Locking band apparatus

Abstract

Locking band apparatus for use on a vessel lid having a frustoconical outer surface, the apparatus comprises a locking band 10 and an actuation mechanism. The actuation mechanism comprises a first act

Description

FIELD OF THE INVENTION The invention relates to a locking band apparatus, and particularly to locking bands for hydrodynamic containment vessels. BACKGROUND OF THE INVENTION In known hydrodynamic containment vessels, a single band multi-segmented locking band is used to trap the vessel lid against the opening of the vessel. A portion of the band is lifted out from this trapped state, then the band is contracted to allow the vessel to open. It has not been appreciated that the tolerances between these parts ought to be minimized so that there is limited motion between the parts in use. This means that in the prior art, the locking band is contracted in an uncontrolled manner, usually by a handle moving along a horseshoe shaped path to bring the ends of the band together. This essentially pulls one end of the band and progressively removes the band from the trapped or locked state. However, hydrodynamic containment vessel lids are usually of a frustoconical shape. This means that this uncontrolled contraction of the locking band also results in a band which has different displacements from the base of the vessel at different locations around the band. This prevents the minimization of tolerances between parts. Hydrodynamic containment vessels are often used for explosive tests, and in these operations, a large amount of force is applied to the lid. If tolerances of the locking parts are not minimized, the applicants have appreciated that there can be damage caused to the lid and locking parts, due to the momentum they receive during tests. There is also significant leakage from the vessel due to vibration at the seal interface, and the higher the tolerance the greater the leakage. SUMMARY OF THE INVENTION According to a first embodiment of the invention, there is provided a locking band apparatus for use on a vessel lid having a frustoconical outer surface, the apparatus comprising: a locking band, and an actuation mechanism comprising: a first actuator configured to apply a force to a first end of the locking band, and a second actuator configured to apply a force to a second end of the locking band, wherein the force applied to the first and second ends causes the locking band to contract from a locked position to an unlocked position wherein the ends of the locking band move from a respective start position to a respective finish position, and wherein the force is applied in a retraction vector extending from the start position of the respective end of the locking band to the end position of the respective end of the locking band. The arrangement of elements provide force to the locking band in an advantageous direction, ensuring that the height of the locking band above the base of the vessel is constant at all times during a contraction process along the frustoconical vessel lid surface. Preferably, the locking band actuation mechanism further comprises a third actuator configured to remove a locking segment from the locking band, wherein when the locking band is in the locked position the band locking segment engages with at least one end of the locking band. It will be appreciated that to reduce the diameter of the locking band, it is necessary to remove a portion, and this portion can be removed in a number of ways. However, by including a mechanism to remove the band locking segment in the locking band actuation mechanism, the ease of use of the whole system is improved. Preferably, the first and second actuators each comprise a carriage connected to the respective first and second ends of the locking band and a first drive mechanism configured to move the carriage. Providing a separate drive mechanism and carriage allows for the carriage to be locked into place using the drive mechanism. This prevents accidental release of the locking band, which could cause damage, and prevent the vessel from being opened. Preferably, the first drive mechanism is oriented to move the carriage in the retraction vector. Moving the carriage in the retraction vector allows for the locking band to be retracted whilst maintaining a constant height above the base of the vessel lid. Preferably, the carriage is connected to the respective end of the locking band by a flexible connector. In a further example the flexible connector is a clevis fastener. To maintain the applied force in the most advantageous direction, it is beneficial to allow the ends of the locking portions to move with respect to the mechanism. Preferably, the first drive mechanism is a lead screw mounted in a carriage guide. A lead screw both allows for a force applied to move the locking band to be multiplied, and also allows for one way operation, where the lead screw can move the carriage, but the carriage cannot turn the lead screw. This means that the energy stored in the locking band when retracted cannot be released accidentally, and the locking band can be held in the retracted state. Preferably, the first and second actuators further comprise an input device configured to transmit external force to the first drive mechanism. In a further example the input device is a manually operated handle. A handle can act as a torque multiplier to allow the carriage to be moved using the range of force which can be applied by a human. Preferably, the input device is a motor. A motor allows for the application of torque to the drive mechanism without human input or allows for human input to be assisted. Preferably, the input device is connected to the first drive mechanism via a flexible shaft. Flexible shafts allow for an input device to be located remotely from the drive mechanism. This is advantageous when the drive mechanism is close to the vessel lid as can be necessary to accommodate other features on the lid, and also where it may be dangerous to be too close to the locking band or the vessel lid. Preferably, the third actuator comprises a clamp configured to removably attach to the band locking segment and a second drive mechanism configured to: retract the band locking segment along the frustoconical outer surface of the vessel lid and then lift the band locking segment clear of the locking band. The clamp of the third actuator