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CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority of U.S. provisional patent application Ser. No. 62/360,562 filed Jul. 11, 2016, which is incorporated by reference into this application in its entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    The present disclosure is related to the field of quick actuating closures for providing rapid access to, and sealing the end of, a pressure vessel or pipeline, in particular, to clamp-style closures with an improved means of safeguarding against unintentional operation and providing an element of redundancy in retaining the holding elements. 
       BACKGROUND 
       [0003]    There have been many variations in the design of quick actuating closures over the last many decades. Most provide a means for rapid access to a pressure vessel or pipeline as compared to bolted flange connections. They employ various means to seal and support the end load created by internal and external pressures including screw threads whereby external threads on a hub interconnect with the internal threads of the door, conical bands whereby a split or segmented band is actuated into an annular groove between the hub and door, bayonet connections whereby interlocking segments of the hub are engaged with mating segments of the door by partial rotation and clamps whereby a split clamp ring is engaged on raised collar on the hub and door and are held together by toggles, bolts or other mechanisms. 
         [0004]    It is, therefore, desirable to provide a quick clamping mechanism that overcomes the shortcomings of the prior art. 
       SUMMARY 
       [0005]    The present disclosure deals with the clamp ring style of closure. In some embodiments, an annular hub can be attached to the mating pressure vessel or pipeline, and can function as an access port to the interior of the pressure chamber. A door can be sized to match the mating dimensions of the hub and provides a means to close access to the pressure vessel or pipeline. In some embodiments, both the hub and door can have a raised annular collar located at each end of their respective contacting surfaces. A hinge arrangement can be attached to both the hub and door to allow for pivoting the contact surfaces of the door to align with the contact surfaces of the stationary hub. After the surfaces are drawn together in opposition, two halves of a split annular ring can be rotated via hinge arrangement over the hub/door flange, with the ends drawn together with a toggle mechanism. 
         [0006]    Once the toggle mechanism has been fully actuated, circular openings contained within the toggle linkages, and circular openings within the blocks attaching the toggle mechanism to the split annular ring, can align linearly. This linear arrangement can allow the passage of a locking pin of largely round cross section to pass axially through the circular openings, thereby locking the split annular rings and toggle mechanism in the closed position. 
         [0007]    The locking pin described above can contain a circular radial hole offset from one end of the locking pin opposite the portion enclosed by the linearly arranged holes contained within the toggle linkages and blocks. This hole can be aligned perpendicular to the axis of the hub by means of one or more planar surfaces disposed on one or both of the top and the bottom of the locking pin, the one or more planar surfaces orientated parallel to the axis of the hub that pass through a hole contained in a stem housing that is attached radially to the hub. The stem housing can contain a circular hole orientated radially with the hub axis and is concentric to a tapped hole passing completely through the hub wall. A threaded bushing can be installed into the tapped hole and can further contain a centrally located tapped hole to accept a pressure alert stem. 
         [0008]    In some embodiments, the pressure alert stem can be sealed against the threaded bushing by means of an elastomer o-ring. The threaded portion of the pressure alert stem can be interrupted by an axial slot extended the entire length of the thread to a depth below the minor diameter of the thread. This can act as a safety feature in that if the interior portion of the hub is under differential pressure, and if an attempt is made to remove the pressure alert stem from the threaded bushing, the seal created by the o-ring would be compromised and the interior pressure contained within the hub would pass unobstructed through the thread groove, alerting the operator of a differential pressure situation with the closure assembly. 
         [0009]    When fully assembled, the pressure alert stem can pass through the radial circular hole in the locking pin and the threaded bushing installed in the hub wall. In this position, the pressure alert stem can extend fully through the locking pin, preventing the locking pin from translating linearly through the toggle assembly and subsequently locking the toggle and split annular rings in the closed position. As a consequence, in order to operate the toggle mechanism to open the closure door, the pressure alert stem must be removed completely from the closure assembly in order for the locking pin to be translated linearly out of the toggle hole alignment. This embodiment constitutes a safety feature of the closure in that the pressure alert stem must be removed, thus alerting the operator of differential pressure within the closure hub, before the locking pin can be removed to allow the toggle mechanism to function and, thus, opening the closure door. With the locking pin in the extended position, the locking pin can create an interference within the stem housing preventing the pressure alert stem from being installed into the threaded bushing until the locking pin and toggle assembly are fully engaged in the closed position. 
         [0010]    A better understanding of these features can be obtained from the description of the drawings and detailed description of the embodiments that follow. 
         [0011]    Broadly stated, in some embodiments, a closure device can be provided for a pressure vessel or a pipeline, the closure device comprising: a hub comprising a central opening configured to correspond to an opening in the pressure vessel or pipeline; a door configured to contact the hub and close access to the hub central opening; a hinge assembly operatively coupling the door to the hub; a split annular ring assembly operatively coupled attached to the hub and further comprising opposing ring sections configured to move between an open position to a closed position, the opposing ring sections each comprising an inner channel configured to engage corresponding flange elements disposed on both the door and the hub; an actuating mechanism configured to cause the split annular ring assembly to engage the flange elements thereby fastening the door to the hub; a locking pin configured to inhibit movement of the actuating mechanism when the actuating mechanism is in a locked position; and a pressure alert assembly operatively coupled to the hub, the pressure alert assembly configured to inhibit movement of the locking pin when the actuating mechanism is in the locked position. 
         [0012]    Broadly stated, in some embodiments, the closure device can further comprise a seal disposed between the door and hub. 
         [0013]    Broadly stated, in some embodiments, the hub can be configured to be welded or bolted to the pressure vessel or the pipeline. 
         [0014]    Broadly stated, in some embodiments, the hinge assembly can further comprise: upper and lower blocks operatively coupled to the door, further comprising a plain pin and a threaded adjustment pin arrangement configured to manipulate a vertical location of the door in relation to the central opening; upper and lower flange plates operatively coupled to the upper and lower blocks on the door, and further comprising a gusset body disposed between the upper and lower flange plates; a hinge shaft; and a hinge adjustment assembly operatively coupling the upper and lower flange plates to the hinge shaft, the hinge adjustment assembly configured to manipulate a position of the door relative to the hub, wherein the hinge assembly can support the door and allow rotation of the door about the hinge shaft. 
