling fluid flow through the internal bore; the male and female connectors each having a respective mating end; an actuator disposed between the first and second check valves for moving the first and second check valves between an open position in which hydraulic fluid may flow through the respective internal bore and a closed position in which the flow is interrupted, depending on the distance between the first and second check valves; the male and female connectors being movable between an uncoupled position in which the mating ends are separated and the first and second check valves are in the closed position and a coupled position in which the male and female connectors are engaged at their mating ends and extend along a longitudinal axis; wherein the first and second check valves are first and second ball check valves. 
         [0017]    Conventionally poppet check valves are used in hydraulic couplers with an actuator that is fixed to, or forms an integral part of, the poppet valve. 
         [0018]    The actuator is preferably not fixed to either of the first and second ball check valves. One end of the actuator may be in abutment with the first ball check valve. It may be in abutment even when the connectors are not coupled. 
         [0019]    The actuator may be of any suitable shape in cross-section and may be an elongate member supported by one or other of the male or female connectors. The actuator may be supported in the internal bore of the male member. Preferably there is a clearance between the internal bore and the actuator to allow for the flow of fluid along the actuator. The clearance may be defined by recess, grooves or otherwise defined in the surface of the actuator. 
         [0020]    The actuator may have a stop feature for engagement with a surface defined in the internal bore of the male member to limit its movement in the direction away from the first check valve. The stop feature may be a stepped shoulder defined on the actuator and the surface may be a stepped shoulder defined in the internal bore of the male member. The actuator may be held in abutment with the first check valve by the engagement of the stop feature with the surface defined in the internal bore. 
         [0021]    The male and female connectors may each comprise an outer body with a removable insert. 
         [0022]    The first and second ball check valve may each comprise a ball valve member biased against a valve seat by a spring. The spring may be supported on a spigot that limits travel of the ball valve member away from the valve seat. The valve seat may comprise a principal seat made of any suitable material such as, for example, PEEK and a back-up seat comprising an annulus of any suitable material such as, for example, metal. 
         [0023]    According to a third aspect of the present invention there is provided a hydraulic coupling comprising: a male connector having an outer body defining an internal bore in which there is a removable insert defining a male member, and a first check valve for controlling fluid flow through the internal bore; a female connector having an outer body defining an internal bore in which there is a removable insert defining a chamber for receipt of the male member, and a second check valve for controlling fluid flow through the internal bore; the first and second check valves being movable between open and a closed position by an actuator; the male and female connectors being movable between an uncoupled position in which the first and second check valves are biased to the closed position and a coupled position in which the male member is received in the chamber of the female connector in a sealed relationship and the male and female connectors interact so as to move the actuator to urge the first and second check valves to the open positions; wherein the outer bodies are substantially identical. 
         [0024]    The actuator may move the first and second check valves between an open position in which hydraulic fluid may flow through the respective internal bore and a closed position in which the flow is interrupted, depending on the distance between the first and second check valves. 
         [0025]    The male member may have an engagement portion that occupies the chamber of the female connector in a sealed relationship when in the coupled position. The engagement portion may have an external surface for sealing against an internal surface of the chamber. 
         [0026]    A first annular seal may be disposed in the chamber of the female connector, the sealed relationship being provided by the first annular seal in sealing engagement with the external surface of the engagement portion. A second annular may seal between the external surface of the engagement portion and the internal surface of the chamber. 
         [0027]    The outer bodies may each define a port for connection to a hydraulic line. 
         [0028]    The actuator may comprise an elongate member supported by one or other of the male or female connectors. The actuator is supported in the internal bore of the male member. A clearance between a wall defining the internal bore and the actuator may be provided to allow the passage of fluid along the actuator. 
         [0029]    The male and female connectors may each comprise an outer body with a removable insert. The removable insert of the male connector may define the male member and the removable insert of the female connector may define the chamber. The removable inserts may each abut a respective one of the check valves. 
