The present invention relates to valves for controlling flow of fluids in a conduit and, in particular though not exclusively, to microvalves which can be manufactured in very small formats.

There are many devices in which miniaturised flow control valves can be useful to control flow of fluids to, from or within the device. An example of such a device is an electrochemical fuel cell stack where, in particular, gaseous fuel flows into the stack and into individual cells within the stack may require controlling. The expression "flow control" as used herein is intended to encompass both variable control of a flow rate and on-off flow control. Typical gaseous fuel flows in a fuel cell stack that require such control may include hydrogen flows to cells in the fuel cell stack. It is an object of the invention to provide improved arrangements of valves suitable for controlling flow of fluids.

According to one aspect, the present invention provides a valve assembly comprising: a fluid flow conduit;

a closure member operable to open and close the fluid flow conduit by displacement between a first position in which the conduit is closed or restricted and a second position in which the conduit is open;

a single actuator operable to drive the closure member between the first and second positions; and

a latching mechanism driven by the single actuator and operable to alternatingly latch the closure member in the first and second positions.

The actuator may comprise a tension wire being controllable in length. The tension wire may be controllable in length by passage of electric current therethrough. The tension wire may be configured to undergo a phase change causing a change of length upon thermal actuation. The tension wire may be a shape memory alloy wire. The latching mechanism may comprise a latching member which is engaged with the closure member and which rotates about an axis orthogonal to an axis of displacement of the closure member between the first and second positions. The latching mechanism may comprise a rotatable cam member defining at least two different radii of cam surface operable to maintain the closure member respectively in the first and second positions. The rotatable cam member may define a cam surface having at least two detents corresponding to the first and second positions. The rotatable cam member may define a plurality of detent positions around its circumference, each corresponding to a position of axial displacement of the closure member. The rotatable cam member may include a ratchet surface and the actuator may comprise a pawl engaging with the ratchet surface. The latching mechanism may comprise a link member, the link member being pivotally coupled to the closure member and having an engagement portion configured to travel between at least two detent positions provided by a latching structure. The valve assembly may further include a first bias member coupled to the closure member to bias the closure member to the first position and second bias member coupled to the link member to bias the link member into a detent position provided by the latching structure. The latching mechanism may comprise an axially displaceable, rotating ratchet cylinder having at least two slots of different depths, and an engagement element configured to engage with either of said slots of different depths to latch the ratchet cylinder to a respective an axial displacement position, and an axially travelling drive element coupled to the actuator and configured to engage the ratchet cylinder to axially displace and rotate the ratchet cylinder.

According to another aspect, the present invention provides a valve assembly comprising: a flexible fluid flow pipe having a fold across the flow axis of the pipe, the fold providing a first radius of curvature of the pipe sufficient to occlude flow of fluid through a lumen of the pipe at the fold;

an actuator operable to displace the fold in the flexible pipe so as to increase the radius of curvature of the pipe at the fold to a second radius of curvature in which the occlusion of flow of fluid is reduced.

The first radius of curvature of the pipe may be small enough to completely close the pipe lumen. The actuator may be configured to vary a lateral displacement of the flow axis of the pipe at the fold location. The actuator may comprise a tension wire being controllable in length. The tension wire may be controllable in length by passage of electric current therethrough. The tension wire may be configured to undergo a phase change causing a change of length upon thermal actuation. The tension wire may be a shape memory alloy wire. The tension wire may be coupled to the flexible pipe at the fold location. The tension wire may extend along a length of the flexible pipe around the fold. The valve assembly may further include a latching mechanism operable to maintain the flexible pipe in either of the first radius of curvature and second radius of curvature configurations.