is removably attached to the band locking segment so that the entire third actuator can be removed when not in use. The vessel lid can then be used to host other apparatus when the band is locked. Preferably, the second drive mechanism comprises a lead screw configured to engage with a parallel linkage in turn connected to the clamp. A lead screw both allows for a force applied to move the clamp, and thus the band locking segment to be multiplied, and also allows for one way operation, where the lead screw can move the carriage, but the carriage cannot turn the lead screw. This means that the energy stored in the band locking segment when raised up cannot be released accidentally by falling back towards the vessel lid. Preferably, applying a turning force to the lead screw causes the clamp to first retract towards the third actuator and second raise the clamp upwards from the locking band. By using a lead screw to perform two actions, the ease of use by the user is increased, and the process can be automated simply. Preferably, the third actuator further comprises an input device configured to transmit external force to the first drive mechanism. In a further example the input device is a manually operated handle. A handle can act as a torque multiplier to allow the carriage to be moved using the range of force which can be applied by a human. Preferably, the input device is a motor. A motor allows for the application of torque to the drive mechanism without human input or allows for human input to be assisted. Preferably, the input device is connected to the first drive mechanism via a flexible shaft. Flexible shafts allow for an input device to be located remotely from the drive mechanism. This is advantageous when the drive mechanism is close to the vessel lid as can be necessary to accommodate other features on the lid, and also where it may be dangerous to be too close to the locking band or the vessel lid. According to a second embodiment of the present invention, there is provided a hydrodynamic containment vessel closure system, comprising: a vessel lid having a frustoconical outer surface, a locking band arranged to sit on the frustoconical outer surface of the vessel lid, and movable between a locked position and an unlocked position, wherein in the unlocked position the locking band has a smaller diameter than in the locked position, and a locking band actuation mechanism configured to contract the locking band to the unlocked position such that the locking band remains substantially concentric to the vessel lid during contraction from the locked position to the unlocked position. By maintaining concentricity of the locking band as it is contracted, all portions of the locking band remain at the same heigh on the frustoconical section during the contraction. This means that the band can be retracted from a retaining portion which closely matches the height of the band. If the concentricity is not maintained, the band can be become trapped as it rotates relative to the frustoconical plane of the lid. This means that, by maintaining concentricity, tolerances between the vessel lid, the locking band, and the vessel itself can be reduced or eliminated. This allows for a sturdier vessel for hydrodynamic testing of explosives. By essentially maintaining contact between the vessel lid and its retaining mechanism, the locking band, the elements cannot move during a test, and as such have no momentum and no ability to become loose. Preferably, the locking band comprises a pair of substantially semi-circular vessel locking portions each having first and second ends. By providing two vessel locking portions it is possible to more closely control the contraction of the locking band, to further reduce the tolerances between the lid, vessel and locking band. When contracted, the first and second ends of one portion of the locking portions move towards the respective ends of the second, such that in the locked state there is a large gap between the ends, and in the unlocked state the ends are closer together or touching. Preferably, each vessel locking portion comprises a carrier and a plurality of segments carried by the carrier. Preferably, the carrier band is flexible to facilitate contraction of the locking band from the locked position to the unlocked position and vice versa. Preferably, the carrier is elastically deformed by contraction of the locking band from the locked position to the unlocked position and vice versa. Preferably, the elastic deformation of the carrier is increased during contraction of the locking band from the locked position to the unlocked position, and decreased during release of the locking band from the unlocked position to the locked position. A combination of a carrier and segments carried by the carrier provides the strength needed to transfer energy from use of the hydrodynamic containment vessel, whilst also allowing the band to contract when actuated upon. Preferably, the carrier is formed from steel or steel alloys conforming to BE EN 10083-3 1.7225. Preferably, the plurality of segments is formed from steel or steel alloys conforming to BE EN 10083-3 1.7225. Preferably, the locking band comprises a pair of band locking segments movable from a first position to a second position, wherein when the pair of band locking segments are in the first position, they are configured to engage with one end of each vessel locking portion and when the band locking segments are in the second position they are configured not to engage with the respective ends of the vessel locking portion. The band locking segments essentially complete the locking band when in the locked position, by filling the gaps left when the locking portions are expanded to the locked position. Preferably, the locking band segments are formed from steel or steel alloys conforming to BE EN 10083-3 1.7225. Preferably, when the band locking segments are in the first position, between about 5 percent and 15 percent of the perimeter of the locking band is defined by the pair of band locking segments. Preferably, the carrier band is not in contact with the hydrodynamic containment vessel or the vessel lid. The carrier band does not act as a force transferring member from the vessel lid but acts as a means to carry the force transferring segments, and so to prevent damage the carrier band is removed from any application offeree during