         [0030]    According to a fourth aspect of the present invention there is provided a hydraulic coupling comprising: a male connector having a body defining a male member, and having an internal bore and a first check valve for controlling fluid flow through the internal bore; a female connector having a body defining an internal bore with a chamber for receipt of the male member and a second check valve for controlling fluid flow through the internal bore; an actuator disposed between the first and second check valves for moving the first and second check valves between an open position in which hydraulic fluid may flow through the respective internal bore and a closed position in which such flow is interrupted, depending on the distance between the first and second check valves; the male and female connectors being moveable between an uncoupled position in which the check valves are in the closed position and a coupled position in which the male and female connectors are engaged and extend along a longitudinal axis with the male member having an engagement portion that occupies the chamber of the female connector in a sealed relationship, the engagement portion having an external surface; a first annular seal disposed on the engagement portion of male member; a second annular seal disposed in the chamber of the female connector; the sealed relationship being provided by the first annular seal in sealing engagement with a first sealing surface defined by the chamber of the female connector and the second annular seal in sealing engagement with a second sealing surface defined on the external surface of the engagement portion of the male member; wherein in the coupled position the first and second annular seals are spaced apart in the chamber at opposite ends thereof and the distance between the first and second check valves is such that the actuator urges them to their open positions. 
         [0031]    The arrangement ensures that fluid (such as seawater in the instance of the coupling being used sub sea) trapped between the male and female connectors is allowed to escape when the connectors are moved between the uncoupled and coupled positions. The disposition of the first and second annular seals allows the trapped fluid to escape before the engagement portion of the male connector and the chamber of the female connector enter the sealed relationship. Moreover, once the sealing relationship is complete any remaining trapped fluid does not significantly resist further axial engagement of the connectors in the coupled position since the actuator urges check valves are open to allow flow out of the coupling. 
         [0032]    The arrangement is such that the connectors are sealed together at opposite ends of the chamber only when the connectors have reached the end or near the end of the length of relative travel required to attain the coupling position. 
         [0033]    The first and second annular seals may be arranged such that they enter the sealing relationship substantially simultaneously when the male and female connectors are moved from the uncoupled to the coupled position. For example, the distance between the first annular seal and the sealing surface on the engagement portion of the male member may be substantially equal to the distance between the second annular seal and the sealing surface defined by the surface of the chamber. 
         [0034]    The engagement portion may extend along part or substantially all of the length of the male member. 
         [0035]    In the sealed relationship a radially outer surface the first annular seal is supported by the first sealing surface of the chamber of the female connector and a radially inner surface of the second annular seal is supported by the second sealing surface of the engagement portion. 
         [0036]    The first and second annular seals may comprise one or more suitable sealing elements. For example they may include an O-ring and a supplementary seal or a pair of supplementary seals disposed on each side of an O-ring. 
         [0037]    The second sealing surface may be provided on a terminal tip of the engagement portion of the male member. The terminal tip may have a diameter that is larger than an adjacent part of engagement portion. 
         [0038]    The internal bore of the female connector may comprise a relatively large diameter bore with an open end for receipt of the male connector and relatively small diameter bore in which the second check valve is disposed. 
         [0039]    The first sealing surface and the second sealing surface may occupy substantially the same diameter with respect to the longitudinal axis. This means that the forces applied by the pressurised fluid at the first and second annular seals are substantially equal. 
         [0040]    The first annular seal may be supported in a groove in the male member and the second annular seal may be supported in a groove in the chamber of the female connector. 
         [0041]    The actuator may take any suitable form and may be supported by one or other of the male or female connectors. For instance it may comprise an elongate member, such as a pin which may have paths such as channels, recesses or the like to allow the passage of fluid along its length. The actuator may be supported by the male connector such as in the internal bore defined by the male member. It may have the cross-sectional shape of a cross. The actuator is preferably of a predetermined length such that it engages the first and second check valves so as to urge them to the open position when the male and female connectors are moved to the coupled position. 
         [0042]    The male and female connectors may each comprise an outer body with a removable insert which may be removably connected by any suitable connection means including for example a thread, a bayonet type fitting or any suitable latched connection. This provides for a modular configuration and the outer bodies of the female and the male connectors may be substantially identical and therefore interchangeable. The removable insert of the male connector may define the male member and the removable insert of the female connector may define the chamber. The removable insert for the male connector may abut the first check valve and the removable insert for the female connector may abut the second check valve. 