         [0015]    Broadly stated, in some embodiments, the hinge shaft can comprise an axis that ranges from being substantially vertical to substantially horizontal. 
         [0016]    Broadly stated, in some embodiments, the actuating mechanism can further comprise: blocks attached to each of the opposing ring sections, each block comprising a longitudinal through-hole comprising an axis substantially parallel with a plane defined by the split annular ring assembly, wherein the longitudinal through-holes of the blocks substantially align with each other when the opposing ring sections are in the closed position; toggle linkages disposed on anterior and posterior sides of a first of the blocks operatively coupling the first of the blocks to a toggle handle, the toggle handle operatively coupling a second of the blocks to the toggle linkages, the toggle handle configured to move the opposing ring sections between the open and closed positions; and wherein the toggle linkages further comprise second longitudinal through-holes configured to align with the longitudinal through-holes of the blocks when the opposing ring sections are in the closed position. 
         [0017]    Broadly stated, in some embodiments, the locking pin can further comprise: a cylindrical member comprising a diameter substantially corresponding to the longitudinal through-holes of the blocks and the toggle linkages, the cylindrical member comprising a largely circular cross-section further comprising at least one planar surface configured to inhibit rotation of the locking pin when disposed in a supporting housing comprising an opening disposed therethrough having a similar cross-section as the locking pin; a bolt hole disposed through the locking pin, the axis of the bolt hole substantially perpendicular to the axis of the locking pin, the bolt hole disposed at a location offset from a first end of the locking pin; a lip of circular cross section disposed at a second end of the locking pin; and a radial handle extending substantially perpendicular from the locking pin near the first end thereof, the radial handle extending along a plane substantially parallel to the at least one planar surface. 
         [0018]    Broadly stated, in some embodiments, the bolt hole can be configured for allowing a locking bolt to pass therethrough and prevent the locking pin from moving within the supporting housing. 
         [0019]    Broadly stated, in some embodiments, the locking bolt can comprise a pressure alert stem operatively coupled to the hub. 
         [0020]    Broadly stated, in some embodiments, the closure device can further comprise a pressure alert assembly comprising: a stem housing operatively coupled to the hub, the stem housing further enclosing a radial hole disposed through the hub to provide communication with an interior of the pressure vessel or the pipeline; a threaded bushing disposed in the radial hole, the threaded bushing configured to threadably receive an interrupted thread of a pressure alert stem, the threaded bushing further comprising a sealing surface to contact an o-ring seal disposed on the pressure alert stem; and a third longitudinal through-hole disposed through the annular external housing, the third longitudinal through-hole substantially aligned with the longitudinal through-holes of the blocks and with the second longitudinal through-hole when the opposing ring sections are in the closed position. 
         [0021]    Broadly stated, in some embodiments, the closure device can further comprise the locking pin disposed in the longitudinal through-holes when the opposing ring sections are in the closed position, the locking pin further comprising a stem hole disposed through the locking pin, the axis of the stem hole substantially perpendicular to the axis of the locking pin, the stem hole disposed at a location offset from a first end of the locking pin and configured to have the pressure alert stem pass therethrough when the pressure alert stem is threaded into the threaded bushing thereby preventing the locking pin from being removed from the longitudinal through-holes without first removing the pressure alert stem from the threaded bushing. 
         [0022]    Broadly stated, in some embodiments, the interrupted thread can be configured to close off communication to the interior of the pressure vessel or the pipeline when the pressure alert stem is fully threaded and seated in the threaded bushing, and to provide communication to the interior of the pressure vessel or the pipeline when the pressure alert stem is at least partially unthreaded from the threaded bushing. 
         [0023]    Broadly stated, in some embodiments, the pressure alert stem can comprise a tee-shaped handle. 
         [0024]    Broadly stated, in some embodiments, the pressure alert assembly can further comprise a key lock assembly comprising a retractable locking pin configured to engage a circumferential groove disposed around the pressure alert stem. 
         [0025]    Broadly stated, in some embodiments, the hinge assembly can further comprise: upper and lower bearing blocks operatively coupled to the hub; a substantially vertical hinge shaft disposed between and at least partially through each of the upper and lower bearing blocks, the hinge shaft comprising an upper threaded end and a lower threaded end, each of the upper and lower threaded ends comprising upper and lower threaded fasteners, respectively, the threaded fasteners configured to retain the hinge shaft to the upper and lower bearing blocks; a hinge arm comprising a first end operatively coupled to the door, and a second end rotatably disposed about the hinge shaft; one or more stop collars disposed on the hinge shaft, the one or more stop collars configured to lock the second end of the hinge arm in a fixed position on the hinge shaft; and a hinge adjustment assembly configured to manipulate a vertical position of the door relative to the hub, wherein the hinge adjustment assembly can support the door, and wherein the hinge adjustment assembly further comprises the upper and lower threaded fasteners, wherein rotating the upper threaded fastener adjusts the vertical position of the door relative to the upper and lower bearing blocks, and wherein rotating the lower threaded fasteners locks or unlocks the vertical position of the door relative to the upper and lower bearing blocks. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0026]      FIG. 1 a    is a front elevation view depicting one embodiment of a closure assembly in its locked and closed position. 
           [0027]      FIG. 1 b    is a front elevation view depicting a second embodiment of a closure assembly in its locked and closed position. 
           [0028]      FIG. 2 a    is a side elevation cross-section view depicting the closure assembly of  FIG. 1 a    along section lines  1 - 1 . 
           [0029]      FIG. 2 b    is a side elevation cross-section view depicting the closure assembly of  FIG. 1 b    along section lines  1 - 1 . 
           [0030]      FIG. 3 a    is a front perspective view depicting the closure assembly of  FIG. 1 a    in a locked and closed position. 