testing using the hydrodynamic containment vessel. Preferably, when the band moves from the locked position to the unlocked position, the ends of each substantially semi-circular vessel locking portions move from a respective start position to a respective finish position, and wherein the locking band actuation mechanism is configured to apply a force to the ends of the at least one vessel locking portions in a vector extending from a start position of the respective end of the locking band to the end position of the respective end of the locking band. Force is applied to the locking portions to move them from the locked to the unlocked positions. This can be applied at any point on the locking portion and in any direction. For example, it is possible to apply a force to the ends of the locking portions in a vector extending directly from each end, i.e., perpendicular to a tangent of the locking band drawn at the centre point of the band. It is also possible to apply a force perpendicular to the ends of the locking band, i.e., pointing towards the centre of the locking band. All of these arrangements will contract the band, however by applying the force in a direction extending from the start position of the ends to the intended end position the band is contracted in a uniform manner. Preferably, a bottom surface of the locking band is configured to engage the frustoconical surface of the vessel lid. By ensuring communication between the lid and the locking band, the vessel lid will not strike the locking band during use of the vessel. Preferably, a bottom surface of the locking band has a profile complementary to the profile of the frustoconical perimeter of the vessel lid. In a further example the locking band is configured to remain substantially engaged with the frustoconical perimeter of the vessel lid during the retraction process. As it is desirable to maintain a minimum separation between the vessel lid, the locking band, and the vessel itself, or a portion thereof which engages with the locking band, by providing complementary surfaces of the lid and the band, the band can slide across the lid with ease. Preferably, the locking band actuation mechanism comprises a locking segment removal mechanism configured to remove the band locking segment of the locking band. It will be appreciated that to reduce the diameter of the locking band, it is necessary to remove a portion, and this portion can be removed in a number of ways. However, by including a mechanism to remove the band locking segment in the locking band actuation mechanism, the ease of use of the whole system is improved. Preferably, the locking band actuation mechanism is configured to: retract the band locking segments along the frustoconical outer surface of the vessel lid, then lift the band locking segments clear of the vessel locking portions. The movement of the band locking segment is designed to allow a minimum tolerance between the lid, vessel and band, by sliding the segment out from the retaining portion of the vessel. However, this leaves the segment in the path of the locking portions, and so the locking band actuation mechanism is configured to then lift the band locking segment clear of the vessel lid. Preferably, the third actuator comprises a handle configured to retract the locking segment along the frustoconical outer surface of the vessel lid and a lead screw configured to lift the locking segment clear of the locking band, and in a further example applying a turning force to the lead screw causes the clamp to raise upwards from the locking band. By providing a handle and a lead screw to carry out the two actions required to clear the band locking segment from the path of the locking band, the mechanism is simplified, and further allows for more control over the parts of the locking mechanism when removing or inserting the band locking segments. Preferably, the locking band actuation mechanism comprises a locking band retraction mechanism configured to retract the locking band to the unlocked position. The locking band actuation mechanism also contains a means for retracting the locking band into the unlocked position, as it facilitates applying force in the direction in which the band can be pulled to achieve a minimum tolerance between the vessel, lid and band. Preferably, the locking band retraction mechanism is attached to each first and second end of the vessel locking portions by a flexible connector. In a further example the connector is a clevis fastener. To maintain the applied force in the most advantageous direction, it is beneficial to allow the ends of the locking portions to move with respect to the mechanism. Preferably, the clevis fastener is connected to the outermost two locking band segments through a hole in the carrier band. The carrier band is designed to hold the segments of the locking portions in place whereas the segments are designed to receive force during use of the vessel. To ensure the strength of the whole closure system, and how it is actuated, the attachment point of the locking band actuation mechanism is to the segment, not the carrier band. Thus, the segment is pulled directly and cannot become removed from the carrier and left in the locked position. Preferably, each locking band actuation mechanism is removably attached to the lid. The mechanisms can be removed to allow for other fitments to be attached when it is not necessary to actuate the locking mechanism. Preferably, the locking band actuation mechanism comprises a pair of locking band actuation mechanisms located on opposite sides of a diameter of the vessel lid. In an embodiment where there are two locking portions, the locking band actuation mechanisms can be located to operate each end of the two locking portions. Preferably, the plurality of rigid segments is connected to the flexible carrier by bolts. By using a removable attachment, the ability to refurbish and repair sections of the locking band is increased. Preferably, the vessel lid is configured to retain the locking portions when in the unlocked position. The locking portions are held in the locked position by the vessel and the lid, however in the unlocked position the portions are only retained by the attachment to the locking band actuation mechanism. However, the vessel lid is also configured to retain the locking band when it reaches the unlocked position. Preferably, during