         [0043]    The removable insert of the male connector may project from the outer body of the male connector and the removable insert of the female connector may project from the outer body of the female connector, the projecting part of the male insert being received in the chamber of the female connector and the projection part of the female insert being received between the outer body and the insert of the male connector. 
         [0044]    The outer bodies may receive the respective check valves whereas the inserts may be designed to interconnect the connectors of the coupling. The removable insert may be sealed to the respective outer body of each connector by an appropriate seal. The internal bore of the male connector may comprise a first portion defined by the outer body and which may house the first check valve and a second portion defined by the removable insert and which may receive the actuator. 
         [0045]    The outer bodies of each male and female connector may each define a port for connection to a hydraulic line. The first check valve may be disposed between the removable insert of the male connector and the respective port and similarly the second check valve may be disposed between the removable insert of the female connector and the respective port. 
         [0046]    The first and/or second check valve may comprise a removable cartridge which may comprise a movable valve member and a valve seat against which the valve member seals when in the close position. The movable valve member may be biased to the closed position by a biasing member which may be any form of resilient member such as, for example, a spring. The valve member may be in the form of a ball. When the male and female members are in the coupled position the actuator may engage each valve member so as to move it, against the biasing force of the biasing member, away from the respective valve seat. A supplementary valve seat may be provided in addition to the (principal) valve seat and which acts to seal against the valve member should the principal valve seat fail. 
         [0047]    The valve cartridge may comprise a stop that limits the length of travel of the valve member away from the valve seat. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0048]    Specific embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: 
           [0049]      FIG. 1  is a cross-section view along line A-A of  FIG. 2 , the plane of the section intersecting the longitudinal axis of a hydraulic coupling in accordance with at least one aspect of the present invention, the coupling shown disconnected and mounted on respective supports; 
           [0050]      FIG. 2  is an end view of the coupling of  FIG. 1 ; 
           [0051]      FIG. 3  is a view corresponding to that of  FIG. 1  with the coupling shown in a position just before being fully coupled; 
           [0052]      FIG. 4  is a view corresponding to those of  FIGS. 1 and 3 , with the coupling shown fully coupled; 
           [0053]      FIG. 5  is an axial cross-section of an alternative coupling embodiment in accordance with at least one aspect of the present invention, the coupling shown disconnected; 
           [0054]      FIG. 6  is a view corresponding to that of  FIG. 5 , with the coupling shown in a first partially coupled position; 
           [0055]      FIG. 7  is a view corresponding to that of  FIG. 5 , with the coupling shown in a second partially coupled position; and 
           [0056]      FIG. 8  is a view corresponding to that of  FIG. 5 , with the coupling shown fully coupled. 
       
    
    
     DETAILED DESCRIPTION 
       [0057]    Referring now to the  FIGS. 1 to 4  of the drawing the hydraulic coupling, indicated generally by reference numeral  10 , comprises male and female connectors  11 ,  12  both of which are generally cylindrical and have identical outer bodies  13  each with an interior bore  14 . 
         [0058]    In  FIG. 1 , the male and female connectors  11 ,  12  are depicted in coaxial alignment just prior to their connection. They are brought into register by relative axial movement towards each other to a position as shown in  FIG. 3  where they are almost fully coupled and then further moved in the same direction to complete the engagement and provide a sealed connection as shown in  FIG. 4 . 
         [0059]    Each of the interior bores  14  has a relatively large diameter opening  15  at a mating end and a relatively small diameter port  16  at the opposite end. The port  16  is internally threaded for connection to an end fitting of a hydraulic fluid line (neither of which are shown in the figures). From the large diameter opening  15  the internal bore  14  extends rearwardly towards the port  16  and is radially inwardly stepped at  17  such that it separates the bore  14  into a first chamber  14   a  that is designed to receive a male or female nose insert  18 ,  19  and a second bore  14   b  in which a check valve assembly  20  is disposed. 
