Patent Description:
Anti-ice systems for aircraft are used to deliver heated air to aircraft surfaces to prevent or reduce ice build-up e.g. to the leading edge of a wing or an engine nacelle. They comprise valves operable to regulate the delivery of the heated air, and different type of valve can have different advantages and disadvantages.

For example, butterfly valves have a relatively high maximum mass flow rate when they are fully open compared to other types of valves, and such high mass flow rate can be preferable during engine start-up to deliver as much hot air as quickly as possible. As such, butterfly valves are often preferred. However, butterfly valves are less capable than other types of valve in maintaining linearity throughout their operational ranges, and are therefore less desirable at higher mass flows.

<FIG> shows a valve assembly <NUM>, comprising a valve body <NUM>, defining a valve inlet <NUM> and a valve outlet <NUM>. The valve assembly <NUM> includes a shut-off piston <NUM> for shutting off mass flow to the outlet <NUM> from the inlet <NUM>, and a regulating piston <NUM> for regulating the amount of mass flow through the valve assembly <NUM> based on downstream pressure e.g. pressure downstream of the outlet <NUM>. During use, the regulating piston <NUM> will be moved depending on a pressure difference between downstream pressure and pressure in a regulating chamber 14a, which in turn will change the amount of mass flow through the valve assembly <NUM>.

The valve assembly <NUM> of <FIG> is generally better than a butterfly valve at maintaining linearity for higher mass flows, but is less capable of high-mass flow at lower ranges. Conversely, butterfly valves are generally more capable of providing high-mass flow at lower mass-flow ranges, but are less capable of linear regulation of output pressure based on input pressure than are valves such as the valve assembly of <FIG>. Improvements for pressure-regulating valves are therefore desirable.

<CIT> discloses a non-return valve and a safety fitting to prevent contamination of drinking water by non-potable water due to backflow. The safety fitting comprises: a first non-return valve comprising a cup-like element, and a second non-return valve. The second non-return valve is integrated into the bottom of the cup-like element, so that it is connected in parallel to the first non-return valve.

<CIT> discloses a regulating piston for a pressure regulating shut-off valve, a pressure regulating shut-off valve comprising such a regulating piston, and methods of manufacturing such a regulating piston and pressure regulating shut-off valve. With reference to the subject-matter of claim <NUM>, the document <CIT> does not disclose a piston corresponding to the first piston.

<CIT> discloses a backflow preventer device and its working method which can adjust the positive pressure difference and flow resistance of the return seat.

According to a first aspect of the invention there is provided a valve assembly for an anti-ice system of an aircraft, comprising: a valve body; a first piston; and a regulating piston; wherein the valve body defines a valve inlet, a valve outlet, a fluid passage between the valve inlet and the valve outlet, and a core portion defining a first chamber by cooperation with the first piston and a regulating chamber by cooperation with the regulating piston; wherein the first piston is moveable between a first position and a second position; wherein the regulating piston comprises an inlet port arranged to permit fluid flow between the exterior and interior of the regulating piston, and an outlet arranged to permit fluid flow from the interior of the regulating piston to the valve outlet, the regulating piston being movable between a first position in which the inlet port permits fluid flow between the valve inlet and the valve outlet via the fluid passage and the interior of the regulating piston, and a second position in which the inlet port is located within the core portion of the valve body so that the regulating piston prevents fluid flow from the valve inlet to the valve outlet; and wherein the first piston overlaps the regulating piston when the first piston is in its first position and the regulating piston is in its second position.

The regulating piston may therefore be at least partially inside the first piston in at least one configuration of the valve assembly. The regulating piston may be partially inside the first piston in multiple configurations of the valve assembly, for example the regulating piston may be partially inside the first piston when the regulating piston is in its first position and when the regulating piston is in its second position. Alternatively, the regulating piston may not be inside the first piston when the regulating piston is in its first position. For example, the first piston may comprise a substantially tubular portion (e.g. a skirt portion) that is large enough to permit one end of the regulating piston to be within the volume delimited by the first piston. Thus, the first piston may be wider than the regulating piston e.g. have a greater radial extent e.g. in a direction perpendicular to a direction between the valve inlet and the valve outlet. The first piston may therefore be sized so that a portion of the regulating piston may be accommodated in the volume within the first piston. Thus, the first piston and the regulating piston may be provided in a nested arrangement.

As a consequence of the overlap of the first piston and the regulating piston, the first piston and/or the regulating piston may have a greater stroke length within the valve assembly compared to prior valve assemblies, e.g. because the stroke length of one piston does not need to affect (e.g. limit) the stroke length of the other piston (see e.g. <FIG> where a shut-off piston <NUM> and a regulating piston <NUM> are arranged end-to-end so that they each limit the distance the other can travel). As a consequence of the increased stroke length of the first piston and/or the regulating piston, the valve assembly may have an increased maximum airflow e.g. in its fully open configuration.