           [0031]      FIG. 3 b    is a front perspective view depicting the closure assembly of  FIG. 1 b    in a locked and closed position. 
           [0032]      FIG. 4 a    is a front perspective view depicting the closure assembly of  FIG. 1 a    in an unlocked and open position. 
           [0033]      FIG. 4 b    is a front perspective view depicting the closure assembly of  FIG. 1 b    in an unlocked and open position. 
           [0034]      FIG. 5 a    is a top plan view depicting the closure assembly of  FIG. 1 a    in its locked and closed position. 
           [0035]      FIG. 5 b    is a top plan view depicting the closure assembly of  FIG. 1 b    in its locked and closed position. 
           [0036]      FIG. 6 a    is a top plan view depicting the closure assembly of  FIG. 1 a    in an unlocked and open position. 
           [0037]      FIG. 6 b    is a top plan view depicting the closure assembly of  FIG. 1 b    in an unlocked and open position. 
           [0038]      FIG. 7 a    is a side elevation cross-section view depicting a hinge of the closure assembly of  FIG. 1 a    along section lines  2 - 2 . 
           [0039]      FIG. 7 b    is a side elevation cross-section view depicting a hinge of the closure assembly of  FIG. 1 b    along section lines  2 - 2 . 
           [0040]      FIG. 8 a    is a top plan cross-section view depicting the hinge of  FIG. 7 a    along section lines  5 - 5 . 
           [0041]      FIG. 8 b    is a top plan cross-section view depicting the hinge of  FIG. 7 b    along section lines  5 - 5 . 
           [0042]      FIG. 9 a    is a close-up perspective view depicting the toggle mechanism/locking pin arrangement of the closure assembly of  FIG. 1 a    in a closed and locked position, as viewed from the anterior end. 
           [0043]      FIG. 9 b    is a close-up perspective view depicting the toggle mechanism/locking pin arrangement of the closure assembly of  FIG. 1 b    in a closed and locked position, as viewed from the anterior end. 
           [0044]      FIG. 10 a    is a close-up perspective view depicting the toggle mechanism/locking pin arrangement of the closure assembly of  FIG. 1 a    in an open and unlocked position, as viewed from the anterior end. 
           [0045]      FIG. 10 b    is a close-up perspective view depicting the toggle mechanism/locking pin arrangement of the closure assembly of  FIG. 1 b    in an open and unlocked position, as viewed from the anterior end. 
           [0046]      FIG. 11 a    is a close-up perspective view depicting the toggle mechanism/locking pin arrangement of the closure assembly of  FIG. 1 a    in a closed and locked position, as viewed from the posterior end. 
           [0047]      FIG. 11 b    is a close-up perspective view depicting the toggle mechanism/locking pin arrangement of the closure assembly of  FIG. 1 b    in a closed and locked position, as viewed from the posterior end. 
           [0048]      FIG. 12 a    is a close-up perspective view depicting the toggle mechanism/locking pin arrangement of the closure assembly of  FIG. 1 a    in an open and unlocked position, as viewed from the posterior end. 
           [0049]      FIG. 12 b    is a close-up perspective view depicting the toggle mechanism/locking pin arrangement of the closure assembly of  FIG. 1 b    in an open and unlocked position, as viewed from the posterior end. 
           [0050]      FIG. 13 a    is a close-up side elevation cross-section view of the closure assembly of  FIG. 5 a    along section lines  3 - 3 . 
           [0051]      FIG. 13 b    is a close-up side elevation cross-section view of the closure assembly of  FIG. 5 b    along section lines  3 - 3 . 
           [0052]      FIG. 14 a    is a close-up side elevation cross-section view of the closure assembly of  FIG. 6 a    along section lines  4 - 4 . 
           [0053]      FIG. 14 b    is a close-up side elevation cross-section view of the closure assembly of  FIG. 6 b    along section lines  4 - 4 . 
           [0054]      FIG. 15 a    is a perspective view depicting a pressure alert stem for use with the closure assembly of  FIG. 1   a.    
           [0055]      FIG. 15 b    is a perspective view depicting a pressure alert stem for use with the closure assembly of  FIG. 1   b.    
           [0056]      FIG. 16 a    is a perspective view depicting a locking pin for use with the closure assembly of  FIG. 1   a.    
           [0057]      FIG. 16 b    is a perspective view depicting a locking pin for use with the closure assembly of  FIG. 1   b.    
           [0058]      FIG. 17  is a close-up cross-section view depicting the closure assembly of  FIG. 2   b.    
           [0059]      FIG. 18  is a partial cutaway, front perspective view depicting the closure assembly of  FIG. 14 b    with the pressure alert stem prior to being inserted therein. 
           [0060]      FIG. 19  is partial cutaway, front perspective view depicting the closure assembly of  FIG. 18  with the pressure alert stem inserted and locked thereto. 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0061]    In this description, references to “one embodiment”, “an embodiment”, or “embodiments” mean that the feature or features being referred to are included in at least one embodiment of the technology. Separate references to “one embodiment”, “an embodiment”, or “embodiments” in this description do not necessarily refer to the same embodiment and are also not mutually exclusive unless so stated and/or except as will be readily apparent to those skilled in the art from the description. For example, a feature, structure, act, etc. described in one embodiment may also be included in other embodiments, but is not necessarily included. Thus, the present technology can include a variety of combinations and/or integrations of the embodiments described herein. 
         [0062]    Illustrated in this specification are two embodiments of closure assembly  10 . A first embodiment is illustrated in the figures labeled with an “a” suffix, that is:  1   a,    2   a,  etc. A second embodiment is illustrated in the figures with a “b” suffix, that is:  1   b,    2   b,  etc. Reference characters for elements or features specific to the first embodiment are appended with the “a” suffix, whereas reference characters for elements or features specific to the second embodiment are appended with the “b” suffix. Reference characters for elements or features that are common to the first and second embodiments have no “a” or “b” suffix. 
