Patent Publication Number: US-2022235876-A1

Title: Butterfly valve assembly

Description:
This application claims priority to European Patent Application No. 21152975.5 filed Jan. 22, 2021, the entire contents of which is incorporated herein by reference. 
     FIELD 
     The present invention relates to a butterfly valve assembly, particularly to a butterfly valve assembly comprising a relief valve comprising an adjustment mechanism, and/or to a butterfly valve assembly comprising a manual override. 
     BACKGROUND 
     Butterfly valves are typically provided to regulate downstream pressure in fluid in a conduit. They comprise a butterfly element, such as a disc or gate, inside the conduit which is rotatable to regulate fluid flow through the conduit depending on the degree of rotation of the butterfly element. Since butterfly valves are provided to regulate pressure, they typically include a feedback mechanism controlling the rotation of the butterfly element based on the pressure downstream thereof. 
     One mechanism for an electronically controlled butterfly valve includes a pressure sensor and a motor to drive the butterfly element in response to signals from the pressure sensor. Such electronic valves are at risk in high temperature environments because of their electronic components. Further, the need to be failsafe (so that the butterfly element is open in the event of a failure) increases electronic valves&#39; design complexity. 
     For high temperature environments, fluid-driven butterfly valves, such as pneumatic or hydraulic valves, may be used instead. However, the need to calibrate the butterfly valve for each particular system requires that they be adjustable. The mechanisms for such adjustment are typically difficult to access and require significant force to change. Moreover, such valves have limited functionality. There therefore exists a need for improvement of butterfly valves, particularly for butterfly valves for use in high temperature environments (e.g. in aircraft) that lack electronic control. 
     SUMMARY 
     According to a first aspect of the invention there is provided a butterfly valve assembly comprising: a butterfly element configured to control fluid flow through a main conduit; and a butterfly controller configured to control the butterfly element, comprising a first chamber for receiving fluid at a first pressure, a second chamber for receiving fluid at a second pressure, and an actuator responsive to the first pressure and the second pressure; and a relief valve arranged to regulate the first pressure in the first chamber within a predetermined pressure range, wherein the relief valve comprises an adjustment mechanism for adjusting the predetermined pressure range. 
     The operation of the butterfly valve assembly may therefore be controlled by adjusting the adjustment mechanism of the relief valve, to thereby adjust the predetermined pressure range. By adjusting the predetermined pressure range, the first pressure of the fluid in the first chamber can be controlled so that movement of the actuator can be affected, which in turn affects movement of the butterfly element and fluid flow through the butterfly valve assembly. Since adjustment is provided by the adjustment mechanism of the relief valve, it can be easier to adjust (e.g. require less force) than an alternative arrangement (e.g. in which the butterfly controller itself is adjusted). The adjustment mechanism may also be more easily accessible than if it were part of the butterfly controller (e.g. disposed within the first or second chamber). 
     The butterfly valve assembly may comprise the main conduit. The butterfly element may be within the main conduit. The butterfly element may be configured to control fluid flow through the main conduit by rotation between a first butterfly element position and a second butterfly element position. The butterfly element may permit as much fluid flow as possible through the main conduit in the first butterfly element position, and/or may prevent as much fluid flow as possible through the main conduit in the second butterfly element position. The butterfly element may also take any position between the first butterfly element position and the second butterfly element position, and may thereby control or regulate fluid flow through the main conduit. The butterfly element may be rotatable about an axis through the centre of the conduit e.g. about an axis coinciding with a diameter of the main conduit. The butterfly element may therefore comprise a shaft for rotation about the axis. The axis may be perpendicular to the direction of fluid flow through the main conduit during use. The butterfly element may therefore rotate to control fluid flow through the conduit. Different degrees of rotation may permit (or prevent) different amounts of fluid to flow past the butterfly element along the main conduit. 
     The butterfly element may be shaped to match or complement a cross-section of the main conduit. For example, the butterfly element may be a disc, and the cross-section of the main conduit may be circular. The butterfly element may have an area slightly smaller than the cross-section of the main conduit, so that when it is in the first butterfly element position it closes substantially the entire cross-section of the main conduit. The butterfly element may be generally flat, and may preferably be substantially planar, so that when rotated to the second butterfly element position it obscures as little of the main conduit as possible. However, the butterfly element may have any suitable shape for rotation within the main conduit to thereby control fluid flow. 
     The butterfly controller may be configured to control rotation of the butterfly element between the first butterfly element position (e.g. a fully open position) and the second butterfly element position (e.g. a fully closed position). The actuator may move between a first position at one extreme of its travel (e.g. a fully open position) and a second position at the other extreme of its travel (e.g. a fully closed position). The actuator of the butterfly controller may comprise a piston. The piston may be moveable between a first piston position and a second piston position. The first chamber and the second chamber may be defined as complementary portions of a fluid chamber of the butterfly controller. The piston may be disposed in the fluid chamber. The piston may be disposed between the first chamber and the second chamber. The piston may delimit the first chamber and the second chamber in the fluid chamber. The piston may therefore be exposed to the first and second fluid pressures, and may be moveable in response thereto. 