The first piston and the regulating piston may be co-axial. The valve assembly may therefore comprise a dual co-axial piston configuration with overlapping dual pistons. The first piston may be another regulating piston and may be movable to any location between its first position and its second position to regulate fluid flow through the valve assembly. However, the first piston may also be a shut-off piston. The shut-off piston may be moveable between its first position in which it permits fluid flow through the valve assembly, and its second position in which it prevents fluid flow through the valve assembly. The first piston is disposed to open and/or close the valve inlet. The first piston may open the valve inlet in its first position, and may close the valve inlet in its second position. The first position of the first piston may therefore be a fully open positon, and the second position of the first piston may be a fully closed position.

Pressure in the first chamber may urge the first piston to its second position, away from its first position e.g. during use of the valve assembly. The first piston may therefore be actuable by controlling (e.g. increasing) pressure in the first chamber. The valve assembly may be arranged to pressurise the first chamber in order to move the first piston from its first position to its second position. For example, a solenoid valve may be provided as part of the valve assembly and may be operable to supply fluid (e.g. from the valve inlet or upstream thereof) to pressurise the first chamber and thereby actuate the first piston. The solenoid valve may be operable to prevent fluid flow to the first chamber to prevent the first chamber from being pressurised. The first chamber may therefore be a shut-off chamber i.e. operable to shut-off fluid flow through the valve assembly using the first-piston.

The first piston may comprise an end face that closes and substantially seals the valve inlet when the first piston is in its second position. The first piston may seat against an interior surface of the valve body to prevent fluid flow from the valve inlet passing through the valve along the fluid passage. The whole of the end face may be exposed to fluid in the fluid passage from the valve inlet to the valve outlet. During use, pressure acting at the valve inlet may urge the first piston to its first position (e.g. open position), counteracting pressure in the first chamber. The valve assembly may be arranged so that pressure at the valve inlet acts on the whole of the end face of the first piston to urge it to its first position. Therefore, the first piston may be more responsive to pressure at the valve inlet than prior valve assemblies that include a nose portion and an associated nose chamber at ambient pressure (see e.g. the valve assembly of <FIG>). Indeed, the entire outermost surface of the first piston may be exposed to mass flow in the fluid passage between the valve inlet and the valve outlet.

The regulating piston and the first piston may be tubular and may be substantially cylindrical. The regulating piston may have a smaller width (e.g. diameter) than the first piston. The smaller diameter of the regulating piston may therefore enable it to move inside the first piston, at least in the second position of the regulating piston. Thus, the regulating piston may be narrower than the first piston.

When the regulating piston is in its first position, fluid may flow during use from the exterior of the regulating piston to the interior of the regulating piston, then may flow out of the outlet of the regulating piston to the valve outlet. Thus, the interior of the regulating piston may provide part of the fluid passage between the valve inlet and the valve outlet. The first position of the regulating piston may therefore be a fully open position e.g. allowing as much fluid flow into the regulating piston as possible. In the second position, the regulating piston may be arranged so that fluid flow from the valve inlet is prevented from flowing from the exterior of the regulating piston into its interior, for example by a portion of the valve body e.g. the (stationary) core portion providing the regulating chamber. The second position of the regulating piston may therefore be a fully closed position e.g. preventing as much fluid flow into the regulating piston as possible. The regulating piston may be moveable to any position between its first position and its second position. During use, the regulating piston may be movable to different positions in response to a pressure difference between upstream and downstream, and may thereby regulate fluid flow through the valve assembly. In particular, the regulating piston may move in response to a pressure differential between the regulating chamber and the fluid passage e.g. across an upstream end of the regulating chamber.

The regulating piston may be supported for movement within the valve body e.g. by the core portion and an outlet portion of the valve body (e.g. a portion of the valve body defining the valve outlet). The regulating portion may therefore bridge a gap in the valve body between the core portion and the outlet portion. The regulating piston may always bridge the gap between the core portion and the outlet portion e.g. in its first position and in its second position. As such, the valve assembly may be arranged so that no part of the valve body is within the regulating piston. This arrangement may allow the interior of the regulating piston to provide a relatively unobstructed portion of the fluid passage, and thereby allow as much fluid flow through the fluid passage as possible. Thus, there may be nothing within the regulating piston that is not part of the regulating piston itself, and hence moveable rigidly therewith. The regulating piston may be supported for movement within the valve body by contact with the valve body on its outer surface, and may be so supported only by contact on its outer surface. In contrast, the first piston may be supported for movement by contact with the valve body on an inner surface, and may be so supported only by contact with the valve body on the inner surface. This arrangement may therefore permit the regulating piston to be disposed within the first piston, each supported for movement by the core portion of the valve body.

The regulating piston may be received by and/or mounted within the core portion of the valve body, and may slide and/or move glidingly in the core portion during use. The regulating chamber may be defined between the core portion of the valve body and an end of the regulating piston. The core portion may enclose the regulating chamber. The regulating chamber may therefore be defined by the volume within the core portion and delimited by the regulating piston. The regulating chamber may therefore be entirely with the core portion. The regulating chamber may therefore be defined by cooperation of the regulating piston with an inner (e.g. inward facing) surface of the core portion. The regulating chamber may be at least partially (and may be mostly or wholly) inside the first piston when the first piston is in its first position. The first piston may therefore be disposed about the regulating chamber e.g. in its first position.