Embodiments of the present invention will now be described by way of example and with reference to the accompanying drawings in which:

Figure 1 shows a schematic cross-sectional view through a valve;

Figure 2 shows a perspective view of a latching mechanism used in the valve of figure 1 and figure 2a shows the latching mechanism of figure 2 in more detail;

Figure 3 shows a more detailed plan view of a cam arrangement in the latching mechanism of figure 2;

Figure 4 shows a chassis for the valve of figure 1 ;

Figure 5 shows a schematic plan view of an alternative valve arrangement;

Figure 6 shows a chassis for the valve of figure 5 and figure 6a shows in more detail components of the latching structure on the chassis;

Figure 7 shows a schematic plan view of another valve arrangement;

Figure 8 shows a perspective view of a latching member used in the valve of figure

7;

Figure 9 shows a schematic diagram illustrating the principles of operation a latching member useful in the implementation of a valve similar to that shown in figure 7;

Figure 10 shows a schematic cross-sectional view of another valve arrangement in a closed condition; and

Figure 11 shows a schematic cross-sectional view of the valve arrangement of figure 10 in an open condition. A first arrangement of valve assembly 30 is now described with reference to figures 1 to 4. A fluid flow conduit exemplified by a flexible walled tube 1 is disposed against a retaining wall 2 of a chassis 3. A closure member is exemplified by a shaft 4 which has a long axis and is retained in position on the chassis 3 by support members 6. The shaft is axially displaceable within the support members 6. The shaft 4 has a proximal end 5 which is configured to compress the tube 1 when the shaft is displaced axially towards the retaining wall 2 and to decompress the tube 1 when the shaft is displaced axially away from the retaining wall 2. The shaft 4 has a distal end 7 which bears against a rotatable cam 8 of a latching member 10 (figure 2). The shaft 4 has a collar portion 9 which serves as a seat for a spring 11 which exemplifies a bias member operative to bias the shaft 4 axially towards the rotatable cam 8. At its other end, the spring 11 bears against one of the support members 6.

The latching member 10 comprises the rotatable cam 8 discussed above which is rotatably mounted on a pivot pin 12 which extends in a direction generally orthogonal to the axis of the shaft 4. The rotatable cam 8 is connected to, or integrally formed as a part of, and driven by a ratchet wheel 13 such that both the rotatable cam and ratchet wheel rotate around the pivot pin 12 together. A toothed driving wheel 14 also rotates around the axis of the pivot pin 12 and is driven by an actuator wire 15 coupled to the driving wheel 14 at anchor 16. Anchor 16 is also coupled to a return spring 17 which acts against the actuator wire 15 to maintain tension in the wire and to return the driving wheel 14 to a home position when the actuator wire 15 is deactivated. The teeth 8 of the driving wheel 14 operate in similar manner to a pawl when engaging with recesses 19 in the ratchet wheel 13 such that anticlockwise rotation of the driving wheel 14 (as viewed from the plan view of figure 2) causes driving engagement of the teeth 18 with the ratchet wheel 13, whereas clockwise rotation of the driving wheel 14 allows the ratchet wheel 13 to remain rotationally stationary by small axial displacement of the ratchet wheel on the pivot pin 12 (i.e. by rising slightly on the pivot pin 12 as viewed in figure 2). The rotatable cam 8 has at least two different radii of cam surface relative to the pivot axis of pivot pin 12, which may be achieved by the lobed profile seen in figure 2 and 3. A maximum radius 20 and a minimum radius 21 provide first and second surfaces 20a, 21a corresponding to a first position of the shaft 4 in which the flexible walled tube is compressed by the proximal end 5 of the shaft and a second position of the shaft 4 in which the flexible walled tube is less compressed or uncompressed by the proximal end of the shaft 4.

In use, the actuator wire 15 is actuated to rotate the driving wheel 14, against the bias of the return spring 17, in an anticlockwise direction as viewed in the plan view of figure 3, thereby also rotating the cam 8 such that the distal end of the shaft 4 is guided from a first position corresponding to maximum radius 20 to a second position corresponding to minimum radius 21. When the actuator wire 15 is deactuated, the driving wheel 14 returns to its clockwise home position, but the ratchet wheel 13 and cam 8 remain in position. Thus, in this first actuation of the actuator wire 15, the shaft 4 of the valve has moved from a "tube closed" condition to a "tube open" condition. A further actuation of the actuator wire 15 will repeat the rotation operation, but on this occasion the distal end of the shaft 4 is guided by the cam 8 from a minimum radius position to a maximum radius position, thereby re-closing the lumen of the flexible tube 1 by compression of the tube walls by the proximal end 5 of the shaft 4.