contraction from the locked position to the unlocked position a plane described by the surface of the locking band remains substantially parallel to a plane described by the base of the frustoconical outer portion of the lid. Preferably, the height any portion of the locking band measured from the base of the vessel lid remains substantially the same as the height of any other portion of the locking band during contraction from the locked position to the unlocked position. These parameters ensure that the minimum tolerance can be achieved between the vessel lid and the locking band, and in addition the retaining portion of the vessel. Preferably, the vessel lid comprises a raised centre portion having a diameter complementary to the diameter of the locking band in the unlocked position and wherein the perimeter of the raised centre portion comprises an inclined cleat configured to engage a complementary surface on the locking band. The cleat mechanism is a simple way of retaining the locking band. Because it uses no moving parts, just an inclined portion which engages with a complementary potion of the locking band, which engages the locking band preventing it from moving upwards without first expanding, the mechanism is simpler and less prone to maintenance requirements. Preferably, during contraction from the locked position to the unlocked position a plane described by the surface of the locking band remains substantially parallel to a plane described by the base of the frustoconical outer portion of the lid. Preferably, the height any portion of the locking band measured from the base of the vessel lid remains substantially the same as the height of any other portion of the locking band during contraction from the locked position to the unlocked position. These exemplary embodiments have the same advantages as described above with respect to ensuring the concentricity of the locking band during retraction. As the outer portion of the vessel lid describes a portion of a cone, keeping the elements of the closure system parallel to the base of the lid ensures this concentricity. According to a further embodiment of the invention, there is provided a hydrodynamic containment vessel comprising: a vessel body having an opening and an annular lip surrounding the opening, and a locking band apparatus as described above. Preferably, the locking band is configured to retain the vessel lid by transferring force from the hydrodynamic containment vessel to the lid of the vessel. The vessel essentially traps the locking band between itself and the lid, to allow the lid to be held closed. Preferably, a top surface of the locking band is configured to engage a bottom surface of the annular lip disposed on the hydrodynamic containment vessel when in the locked position. The locking can be achieved by engaging the vessel lid and the vessel itself with the locking band. This is achieved by providing a lip on the vessel, above the lid, for the locking band to engage. Preferably, the locking band has a smaller circumference than the annular lip when in the unlocked position. The lip is larger than the lid, so that the lid can be entirely removed through the centre of the lip. The locking band is angled such that force can be transferred from the lip to the lid via the locking band, yet the lid can be removed from the vessel entirely. Preferably, the hydrodynamic containment vessel includes a second containment barrier disposed above the vessel lid, which in one example comprises a second volume disposed above the vessel lid and bounded by a second lid. By providing a secondary containment barrier with a lid, leaks or potential failures of the vessel closure system can be identified before they become dangerous. The above and other features will become apparent from the following description and accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Various aspects of at least one embodiment are discussed below with reference to the accompanying figures, which are not intended to be drawn to scale. The figures are included to provide illustration and a further understanding of the various aspects and embodiments, and are incorporated in and constitute a part of this specification, but are not intended as a definition of the limits of the invention. In the figures, each identical or nearly identical component that is illustrated in various figures is represented by a like numeral. For purposes of clarity, not every component may be labelled in every figure. In the figures: FIG. 1 is a general arrangement of a vessel closure system according to the present invention; FIG. 2 is a locking band for a vessel closure system according to the present invention; FIG. 3 is a representation of a locking band segment and locking band carrier for a vessel closure system according to the present invention; FIG. 4 is a locking band retraction mechanism for a vessel closure system according to the present invention; FIG. 5 is a cut through general arrangement for a vessel closure system according to the present invention; FIG. 6 is a representation of the locking band operation path of the vessel closure system according to the present invention; FIG. 7 is a plan view of a vessel closure system according to the present invention; FIG. 8 is a locking band actuation mechanism according to the present invention; FIG. 9 is a band locking segment removal mechanism according to the present invention; FIG. 10 is a plan view representation of a portion of a locking band for a vessel closure system according to the present invention; FIG. 11 is a side view cut through representation of a portion of a locking band for a vessel closure system according to the present invention; and FIG. 12 is a representation of a hydrodynamic containment vessel. DETAILED DESCRIPTION Aspects and embodiments described herein are directed to a vessel closure system for a hydrodynamic containment vessel. FIG. 1 shows a general overview of a vessel closure system 1 for a hydrodynamic containment vessel 120. Shown is a locking band 10 which sits on the frustoconical portion 54 of a vessel lid 52. The vessel lid 52 also contains a centre raised portion 56, and the locking band 10 is free to move along the frustoconical portion 54 between its perimeter and the raised portion 56 to lock and unlock the vessel. The locking band 10 comprises a plurality of segments 12 held by a carrier band 14, as