The core portion may be surrounded by the fluid passage from the valve inlet to the valve outlet, and may be entirely surrounded by the fluid passage. The core portion may be within the fluid flow passage e.g. fluid may flow around the core portion during use, between the valve inlet and the valve outlet. The core portion may be entirely within the rest of the valve body. Put simply, the core portion of the valve body may at the heart (i.e. at the core) of the valve assembly.

The first chamber and the regulating chamber may be fluidly isolated from each other within the valve assembly, and may occupy different, distinct volumes within the valve assembly. The first piston may at least partially surround the regulating chamber e.g. when the first piston is in its first configuration. The first piston may surround the first chamber, and may entirely surround the first chamber. Indeed, the first chamber may be defined by the volume within the first piston and delimited by the core portion of the valve body. The core portion of the valve body itself may not enclose any of the first chamber. The first chamber may therefore be defined by cooperation of the first piston with an outer (e.g. outward facing) surface of the core portion.

The valve assembly may be a pressure-regulating shut-off valve. The valve assembly may be a linear valve assembly, so that output pressure is substantially linearly proportional to input pressure. The valve assembly may be an anti-ice valve for an anti-ice system of an aircraft.

The valve assembly may comprise a biasing device arranged to urge the first piston to its second position. The biasing device may be a spring, or any suitable biasing mechanism for urging the first piston to the second position. The biasing device may be disposed within the first chamber, and may therefore work together with pressure in the first chamber to urge the first piston to its second position. The biasing device may be arranged so that when pressure in the first chamber is substantially equal to pressure outside the first piston, the biasing device urges the first piston into its second position. The first piston may therefore be in its second position by default, unless acted upon by pressure differences e.g. a pressure differential between fluid at the valve inlet and fluid in the first chamber, acting across the first piston.

The first piston may be mounted on (and may partially surround) part of the core portion of the valve body. The first piston may be glidingly mounted (or slide) on the core portion of the valve body. The first chamber may be the volume enclosed by the first piston and the core portion, and the first chamber may therefore be within the first piston e.g. fully within the first piston. The biasing device may be entirely within the first piston, and may be entirely within the first chamber.

The biasing device may be arranged so that during use pressure from fluid at the valve inlet above an inlet pressure threshold will move the first piston to its first position. The biasing device may be configured so that when fluid in the valve inlet has a pressure greater than the inlet pressure threshold, the force from the fluid acting on the first piston overcomes the force from the biasing device, and therefore urges the first piston to its first (e.g. open) position. The inlet pressure threshold may be a predetermined threshold above which the valve assembly is expected to operate normally, so that during use the first piston will be urged by fluid entering the valve inlet to its first position unless the first chamber is pressurised to move the first piston to its second position. Then, the first piston may always allow fluid flow through the valve assembly during use unless the first chamber is pressurised to overcome pressure from fluid in the valve inlet acting on the end face of the first piston.

The first piston may comprise an internal projection that cooperates with a projection of the core portion in the first chamber to guide movement of the first piston between its first position and its second position. The internal project may be at the centre of the first piston e.g. co-axial with the first piston and the valve assembly. The projection of the core portion may be co-axial with the internal projection of the first piston. The core portion of the valve body may therefore comprise a projection that mates with the internal projection of the first piston. The projection may help to stabilise the first piston during movement between its first position and its second position. The projection of the core portion may comprise a seal, arranged to seal with the internal projection of first piston e.g. with an inward-facing surface of the internal projection. The projection of the core portion may be within the internal projection of the first chamber. The mating projections may allow simplified mounting of the first piston to the core portion of the valve body.

The biasing device may be arranged about the internal projection and the projection of the core portion. For example, the biasing device may be a spring arranged coaxially with the internal projection of the first piston and the projection of the core portion of the valve body. Alternatively, the biasing device may be arranged within either or both of the projections.

The whole of the external (e.g. outermost) surface of the first piston may be exposed to fluid within the fluid passage. The first piston may therefore be more responsive and/or sensitive to pressure from within the fluid passage between the valve inlet and the valve outlet. The valve assembly may be arranged so that pressure from fluid at the valve inlet acts on the whole of the end face of the first piston. The outer surface of the first piston may therefore define a portion of the fluid passage (together with the valve body). Put another way, an inward-facing surface of the first piston may confront an outward facing surface of the core portion in order that the first piston is mounted.

This arrangement may be possible by provision of the biasing device and the cooperating projections, since those features allow a nose portion and an associated nose chamber of the prior art (see e.g. <FIG>) to be absent. This also allows as much mass flow through the valve assembly as possible, since there is no nose portion and no associated nose chamber to reduce the flow cross-section at the valve inlet.

The core portion may comprise a seal arranged to seal the first chamber. The seal may be disposed on an outer surface of the core portion, and may be stationary during use of the valve assembly, particularly during movement of the first piston between its first and second positions. The seal may seal against an interior (e.g. inward-facing) surface of the first piston. Prior valve assemblies include a seal for the first piston on the piston itself rather than on the valve body, but by locating the seal on the core portion, assembly of the present valve assembly can be simplified.