The actuator wire 15 is preferably a shape memory alloy wire. Shape memory alloy (SMA) wire is preferred as an actuator because by comparison with some other actuators of similar mass and size, SMA wires can produce more work output. SMA wires can undergo a phase transition as a function of temperature which enables an SMA wire to be configured to have a temperature-to-length relationship at least a part of which has a negative characteristic. The SMA wire may be actuated by electrical heating, e.g. electrical resistance heating by the passage of current therethrough. Thus, an electrical current passed through the wire can be used to transiently shorten the length of the SMA wire such that the cam 8 is rotated from first position to second position, opening the valve. When the electrical current ceases, the SMA wire will relax, e.g. undergo a reverse phase change and return to its longer length, but the valve will remain open. When the next electrical current is passed through the wire, the valve is reclosed. A particular feature of this arrangement is that the valve is bistable in that no actuator power is needed to keep the valve in either the open or closed condition. Very low currents are required to operate the valve and are only required during switching.

As shown in figure 3, the stability of the valve can be enhanced by the provision of a detent 22 at any or all of the maximum radius positions. This detent 22 will tend to capture the distal end 7 of the shaft 4 and prevent any backlash of the cam / ratchet wheel 13 when the driving wheel 14 rotates back to the home position. The minimum radius positions generally do not need a detent, since the minimum radius generally can act as a detent. The detent can be a small depression in the cam surface or any suitable profile of surface capable of providing a localised position of slightly higher resistance to rotation of the cam 8 relative to the distal end 7 of the shaft 4, which slightly higher resistance can be overcome by the actuator wire in a pull phase, but not in a relax phase. A detent might not be necessary if sufficient friction is achieved by the pressure of the shaft on the cam 8. A number of modifications to the valve arrangement of figures 1 to 4 can be made. The rotatable cam 8 is shown with three lobes corresponding to three maximum radius positions 20 and three minimum radius positions 21. However, any number of such radius positions with or without detents 22 can be deployed. In the example described, the maximum radius positions 20 may correspond to a valve fully closed condition and the minimum radius positions may correspond to a valve fully open condition. However, these positions could correspond to partially open or partially closed conditions. Intermediate positions could also be implemented, e.g. detents or local maxima or minima in the cam surface corresponding to partially open / partially closed conditions of the valve. In this way, repeated operation of the actuator wire 15 may be used to step through a cyclic series of open, closed and/or partially open conditions. Each of these intermediate positions, as well as a maximum radius position and a minimum radius position can be configured to be stable, i.e. requiring no actuator power to maintain the valve in that condition. Providing several maximum radius positions and minimum radius positions around the cam 8 may be advantageous in that it can shorten the range of movement required of the actuator wire 15 to move the cam from one detent position to the next, e.g. between valve-open and valve-closed positions. In the arrangement shown in figure 3, the actuation requires the actuator wire 15 to change in length, for each actuation, by an amount approximately equal to one-sixth of the circumference of the rotatable cam 8. Increasing the number of lobes of the cam 8 will reduce the actuator length change required. This may be beneficial for speed of actuation and / or energy efficiency.

A particular feature of the valve arrangements described is that the valve can be made bistable, tristable or multistable, i.e. latchable in two, three or more equilibrium states corresponding to open, closed or partially open conditions without energy input required to maintain those stable positions. A still further feature of the valve arrangements described is that only a single actuator is required. In the examples described, only a single actuator wire (e.g. shape memory alloy wire) is required to control both opening and closing (and partial opening / partial closing) operations. Thus, only a single actuator control system, single actuator control line / channel and / or single actuator circuit is required to operate the valve through two, three or more stable positions or to provide both closing and opening operations. This also offers significant benefits in miniaturization of the valve since separate push and pull actuators and separate control circuits can be eliminated. Thus, in a general aspect, the valve assembly 30 provides a latching mechanism driven by a single actuator which is operable to alternatingly latch the closure member in at least first and second positions. It can be readily adapted to further latch the closure member in intermediate positions between the alternating first and second positions.