         [0063]    Referring to  FIGS. 1 a    and  2   a,  a first embodiment of a clamp style closure device for a pressure vessel or pipeline is shown. In some embodiments, closure assembly  10   a  can comprise hub  11   a,  which can be adapted to be attached to pressure vessel opening (not shown) or end of pipe (not shown) by welding with use of an appropriately sized bevel  13  located on the posterior portion of hub  11   a  matching that of the pressure vessel opening or pipe end. On the anterior end of hub  11   a,  male flange  14  can be provided extending outwardly from the body and circumferentially around the hub edge. Hub  11   a  can comprise circular bore  12 , which can define the central axis of the closure assembly. 
         [0064]    In some embodiments, door  21   a  can be pivotally attached to hub  11   a  via hinge mechanism  31   a  for opening and closing closure assembly  10   a.  In some embodiments, door  21   a  can be circular in configuration with male flange  22  that is matched dimensionally with male flange  14  of hub  11   a.  Anterior end  23  and posterior end  24  of door  21   a  can be planar and parallel. Door  21   a  can comprise groove  127   a  offset from posterior end  24  of door  21   a  in a gland-type configuration that can accept elastomer seal  25  in the form of an o-ring or other configuration that can create a pressure tight seal between hub  11   a  and door  21   a.  In some embodiments, the axis of sealing surface  27  of hub  11   a  can be concentric with that of hub  11   a,  and can be inclined between zero degrees (parallel to hub bore  12 ) and fifteen degrees to better accept the seal contained within door  21   a.    
         [0065]    Referring to  FIGS. 1 b    and  2   b,  a second embodiment of a clamp style closure device for a pressure vessel or pipeline is shown. In some embodiments, closure assembly  10   b  can comprise hub  11   b,  which can be adapted to be attached to pressure vessel opening (not shown) or end of pipe (not shown) by welding with use of an appropriately sized bevel  13  located on the posterior portion of hub  11   b  matching that of the pressure vessel opening or pipe end. On the anterior end of hub  11   b,  male flange  14  can be provided extending outwardly from the body and circumferentially around the hub edge. Hub  11   b  can comprise circular bore  12 , which can define the central axis of the closure assembly. 
         [0066]    In some embodiments, door  21   b  can be pivotally attached to hub  11   b  via hinge mechanism  31   b  for opening and closing closure assembly  10   b.  In some embodiments, door  21   b  can be circular in configuration with male flange  22  that is matched dimensionally with male flange  14  of hub  11   b.  Anterior end  23  and posterior end  24  of door  21   b  can be planar and parallel. Door  21   b  can comprise groove  127   b  offset from posterior end  24  of door  21   b  in a face-type configuration that can accept elastomer seal  25  in the form of an o-ring or other configuration that can create a pressure tight seal between hub  11   b  and door  21   b.  In some embodiments, the plane of sealing surface  28  of hub  11   b  can be substantially perpendicular to the axis of hub bore  12 , and can be further inclined between zero degrees and fifteen degrees (relative to the normal of the axis of hub bore  12 ) to better accept the seal contained within door  21   b.    
         [0067]      FIGS. 1 a  to 6 a    illustrate two halves of split annular ring  41  and  42 , for use with closure assembly  10   a,  that can be split equally with a vertical plane passing through the axis of hub  11   a.  Pivot blocks  43   a  and  44   a  can be attached to the bottom portion of split annular ring  41  and  42 , which can contain through holes  49  and  50 , respectively. In some embodiments, hub pivot block  46   a  can be attached to the bottom of the outer surface of hub  11   a  with circular hole  51  parallel to the axis of hub  11   a.  In some embodiments, the alignment of holes  49 ,  50  and  51  can be such that pivot pin  150  can pass axially through all holes and allow the two halves of split annular ring  41  and  42  to rotate about the axis of pivot pin  150 . Pivot pin  150  can comprise external threads for installation of jam nuts  48  to secure the split annular ring assembly in place. In some embodiments, spacer cylinder  47   a  can be installed between pivot block  44   a  and hub pivot block  46   a  to maintain alignment of split annular ring  41  and  42 , mating hub flange  14  and door flange  22 . 
         [0068]    To maintain planar movement of split annular ring  41  and  42  about hub contact face  28 , guide bar  240  can attach to the outer periphery of hub  11   a  and can be captured within a slot created by the attachment of guide bar  241  and the posterior face of split annular ring  41  and  42 . As split annular ring  41  and  42  advances to the open position, surfaces  242  and  243 , as shown in  FIGS. 11   a,  can come into contact and limit the movement of split annular ring  41  and  42  about pivot pin  150 . In some embodiments, one set of guide bars  240 ,  241  can be mirrored about hub  11   a  vertical plane for each split annular ring  41  and  42 . 
         [0069]      FIGS. 1 b  to 6 b    illustrate two halves of split annular ring  41  and  42 , for use with closure assembly  10   b,  that can be split equally with a vertical plane passing through the axis of hub  11   b.  Pivot blocks  43   b  and  44   b  can be attached to the bottom portion of split annular ring  41  and  42 , which can contain through holes  49   b  and  50   b,  respectively. In some embodiments, hub pivot block  46   b  can be attached to the bottom of the outer surface of hub  11   b  with circular hole  51  parallel to the axis of hub  11   b.  In some embodiments, the alignment of holes  49   b,    50   b  and  51  can be such that pivot pin  150  can pass axially through all holes and allow the two halves of split annular ring  41  and  42  to rotate about the axis of pivot pin  150 . Pivot pin  150  can comprise external threads for installation of jam nuts  48  to secure the split annular ring assembly in place. In some embodiments, spacer washer  47   b  can be installed between pivot block  44   b  and pivot pin  150  to maintain alignment of split annular ring  41  and  42 , mating hub flange  14  and door flange  22 . 