         [0060]    The female nose insert  19  is generally cylindrical with an internal bore defining a chamber  21  for sealing engagement with the male nose insert  18 . The insert  19  has a first end  22  that abuts the check valve assembly  20  and a second end  23  for mating with the male nose insert  18  of the male connector  11 . An external surface of the female nose insert  19  has a threaded portion  24  at the first end  22  to allow screw connection to a corresponding threaded portion in the wall of the internal bore  14  of the outer body  13 . Further towards the second end  23  of the insert  19 , the outer surface has a pair of axially spaced annular grooves  25 ,  26  designed to receive seal elements for sealing against the internal surface of the outer body  13 . The seal elements in each groove  25 ,  26  each comprise an O-ring seal  27 ,  28  and a back-up annular PTFE seal  29 ,  30 . These serve to seal together the two parts (i.e. the outer body  13  and the female nose insert  19 ) of the female connector  12  against the ingress or egress of fluid. It is to be appreciated that other appropriate seal elements may be used. The surface of the internal chamber  21  of the female nose insert  19  similarly has an annular groove  32  disposed axially between the groove  25  and the first end  22  and receives an O-ring seal  33  disposed between a pair of PTFE secondary seals  34  (it will again be appreciated that any suitable sealing arrangement may be provided). This seal arrangement is designed to provide a sealed connected between the male and female connectors  11 ,  12  when fully coupled together. 
         [0061]    The male nose insert  18  has a first end  40  for engagement with the check valve assembly  20  and an elongate second end  41  for connection to the female nose insert  19 . The first end  40  has substantially the same diameter as the corresponding part of the female nose insert  19  and the outer surface has a threaded section  42  (at the first end  40 ) for screw-threaded engagement with a corresponding threaded portion defined on the surface of the internal bore  14  of the outer body and a pair of axially spaced annular grooves  43 ,  44  for receipt of seal elements. Each of the annular grooves  43 ,  44  houses an O-ring seal  45  and a back-up PTFE seal  46  for sealing engagement with the surface of the inner bore  14  of the outer body  13 . Once again, it is to be appreciated that any suitable sealing arrangement may be provided. The second end  41  is elongate and designed to be received in the chamber  21  of the female nose insert  19 . It has a further annular groove  47  defined on its external surface, adjacent to the intermediate portion  41  and for receipt of sealing elements designed to seal with the female nose insert  19  when the two connectors  11 ,  12  are engaged. The sealing elements are identical to those provided in groove  32  of the female nose insert  19  and comprise an O-ring  48  sandwiched between PTFE secondary annular seals  49 . The second end  41  has a further reduced diameter portion  50  defined between the region where the seals  48 ,  49  are supported and a terminal tip  51  designed to seal against the seals  33 ,  34  provided in the female nose insert  19 . 
         [0062]    The male nose insert  18  is penetrated by an internal bore  52  that receives an elongate actuator pin  53  that has the shape of a cross in cross-section. There is a small radial clearance between the pin  53  and the bore. This clearance together with the spaces between the limbs of the cross afford paths for hydraulic fluid to flow along the pin  53  when the coupling is complete. The actuator pin  53 , which projects slightly from the first end  40  and more significantly from the second end  50 , is not fixed to either of the check valve assemblies  20 . It is held captive in the bore  52  by a stepped shoulder  70  that engages with a corresponding stepped shoulder  71  formed in the internal surface of the bore  52  to prevent the pin  53  being withdrawn out of the mating end of male nose insert  19 . The engagement of the stepped shoulders  70 ,  71  thus limit movement of the actuator away from the check valve assembly of the male connector  11 . 
         [0063]    The check valve assemblies  20  are each identical in the form of a cartridge  54  having a plastics or metal cage that supports a valve ball  55  and its seat  56 . The cartridge  54  is received in the second chamber  14   b  of the bore  14  with the cage receiving the valve ball  55  which is retained in place by an annular valve seat  56  of any suitable material such as, for example, PEEK (polyetheretherketone) that abuts against the first end  22 ,  40  of the respective female or male nose insert  19 ,  18 . The ball  55  is biased towards the respective valve seat  56  by a spring  57  supported on a spigot  58  that also acts to limit the travel of the ball  55  away from its seat  56 . A small annulus of metal  59  is received in the valve seat  56  and also abuts the first end  22 ,  40  of the respective insert  19 ,  18  and serves as a back-up seat to the PEEK seat  56 . 