Figures 5, 6 and 6a show an alternative valve assembly 50 offering many similar performance characteristics to those described in connection with the valve of figures 1 to 4. A fluid flow conduit exemplified by a flexible walled tube 51 is disposed against a retaining wall 52 of a chassis 53. A closure member is exemplified by a shaft 54 which has a long axis and is retained in position on the chassis 53 by a support member 56. The shaft 54 is axially displaceable within the support member 56. The shaft 54 has a proximal end 55 which is configured to compress the tube 51 when the shaft 54 is displaced axially towards the retaining wail 52 and to decompress the tube 51 when the shaft is displaced axially away from the retaining wall 52. The shaft 54 has a distal end 57 which is pivotally coupled to a link member 58 of a latching assembly 60. The shaft 54 has a collar portion 59 which serves as a seat for a compression spring 61 which exemplifies a bias member operative to bias the shaft 54 axially towards the tube 51. At its other end, the compression spring 61 bears against the support member 56.

The latching assembly 60 comprises the link member 58 discussed above which has a first end 62 pivotally coupled to distal end 57 of the shaft 54 and a second end 63 having a pin 64 which exemplifies an engagement portion that travels within a path 70 of a latching structure 71. A tension spring 67 is coupled to provide lateral bias to the link member 58 to assist the pin 64 in travelling along the path 70 of the latching structure, such that it is biased into a detent position provided by the latching structure 71.

An actuator wire 65 is tensioned between two fixed anchorages 68 on the chassis 53 and passes through or around an anchor point 66 on the shaft 54. The actuator wire 65 may be maintained in tension by the action of the compression spring 61 on the shaft 54. The latching structure 71 may comprise a pair of c-shaped cup elements 72, 73 which together define the path 70 through which the pin 64 travels (shown separately in more detail in figure 6a), providing at least two stable or equilibrium positions as will be described. In use, the actuator wire 65 is actuated to pull the shaft 54 away from the tube 51 against the bias of the compression spring 61 , i.e. in a rightward direction as viewed in figure 5. This causes the distal end 57 of the shaft 54 to drive the link member 58 in the same direction such that the pin 64 passes over and at least partially around first cup element 72 and strikes second cup element 73. Cup element 73 thereby resists any overpull of the link member 58 by the actuator wire 65 while the tension spring 67 ensures that the pin 64 will follow a path into the recess / detent defined by first cup element 72 when the actuator wire 65 is deactuated. When the actuator wire 65 is deactuated, the shaft 54 is prevented from returning to the "tube closed" (left-most) position because the pin 64 has been captured, under the combined bias of tension spring 67 and spring 61 , into the detent of cup element 72. This corresponds to a "tube open" condition. Thus, in this first actuation of the actuator wire 65, the shaft 54 of the valve has moved from a "tube closed" condition to a "tube open" condition. A further actuation of the actuator wire 65 again tensions the wire to drive the shaft 54 in a direction away from the tube 51 , but this time the pin 64 of the link member 58 is not constrained by the second cup element 73 as the tension spring pulls the second end 63 of the link member 58 and the pin 64 away from the second cup element 63 and around the distal periphery 74 of the first cup element 72. When the actuator wire 65 is deactuated, the shaft 54 is once again free to pass to the "tube closed" position where the proximal end 55 compressed the tube 51. The second end 63 of the link member 58 is prevented from overbias away from the first cup element 72 by a guiding peg 75 positioned between the first and second ends 62, 63 of the link member 58. From this position, the cycle can be repeated. An end stop may be provided on the shaft 54 to engage with the support member 56 on the distal end side of the support member so as to limit the axial travel of the shaft 54 towards the closed condition (leftwards in figure 5). This may be used to prevent the actuator wire 65 being constantly under tension when the valve is in the closed condition. Similarly, this feature can be used to limit the compression applied to the tube 51 by the proximal end 55 of the shaft 54 in tube closed condition.