well as two band locking segments 16. The locking band 10, when used to lock the vessel, essentially traps the frustoconical portion 54 of the vessel lid against a surface of the vessel inlet to close the vessel. To unlock the vessel lid 52 the locking band 10 is retracted up the frustoconical surface 54 of the vessel lid. This is achieved by the locking band retraction mechanism 40, which moves a flexible connection 47 connected to ends of the two locking segments 20 of the locking band 10. Once the band locking segments 16 are removed from the locking band 10 the ends of the two locking segments 20 can be pulled towards their opposite locking segment 20 to retract the locking band 10 to allow the vessel to be unlocked. FIG. 2 shows the locking band 10 in an isometric view with the carrier band 14, segments 12, and band locking segments 16 being visible. The locking segments 20 are shown more clearly, as approximately half of the locking band 10. In the side view of one locking segment 20 below, the inclined top surface 24 can be seen, complementary to the bottom surface 22, which is in turn complementary to the frustoconical portion as will be shown with respect to FIG. 11. The top surface 54 of the locking band 10 engages with an annular lip 124 of the hydrodynamic containment vessel. This essentially stacks the locking band 10 between the annular lip 124 and the vessel lid 52, when the vessel lid 52 sits on a rim of the vessel. Thus, the vessel lid 54 cannot be removed when the locking band is engaged. When the locking band 10 is retracted, the top surface 24 of the locking band 10 is no longer engaged with the annular lip 124 of the vessel. This therefore allows the lid 52 to be removed. It is important to the invention that the locking band 10 remains concentric to the vessel lid 52 when it is retracted. This means that the locking band 10 remains at the same height relative to the base of the vessel lid 52 as it is retracted. Because of this arrangement, when the vessel lid 52 is closed, the top surface 24 of the locking band 10 can remain in direct contact with the annular lip 124 and the vessel lid 52. This means that tolerances between the components can be minimized to almost zero. Because of the lack of tolerances when the hydrodynamic containment vessel is used, and there are pressure fluctuations inside the vessel, the lid 52 does not move, and thus no force is transferred to the locking band 10. This means that the locking band 10 does not become damaged in use and a more robust locking system is provided. FIG. 2 also shows an expanded view of the locking band showing the segments 12 and carrier 14. Not labelled but shown are bolts which attach the segments 12 to the carrier 14. By providing this simple fastening individual segments 12 may be removed and replace easily, without the need to replace the entire locking portion 20. FIG. 3 shows the two main components of one the locking segments 20. The segment 12 comprises three holes 32, the middle of which receives a bolt which goes through a corresponding hole 34 in the carrier band 14. The remaining two holes are location holes which serve to keep the segments 12 aligned on the carrier band 14. The locking band 10 is formed from a set of segments 12 and a carrier band 14 to provide optimum flexibility for retraction of the locking band 10, or each locking segment 20, whilst providing the structural strength needed to close the hydrodynamic containment vessel. This means that the segments 12 to do not need to be flexible, and instead can be rigid and non-deformable to prevent motion when the hydrodynamic containment vessel is used. The rigidity can be provided by manufacturing the segments from steel. This also means that the carrier band 14 does not need to be so strong enough to withstand forces applied by the vessel and can be designed to have the optimum flexibility and rigidity to allow retraction of the band 10 yet retain the segments 12 in place. In practice, the flexibility of the carrier band 14 is governed by the materials used to manufacture it and the processes they undergo. In some embodiments, the carrier band is manufactured from steel which has a springiness of 200GPa. FIG. 4 shows a carrier band retraction mechanism 40. The mechanism sits on the raised centre portion 56 of the vessel lid 52. The mechanism 40 comprises a carriage guide having a lead screw 42 with a carrier 44 holding a first part 46 of a flexible connector, which runs on a slide plate 48. The lead screw 42 and the slide plate 48 are angled to match the angle of the frustoconical portion 54 of the lid 52. This helps to ensure that the locking band 10 is pulled in a vector which ensures the locking band 10 remains concentric to the vessel lid 52. The other portion of the flexible connector comprises a clevis fastener 47 which has a hinge pin 47’ allowing the locking portion 20 be pulled in along the appropriate vector independent of any rotational forces applied by the carriage 44. The carrier band retraction mechanism 40 allows for torque applied to the lead screw 42 to be translated into movement of the locking band 10. As noted above, the segments 12 of the band actually provide the locking force to the vessel lid 52, whereas the carrier band 14 merely serves to align and hold the segments 12 in place. For this reason, the flexible connector 47 which is connected to the locking band 10 is connected through the carrier band 14 to the end segment 12’ on each locking segment 20, such that when force is applied to the end segment 12’ it is applied directly, not via the carrier band 14. This means that the end segment 12’ in effect pushes on the carrier band 14 to retract, rather than the carrier band 14 pulling on the end segment 12’. This is advantageous, because it prevents the segments 12 from becoming detached from the carrier band 14 when retracted. Due to the tight tolerances and large amounts offeree required to remove the segments 12, it would not be easily rectifiable if one of the end segments 12’ became detached and remained in the locked position during retraction. The use of a screw and nut type carrier arrangement, such as the lead screw 42 and carriage 44, is also advantageous. When the locking segments 20 are retracted, the carrier band 14 is elastically deformed against its locked state and therefore resists the retraction, requiring a large amount offeree to retract