         [0064]    It will be seen from  FIG. 1  that when the male connector  11  is assembled such that the male nose insert  18  is secured to the outer body  13  by the threads  42 , its second end  41  projects significantly from the large opening  15  whereas the first end  40  abuts against the valve seat  56  and back-up seat  59  of the check valve cartridge  54  with one end of the actuator pin  53  projecting from the tip  51  of the second end  41  and the opposite end abutting against the ball  55  of the check valve cartridge  54 . 
         [0065]    Similarly, when the female connector  12  is assembled its second end  23  projects slightly from the large opening  15  of the outer body  13 . 
         [0066]    In each connector  11 ,  12  the check valve assembly  20  is biased closed by means of the spring  57  urging the ball  55  against the seat  56  such that hydraulic fluid flowing from the connected line into the respective connector  10 ,  11  through the port  16  is prevented from egressing into the internal bores  14 . 
         [0067]    In order to connect together the two halves of the coupling  10 , the second ends  23 ,  41  of the male and female nose inserts  18 ,  19  are presented to each other as shown in  FIG. 1 . The longitudinal axes of the two connectors  11 ,  12  are aligned such that the second end  41  of the male nose insert  18  can be received in the chamber  21  of the female nose insert  19  and the second end  23  of the female nose insert  19  can be received within the outer body  13  of the male connector  11  when the two connectors  11 ,  12  are moved axially towards one another as depicted in  FIG. 3 . In this position the two connectors  11 ,  12  are brought into register but are not fully engaged and are not yet sealed to each other. In particular, the surface of the chamber  21  of the female nose insert  19  is about to pass over the seals  48 ,  49  on the outer surface of the second end of the male nose insert  18  and, similarly the outer surface of the tip  51  of the second end of the male nose insert  18  is about to pass inside the seals  33 ,  34  in the internal annular groove  32  of the female nose insert  19 . At this point the ends of the actuator pin  53  abut the respective balls  55  of the check valve assemblies  20 . Prior to this point any seawater trapped in the chamber  21  of the female nose insert  19  has been allowed to escape by virtue of a small radial clearance between the external surface of the second end of the male nose insert  18  and the internal surface of the chamber  21  of the female nose insert  19 . 
         [0068]    In order for the two connectors  11 ,  12  to become fully sealed to each other and for the two check valves  20  to open, the connectors  11 ,  12  must be axially displaced further towards each other by the very short distance x shown in  FIG. 3  until the outer bodies  13  abut one another. 
         [0069]    The connectors  11 ,  12  are shown fully engaged in  FIG. 4 . In this position the radially inner surface of seals  33 ,  34  of the female nose insert  19  are supported on a sealing surface defined on the outer surface of the tip  51  of the male nose insert  18  and the radially outer surface of the seals  48 ,  49  on the outer surface of the male nose insert  18  are brought into engagement with a sealing surface defined by the inner surface of the chamber  21  of the female nose insert  19 . At substantially the same time the ends of the actuator pin  53  forces the balls  55  of the check valve cartridges  54  from their respective seats  56  against the force of the respective biasing springs  57  so as to open the valves and allow hydraulic fluid to flow through the coupling  10  via the paths defined by the actuator pin  53 . 
         [0070]    The two connectors  11 ,  12  are shown mounted on respective supports  60  which in this case are designed to receive only one connector each. Each of the connectors  11 ,  12  is received in an aperture in the respective support  60  and is retained in position by a circlip  61  that is received in an annular groove  62  in the external surface of the outer body  13 . In another embodiment  11 ,  12  the connectors may be welded or otherwise fixed to their supports  60 . In a yet further embodiment the supports  60  may be designed to receive multiple connectors  11 ,  12  that are coupled to each other when the opposite supports  60  are aligned and brought together. 