         [0070]    To maintain planar movement of split annular ring  41  and  42  about hub contact face  28 , guide bar  240  can attach to the outer periphery of hub  11   b  and can be captured within a slot created by the attachment of guide bar  241  and the posterior face of split annular ring  41  and  42 . As split annular ring  41  and  42  advances to the open position, surfaces  242  and  243 , as shown in  FIG. 11   b,  can come into contact and limit the movement of split annular ring  41  and  42  about pivot pin  150 . In some embodiments, one set of guide bars  240 ,  241  can be mirrored about hub  11   b  vertical plane for each split annular ring  41  and  42 . 
         [0071]    Referring to  FIGS. 3   a,    3   b,    4   a  and  4   b,  in some embodiments, split annular ring  41  and  42  can act as a means for drawing hub male flange  14  and door male flange  22  together to facilitate contact between hub contact face  28  and door contact face  29  when rotated into the closed position about pivot pin  150 . Split annular ring  41  and  42  can comprise inner channel  143  concentric to hub bore  12  that is wide enough to accept both the axial width of hub male flange  14  and door male flange  22 . In some embodiments, the sides of inner channel  143 , and the corresponding contact sides of hub male flange  14  and door male flange  22  can be parallel. The included contact angle between opposing sides of inner channel  143  can vary from zero degrees to  10  degrees. In some embodiments, split annular ring  41  and  42  can comprise clearance arcs  51  and  52 , which can further comprise of circular sectors of a diameter exceeding the outer diameter of door male flange  22  as they are projected on split annular ring  41  and  42  in the open position. In some embodiments, arcs  51  and  52  can extend through the anterior outer surface of split annular ring  41  and  42  up to inner channel  143 , which can contact male flange  22 . 
         [0072]    Referring to  FIGS. 1   a,    7   a  and  8   a,  in some embodiments of closure assembly  10   a,  hinge assembly  31   a  can be provided as a means to support the weight of door  21   a  during opening and closing operations and, additionally, to allow door  21   a  to be pivoted about the vertical axis of hinge shaft  134   a  to facilitate access to hub bore  12  by employing use of door handle  120   a.  Hinge assembly  31   a  can comprise upper and lower bearing blocks  33   a  and  34   a,  respectively, that can be affixed to the exterior of mounting plates  35  and  36 , respectively. In some embodiments, mounting plates  35  and  36  can be affixed by cross member  37  to maintain parallelism between mounting plates  35  and  36 . Mounting plates  35  and  36  can comprise two opposing and axial holes that can accept adjustment pin  38  into upper mounting plate  35 , and adjustment bolt  39  into lower mounting plate  36 . In some embodiments, adjustment pin  38  and adjustment bolt  39  can be installed into holes of adjustment blocks  131  and  130 , respectively. Door  21   a  positioning within the vertical plane can be achieved by raising or lowering adjustment bolt  39  by rotating jam nuts  132  and  133 . 
         [0073]    With reference to  FIGS. 7 a    and  8   a,  upper and lower bearing blocks  33   a  and  34   a  (lower bearing block  34   a  not shown), can be attached to mounting plates  35  and  36 , respectively (mounting plate  36  not shown), and can pivot about the axis of hinge shaft  134   a.  Hinge shaft  134   a  can be supported by means of circular upper bearing  135  disposed in upper bearing block  33   a,  and lower bearing  136  disposed in lower bearing block  34   a  (not shown). In some embodiments, the bearings can comprise plain bearings or mechanical bearings, such as roller bearings, ball bearings or tapered bearings. The bearings can be supported axially within the circular center cavity of bearing carrier  149   a.  The outside of bearing carrier  149   a  can comprise of oppositely arranged planar edges  137   a,    138   a,    139   a  and  140   a.  In some embodiments, upper and lower bearing blocks  33   a  and  34   a  can comprise oppositely arranged screws  141 ,  142 ,  143  and  144  located with threaded holes arranged radially with hinge shaft  134   a  axis that can contact edges  137   a,    138   a,    139   a  and  140   a.  By loosening and alternately tightening opposing screws  141 ,  142 ,  143  and  144 , axis hinge shaft  134   a  and, by extension, door contact face  29 , can be tilted in minute increments to achieve parallelism between hub contact face  28  and door contact face  29 , and concentricity between the circular outer edges of hub male flange  14  and door male flange  22 . In some embodiments, circular dished cap  145   a  can be installed over upper and lower bearing blocks  33   a  and  34   a  and be retained by a plurality of screws  146 . In some embodiments, hinge shaft  134   a  can be retained within hinge  147   a.  Hinge  147   a  can be attached to hinge block  148 , which can also be attached to the outer periphery of hub  11 , parallel to the horizontal plane cutting the axis of hub  11   a.    
         [0074]    Referring to  FIGS. 1   b,    7   b  and  8   b,  in some embodiments of closure assembly  10   b,  hinge assembly  31   b  can be provided as a means to support the weight of door  21   b  during opening and closing operations and, additionally, to allow door  21   b  to be pivoted about the vertical axis of hinge shaft  134   b  to facilitate access to hub bore  12  by employing use of door handle  120   b.  Hinge assembly  31   b  can comprise upper and lower bearing blocks  33   b  and  34   b,  respectively, operatively coupled to  11   b  and can either be coupled to hub  11   b  with fasteners, or integral to the structure of hub  11   b.  In some embodiments, door  21   b  can comprise hinge arm  236  to operatively coupled door  21   b  to hinge shaft  134   b.  In some embodiments, hinge arm  236  can comprise hinge bearings  39   b  to provide smooth rotational movement about hinge shaft  134   b.  Hinge arm  236  can further comprise thrust washers  38   b  disposed on an outer surface of bearings  39   b,  and held in place by stop collars  37   b.  Each end of hinge shaft  134   b  can be threaded, and have nut  135   b  threaded thereupon. Coarse adjustment of door  21   b  positioning within the vertical plane can be achieved by loosening stop collars  37   b  and moving door  21   b  to an approximate desired vertical position and then tightening stop collars  37   b  into position, with fine adjustment for raising or lowering door  21   b  by adjusting nuts  135   b  on both ends of hinge shaft  134   b.    