The actuator wire 65 is preferably a shape memory alloy wire. The SMA wire may have a phase transition temperature enabling it to have a temperature-to-length relationship at least a part of which has a negative characteristic. The SMA wire may be actuated by electrical heating, e.g. electrical resistance heating by the passage of current therethrough. Thus, an electrical current passed through the wire can be used to transiently shorten the length of the SMA wire such that the shaft 54 is displaced axially away from the retaining wall 52 and tube 51 , opening the valve. When the electrical current ceases, the SMA wire will relax, e.g. undergo a reverse phase change, and return to its longer length, but the valve will remain open by way of the latching assembly 60. When the next electrical current is passed through the wire, and then stopped, the valve is reclosed.

Thus, this valve arrangement is also bistable in that no actuator power is needed to keep the valve in either the open or closed condition. Very low currents are required to operate the valve and are only required during switching.

The latching assembly 60 can be configured in a number of ways such that it defines a path 70 facilitating different valve conditions, including a valve fully closed condition and a valve fully open condition, as well as valve partially open conditions or partially closed conditions. The path 70 may be configured such that repeated operation of the actuator wire 15 may be used to step through a cyclic series of open, closed and/or partially open conditions. Each of these intermediate positions can be configured to be stable, i.e. requiring no actuator power to maintain the valve in that condition.

Thus, this valve assembly 50 can also be made bistable, tristable or multistable, i.e. latchable in two, three or more equilibrium states corresponding to open, closed or partially open conditions without energy input required to maintain those stable positions. Only a single actuator is required. The single actuator wire (e.g. shape memory alloy wire) is able to control both opening and closing (and partial opening / partial closing) operations. Thus, only a single actuator control system, single actuator control line / channel and / or single actuator circuit is required to operate the valve through two, three or more stable positions or to provide both closing and opening operations. This again offers significant benefits in miniaturization of the valve since separate push and pull actuators and separate control circuits can be eliminated. Thus, in a general aspect, the valve assembly 50 provides a latching mechanism driven by a single actuator which is operable to alternatingly latch the closure member in at least first and second positions. It can be readily adapted to further latch the closure member in intermediate positions between the alternating first and second positions. Figures 7, 8 and 9 illustrate a further valve assembly 70 exemplifying similar principles to those described above.

A fluid flow conduit exemplified by a flexible walled tube 71 is disposed against a retaining wall 72 of a chassis 73. A closure member is exemplified by a shaft 74 which has a long axis and is retained in position on the chassis 73 by a support member 76. The shaft 74 is axially displaceable within the support member 76. The shaft 74 has a proximal end 75 which is configured to compress the tube 71 when the shaft 74 is displaced axially towards the retaining wall 72 and to decompress the tube 71 when the shaft is displaced axially away from the retaining wall 72. The shaft 74 has a distal end 77 which is coupled to a latching assembly which can be a ratchet-based retraction-extension mechanism 80. This can be similar or identical to those conventionally used in ball-point pen retraction mechanisms. A rotating ratchet cylinder 83 shown in figure 8 includes deep slots / detents 90 and shallow slots / detents 91 respectively corresponding to tube closed position and tube open position. Such mechanisms are well known in pen retractors and a schematic diagram of one implementation can be seen in figure 9, in which cylindrical elements are shown schematically flattened out in planar form to illustrate the angular relationship between the components during operation. The latching assembly may include a stationary engagement cylinder 92, an axially travelling indexing drive cylinder 93 and the rotating ratchet cylinder 83. As seen in the schematic diagram of figure 9, axial displacement of the drive cylinder 93 from the position shown in figure 9a to the position shown in figure 9b axially displaces the ratchet cylinder 83 (and thus also the shaft 74) until the engagement cylinder 92 has disengaged from the deep detents 90 of the ratchet cylinder 83. At that point, the indexing drive 93 causes rotation of the rotating ratchet cylinder to an adjacent ratchet position (a shallow detent 91) and the engagement cylinder 92 engages therewith such that upon return axial motion of the indexing drive 93 (figure 9c) the ratchet cylinder 83 is retained in its new rotated position (shown schematically by its movement to the right in the drawings) by the engagement cylinder 92.