         [0071]    The provision of seals  33 ,  34  and  48 ,  49  at opposite, axially spaced, ends of the mating parts of the male and female connectors  11 ,  12  affords a secure sealing arrangement. Moreover, by ensuring that the sealing surface of each sealing arrangement is at the same diameter, the respective forces on the seals are balanced such that there is no tendency to inhibit connection or separation of the connectors  11 ,  12 . 
         [0072]    The seals  33 ,  34  and  48 ,  49  are positioned such that sealing between the male and female connectors  11 ,  12  is made effective just as the check valve assemblies  20  are opened by the actuator pin  53 . This means that any remnant of seawater left in the chamber  21  can pass into the hydraulic line. The sealing is configured such that it does not take effect until the connectors  11 ,  12  are almost fully engaged (between the positions depicted in  FIGS. 3 and 4 ) so that the trapped volume of seawater is substantially negligible and significantly less than in prior art couplings. Similarly, the arrangement allows easy disconnection of the coupling  10  as the check valve  20  is free to close at the point the sealing is broken so that the separation force does not have to act against the force applied by a partial vacuum. 
         [0073]    The use of ball check valves is beneficial over conventional poppet valve designs as the contact sealing area is smaller and is not reliant to the same degree on machining tolerances and surface finishes, resulting in lower spring forces required to hold the valves in the closed positions, leak free. 
         [0074]    The above described design lends itself to a modular configuration in which a single outer body  13  and check valve cartridge  54  can be used for both the male and female connectors  11 ,  12  with just the nose inserts  18 ,  19  being selected to determine whether the connector is male or female. The screw-threaded connection between the inserts  11 ,  12  and the outer bodies  13  allows for simplified manufacture and assembly. Moreover, it allows for ease of servicing, repair or maintenance of the check valve cartridges  54  as they can be accessed and removed easily from the mating end of each of the connectors  11 ,  12  in-situ i.e. without the need to remove the whole connector  11 ,  12  from its respective support  60 . The male or female nose insert  18 ,  19  is simply disconnected from the respective outer body  13  by unscrewing it to provide access to the check valve cartridge  54 . 
         [0075]    Each of the seal arrangements is housed in grooves  32 ,  47  which provide protection to the seals when under pressure. Moreover the provision of secondary seals  34 ,  49  affords additional security. 
         [0076]    The main valve seat (PEEK)  55  is provided with a back-up metal annulus  57  that not only prevents permanent deformation of the main seat  55  at high operating temperatures but also provides an emergency seat should the main seat  55  fail. 
         [0077]    It is will be appreciated by one of ordinary skill in the art that the invention has been described by way of example only, and that the invention itself is defined by the claims. Numerous modifications and variations may be made to the exemplary design described above without departing from the scope of the invention as defined in the claims. For example the check valves may be of any suitable form. Moreover, the material used for each component can be varied to comply with the temperature or pressure requirements of the particular application. 
         [0078]    A second embodiment of the hydraulic coupling having many design features similar to those of the coupling of  FIGS. 1 to 4  will now be described with respect to  FIGS. 5 to 8 . Components that correspond to those of the embodiment of  FIGS. 1 to 4  have been given the same reference numeral but increased by 100 and are not further described except insofar as they differ from their counterparts. 
         [0079]    The male and female parts of the hydraulic coupling of  FIGS. 5 to 8  are shown separate from any support such as that indicated by reference numeral  60  in the above embodiment but it will be understood that it is intended to be used in the same manner. The coupling differs primarily in that seals between the male and female connectors are provided in the female connector only and in that the valves are positioned closer to the mating ends of each connector so that the actuator can be made shorter in length. This renders it less susceptible to damage in circumstances where large forces are required to connect and disconnect the coupling. 