     The piston may comprise a mechanical connection coupling to the butterfly element to rotate the butterfly element with movement of the piston in the fluid chamber. The connection may rotate the butterfly element by approximately 90° between movement of the piston from the first piston position to the second piston position. The piston (or more generally the actuator) may move (e.g. rotate) the butterfly element by different amounts depending upon its position within the fluid chamber, and therefore depending on the first pressure and second pressure in the respective first and second chambers. Higher pressure in the first chamber may cause the actuator to move to its first position, and thereby rotate the butterfly element to its first butterfly element position. Higher pressure in the second chamber may cause the actuator to move to its second position, and thereby rotate the butterfly element to its second butterfly element position. 
     Thus, the interaction of first and second pressures within the first and second chambers will affect the position of the actuator, and hence will also affect the position of the butterfly element. 
     The relief valve may be a pilot valve, and may be operable with relatively little flow. The relief valve may be fluidly connected to the main conduit upstream of the butterfly element. The relief valve may permit fluid flow to the atmosphere (or otherwise out of the butterfly valve assembly) when the first pressure reaches a predetermined threshold, in order to regulate the first pressure within the predetermined pressure range. The adjustment mechanism may be operable to change the predetermined threshold, and thereby adjust the predetermined pressure range. The adjustment mechanism may hence adjust the first pressure of fluid within the first chamber of the butterfly controller, which in turn will affect the behaviour of the actuator in the fluid chamber, and will thereby affect movement of the butterfly element. 
     The adjustment mechanism of the relief valve may comprise a spring and a tuning screw operable to adjust the pressure at which the relief valves opens, to thereby adjust the predetermined pressure range. The adjustment mechanism of the relief valve may be any suitable mechanism for adjusting operation of the relief valve. The adjustment mechanism of the relief valve may be an adjustable spring. The adjustable spring may be adjustable to change when the predetermined threshold at which the relief valve vents fluid from the butterfly valve assembly. The adjustment mechanism may comprise a spring and a tuning screw operable to change preloading of the spring. The tuning screw may therefore be operable to adjust the predetermined threshold of the relief valve, and thereby adjust the predetermined range of the relief valve. 
     The tuning screw may be located in the butterfly valve assembly so that it is always accessible and adjustable from outside the butterfly valve assembly. The tuning screw may be located on an external surface of the butterfly valve assembly. The tuning screw may be accessible (and therefore adjustable) during use of the butterfly valve assembly. The tuning screw may be arranged so that it is accessible (and therefore adjustable) once the butterfly valve assembly is installed in a wider system. The tuning screw may be arranged so that it is accessible before and after assembly of the butterfly valve assembly. The butterfly valve assembly may be configured so that the tuning screw is adjustable without disassembly of the butterfly valve assembly. The tuning screw may therefore be used to calibrate the butterfly valve assembly, even during use e.g. while the butterfly assembly is installed in an anti-ice system. 
     The butterfly controller may comprise a biasing element arranged to bias the actuator to a first position. The biasing element may be within the first chamber of the butterfly controller. The biasing element may bias the piston to the first piston position, which may be associated with the first butterfly element position e.g. the fully open position. The biasing element may be a spring. Thus, the butterfly controller will tend to move the butterfly element to the fully open position, unless the second pressure of fluid in the second chamber prevents it. 
     The buttery valve assembly may not comprise a means of adjusting or preloading the biasing element directly, the biasing element and/or the butterfly controller can therefore be a simpler than in other assemblies e.g. assemblies that comprise means of adjusting the biasing element. 
     The butterfly valve assembly may comprise a shut-off valve arranged to control the second pressure of fluid in the second chamber of the butterfly controller. The shut-off valve may be fluidly connected to the main conduit downstream of the butterfly element. The shut-off valve may be arranged to provide to the second chamber of the butterfly controller either (i) fluid from the main conduit downstream of butterfly element, or (ii) fluid from a source other than the main conduit downstream of the butterfly element. The fluid from the other source may be at a sufficiently high pressure to cause the actuator to move to its second position and thereby move the butterfly element to its fully closed position e.g. fluid at supply pressure. 
     The shut-off valve may therefore be arranged to switch the butterfly valve assembly between two modes. The first mode may be a regulation mode in which the second pressure of the fluid in the second chamber is indicative of fluid pressure in the main conduit immediately downstream of the butterfly element, and the actuator may therefore be responsive to that pressure in order to regulate fluid flow through the butterfly valve assembly. The second mode may be a shut-off mode in which the butterfly element moves to its fully closed position. 
     The butterfly valve assembly may comprise an orifice fluidly connecting the relief valve to the main conduit at a location upstream of the butterfly element, wherein the orifice is configured to restrict fluid flow through itself. 
     The orifice may be immediately upstream of the butterfly element. The orifice may have a smaller cross-section than either the main conduit, or the line to which it passes fluid. The orifice may therefore be a flow restrictor, and may be a fixed flow restrictor e.g. a restrictor of a fixed size. 