         [0075]    With reference to  FIGS. 7 b    and  8   b,  upper and lower bearing blocks  33   b  and  34   b  (lower bearing block  34   b  not shown) can be operatively coupled to hub  11   b,  as described above. Hinge shaft  134   b  can be disposed inside adjustment collar  149   b.  The outside of collar  149   b  can comprise of oppositely arranged planar edges  137   b,    138   b,    139   b  and  140   b.  In some embodiments, upper and lower bearing blocks  33   b  and  34   b  can comprise oppositely arranged screws  141 ,  142 ,  143  and  144  located with threaded holes arranged radially with hinge shaft  134   b  axis that can contact edges  137   b,    138   b,    139   b  and  140   b.  By loosening and alternately tightening opposing screws  141 ,  142 ,  143  and  144 , axis hinge shaft  134   b  and, by extension, door contact face  29 , can be tilted in minute increments to achieve parallelism between hub contact face  28  and door contact face  29 , and concentricity between the circular outer edges of hub male flange  14  and door male flange  22 . In some embodiments, circular dished cap  145   b  can be installed over upper and lower bearing blocks  33   b  and  34   b  and be retained by a plurality of screws. 
         [0076]      FIGS. 9   a,    10   a,    11   a  and  12   a  illustrate, in some embodiments for use with closure assembly  10   a,  an over-center toggle mechanism attached to the top of split annular ring  41  and  42 , which can function to move split annular ring  41  and  42  into its locked position, and to expand split annular ring  41  and  42  into the unlocked position through rotation about pivot pin  150 . Toggle block  61  can be mounted radially on one half of split annular ring  41  on the end opposite pivot block  43   a,  as shown in  FIG. 1  a. Likewise, toggle block  62  can be mounted radially on one half of the annular ring  42  on the end opposite pivot block  44   a.  In some embodiments, toggle block  61  can comprise two tines  63  that can accept the body of toggle block  62  during the locking operation, as shown in  FIG. 9   a.  Toggle blocks  61 ,  62  can further comprise through-hole  164  that can align axially when split annular ring  41  and  42  are in the closed and locked position, and parallel with the axis of hub  11   a.  In some embodiments, toggle handle  66   a  can comprise tines  160  that can straddle toggle block  62 . Toggle linkages  64   a,    65   a  can be installed on either side of toggle blocks  61 ,  62 . In some embodiments, toggle pin  67  can be inserted through holes provided by toggle linkage  64   a,    65   a  and toggle block  61 . Toggle pin  68  can be inserted through holes provided by toggle linkage  64   a,    65   a  and toggle handle  66   a.  Toggle pin  69  can be inserted through holes provided by toggle block  62  and toggle handle  66   a.  During the action of pivoting toggle handle  66   a  about the axis of toggle pin  69 , toggle linkages  64   a,    65   a  can, subsequently, pivot about toggle pins  67 ,  68  forcing the split annular ring  41  and  42  to pivot about pivot pin  150 . Toggle linkages  64   a,    65   a  can comprise through-hole  161  that can align axially with hole  164  on toggle blocks  61 ,  62  when split annular ring  41  and  42  are in the closed and locked position and is parallel with the axis of hub  11   a.    
         [0077]      FIGS. 9   b,    10   b,    11   b  and  12   b  illustrate, in some embodiments for use with closure assembly  10   b,  an over-center toggle mechanism attached to the top of split annular ring  41  and  42 , which can function to move split annular ring  41  and  42  into its locked position, and to expand split annular ring  41  and  42  into the unlocked position through rotation about pivot pin  150 . Toggle block  61  can be mounted radially on one half of split annular ring  41  on the end opposite pivot block  43   b,  as shown in  FIG. 1   b.  Likewise, toggle block  62  can be mounted radially on one half of the annular ring  42  on the end opposite pivot block  44   b.  In some embodiments, toggle block  61  can comprise two tines  63  that can accept the body of toggle block  62  during the locking operation, as shown in  FIG. 9   b.  Toggle blocks  61 ,  62  can further comprise through-hole  164  that can align axially when split annular ring  41  and  42  are in the closed and locked position, and parallel with the axis of hub  11   b.  In some embodiments, toggle handle  66   b  can comprise tines  160  that can straddle toggle block  62 . Toggle linkages  64   b,    65   b  can be installed on either side of toggle blocks  61 ,  62 . In some embodiments, toggle pin  67  can be inserted through holes provided by toggle linkage  64   b,    65   b  and toggle block  61 . Toggle pin  68  can be inserted through holes provided by toggle linkage  64   b,    65   b  and toggle handle  66   b.  Toggle pin  69  can be inserted through holes provided by toggle block  62  and toggle handle  66   b.  During the action of pivoting toggle handle  66   b  about the axis of toggle pin  69 , toggle linkages  64   b,    65   b  can, subsequently, pivot about toggle pins  67 ,  68  forcing the split annular ring  41  and  42  to pivot about pivot pin  150 . Toggle linkages  64   b,    65   b  can comprise through-hole  161  that can align axially with hole  164  on toggle blocks  61 ,  62  when split annular ring  41  and  42  are in the closed and locked position and is parallel with the axis of hub  11   b.    
         [0078]    Referring to  FIG. 15   a,  in some embodiments, closure assembly  10   a  can comprise pressure alert stem  70   a,  further comprising of hexagonal body  71   a  sized to accept industry standard imperial wrench sizes, cylindrical extension  72   a  and threaded body  73   a  on the end opposite hexagonal body  71   a.  In some embodiments, threaded body  73   a  can comprise longitudinal groove  74  parallel with pressure alert stem  70   a  axis. Longitudinal groove  74  can extend from threaded body end  75   a  to o-ring seal groove  77   a  at a depth equal to or greater than the root diameter of the thread. An appropriately sized o-ring  76  can be passed over threaded body  73   a  and installed into o-ring groove  77   a  adjacent end surface  78   a.    