the locking segment 20. By using the lead screw 42, force can only be transmitted one way through the locking band retraction mechanism, i.e., from the lead screw to the carriage 44 and not from the carriage 44 to the lead screw 42. The force applied by the carrier band 14 opposing the retraction therefore cannot be passed back to the lead screw 42 and the locking band 10 is therefore retained in its retracted position. FIG. 5 shows a vessel closure system which also includes the band locking segment removal mechanism 90 as part of the locking band actuation mechanism 50, in addition to the locking band retraction mechanism. Also shown is the input device 80 which provides a turning force to the lead screw 42 of the locking band retraction mechanism. One locking segment 20 is shown as well as two band locking segments 16. It can be seen in this view how the bottom surface 22 of the locking band 10 matches the surface of the frustoconical outer portion 54 of the lid. The inner raised surface 56 can also be seen in this view, and it can be seen that the surface has a return at its perimeter which matches the inner bottom face of each segment of the locking band. This will be described later with respect to FIG. 11. In addition, details of the input device 80 and the band locking segment removal mechanism 90 will be described with reference to FIG. 8 and FIG. 9 respectively. What can also be appreciated is the manner in which all of the components attach to the vessel lid 52. It can be seen that the locking band retraction mechanism 40 and the locking segment removal mechanism 90, as well as the frame for the input device 80, are bolted to the vessel lid 52 and are therefore removable. The vessel lid 52 is heavy and needs to be manoeuvred and held in place using large brackets or lifting devices, not shown. This can cause a conflict with the larger elements, such as the input device 80 and the locking segment removal mechanism 90 on the lid. Thus, they are configured to be removed when not being used for unlocking the lid. FIG. 6 is a representation of the path which the locking segments 20 take when being retracted. The locking segments 20 are retracted by applying a force in a vector 60 which extends from a start point of each end of the locking segment 20 to the intended end point of the respective end of the locking segment 20. This means that the force applied is directed in the direction of movement of the ends of the locking segments 20. As can be seen in examples 62, 64 and 66, there are alternatives to this application of force which do not result in uniform retraction of the locking band 10 and thus do not ensure that the locking band remains concentric to the vessel lid 52 whilst being retracted. In example 62 it can be seen that applying force in a direction perpendicular to the end of the locking segment 20 results in the band not retracting in the centre portion. In example 64 it can be seen that applying a force just to the centre portion of the locking segment 20 results in the ends of the locking segment 20 not retracting at all. Finally, in example 66 it can be seen that applying a force in a vector extending from the ends of the locking segments 20 results in the centre portion retracting and then the end portions retracting. The problem with these methods of retracting the bands is that the locking band 10 does not remain concentric to the vessel lid 52. This means that at some points in the retraction process some portions of the locking band 10 are above or below other sections. As the locking band 10 is not free from the restraints of the lip 124 and the vessel lid 52 until it is fully retracted, any difference in height with respect to the base of the vessel lid 52 means that the tolerances of the lip / band / lid arrangement need to be increased to absorb this height. Alternatively, the locking band 10 would need to have a profile on the top surface 24 which does not perfectly mate with the vessel lip 124, thus reducing the strength of the closure system. In these examples 62, 64, 66, the locking band does retract, and so the ends of the locking segments 20 are moved from their start position to the end position, however the force is not applied in this direction. If force, however, is applied along the vector 60, or the retraction vector, there is no need to have any tolerance fitting between the lip 124, lid 52 and band 10. In practice a very small tolerance may be built in due to manufacturing constraints. FIG. 7 shows a plan view of the vessel closure system in two states. On the left side of FIG. 7, the band is in the locked position, however with the band locking segments removed. On the right side of FIG. 7, the band is in the unlocked position. The mechanics of how force is transferred from the lip 124 to the lid 52 via the locking band 10, or vice versa, can be appreciated in this view. On the left-hand side, it can be seen that the locking band 10 extends past the rim of the vessel, however as was seen in FIG. 5, in this configuration the bottom surface 22 of the locking segments is fully disposed on the top frustoconical portion of the vessel lid. This is because the lip 124 on the vessel, as will be seen in FIG. 12, extends inwards towards the centre of the vessel aperture, but does not extend to the diameter of the vessel lid 52, allowing the lid 52 to be removed via the aperture left by the lip 124. Thus, the force has to be transferred at an angle from the lid to the lip. This angle can be seen for example in FIG. 2 and FIG. 11. This shows the need for the frustoconical perimeter 54 of the vessel lid, as it ensures that force is applied in a straight line from the lid 52 to the lip 124. It can be seen on the right-hand side of FIG. 7 that once the locking band 10 is retracted it is within the diameter of the vessel lid, as such the lid and locking band can be removed through the aperture provided by the lip 124. FIG. 8 shows the input mechanism for the locking band retraction mechanism 40. As the locking band 10 needs to remain concentric to the vessel lid 52 as it is being retracted, it is important to retract both ends of the locking segments 20 simultaneously, thus a single input device which operates both units at the same time aids in the retraction process. Furthermore, due to the location of the locking band, which is well inside the hydrodynamic containment vessel lid, it is