     The orifice may be provided to stabilise operation of the relief valve, and hence stabilise the operation of the butterfly valve assembly. The orifice may reduce the dynamic effect of pressure changes on the relief valve. The orifice may be configured to damped (e.g. reduce the rate of) pressure changes experienced by the relief valve. The orifice may therefore damped pressure changes of the first pressure of fluid in the first chamber. 
     The butterfly valve assembly may comprise another, second orifice fluidly connecting the shut-off valve to the main conduit at a location downstream of the butterfly element. The second orifice may be immediately downstream of the butterfly element. The second orifice may be operable in a similar manner to the first orifice and may comprise analogous features. The second orifice may be configured to damped pressure changes of the second pressure of the fluid in the fluid in the second chamber. 
     The first and second orifices may therefore be configured (e.g. sized) to limit flow therethrough and thereby reduce the rate of pressure changes in the first and second chambers compared to the rate of pressure changes in the main conduit. 
     The butterfly valve assembly may comprise a manual override operable to lock the butterfly element in a fully open position or a fully closed position. The manual override may be operable to restrict movement of the butterfly element. 
     The manual override may be operable to lock the butterfly element in either a fully open configuration or a fully closed configuration, depending on its arrangement. That is, the manual override may be operable to lock the butterfly element in either or both of a fully open and fully closed configuration (albeit at different times—i.e. not both configurations at once). The manual override can therefore be used to fix the butterfly element in its fully open position, and to fix the butterfly element in its fully closed position. Thus, the automatic pressure regulation of the butterfly valve assembly can be overridden. 
     The manual override may comprise an override shaft rotatable between a first neutral position in which rotation of the butterfly element relative to the override shaft is permitted, and a second override position in which rotation of the butterfly element relative to the override shaft is prevented by interaction of part of the butterfly element with part of the override shaft. 
     Thus, the override shaft may be rotated to bring a portion thereof into engagement with a portion of the butterfly element to thereby constrain rotation of the butterfly element. 
     The axis of rotation of the override shaft may be coaxial with the axis of rotation of the butterfly element. The override shaft may be disposed around a shaft the butterfly element. 
     The manual override shaft may be rotatable to a third override position in which rotation of the butterfly element relative to the override shaft is prevented by interaction of part of the butterfly element with part of the override shaft. 
     The override shaft may comprises a slot and the butterfly element comprises a pin constrained within the slot, wherein in the first neutral position the pin is permitted to move by rotation of the butterfly element within the slot, and wherein in the second override position the slot is rotated relative to the butterfly element so that the pin abuts a first abutment surface of the slot. 
     The pin may be rigidly coupled to the butterfly element, and may be spaced from the axis (e.g. spaced from the shaft) about which the butterfly element rotates, so that rotation of the butterfly element causes the pin to move along an arc of a circle. When the override shaft is in the first neutral position, that movement of the pin is accommodated by the slot, which slot may be arcuate or curved to permit free movement of the pin therein. The range of movement of the pin may be limited by the range of movement of the butterfly element e.g. between its first fully open position and its second fully closed position. 
     In the second override position, the slot of the override shaft is rotated relative to the butterfly element and the pin, and therefore reduces the range of movement of the pin. The override shaft may then be rotated until the first abutment surface (e.g. a first end of the slot) contacts the pin, thereby preventing movement of the pin using the first abutment surface. When the butterfly element is in its first fully open position, the pin cannot move in one direction because the butterfly element cannot rotate in that direction, and cannot move in the other direction because the first abutment surface of the slot prevents it. 
     In the third override position, the slot is rotated relative to the butterfly element in the opposite direction, and therefore reduces the range of movement of the pin in the other direction. The override shaft is then rotated until a second abutment surface (e.g. a second end of the slot) contacts the pin, thereby preventing movement of the pin using the second abutment surface. When the butterfly element is in its first fully closed position, the pin cannot move in one direction because the butterfly element cannot rotate in that direction, and cannot move in the other direction because the second abutment surface of the slot prevents it. 
     Although the manual override described in detail herein comprises the slot in the override shaft and the pin as part of the butterfly element, other arrangements may be possible. 
     The butterfly valve assembly may comprise a locking key urged against the override shaft and received in a first recess therein when the override shaft is in the first neutral position. 
     The locking key may be urged by any suitable biasing mechanism such as a locking spring. To rotate the override shaft, sufficient force must be applied to push the locking key back against the urging force and cause it to leave the first recess. 
     The override shaft may comprise a second recess, wherein in the second override position the locking key is received by the second recess. The override shaft may comprise a third recess, wherein in the third override position the locking key is received by the third recess. 
     The override shaft may therefore be held in the second and third override positions by action of the locking key urged into the second and third recesses. The locking key may be held with sufficient force in the recesses so that the override shaft will not be rotated by action of the pin against the first or second abutment surface. 