The regulating piston may comprise a seal on its outer surface. The regulating piston may comprise two seals on its outer surface, and may comprise only two seals (or seals at only two locations along its length). The seal(s) of the regulating piston may contact an interior (e.g. inward-facing) surface the valve body (e.g. of the core portion) and thereby seal the regulating piston within the valve body. The regulating piston may comprise a first seal within the core portion of the valve body, sealing the regulating chamber. The regulating piston may comprise a second seal closer to the end comprising the outlet, which seal may cooperate with the outlet portion of the valve body e.g. with an inward-facing surface of the outlet portion.

The valve assembly may comprise a solenoid valve operable to pressurise the first chamber and thereby close the valve inlet using the first piston. The valve body (e.g. the core portion) may comprise an internal duct arranged to supply fluid to the first chamber under control of the solenoid valve. The solenoid valve may be mounted within a portion of the valve body.

The valve assembly may comprise a relief valve operable to control pressure in the regulating chamber. The valve body (e.g. the core portion) may comprises an internal duct fluidly connecting the regulating chamber to the relief valve. The relief valve may be operable to vent pressure from the regulating chamber if it exceeds a predetermined threshold.

Since the valve assembly dimensions are strictly constrained at a system level, the stroke length of the first piston may be more than <NUM> times that of known valve assemblies (e.g. the valve assembly shown in <FIG>), more than <NUM> times, and/or more than <NUM> times, without increasing the overall length of the valve assembly.

Since the valve assembly dimensions are strictly constrained at a system level, the stroke length of the regulating piston may be more than <NUM> times that of known valve assemblies (e.g. the valve assembly of <FIG>), or more than <NUM> times, and/or more than <NUM> times, without increasing the overall length of the valve assembly.

The regulating piston may comprise a support structure in its interior bridging the inlet port. As a result of the increased stroke length of the regulating piston, the inlet port of the regulating piston is longer (e.g. extends along a greater length of the regulating piston and valve assembly) than a corresponding port of prior valve assemblies. The regulating chamber is also necessarily longer than in prior valve assemblies, in order to accommodate the longer travel of the regulating piston.

The inlet port of the regulating piston may extend about the entire periphery of the regulating piston. The regulating piston may be substantially cylindrical and the inlet port may therefore extend about the whole circumference of the regulating piston such that a ring of the cylinder is absent in order to provide the inlet port. The inlet port may consist of a single contiguous and/or continuous hole in a tubular sleeve of the regulating piston. A higher rate of fluid flow through the inlet port may therefore be possible compared to known pistons in which multiple holes are provided about the circumference of the regulating piston.

The core portion may comprise a longitudinally-extending wall portion, wherein the wall portion comprises an internal duct e.g. the internal duct for the solenoid valve or the internal duct for the relieve valve) extending along the length of the wall portion. The wall portion may extend the majority of the length of the core portion in the longitudinal direction of the valve (i.e. the direction between the valve inlet and the valve outlet). The wall portion may be tubular, and may be substantially cylindrical. The internal duct may extend along more than <NUM>% of the length of the wall portion, and/or more than <NUM>% of the length of the wall portion. The internal duct may extend along substantially the whole length of the wall portion.

The valve body may comprise a limb connecting the core portion to the rest of the valve body e.g. supporting the core portion within the valve body and within the fluid passage. The limb may connect to the wall portion at the downstream end of the wall portion, thereby allowing the first piston to have a stroke length that is a majority of the wall portion. Thus, the first piston may travel a greater distance than was possible in previous valve assemblies.

The internal duct of the wall portion may extend from the limb to the upstream end of the regulating chamber. The internal duct may therefore extend a majority, or nearly the whole length of the wall portion. The internal duct may therefore enable fluid communication from the regulating chamber (e.g. with the relief valve) regardless of the location of the regulating piston. The internal duct may always provide fluid communication out of the regulating chamber e.g. between the regulating chamber and the relief valve.

The arrangement of the core portion of the valve body and the wall portion allows the increased stroke length, and subsequent overlap, of the first piston and the regulating piston. By locating the limb at the furthest downstream end of the core portion, the first piston, mounted outside the wall portion, can travel substantially the whole length of the wall portion. At the same time, the extension of the internal duct along the length of the wall portion allows the regulating piston to travel a greater stroke length (e.g. substantially the whole length of the wall portion), since the larger regulating chamber can still fluidly communicate e.g. with the relief valve. The limb may comprise a second internal duct fluidly connected to the internal duct in the wall portion to the relief valve.

The wall portion may be interposed between the first piston and the regulating piston. An inward-facing surface of the first piston may confront an outward-facing surface of the wall portion, and an inward-facing surface of the wall portion may confront an outward-facing surface of the regulating piston. The first piston, the wall portion, and the regulating piston may therefore be arranged concentrically. The first piston and the regulating piston may engage the same portion of the valve body i.e. the wall portion.