         [0080]    The male and female connectors  111 , 112  again comprise identical outer bodies  113  each with an interior bore  114 . In  FIG. 5  the male and female connectors are shown separated before connection and in coaxial alignment. The interior bores  114  each receive, as before, a respective male and female nose insert  118 ,  119 . In contrast to the inserts  18 ,  19  of the previous embodiment, the internal bores in these inserts  118 ,  119  are configured to receive the check valve assemblies  120  which are again in the form of removable cartridges. Each cartridge comprises a cage  175  and a seat  156  which are connected together and receive between them a ball  155 . The cage supports a spring  157  that acts on one side of the ball  155  to bias it towards the seat  156 . As in the previous embodiment the seat may take any form and material but in one example it is an annular component of PEEK. The outer surface of the cartridge has a groove in which an O-ring seal resides  177 , the seal acting against an internal surface of the respective nose insert  118 ,  119 . 
         [0081]    The actuator  153  is again an elongate member that is received in the internal bore  152  of the male nose insert  118 . In this particular embodiment the actuator is substantially triangular in cross-section although it is to be appreciated that it may take any suitable shape provided it allows for the flow of fluid between its surfaces and the surface of the internal bore  152 . As before, movement of the actuator away from the check valve assembly  20  of the male connector  111  is limited by inter-engagement of stepped shoulders  171 ,  172  defined on the actuator  153  and in the internal bore  152 . These serve to hold the actuator in abutment with the ball  155  of the check valve assembly in the disconnected state shown in  FIG. 5 . 
         [0082]    In each case the nose inserts  118 ,  119  have a flange  176  at the mating end that abuts against an end of the outer body  113 . The flange  176  of the female nose insert  119  is thicker than that of the male nose insert  118  and defines the chamber  121  in which the second end of the male nose insert  118  is received. 
         [0083]    The elongate second end  141  of the male nose insert  118  is designed to be received in the chamber  121  of the female nose insert  119  as before. The chamber  121  has two axially spaced seals  133 ,  148  that are received in respective grooves and are intended to seal against the outer surface of the elongate second end  141  of the male nose insert  118 . The seals  133 ,  148  are axially spaced along the chamber  121 . A first of the seals  133 , nearest to the mating end, is in two parts comprising a graphite annulus alongside a PTFE annulus. A second of the seals  148  comprises a graphite annulus alongside a beryllium clamping ring. The two parts to the seal ensure there is a back-up seal provided in one of the parts fails. It will be understood that any suitable form and material for each seal may be used and that the back-up part of the seal is optional. For example, the graphite annulus may be replaced by any sort of elastomeric material. 
         [0084]    In  FIG. 6  the male and female connectors  111 ,  112  have been moved axially towards one another such that the elongate second end  141  of the male nose insert  118  is received in the chamber  121  of the female connector  112  such that it is in a sealing relationship with the seal  133 . At this point the leading end of the actuator  153  abuts the ball  155  of the check valve assembly  120  in the female connector  112 . Further axial movement towards each other causes the actuator to move at the ball  155  in the female connector  112  away from its seat  156  against the biasing force of the compression spring  157 , thereby opening the check valve  120  as shown in  FIG. 7 . This allows trapped fluid such as seawater to escape into the flow line. At this position the connectors  111 , 112  are almost fully coupled. 
         [0085]    In  FIG. 8  the connectors  111 ,  112  are shown fully engaged such that the flanges  176  of each nose insert  118 ,  119  are in abutment and the elongate second end  141  of the male nose insert  118  is sealed against the wall of the chamber  121  by both seals  133  and  148 . It will be seen that both balls  155  are moved from their respective seats  156  against the force of the biasing springs  157  such that the hydraulic fluid can flow through the coupling. 
         [0086]    The described and illustrated embodiments are to be considered as illustrative and not restrictive in character, it being understood that only the preferred embodiments have been shown and described and that all changes and modifications that come within the scope of the inventions as defined in the claims are desired to be protected. It should be understood that while the use of words such as “preferable”, “preferably”, “preferred” or “more preferred” in the description suggest that a feature so described may be desirable, it may nevertheless not be necessary and embodiments lacking such a feature may be fall within the scope of the invention as defined in the appended claims. In relation to the claims, it is intended that when words such as “a,” “an,” “at least one,” or “at least one portion” are used to preface a feature there is no intention to limit the claim to only one such feature unless specifically stated to the contrary in the claim. When the language “at least a portion” and/or “a portion” is used the item can include a portion and/or the entire item unless specifically stated to the contrary.