     The locking key may ensure that the override shaft is rotated to one of the first neutral position, the second override position, or the third override position. When the override shaft is rotated to one of the above positions, the locking key will be received by the corresponding recess and prevent further rotation without the use of additional force. A user can therefore be confident that the override shaft (and therefore the butterfly element) is in the desired position. 
     The use of a manual override is particularly advantageous for a butterfly valve assembly as described herein, because the assembly lacks an electronic controller that easily allows the valve to be controlled. Thus, despite the lack of an electronic controller or other electronic supervision of the butterfly valve assembly (and particularly of the butterfly element), the assembly can simply and reliable be closed or opened as needed. 
     In fact, the provision of a manual override in the butterfly valve assembly is considered novel and inventive in its own right. Thus, according to a second aspect of the invention there is provided a butterfly valve assembly comprising a butterfly element configured to control fluid flow through a main conduit; and a manual override operable to lock the butterfly element in a fully open position or a fully closed position. 
     The butterfly valve assembly may comprise a butterfly controller configured to control the butterfly element, comprising a first chamber for receiving fluid at a first pressure, a second chamber for receiving fluid at a second pressure, and an actuator responsive to the first pressure and the second pressure; and a relief valve arranged to regulate the first pressure in the first chamber within a predetermined pressure range, wherein the relief valve comprises an adjustment mechanism for adjusting the predetermined pressure range. 
     The butterfly valve assembly of the second aspect of the invention may comprise any of the features described herein with reference to the first aspect of the invention. In particular, the butterfly valve assembly of the second aspect of the invention may comprise the features of the manual override described herein with reference to the first aspect of the invention. 
     The butterfly valve assembly may be an integrated butterfly valve assembly. The assembly may comprise a housing, and the butterfly element, the butterfly controller, and the relief valve may be within the housing. The shut-off valve may be within the housing. The assembly may therefore be a single, unitary product. 
     According to a third aspect of the present invention there is provided an anti-ice system, for example for an aircraft, comprising a butterfly valve assembly. The butterfly valve assembly may a butterfly valve assembly as described herewith with reverence to the first and/or second aspect of the present invention, and may therefore comprise any and/or all of the features described herein with reference to those aspects. 
     According to a fourth aspect of the invention there is provided an aircraft comprising an anti-ice system as recited herein with reference to the third aspect of the invention. 
     According to a fifth aspect of the present invention there is provided a method of manually locking a butterfly element of a butterfly valve assembly in a fully open position and/or a fully closed position, comprising operating a manual override to bring a part of the manual override into contact with a part of the butterfly element to thereby prevent movement of the butterfly element using the manual override. 
     The method may comprise providing the butterfly element with a pin, and providing an override shaft of the manual override with a slot so that movement of the pin is constrained within the slot. The method may comprise rotating the override shaft relative to the pin, to thereby reduce the range of movement of the pin. The method may comprise rotating the override shaft in a first direction to prevent movement of the pin in an opposite, second direction. The method may comprise rotating the override shaft in the second direction to prevent movement of the pin in the opposite, first direction. The method may comprise rotating the override shaft in a first direction to bring a first abutment surface of the slot into contact with the pin and thereby prevent movement of the pin using the first abutment surface. The method may comprise rotating the override shaft in a second direction to bring a second abutment surface of the slot into contact with the pin and thereby prevent movement of the pin using the second abutment surface. 
     The method may comprises using the butterfly valve assembly and/or any of its features as recited herein with reference to the first aspect of the invention and/or the second aspect of the invention. The method may comprise using an anti-ice system and/or any of its features as recited herein with reference to the third aspect of the invention. The method may comprise using an aircraft and/or any of its features as recited herein with reference to the fourth aspect of the invention. 
    
    
     
       FIGURES 
       Certain preferred embodiments of the invention are described below by way of example only and with reference to the accompanying drawings in which: 
         FIG. 1  shows butterfly valve assembly for regulating downstream fluid pressure; 
         FIG. 2A  shows a cross-section through the butterfly valve assembly of  FIG. 1  in a first configuration; 
         FIG. 2B  shows the cross-section of  FIG. 2A  with the butterfly valve assembly in a second configuration; 
         FIG. 3  shows a plot illustrating a regulation band of the butterfly valve assembly; 
         FIG. 4  shows a schematic of the butterfly valve assembly of  FIGS. 1, 2A and 2B ; 
         FIG. 5  shows the schematic of  FIG. 4  during use; 
         FIG. 6  shows a schematic of a manual override for locking the butterfly valve assembly in an open positon or a closed position; 
         FIG. 7A  shows the manual override of  FIG. 6  with a partial cut-away, showing the butterfly valve assembly in a fully open configuration; and 
         FIG. 7B  shows the manual override of  FIGS. 6, and 7A  with a partial cut-away, showing the butterfly valve assembly in a fully closed configuration. 