         [0079]    Referring to  FIG. 15   b,  in some embodiments, closure assembly  10   b  can comprise pressure alert stem  70   b,  further comprising of tee-shaped head  71   b  configured to turned by hand wherein pressure alert stem  70   b  can be tightened hand-tight and not over-torqued with a wrench. Pressure alert stem  70   b  can further comprise cylindrical extension  72   b  and threaded body  73   b  on the end opposite tee-shaped head  71   b.  Cylindrical extension  72   b  can further comprise circumferential groove  79  disposed therearound. In some embodiments, threaded body  73   b  can comprise longitudinal groove  74  parallel with pressure alert stem  70   b  axis. Longitudinal groove  74  can extend from threaded body end  75   b  to o-ring seal groove  77   b  at a depth equal to or greater than the root diameter of the thread. An appropriately sized o-ring  76  can be passed over threaded body  73   b  and installed into o-ring groove  77   b  adjacent end surface  78   b.    
         [0080]    Referring to  FIG. 16   a,  closure assembly  10   a  can comprise locking pin  80   a,  further comprising of a cylindrical body provided with two planar and parallel surfaces  81   a,    82   a  extending the length of locking pin  80   a  up to stop lip  84 . Pin end  86  can remain circular. In some embodiments, through hole  83   a  can be disposed through locking pin  80   a  near end  87   a,  and can be sized to accept the passage of pressure alert stem  70   a.  Locking pin handle  85   a  can be attached to the cylindrical sidewall surface of locking pin  80   a  and disposed near through hole  83   a,  wherein locking pin handle  85   a  can extend away from locking pin  80   a  in a plane substantially parallel to surfaces  81   a,    82   a.    
         [0081]    Referring to  FIG. 16   b,  closure assembly  10   b  can comprise locking pin  80   b,  further comprising of a cylindrical body provided with a planar surface  81   b  extending the length of locking pin  80   b  up to stop lip  84 . Pin end  86  can remain circular. In some embodiments, through hole  83   b  can be disposed through cylindrical portion  300  of locking pin  80   b,  and can be sized to accept the passage of pressure alert stem  70   b.  Locking pin handle  85   b  can be attached to cylindrical portion  300  and disposed near through hole  83   b,  wherein locking pin handle  85   b  can extend away from locking pin  80   b  in a plane substantially parallel to surface  81   b.    
         [0082]    Referring to  FIGS. 13 a    and  14   a,  in some embodiments, radial hole  90   a  can be provided in hub  11   a  having straight or taper thread  91   a  located towards outer surface  92   a  of hub  11   a.  Threaded bushing  94   a,  comprising an external straight or tapered thread matching straight or tapered thread  91   a,  and straight internal thread  95   a  matching the size of threaded body  73   a  of pressure alert stem  70   a,  can be installed into radial hole  90   a.  Stem housing  96   a  can be attached radially to outer surface  92   a  of hub  11   a  with longitudinal hole  97   a  concentric to radial hole  90   a.  In some embodiments, stem housing  96   a  can comprise radial hole  98   a  relative to longitudinal hole  97   a  that can further comprise a profile identical to end profile  87   a  of lock pin  80   a,  and can be parallel to the axis of hub  11   a.  In some embodiments, slot  99   a  (as shown in  FIGS. 11 a  and 12 a   ) can be perpendicular to radial hole  98   a  and longitudinal hole  97   a,  and can further extend into longitudinal hole  97   a  and be sized to accept locking pin handle  85   a.    
         [0083]    Referring to  FIGS. 13 a    and  14   a,  the safety features and characteristics of closure assembly  10   a  are shown. With toggle mechanism  60   a,  split annular ring  41  and  42  and door  21   a  in the closed position, toggle linkage holes  160  and  161 , toggle block holes  164  and  165 , and stem housing radial hole  98   a  can align along a common axis and, thus, allow locking pin  80   a  to be installed until locking pin handle  85   a  contacts the end of slot  99   a  (as shown in  FIGS. 11 a  and 12 a   ) of pressure alert stem housing  96   a,  thus inhibiting the movement and function of toggle mechanism  60   a  and split annular ring  41  and  42 . Pressure alert stem  70   a  can be inserted through longitudinal hole  97   a,  through locking pin hole  83   a,  up to threaded bushing  94   a.  Pressure alert stem  70   a  can then be threaded into threaded bushing  94   a  until stem end surface  78   a  contacts threaded bushing  94   a  and pressure alert stem o-ring  76  is confined within threaded bushing  94   a  effecting a seal. 
         [0084]    Referring to  FIGS. 13 b    and  14   b,  in some embodiments, radial hole  90   b  can be provided in hub  11   b  having straight or taper thread  91   b  located towards outer surface  92   b  of hub  11   b.  Threaded bushing  94   b,  comprising an external straight or tapered thread matching straight or tapered thread  91   b,  and straight internal thread  95   b  matching the size of threaded body  73   b  of pressure alert stem  70   b,  can be installed into radial hole  90   b.  Stem housing  96   b  can be attached radially to outer surface  92   b  of hub  11   b  with longitudinal hole  97   b  concentric to radial hole  90   b.  In some embodiments, stem housing  96   b  can comprise radial hole  98   b  relative to longitudinal hole  97   b  that can further comprise a profile identical to end profile  87   b  of lock pin  80   b,  and can be parallel to the axis of hub  11   b.  In some embodiments, slot  99   b  (as shown in  FIGS. 11 b  and 12 b   ) can be perpendicular to radial hole  98   b  and longitudinal hole  97   b,  and can further extend into longitudinal hole  97   b  and be sized to accept locking pin handle  85   b.    
         [0085]    Referring to  FIGS. 13 b    and  14   b,  the safety features and characteristics of closure assembly  10   b  are shown. With toggle mechanism  60   b,  split annular ring  41  and  42  and door  21   b  in the closed position, toggle linkage holes  160  and  161 , toggle block holes  164  and  165 , and stem housing radial hole  98   b  can align along a common axis and, thus, allow locking pin  80   b  to be installed until locking pin handle  85   b  contacts the end of slot  99   b  (as shown in  FIGS. 11 b  and 12 b   ) of pressure alert stem housing  96   b,  thus inhibiting the movement and function of toggle mechanism  60   b  and split annular ring  41  and  42 . Pressure alert stem  70   b  can be inserted through longitudinal hole  97   b,  through locking pin hole  83   b,  up to threaded bushing  94   b.  Pressure alert stem  70   b  can then be threaded into threaded bushing  94   b  until stem end surface  78   b  contacts threaded bushing  94   b  and pressure alert stem o-ring  76  is confined within threaded bushing  94   b  effecting a seal. 