helpful to provide a remote system to operate the locking band actuation mechanism 40. Thus, the input device 80 is provided with a frame 86 which bolts to the vessel lid 52. The frame has a handle 82 and a pair of gearboxes 88. The gearboxes 88 transfer the rotational movement of the handle 82 in one plane to a perpendicular plane to be output to a flexible drive shaft 84. The flexible drive shaft 84 is then connected to the lead screw 42 to turn the lead screw 42 and move the carriage 44. Because gearboxes 88 are used to transfer the force applied at the handle 82, the gear ratios inside the gearboxes 88 can be optimized so that input to the handle 82 can be used to operate all four locking band retraction mechanisms 40 at once. This means that both locking segments can be retracted simultaneously thereby reducing the work needed. It is possible to use other input devices, such as a wheel or a motor, electric hydraulic or otherwise. In some embodiments some components of the drive mechanism can be removed for simplicity. For instance, a motor may be directly linked to the locking band retraction mechanism 40, as there is no need for human access. The two locking band retraction mechanisms 40 on one side, i.e., which operate ends of two different locking segments 20, such as the pair on the lower left side of FIG. 8, are connected together by internal gearing, such that one drive shaft can be provided to each side of the input mechanism 80. FIG. 9 shows the band locking segment removal mechanism 90. The operation of the band locking segment removal mechanism 90 is to remove the band locking segment 16 prior to retraction of the locking band 10. Firstly, the band locking segment removal mechanism 90 is bolted to the vessel lid 52 and then the clamp 92 is attached to the band locking segment 16 through hole 100 via a bolt or other fastener. This allows the band locking segment removal mechanism 90 to be removed for the reasons set out above. Next, the handle 96 is pushed forwards away from the centre of the vessel lid to pull the band locking segment away from the locking band and out of engagement with the vessel lip 124. Lastly the drive wheel, 96, is turned. The clamp 92 is connected to a carriage on a lead screw 94 of the band locking segment removal mechanism. Turning the drive wheel 96 therefore enables the clamp 92 to be raised upwards and out of the way of the locking segments 20. This means that the band locking segment removal mechanism 90 can be retained on the vessel lid whilst the locking segments 20 are retracted. To replace the band locking segment 16 the process is reversed. It is not necessary to use the handle 94 mechanism to retract the band locking segment. A parallel linkage may be used, which operates similarly to a manual car jack, to first retract the band locking segment 16 and then lift the band locking segment 16 clear of the locking segments 20. There are two band locking segment removal mechanisms 90 on the vessel lid 52, one for each band locking segment 16. The interaction between the band locking segments 16 and the end segments 12’ is shown in FIG. 10. Whilst the majority of the segments 12 of the locking band 10 are cut so as to form a circle when arranged, the band locking segments 16 are cut such that their sides are parallel to a line normal to the centre of the curved inner surface of the band locking segment 16. This is to enable them to be extracted by sliding along the surface of the frustoconical portion 54 of the lid 52. Furthermore, to accommodate this the end segments 12’ are cut to complement the band locking segments 16 on a portion closer to the centre of the vessel lid. However, when retracting the locking band 10, the end segments 12’ of opposite locking segments 20 come into contact, and would foul one another, as such they are cut to complement one another on a portion further away from the centre of the vessel. In this detailed plan view of the locking band 10 the clamp 92 connection hole 100 can be seen on the band locking segments 16. FIG. 11 demonstrates a further advantage of the shape of the segments 12. As noted above, once the locking band 10 is retracted, it cannot spring back to its original shape because of the interaction of the carriage 44 and the lead screw 42 of the locking segment retraction mechanism. This allows the locking band 10 to be trapped in its retracted state. Thus, by providing a return 110 on the centre portion 56 of the vessel lid, the locking band can be retained securely on the vessel lid 52 when it is removed. It can be seen in FIG.11 that the inside face of the segment 12 engages with the return 110 of the raised centre lid portion 56. As this occurs all the way around the locking segments 20, and they are restrained in this position, it is not possible to lift the locking segments away from the vessel lid 52. It is noted that the ends 12’ are restrained still by the locking band retraction mechanisms 20, however by retaining the entire band 10 it is possible to prevent damage to the locking band 10. Finally, FIG. 12 shows a hydrodynamic containment vessel 120. The hydrodynamic containment vessel is used to model the effects of materials under explosive loading. At these loading rates, materials can behave like fluids. The vessel is therefore subject a number of large pressure fluctuations. The hydrodynamic containment vessel has a body 122 and an opening with a lip 124. This lip 124 engages with the locking band 10 to retain the vessel lid 52. The vessel also has a second 5 containment barrier 126 which allows for detection of problems with the vessel closure system 10. If the vessel closure system 10 fails, pressure will leak from the hydrodynamic containment vessel to the second containment barrier 126 and will cause bowing or deformation of a lid which is disposed over the second containment barrier 126. This provides an early warning sign of any potentially dangerous io failures of the vessel closure system 10. Because a pressure leak can develop into a complete failure yet could go undetected if it were not for the second containment barrier 126, the second containment barrier 126 can prevent the leak becoming dangerous by notifying the operators. Furthermore, should the vessel closure system 10 fail, the second containment barrier 126 can prevent operators from 15 coming into contact with components of the damaged vessel closure system.