     
    
    
     DESCRIPTION 
       FIG. 1  shows an anti-ice butterfly valve assembly  100  for regulating downstream pressure of a main conduit  102 . The assembly  100  preferably regulates the downstream pressure within a predetermined regulation band. The butterfly valve assembly  100  comprises an integrated butterfly controller  120 , integrated pressure relief valve  130 , and integrated shut-off valve  140 . The assembly  100  is therefore a single unit in which the components described herein are installed e.g. within a housing. 
       FIG. 2A  shows a cross-section through the butterfly valve assembly  100  when the butterfly valve assembly  100  is in a first configuration e.g. a fully open configuration. The butterfly controller  120  comprises a first chamber  122  and a second chamber  124 , each of which receives fluid at a particular pressure from the main conduit  102 , as explained in more detail below with reference to the  FIG. 4 . The butterfly controller  120  also includes a piston  126  comprising a connection  128 . The piston  126  and connection  128  are moveable in response to a pressure difference between the first chamber  122  and the second chamber  124 . The butterfly controller  120  also comprises a spring  125  in the first chamber  122 , which spring  125  is arranged to urge the piston  126  and connection  128  into a first position (as shown in  FIG. 2A ). When the force of the spring  125  and the force from pressurised fluid in the first chamber  122  are together greater than the force from the pressurised fluid in the second chamber  124 , the piston  126  moves towards the first position, typically its fully open position so that the butterfly valve assembly  100  permits as much fluid as possible through the main conduit  102 . As can be seen from  FIG. 2A , the first chamber  122  and second chamber  124  are complementary divisions of a larger fluid chamber  121  in which the piston  126  moves during use. 
       FIG. 2B  shows the configuration of the butterfly valve assembly  100  when pressure in the second chamber  124  increases so the force therefrom on the piston  126  overcomes the combined force from the spring  125  and fluid pressure in the first chamber  122 . Consequently, the piston  126  and connection  128  move to a second position, depicted in  FIG. 2B . 
     The connection  128  mechanically couples the piston  126  to a shaft  112  of a butterfly element  110  (see  FIG. 3 ) in the conduit  102 , so that movement of the piston  126  and connection  128  rotate the shaft  112  about its axis (the axis is substantially normal to the page as shown in  FIGS. 2A and 2B ), and thereby rotate the butterfly element  110  in the conduit  102 . The butterfly element  110  is a disc disposed within the conduit  102 , and the shaft  112  extends substantially along a diameter of the disc and a cross-section of the main conduit  102 . The area of the butterfly element  110  is only slightly smaller than the cross-section of the main conduit  102 , so that different degrees of rotation of the butterfly element  110  cause it to cover or block different amounts of the cross-section of the main conduit  102 . When the butterfly element  110  is rotated to substantially cover the entire cross-section of the main conduit  102 , the butterfly valve assembly  100  is in its fully closed position, since the butterfly element  110  prevents as much fluid flow through the main conduit  102  as possible. When the butterfly element  110  is rotated by approximately 90° to its fully closed orientation, it covers or blocks as little of the cross-section of the main conduit  102  as possible (and instead extends as far as possible along the length of the main conduit  102 ), and the butterfly valve assembly  100  is in its fully open configuration, since the butterfly element  110  permits as much fluid flow through the main conduit  102  as possible. 
     In  FIG. 2A , the shaft  112  and butterfly element  110  are in the fully open position, and in  FIG. 2B , the shaft  112  and butterfly element  110  are rotated to the fully closed position. In the second position shown in  FIG. 2B , the connection  128  abuts an adjustment screw  170  provided to limit movement of the connection  128  and thereby limit rotation of the shaft  112  and butterfly element  110 . In the first position shown in  FIG. 2A , the piston  126  abuts the end of the second chamber  124  to thereby limit rotation of the shaft  112  and butterfly element  110  in the other direction. 
     Thus, the balance of pressures in the first chamber  122  and second chamber  124  against the piston  126 , together with the spring  125 , control movement of the piston  126  and the connection  128 , which in turn controls the rotational position of the shaft  112  and butterfly element in the main conduit  102 . The butterfly element  110  is thereby rotated to open, regulate, or close the main conduit  102 . Depending on the position of the piston  126  in the fluid chamber  121 , and hence the degree of rotation of the butterfly element  110 , different amounts/rates of fluid will be permitted through the conduit  102  by the butterfly element  110 . 
     In conventional assemblies, since the spring of the butterfly controller is fundamental to the movement of the piston (and hence to the opening and closing of the butterfly element) it must be carefully calibrated and tuned during installation to ensure that the butterfly element rotates as desired, and thereby regulates fluid flow through the conduit as needed. The spring is therefore typically provided with a means to adjust it, such as a means to adjust preloading of it. However, the spring is relatively large and is necessarily located within the butterfly controller, so it is difficult to access and calibrate. This leads to imprecision in the operation of the piston, which then manifests as a relatively wide regulation band within which the butterfly assembly controls the pressure. 