The proximal end 75 of the shaft 74 is shown schematically in relation to the tube 71 shown in dashed outline below, illustrating an open position (figure 9a) and closed positions (figures 9b and 9c) where the tube 71 would clearly be compressed. Repetition of the axial reciprocation motion of axially travelling indexing drive 93 effects a further rotation of the ratchet cylinder 83 after which the engagement cylinder once again resides in the deep detents 90. In this arrangement, an actuator wire 85 is tensioned between two fixed anchorages 88 on the chassis 73 and passes through or around an anchor point 86 on the indexing drive 93. In use, the actuator wire 85 is actuated to pull the indexing drive 93 towards the tube 71 against the bias of a spring 87, i.e. in a leftward direction as viewed in figure 7. This initiates the first part of the reciprocal motion of the indexing drive 93 as discussed above and causes the proximal end 75 of the shaft 74 to compress the tube 71. When the actuator wire 85 is deactuated, the rotating ratchet cylinder 83 is held in the extended position, ensuring the tube 71 remains closed. Repeat actuation and deactuation of the actuator wire 85 reverses the operation to reopen the tube. The actuator wire 85 is preferably a shape memory alloy wire and may have a phase transition temperature enabling it to have a temperature-to-length relationship at least a part of which has a negative characteristic. The SMA wire may be actuated by electrical heating, e.g. electrical resistance heating by the passage of current therethrough. Thus, an electrical current passed through the wire can be used to transiently shorten the length of the SMA wire such that the shaft 74 is displaced axially towards the retaining wall 72 and tube 71. When the electrical current ceases, the SMA wire will relax, e.g. undergo a reverse phase change, and return to its longer length, but the valve will remain closed by way of the latching assembly 80. When the next electrical current is passed through the wire, and then stopped, the valve is reopened.

Thus, this valve arrangement is also bistable in that no actuator power is needed to keep the valve in either the open or closed condition. Very low currents are required to operate the valve and are only required during switching. The latching assembly 80 can be configured in a number of ways such that it defines a rotating ratchet cylinder 83 having different depths of detents 90, 91 facilitating different valve conditions, including a valve fully closed condition and a valve fully open condition, as well as valve partially open conditions or partially closed conditions. It may be configured such that repeated operation of the actuator wire 85 may be used to step through a cyclic series of open, closed and/or partially open conditions. Each of these intermediate positions can be configured to be stable, i.e. requiring no actuator power to maintain the valve in that condition.

Thus, this valve assembly 70 can also be made bistable, tristable or multistable, i.e. latchable in two, three or more equilibrium states corresponding to open, closed or partially open conditions without energy input required to maintain those stable positions. Only a single actuator is required. The single actuator wire (e.g. shape memory alloy wire) is able to control both opening and closing (and partial opening / partial closing) operations. Thus, only a single actuator control system, single actuator control line / channel and / or single actuator circuit is required to operate the valve through two, three or more stable positions or to provide both closing and opening operations. This again offers significant benefits in miniaturization of the valve since separate push and pull actuators and separate control circuits can be eliminated. Thus, in a general aspect, the valve assembly 70 provides a latching mechanism driven by a single actuator which is operable to alternatingly latch the closure member in at least first and second positions. It can be readily adapted to further latch the closure member in intermediate positions between the alternating first and second positions. Figures 10 and 11 illustrate a further valve assembly 100 which may be operated using only a single actuator wire, for opening and closing operations, though without latching.