Given strict weight and size requirements for aircraft components, the total dimensions of the valve assembly may be strictly controlled. It may therefore not be possible to simply make the valve assembly longer in order to achieve a longer piston stroke for the first piston and/or the regulating piston. The valve assembly may therefore have the same length as prior valve assemblies (e.g. the same length as the valve assembly of <FIG>).

According to a second aspect of the invention there is provided an anti-ice system for an aircraft comprising the valve assembly as recited herein with reference to the first aspect of the invention. According to a third aspect of the invention there is provided an aircraft comprising the anti-ice system of the second aspect of the invention, and/or the valve assembly of the first aspect of the invention.

According to another aspect of the invention there is provided an anti-ice valve comprising two pistons, wherein the two pistons are coaxial and wherein the pistons overlap each other in at least one configuration. One piston may be disposed partially within the volume delimited by the other piston in the at least one configuration. The anti-ice valve may comprise any and all of the features of the valve assembly as recited herein with reference to the first aspect of the invention.

Certain preferred embodiments of the invention are described below by way of example only and with reference to the accompanying figures in which:.

<FIG> shows a valve assembly <NUM> comprising a valve body <NUM> defining a valve inlet <NUM> and a valve outlet <NUM>. The valve assembly <NUM> includes a shut-off piston <NUM> for shutting off mass flow (e.g. fluid flow) from the valve inlet <NUM> to the valve outlet <NUM>. A shut-off chamber 12a can be pressurised by a solenoid valve <NUM> in order to drive the shut-off piston <NUM> to close the inlet <NUM>. The shut-off piston <NUM> moves left in the orientation of <FIG> in order to block fluid flow from the valve inlet <NUM> travelling to the valve outlet <NUM>.

The shut-off piston <NUM> comprises a nose portion received by a nose chamber <NUM> of the valve body <NUM>. The nose chamber <NUM> is vented to the atmosphere and is therefore at ambient pressure so that the nose portion of the shut-off piston <NUM> can move easily into the nose chamber <NUM>. Only a portion of the outer surface of the shut-off piston <NUM> is exposed to fluid from the valve inlet <NUM>.

The valve assembly <NUM> also comprises a regulating piston <NUM> for regulating the amount of mass/fluid flow through the valve assembly <NUM> based on the downstream pressure. During use, the regulating piston <NUM> is moved (left and right in the orientation of <FIG>) depending on a pressure differential between the downstream pressure and a pressure in a regulating chamber 14a that receives the regulating piston <NUM>, and thereby closes or opens an inlet port 14b in the regulating piston <NUM>. The regulating piston <NUM> therefore restricts or increases fluid/mass flow through the valve assembly <NUM> and thereby regulates downstream pressure.

Schematic fluid flow lines 16a are shown through the valve assembly <NUM> to illustrate fluid flow though the fluid passage therein. The valve assembly <NUM> of <FIG> includes three restrictions <NUM> in the flow path from the inlet <NUM> to the outlet <NUM>. The first restriction 18a is caused by the nose chamber <NUM> immediately downstream of the inlet <NUM>. The second restriction 18b is caused by a shoulder of the shut-off piston <NUM>. The third restriction 18c is caused by the inlet port 14b of the regulating piston. These restrictions <NUM> limit fluid flow through the valve assembly <NUM>.

The plot <NUM> in <FIG> shows the flow area for fluid associated with each of these restrictions <NUM>, labelled as <NUM>, <NUM>, and <NUM> for restrictions 18a, 18b and 18c respectively. Also shown in plot <NUM> is the flow area through a mid-portion of the valve assembly <NUM> between restrictions 18b and 18c. The plot <NUM> shows that the flow area through the restrictions <NUM> is less than that in the mid-portion of the valve assembly <NUM>. As such, the restrictions <NUM> reduce the maximum mass flow through the valve assembly <NUM>.

<FIG> shows a cross-section through a valve assembly <NUM> comprising a first piston e.g. a shut-off piston <NUM>, and a regulating piston <NUM>, wherein the shut-off piston <NUM> has a greater diameter than that of the regulating piston <NUM> and can therefore overlap the regulating piston <NUM>, at least in some configurations of the valve assembly <NUM>. The valve assembly <NUM> comprises a valve body <NUM> defining a valve inlet <NUM> and a valve outlet <NUM>, with a fluid flow passage between the valve inlet <NUM> and the valve outlet <NUM>. The valve body <NUM> also defines a core portion <NUM> within the fluid flow passage i.e. a portion of the valve body <NUM> at the core of the assembly <NUM>, surrounded by the rest of the valve body <NUM>. The valve body <NUM> is substantially rigid, and all parts of the valve body <NUM> are stationary with respect to the other parts.