       FIG. 3  shows a plot with an example of the regulation band  300  for the butterfly valve assembly  100 . The different lines on the plot show the relationship between an input pressure  310  to the butterfly valve assembly  100  and an output pressure  320  from the butterfly valve assembly  100  for different temperatures. For low input pressures  310 , the output pressure  320  increases approximately constantly with the input pressure  310 . However, once the input pressure  310  reaches a threshold  302  (shown approximately), the butterfly valve assembly  100  regulates the output pressure  320  within the regulation band  300  indicated approximately by the arrows. Thus, as the input pressure  310  increases beyond the threshold  302 , the butterfly valve assembly  100  maintains the output pressure  320  within the regulation band. As the input pressure  310  drops, the output pressure  320  is maintained within the regulation band  300 , but need not take the same value it did when the input pressure was increasing. The regulation band  300  can therefore be thought of a the limits of the hysteresis described by the progression of output pressure  320  with respect to input pressure  310 . In general, significant variation of regulated output pressure  320  for a given input pressure  310  is undesirable, and it is therefore preferable to make the regulation band  300  as narrow as possible i.e. to control the output pressure  320  based on the input pressure  310  as precisely as possible. 
     To narrow the regulation band  300 , to improve control over operation of the butterfly controller  120 , and hence over the rotation of the butterfly element  110  and the pressure regulation of the butterfly valve assembly  100 , the butterfly valve assembly  100  comprises a relief valve  130  arranged to regulate pressure within the first chamber  122  of the butterfly controller  120 . The relief valve  130  is a pilot valve that works on relatively little flow. As seen in  FIGS. 1, 2A and 2B , it is located on an outer surface of the butterfly valve assembly  100  and is therefore accessible and adjustable after assembly and/or installation of the butter valve assembly  100 . The relief valve  130  comprises a spring  132  and a tuning screw that is accessible once the butterfly valve assembly  100  has been assembled. As such, the relief valve  130  may be adjusted during use (i.e. during pressure regulation) of the butterfly valve assembly  100 . 
       FIG. 4  shows a schematic of the butterfly valve assembly  100 . The butterfly element  110  is disposed within the main conduit  102 , and is rotatable about its shaft  112  to open, regulate, and close the main conduit  102  depending on its rotational position. The piston  126  of the butterfly controller  120  is mechanically coupled to the shaft  112  of the butterfly element  110  by the connection  128  as described above. Movement of the piston  126  is determined by the pressure difference between the first chamber  122  and the second chamber  124 , together with the spring  125 . 
     The assembly  100  also includes the relief valve  130  fluidly connected to the main conduit  102  upstream of the butterfly element  110  via an orifice  104 . The relief valve  130  is also fluidly connected to the first chamber  122  of the butterfly controller  120 , so as to regulate pressure therein. The relief valve  130  will crack when pressure in the line  105  increases beyond a predetermined threshold which is set by a spring  132  of the relief valve  130 , together with a tuning screw  134 . Thus, the relief valve  130  will prevent pressure in the first chamber  125  increasing beyond the predetermined threshold. The relief valve  130  therefore decouples pressure in the line  105  and the first chamber  122 , from the pressure in the main conduit  102  upstream of the butterfly element  110 . 
     Moreover, the spring  132  of the relief valve  130  is adjustable by action of the tuning screw  134 , and is smaller and therefore more easily tuned than the spring  125  of the butterfly controller  120 . Further, the tuning screw  134  is accessible even after assembly of the butterfly valve assembly  100 , so calibration and tuning of the valve assembly  100  can be simply accomplished. As a consequence, pressure in the first chamber  122  of the butterfly controller  120  can be regulated by use of the tuning screw  134  the relief valve  130  as needed, instead of e.g. tuning a spring analogous to the spring  125  of the butterfly controller  120 . Thus, the regulation band  300  of the butterfly valve assembly  100  can be tighter than for conventional butterfly valve assemblies. 
     The orifice  104  is a fixed orifice and can be sized to provide a predetermined restriction of fluid flow (and hence of pressure drop). It also helps dampen the response of the butterfly valve assembly  100 , so that pressure regulation is smooth. That is, the orifice  104  reduces the rate of pressure changes in the portion of the circuit comprising the first chamber  122  and relief valve  130 , relative to pressure changes in the main conduit  102 . The orifice  104  therefore helps to stabilise operation of the relief valve  130 , the first pressure in the first chamber  122 , and thereby the operation of the entire butterfly valve assembly  100 . The orifice  104  may be a fixed size, and is narrower than the main conduit and the line  105  that it connects. It thereby restricts fluid flow from the main conduit  102  to the line  105  and reduces the dynamic effects of pressure changes on the relief valve  130  and the first pressure in the first chamber  122 . 