A flexible fluid flow pipe exemplified by a flexible tube 101 is held in position between two guiding pegs 102 around which travels an actuator wire 103. The actuator wire 103 is anchored at two anchor points 104 on a substrate 105 (which may form part of a chassis), and retains the flexible tube 101 in position between the pegs 102 by extending along the tube and around the outside of a bend 06 of the tube. The wire may be coupled to the tube at bend 106 so that it does not become dislodged. The flexible tube 101 as a whole is biased towards the substrate 105, for example by an inherent resilience in the tube which is supported in position by support points 108 along the lengths 107 of the tube distal to the bend 106. The support points 108 may be coupled to the same substrate 05 as the anchor points 104. Instead of solely relying, or partly relying, on the resilience of the tube for bias towards the substrate 105, a bias member such as a spring may be provided (not shown) to urge the tube 101 towards and into the gap between the guiding pegs 102. The bias member may be configured to act upon the tube 103 at the inside of the bend 106. In the configuration of figure 10, the actuator wire 103 is of sufficient length that the flexible tube 101 can extend a distance Xi through the gap defined by the guiding pegs 102. This holds the flexible tube in a tight crimp position, such that the tube has a fold across the flow axis of the tube at bend 106. This effectively occludes (fully or partially) a lumen of the tube 101 , by imposing a small radius of curvature on the bend 106 in the tube sufficient to create the occlusion. This configuration thereby corresponds to a closed position of the valve assembly 100. In the configuration of figure 11 , the actuator wire 103 has been actuated such that it is shorter in length than as seen in figure 10. This shortening of the actuator wire displaces the tube 101 , against the bias, away from the substrate 105, such that it extends only a distance x ₂ through the gap defined by the guiding pegs 102. The tube 101 is therefore forced out of the gap between the guiding pegs 102 and towards the support points 108 along the length 107 of the tube. This displaces the bend 106 in the tube and reduces the crimp or fold therein, thereby creating a bend 106 of increased radius of curvature. This opens up the lumen of the tube 101 , thereby opening the valve. More generally, the actuator wire 103 may be configured to displace the bend 106 in the tube 101 relative to the support points 108, e.g. by movement of the support points 108 by the actuator wire relative to a retaining structure of the tube 101 at the bend 106.

The actuator wire 85 is preferably a shape memory alloy wire and may have a phase transition temperature enabling it to have a temperature-to-length relationship at least a part of which has a negative characteristic. The SMA wire may be actuated by electrical heating, e.g. electrical resistance heating by the passage of current therethrough. Thus, an electrical current passed through the wire can be used to transiently shorten the length of the SMA wire such that the fold in the tube is displaced to open the lumen of the tube. When the electrical current ceases, the SMA wire will relax, e.g. undergo a reverse phase change, and return to its longer length, and the valve will reclose. Thus, this arrangement can provide a valve which is normally closed, and which opens upon actuation of an actuator wire.

A reverse arrangement, i.e. a normally open valve which closes upon actuation, can also be realised, for example by providing an actuator wire which lengthens on actuation. The actuated and non-actuated positions can correspond to positions where the tube has a completely restricted and a completely unrestricted lumen, or varying degrees in between. The degree of actuation may also be varied, e.g. by varying the electrical current passing through a shape memory alloy wire. If the actuator wire is coupled to the bend 106 in the tube 101 by way of a latching mechanism, such as that described in connection with figures 7 to 9, the valve of figures 10 and 11 may be configured as a latching valve, e.g. with bistable, tristable or multistable equilibrium states corresponding to open, closed or partially open conditions without energy input required to maintain those stable positions.

The actuator could alternatively be implemented by any mechanical or electromechanical mechanism suitable for lengthening and shortening the wire constraining the tube. Alternatively, the wire could be replaced with an alternative mechanism for displacing the bend of the pipe such that the fold changes between a first radius of curvature and a second radius of curvature different from the first, e.g. by varying a lateral displacement of the flow axis of the pipe at the fold location.

In all the arrangements described, the actuator wire 15, 65, 85, 103 may be thermally insulated with a suitable elastic medium such as silicone to reduce the energy required to initiate the phase transition change that shortens the wire. Such a thermal insulation may also serve to provide heat protection to, e.g., the tube 101 or other elements in the valve assembly. The thermal insulation material may also serve as a bonding agent for retaining the actuator wire in place, e.g. in relation to the tube 101. The valve assemblies may be configured such that the actuator wire is kept in tension at all times by bias elements within the valve assemblies, or limit stops may be used to enable to actuator wire to be in a generally slack condition when not actuated.

Other embodiments are intentionally within the scope of the accompanying claims.