The shut-off piston <NUM> and the regulating piston <NUM> are mounted with the core portion <NUM>, and are glidingly engaged therewith e.g. so that they move back and fore with respect to the core portion <NUM>. The shut-off piston <NUM> is mounted about the core portion <NUM> and is moveable between a first position e.g. an open position (rightmost in the orientation of the Figures, shown in <FIG>) and a second position e.g. a closed configuration (leftmost in the orientation of the Figures, shown in <FIG>). The shut-off piston <NUM> is mounted around a longitudinally extending wall portion <NUM> of the core portion <NUM>, and thereby co-operates with the core portion <NUM> to define a shut-off chamber <NUM> within the shut-off piston <NUM>. The valve assembly <NUM> comprises a solenoid valve <NUM> operable to pressurise the shut-off chamber <NUM> and thereby actuate the shut-off piston <NUM> from its open position (rightmost, <FIG>) to its closed position (leftmost, <FIG>). The valve assembly <NUM> also comprises a biasing device e.g. a spring <NUM> arranged to urge the shut-off piston <NUM> to its closed position. The shut-off chamber <NUM> will increase in volume as the shut-off piston <NUM> moves to its second position, and will decrease in volume as the shut-off piston <NUM> moves to its first position.

During operation of an anti-ice system including the valve assembly <NUM>, pressure from fluid at the valve inlet <NUM> will act on an end face <NUM> of the shut-off piston <NUM>, urging the shut-off piston <NUM> its first position (shown in <FIG>). The spring <NUM> may be selected (and the valve assembly <NUM> may be configured) so that an inlet pressure threshold for moving the shut-off piston <NUM> to its first position is equal to the lowest end of an expected operational pressure range for the valve assembly <NUM>. As such, the shut-off piston <NUM> will normally be open during operation of the valve assembly <NUM> because of fluid pressure at the valve inlet <NUM>, unless the shut-off chamber <NUM> is pressurised to overcome force on the shut-off piston from fluid pressure at the valve inlet <NUM>.

<FIG> shows the shut-off piston <NUM> in its closed position, with an end face <NUM> thereof blocking the valve inlet <NUM> and thereby preventing fluid flow through the valve assembly <NUM>. The end face of the shut-off piston <NUM> seats against an interior surface of the valve body <NUM> to close the valve inlet <NUM>. Force from the spring <NUM> acts together with fluid pressure in the shut-off chamber <NUM> to urge the shut-off piston <NUM> to its closed position.

A seal <NUM> is provided on the core portion <NUM> of the valve body <NUM> to seal against an internal (e.g. inward-facing) surface of the shut-off piston <NUM> e.g. against a skirt portion <NUM> of the shut-off piston <NUM>. The seal <NUM> is therefore stationary during operation of the valve assembly <NUM>, and does not move with the shut-off piston <NUM>. The location of the seal <NUM> on an exterior part of the core portion <NUM> (instead of e.g. on the shut-off piston as in the assembly of <FIG>) simplifies construction of the valve assembly <NUM>.

The shut-off chamber <NUM> is defined by the interior volume of the shut-off piston <NUM> as limited by the core portion <NUM> of the valve body <NUM>. The shut-off chamber <NUM> is therefore external to the core portion <NUM> of the valve body <NUM>, and internal to the shut-off piston <NUM>. The shut-off chamber <NUM> is entire within the shut-off piston <NUM>.

The shut-off piston <NUM> also comprises an internal projection <NUM> that engages a projection <NUM> of the core portion <NUM> so that movement of the shut-off piston <NUM> is guided thereby. As such, the valve assembly <NUM> does not require a nose portion and a nose chamber (e.g. as in the assembly <NUM> of <FIG>). The whole external surface of the shut-off piston <NUM> is therefore disposed in the fluid passage. The valve assembly <NUM> of <FIG> therefore does not comprise a restriction analogous to the restriction 18a of <FIG>. A relatively greater mass flow is therefore possible through the valve assembly <NUM> than through the valve assembly <NUM>.

The upstream end of the regulating piston <NUM> (i.e. the end closest to the valve inlet <NUM>) is received within the core portion <NUM> and co-operates therewith to define a regulating chamber <NUM>. The regulating piston <NUM> is movable between a first position e.g. an open position (rightmost in the orientation of the Figures, as shown in <FIG>) and a second position e.g. a closed position (leftmost in the orientation of the Figures, shown in <FIG>). A pressure differential between fluid downstream of the valve assembly <NUM> and fluid in the regulating chamber <NUM> will act on the upstream end of the regulating piston <NUM> and cause it to move to any location between the open and closed positions. An inlet port <NUM> is defined in a sleeve <NUM> of the regulating piston <NUM> and enables fluid flow from the exterior of the regulating piston <NUM> (e.g. from the valve inlet <NUM>) to enter the interior of the regulating piston <NUM>, and to subsequently flow to an outlet <NUM> of the regulating piston <NUM>. Movement of the regulating piston <NUM> then moves the inlet port <NUM> relative to the valve body <NUM> and the core portion <NUM>, so that the inlet port <NUM> is sheathed (partially or completely) within the core portion <NUM> (e.g. within the wall portion <NUM>) to reduce or increase fluid flow through the fluid flow passage accordingly. <FIG> shows the regulating piston <NUM> in its second, closed position with the inlet port <NUM> sheathed entirely within the wall portion <NUM> of the core portion <NUM>, so that the sleeve portion <NUM> blocks mass flow through the fluid passage of the valve assembly <NUM>.