     The butterfly valve assembly  100  also comprises a shut-off valve  140 , which controls fluid flow to the second chamber  124  of the butterfly controller  120 . The shut-off valve is actuated by a solenoid  142  between a first position and a second position, and is fluidly connected by a line  107  to the main conduit  102  downstream of the butterfly element  110 , via a second orifice  106 . The shut-off valve  140  is also fluidly connected to a line containing fluid at supply pressure. The solenoid  142  is therefore operable to switch between supplying fluid to the second chamber  124  from the line  107 , or supplying fluid to the second chamber  124  from the line at supply pressure. The force on the piston  126  from the fluid at supply pressure will always be greater than the combined force from the spring  125  and regulated fluid pressure in the first chamber  122 , and therefore when the shut-off valve  140  is configured to provide to fluid at supply pressure to the second chamber  124 , the piston  126  will be moved to its second position, rotating the butterfly element  110  to close the main conduit  102 . The shut-off valve  140  is therefore simply operable to move the butterfly valve assembly  100  to its fully closed configuration. It can also be operated to move the butterfly valve assembly  100  to a regulated mode in which the pressure in the second chamber  124  is related to output pressure  320  of the assembly  100 , so that the output pressure  320  is automatically regulated by movement of the piston  126 . 
     Similarly to the orifice  104 , the orifice  106  is of a fixed size and is configured to provide a predetermined restriction of fluid flow (and hence a pressure drop). It also helps dampen the response of the butterfly valve assembly  100 , so that pressure regulation is smooth. 
       FIG. 5  shows the schematic of  FIG. 4  with exemplary pressures indicated. Upstream of the butterfly element  110  in the main conduit  102 , fluid pressure is at supply pressure P SUPPLY . Pressure in the line  105  and first chamber  122  is at P REG , and is controlled by the relief valve  130  with the adjustable spring  132 . The pressure in line  107  and the second chamber  124  is indicative of the pressure P OUT . 
     During use, as the pressure P SUPPLY  in the main conduit  102  upstream of the butterfly element  110  increases from ambient pressure P AMB , the pressure P REG  increases approximately in line with P SUPPLY . Once P REG  approaches the predetermined threshold set by the adjustable spring  132  and tuning screw  134 , the relief valve  130  operates to prevent further pressure increase, thereby constraining P REG  to below the predetermined threshold, causing its increase to plateau. The pressure P REG  in the first chamber  122  then acts (together with the force from the spring  125 ) on the piston  126  against the pressure P OUT  in the second chamber  124 . 
     If the pressure P OUT  downstream of the butterfly element  110  increases (e.g. because P SUPPLY  increases), then the force on the piston  126  in the second chamber  124  will increase compared to the pressure P REG  in the first chamber  122  regulated by the relief valve  130 . The piston  126  will therefore move towards the second position, rotating the butterfly element  110  towards its closed position and thereby reducing fluid flow through the main conduit  102 . Thus, P OUT  will be decreased and the downstream pressure will be controlled (e.g. as shown in  FIG. 3 ). 
     If on the other hand, the pressure P OUT  decreases compared to the pressure P REG , then the piston  126  will be moved towards its first position, opening the butterfly element  110  more, and thereby increasing the fluid flow through the conduit  102  and subsequently raising the pressure P OUT . The pressure P REG  will change more slowly than the pressure P SUPPLY  because the orifice  104  will dampen the changes. 
     The butterfly valve assembly  100  may therefore regulate downstream pressure automatically. The provision of the adjustable spring  132 , which is easier to adjust than the spring  125  because the tuning screw  134  is at an external surface of the assembly  100  and accessible during use, allows the regulation of pressure P REG  so that the operation of the butterfly controller  120  is more easily controlled. It is also easier to calibrate the assembly  100  after installation in e.g. an anti-ice system. 
     The butterfly valve assembly  100  may not have any electronic components except for the solenoid  142 , and can therefore be used in higher temperature environments than e.g. electrically driven, motor controlled butterfly valves. 
     Although the butterfly valve assembly  100  can automatically regulate pressure, it is sometimes desirable to manually override that function.  FIG. 6  shows a schematic of a manual override  200  for the butterfly valve assembly  100 . The manual override  200  is provided with the shaft  112  of the butterfly element  110 , and comprises a manual override shaft  212  disposed about the shaft  112 , and rotatable relative thereto. The manual override shaft  212  also comprise an arcuate (curved) slot  220  defined therein. A pin  114  is constrained within the slot  220 . The pin  114  is adjacent the shaft  112  and rigidly coupled to the butterfly element  110  and/or shaft  112  so that it rotates therewith about the same axis as the shaft  112  and butterfly element  110 . The pin  114  is therefore off-axis. Since, the pin  114  is spaced a fixed distance from the axis about which the shaft  112  rotates, when the butterfly element  110  rotates, the pin  114  moves along an arc, all the while being constrained within the slot  220  of the override shaft  212 . 
       FIG. 6  shows a schematic of the configuration of the manual override  200  when the butterfly valve assembly  100  is operating as normal i.e. automatically regulating downstream pressure  320 . The butterfly element  110  is partially open, rotated about half-way between its fully open position and its fully closed position. The pin  114  is therefore approximately mid-way along the slot  220 . 
     A locking key  230  is biased by a locking spring  232  against the override shaft  212 , and mates with a first recess  214  on the outer surface of the override shaft  212  to thereby hold the override shaft  212  (and hence also the slot  220 ) in the position shown. 