Claims

1. Locking band apparatus for use on a vessel lid having a frustoconical outer surface, the apparatus comprising:a locking band; andan actuation mechanism comprising:a first actuator configured to apply a force to a first end of the locking band; anda second actuator configured to apply a force to a second end of the locking band;wherein the force applied to the first and second ends causes the locking band to contract from a locked position to an unlocked position wherein the ends of the locking band move from a respective start position to a respective finish position, and wherein the force is applied in a retraction vector extending from the start position of the respective end of the locking band to the end position of the respective end of the locking band.

2. The locking band apparatus of claim 1, further comprising a third actuator configured to remove a band locking segment from the locking band, wherein when the locking band is in the locked position the band locking segment engages with at least one end of the locking band.

3. The locking band apparatus of claim 1 or claim 2, wherein the first and second actuators each comprise a carnage connected to the respective first and second ends of the locking band and a first drive mechanism configured to move the carriage.

4. The locking band apparatus of claim 3, wherein the first drive mechanism is oriented to move the carriage in the retraction vector.

5. The locking band apparatus of claim 3 or claim 4, wherein the carriage is connected to the respective end of the locking band by a flexible connector.

6. The locking band apparatus of claim 5, wherein the flexible connector is a clevis fastener.

7. The locking band apparatus of any of claim 3 to claim 6, wherein the first drive mechanism is a lead screw mounted in a carriage guide.

8. The locking band apparatus of any of claim 3 to claim 7, wherein the first and second actuators further comprise an input device configured to transmit external force to the first drive mechanism.

9. The locking band apparatus of claim 8, wherein the input device is a manually operated handle.

10. The locking band apparatus of claim 8, wherein the input device is a motor.

11. The locking band apparatus of any of claim 8 to claim 10, wherein the inputdevice is connected to the first drive mechanism via a flexible shaft.

12. The locking band apparatus of any of claim 2 to claim 11, wherein the third actuator comprises a clamp configured to be removably attached to the band locking segment13. The locking band apparatus of any of claim 2 to claim 12, wherein the third actuator comprises a second drive mechanism configured to retract the band locking segment along the frustoconical outer surface of the vessel lid and lift the band locking segment clear of the locking band.

14. The locking band apparatus of claim 13, wherein the second drive mechanism comprises a lead screw configured to engage with a parallel linkage in turn connected to the clamp.

15. The locking band apparatus of claim 14, wherein applying a turning force to the lead screw causes the clamp to first retract towards the third actuator and second raise upwards from the locking band.

16. The locking band apparatus of any of claim 12 to claim 15, wherein the third actuator further comprises an input device configured to transmit external force to the second drive mechanism.

517. The locking band apparatus of claim 16, wherein the input device is a manually operated handle.

18. The locking band apparatus of claim 16, wherein the input device is a motor, io24

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