The regulating piston comprises seals <NUM>, one near the upstream end of the regulating piston <NUM> arranged to seal with an interior (e.g. inward-facing) surface of the wall portion <NUM> of the core portion <NUM> to seal the regulating chamber <NUM>, and one further downstream of the regulating piston <NUM> to seal the sleeve portion <NUM> of the regulating piston <NUM> on an interior (e.g. inward-facing) surface of the valve body <NUM> e.g. of an outlet portion <NUM>. The outlet portion <NUM> of the valve body <NUM> is the portion in which the valve outlet <NUM> is defined i.e. the portion of the valve body <NUM> near the downstream end of the assembly <NUM>. The regulating piston <NUM> therefore bridges the fluid flow passage within the valve body <NUM>, and is supported within the valve body <NUM> by contact therewith at its outer surface.

The interior of the regulating piston <NUM> provides a length of the fluid flow passage from the valve inlet <NUM> to the valve outlet <NUM>. No part of the valve body <NUM> (e.g. no stationary part of the valve assembly <NUM>) is disposed within the regulating piston <NUM> (e.g. within the volume delimited by the regulating piston <NUM>), and therefore everything within the regulating piston <NUM> is part of the regulating piston <NUM> itself and is movable rigidly therewith. This arrangement helps ensure as high as possible mass flow through the valve assembly <NUM>.

The regulating piston comprises a support <NUM> in its interior, which moves rigidly with the regulating piston. The support <NUM> is disposed centrally within the regulating piston <NUM>, extending along a central axis thereof. The support <NUM> may be the only structure within the volume of the regulating piston <NUM>. The support <NUM> bridges the inlet port <NUM>, connecting the upstream end of the regulating piston <NUM> to the downstream sleeve portion <NUM>. The inlet port <NUM> extends around the entire periphery of the regulating piston <NUM>. That is, the inlet port <NUM> is contiguous and continuous about the entire circumference of the regulating piston <NUM> such that a ring of the regulating piston is absent in order to provide the inlet port <NUM>. Put simply, the inlet port <NUM> is a single hole extending around the entire periphery of the regulating piston <NUM>. The support <NUM> therefore connects the upstream end of the regulating piston <NUM> to the sleeve portion <NUM>. The regulating piston <NUM> may be formed by additive manufacturing. As a result of the increased stroke length of the regulating piston <NUM>, the inlet port <NUM> is longer than in previous valve assemblies, and the support <NUM> therefore bridges a larger distance.

The valve assembly comprises a relief valve <NUM> in fluid communication with the regulating chamber <NUM>. The relief valve <NUM> is configured to vent fluid to reduce pressure in the regulating chamber <NUM> in the event that pressure in the regulating chamber <NUM> exceeds an upper threshold (e.g. a regulating chamber pressure threshold). The relief valve <NUM> therefore controls the pressure differential across the upstream end of the regulating piston <NUM>, and hence controls the movement of the regulating piston <NUM>.

<FIG> shows the valve assembly <NUM> with the shut-off piston <NUM> in its open position, and the regulating piston <NUM> in its closed position. The upstream end of the regulating piston <NUM> is within the volume delimited by the shut-off piston <NUM>, and the shut-off piston <NUM> therefore overlaps with the regulating piston <NUM>. The shut-off chamber <NUM> and the regulating chamber <NUM> are separate and distinct from one another, and while the shut-off chamber <NUM> is outside the core portion <NUM> of the valve body <NUM>, the regulating chamber is inside the core portion <NUM>. Indeed, the shut-off chamber <NUM> is fully outside the core portion <NUM> and fully inside the shut-off piston <NUM>. In contrast, the regulating chamber <NUM> is fully inside the core portion <NUM>.

The core portion <NUM> comprises the longitudinally-extended wall portion <NUM>, which may be substantially tubular e.g. cylindrical. Together with the regulating piston <NUM>, the wall portion <NUM> defines the regulating chamber <NUM> and therefore receives the upstream end of the regulating piston <NUM> therein. The regulating piston <NUM> is therefore in sliding contact with the interior of the wall-portion <NUM>. Thus, an outward facing surface of the regulating piston <NUM> confronts and inward facing surface of the wall portion <NUM>. The shut-off piston <NUM> is mounted around the outside of the wall portion <NUM> and slides along the wall portion <NUM> during use. The skirt portion <NUM> (e.g. a substantially cylindrical portion) of the shut-off piston <NUM> is therefore in sliding contact with the exterior of the wall portion <NUM> during use. Thus, an inward facing surface of the shut-off piston <NUM> confronts and outward facing surface of the wall portion <NUM>. The wall portion <NUM> is therefore disposed between the regulating piston <NUM> and the shut-off piston <NUM>. The wall portion <NUM> encloses the regulating chamber <NUM>, which is limited by the upstream end of the regulating piston <NUM>. The regulating chamber <NUM> is therefore entirely within the core portion <NUM>, and outside the regulating piston <NUM>. In contrast, the shut-off chamber <NUM> is entirely within the shut-off piston <NUM> and outside the core portion <NUM>. Thus, the regulating piston <NUM> and the shut-off piston <NUM> are both immediately adjacent the same portion of the valve body <NUM>, specifically the wall portion <NUM> of the core portion <NUM>.