     When the butterfly element  110  rotates to its fully open position, the pin  114  travels within the slot  220  to the position indicated by the dashed outline  114   a . When the butterfly element  110  rotates to its fully closed position, the pin  114  travels within the slot  220  to the position indicated by the dashed outline  114   b.    
     As described above, the movement of the butterfly element  110  is constrained by the travel of the piston  126  and connection  128 . In its first position, the piston  126  abuts the end of the second chamber  124  and therefore prevents further rotation of the butterfly element  110  in that direction. In its second position, the connection  128  abuts the adjustment screw  170 , thereby preventing further rotation of the butterfly element  110  in that direction. (The adjustment screw  170  is provided to calibrate the travel of the butterfly element  110  after assembly of the butterfly valve assembly  100 .) 
     The override shaft  212  is rotatable about the same axis of rotation as the shaft  112  of the butterfly element  110  (the axis is normal to the page in  FIG. 6 ). To manually override the position of the butterfly element  110 , the override shaft  212  is rotated about its axis (normal to the page in  FIG. 5 ) in the desired direction, so that the pin  114  abuts a first abutment surface  222  of the slot  220 , or a second abutment surface  224  of the slot  220 . 
       FIG. 7A  shows the manual override  200  with a partial cut-away (so the figure shows two different depths of the manual override  200  within the assembly  100 ). The pin  114  has been rotated clockwise about the shaft  112  by rotation of the butterfly element  110  so that it has moved to its fully open position  114   a . In  FIG. 7A , the override shaft  212  is in its neutral position, allowing automatic pressure regulation by the assembly  100  (i.e. not manually overriding the rotation of the butterfly element  110  and pressure regulation progress described above). The pin  114  cannot travel further in the clockwise direction because the piston  126  is in abutment with the far end of the second chamber  124 . 
     To lock the butterfly element  110  in the fully open position, the override shaft  212  is rotated in the clockwise direction, rotating the slot  220  clockwise until the first abutment surface  222  contacts the pin  114 . The pin  114  then cannot travel in the anticlockwise direction because it is prevented by contact with the first abutment surface  222  of the slot  220 . The pin  114  is therefore held stationary, and since the pin  114  is rigidly connected to the butterfly element  110  and/or shaft  112 , the butterfly element  110  is locked in the fully open position. 
     As a force is applied to rotate the override shaft  212  in the clockwise direction, the locking key  230  is forced from the first recess  214  and pushed in against the action of the locking spring  232 . The override shaft  212  then rotates until a second recess  216  reaches the locking key  230  and the locking key  230  is urged into the second recess  216  by the locking spring  232 . The force from the locking spring  232  acting to hold the locking key  230  in the second recess  216  is sufficient to prevent unwanted rotation of the override shaft  212  e.g. by force from the pin  114  acting on the first abutment surface  222 . 
       FIG. 7B  shows the manual override  200  with the same partial cut-away as shown in  FIG. 7A . In the depicted case though, the butterfly element  110  has been rotated anticlockwise about the shaft  112  so that it has moved to its fully closed position  114   b . The pin  114  cannot travel further in the anticlockwise direction because the connection  128  is in abutment with the adjustment screw  170 . 
     To lock the butterfly element  110  in the fully closed position, the override shaft  212  is rotated in the anticlockwise direction, rotating the slot  220  anticlockwise until the second abutment surface  224  contacts the pin  114 . The pin  114  then cannot travel in the clockwise direction because it is prevented by the second abutment surface  224  of the slot  220 . The pin  114  is therefore held stationary, and since the pin  114  is rigidly connected to the butterfly element  110  and/or shaft  112 , the butterfly element  110  is locked in the fully closed position. 
     Similarly to the process described above for locking the override shaft  212  in the manual override fully open position, as a force is applied to rotate the override shaft  212  in the anticlockwise direction, the locking key  230  is forced from the first recess  214  and pushed in against the action of the locking spring  232 . The override shaft  212  then rotates until a third recess  218  reaches the locking key  230  and the locking key  230  is urged into the third recess  216  by the locking spring  232 . The force from the locking spring  232  acting to hold the locking key  230  in the third recess  218  is sufficient to prevent unwanted rotation of the override shaft  212  e.g. by force from the pin  114  acting on the second abutment surface  224 . 
     Thus, the butterfly element  110 , and hence the butterfly valve assembly  100 , can be manually overridden by the manual override  200  so that it is locked in the fully open position or the fully closed position. The provision of the first, second and third recesses  214 ,  216 ,  218  also ensures that a user will rotate the override shaft  212  to the desired position, because the user will feel the locking key  230  slip into place in the relevant recess. 
     The override shaft can  212  be rotated by any suitable means, for example using a square key at one end (e.g. having a square recess for receiving the key extending from the assembly  100 ), a handle, a lever, or the like. The use of a key may be preferred to ensure that the manual override is not engaged inadvertently.