         [0086]    Referring to  FIG. 18 , pressure alert stem  70   b  is shown being inserted into longitudinal hole  97   b.  Disposed in recess  194  pressure alert stem housing  96   b  can be lock mechanism  191 . As shown in  FIG. 18 , when key  192  is turned to the “unlock” position as shown, locking pin  193  retracts into lock mechanism  191 , as shown. Referring to  FIG. 19 , pressure alert stem  70   b  is shown fully inserted in longitudinal hole  97   b,  wherein key  192  can be turned to the “lock” position (as shown) thereby causing locking pin  193  to extend from lock mechanism  191  into groove  79  of pressure alert stem  70   b  thereby preventing pressure alert stem  70   b  from being removed from longitudinal hole  97   b  thus locking closure assembly  10   b.    
         [0087]    In some embodiments, closure assembly  10   b  can comprise an alternate sealing configuration, as shown in  FIG. 17 . In some embodiments, hub  11   b  can comprise concentric recess  129  disposed therearound about hub bore  12 , wherein recess  129  is configured to receive concentric protrusion  128  disposed adjacent groove  127   b  disposed on door  21   b.  Protrusion  128  and recess  129  can comprise complimentary profiles wherein protrusion  128  is disposed in recess  129  when door  21   b  is closed and joined together with hub  11   b  by split annular rings  41  and  42 , and wherein protrusion edge  170  overlaps with ledge  171  of recess  129 . As gas or fluid pressures increase within hub bore  12  within closure assembly  10   b,  the pressure can urge door  21   b  away from hub  11   b.  As this occurs, protrusion  128  can partially retract from recess  129  but still maintain retention of o-ring seal  25  within groove  127   b.  Without this configuration of protrusion  128  and recess  129 , excessive pressure within closure assembly  10   b  could otherwise cause o-ring seal  25  to expand outward from groove  127   b  into the interstitial gap between door  21   b  and hub  11   b,  thus resulting in a breach in the seal therebetween. 
         [0088]    With the embodiments in the foregoing fully engaged, closure actuation is prevented until it can be verified no differential pressure exists within hub bore  12 . To accomplish this, pressure alert stem  70   a  or  70   b  can be rotated counter clockwise until o-ring seal  76  backs out of threaded bushing  94   a  or  94   b.  If differential pressure exists within hub bore  12 , the media (liquid and/or gas) present within hub  11   a  or  11   b  would expel through longitudinal groove  74 , alerting the operator of a differential pressure condition within hub  11   a  or  11   b.  With o-ring seal  76  broken and media venting, threaded body  73   a  or  73   b  would still be sufficiently engaged to prevent pressure alert stem  70   a  or  70   b  from being expelled out of longitudinal hole  97   a  or  97   b,  thus preventing harm to the operator. When alerted to a differential pressure situation within hub  11   a  or  11   b,  the operator can then rotate pressure alert stem  70   a  or  70   b  clockwise to re-seal o-ring  76  within threaded bushing  94   a  or  94   b  and follow procedures to reduce the differential pressure to zero. 
         [0089]    If, during the counter clockwise rotation of pressure alert stem  70   a  or  70   b  and breaking of o-ring seal  76 , that no differential pressure is observed, pressure alert stem  70   a  or  70   b  may be fully extracted from threaded bushing  94   a  or  94   b  as well as from locking pin hole  83   a  or  83   b  and finally out of stem housing  96   a  or  96   b.  Only then can locking pin  80   a  or  80   b  be disengaged by sliding the pin longitudinally through toggle linkage holes  160  and  161 , toggle block holes  164  and  165 , and stem housing radial hole  98   a  or  98   b  until stop lip  84  enters circular recess  190   a  or  190   b  within stem housing  96   a  or  96   b  effecting cessation of locking pin  80   a  or  80   b  movement. Toggle mechanism  60   a  or  60   b  can then be actuated causing split annular ring  41  and  42  to rotate around pivot pin  150  and allow door  21   a  or  21   b  to rotate about hinge shaft  134   a  or  134   b  axis. 
         [0090]    In some embodiments, locking pin  70   a  or  70   b  can provide an additional advantage over the prior art in that it can incorporate an extra layer of redundancy to the holding characteristics of toggle mechanism  60   a  or  60   b.  If, in the event that a failure should occur in one or more features of toggle mechanism  60   a  or  60   b,  locking pin  70   a  or  70   b  would remain engaged within toggle blocks  61  and  62 , thereby reducing the possibility of split annular ring  41  and  42  movement and door  21   a  or  21   b  opening while hub  11   a  or  11   b  contains differential pressure. 
         [0091]    Although a few embodiments have been shown and described, it will be appreciated by those skilled in the art that various changes and modifications can be made to these embodiments without changing or departing from their scope, intent or functionality. The terms and expressions used in the preceding specification have been used herein as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding equivalents of the features shown and described or portions thereof, it being recognized that the invention is defined and limited only by the claims that follow.

Summary:
A closure is provided for a pressure vessel or pipelines that can provide quick and easy access to the interior of a pressure vessel or pipeline, and means for a pressure tight seal between the hub and door. The closure can incorporate means for mechanically fastening the door to the hub using an external split clamp ring actuated by a toggle mechanism. A locking mechanism can be provided to safeguard against unintended closure actuation, and provides a layer of redundancy to the holding characteristics of the toggle mechanism. The locking mechanism can be interlocked to a pressure alert system to ensure any differential pressure condition contained within the closure is detected prior to disengaging the locking mechanism and actuating the toggle mechanism.