The valve body <NUM> also comprises a limb <NUM> provided to support the core portion <NUM> within the fluid passage of the valve assembly <NUM>. The limb <NUM> is disposed at the downstream end (i.e. closest to the valve outlet <NUM>) of the core portion <NUM> to allow the shut-off piston <NUM> to travel most of the length of the core portion <NUM>. As such, the location of the limb <NUM> at the downstream end of the core portion <NUM> enables the increased stroke length of the shut-off piston <NUM>.

The wall portion <NUM> comprises an internal duct <NUM> therein, provided to enable fluid communication between the regulating chamber <NUM> and the relief valve <NUM> via a limb duct <NUM> extending through the limb <NUM>. The internal duct <NUM> connects the upstream end (i.e. the end closest to the valve inlet <NUM>) of the regulating chamber <NUM> with relief valve <NUM> via the limb <NUM>. Since the limb <NUM> is provided at the downstream end of the wall portion <NUM>, and since the duct <NUM> should provide fluid communication with the regulating chamber <NUM> regardless of the position of the regulating piston <NUM>, the internal duct <NUM> extends a majority of the length of the wall portion <NUM> to connect into the regulating chamber <NUM> at its most upstream end. The internal duct <NUM> may extend substantially the whole length of the wall portion <NUM>. The internal duct <NUM> may therefore be disposed between the regulating piston <NUM> and the shut-off piston <NUM>, at least in one configuration of the valve assembly <NUM>.

<FIG> shows a cross-section through the valve assembly <NUM> of <FIG>, taken at an alternative angle. As can be seen from <FIG>, the valve assembly <NUM> comprises a second limb <NUM> connecting to the wall portion <NUM> of the core portion <NUM>. A second internal duct <NUM> is provided to enable fluid communication between the solenoid valve <NUM> and the shut-off chamber <NUM>. The second internal duct <NUM> may be substantially the same as the internal duct <NUM>, and may extend most or substantially all of the length of the wall portion <NUM>. The second internal duct connects to a second limb duct <NUM>, which in turn connects to the solenoid valve <NUM> for pressurising the shut-off chamber <NUM>.

As a result of the arrangement depicted in <FIG> and <FIG>, both the shut-off piston <NUM> and the regulating piston <NUM> have a longer stroke length (i.e. a greater distance between their first and second positions) than the pistons <NUM> and <NUM> of the valve assembly <NUM> of <FIG> for the same overall valve assembly length. Both the shut-off piston <NUM> and the regulating piston <NUM> may have any suitable stroke length. Thus, the shut-off piston <NUM> and the regulating piston <NUM> travel a greater proportion of the length of the valve assembly <NUM> than analogous pistons <NUM>, <NUM> in the assembly of <FIG>. As such, the valve assembly <NUM> permits a much greater mass flow past each piston <NUM>, <NUM> e.g. compared to restrictions 18b and 18c. Moreover, as noted above, the shut-off piston <NUM> does not require a nose portion an hence the valve assembly <NUM> does not require a nose chamber <NUM>, and permits greater fluid flow than is possible past restriction 18a.

<FIG> shows an updated version of plot <NUM> in <FIG>, showing the flow area at corresponding locations of the valve assembly <NUM> and the valve assembly <NUM>. The flow area <NUM> in valve assembly <NUM> at the inlet port of the regulating piston <NUM> (corresponding to restriction 18c) is significantly less than the flow area <NUM> of valve assembly <NUM> at the inlet port <NUM> of the regulating piston <NUM>. Flow areas <NUM> and <NUM> of the valve assembly <NUM> (corresponding to restrictions 18b and 18a) are significantly less than the flow areas <NUM> and <NUM> of corresponding locations in valve assembly <NUM>. The flow area <NUM> at the mid-position of the valve assembly <NUM> is also greater than the flow area <NUM> at the mid-position of the valve assembly <NUM>. The valve assembly <NUM> is therefore capable of greater mass flow in its fully open configuration than is valve assembly <NUM>. As a consequence of the increased maximum mass flow, the valve assembly <NUM> can supply an increased fluid flow in its fully open configuration e.g. during engine start-up.

<FIG> shows a plot comparing experimental data for the valve assembly of <FIG> (line <NUM>), experimental data for an alternative butterfly valve (line <NUM>), and simulation data for the valve assembly of <FIG> (line <NUM>). The plot shows different characteristic curves of the different control valves, with the pressure drop as a function of the correct flow rate. The typical behaviour for a valve with butterfly architecture (line <NUM>) shows the pressure drop rapidly growing with the flow, whereas the behaviour for a typical valve with piston architecture (line <NUM>) shows that the pressure drop is less affected by the flow rate. The valve assembly <NUM> (line <NUM>) shows an intermediate behaviour between the two typical curves. Although the butterfly valve <NUM> may be superior in the depicted range of values, the assembly of <FIG> (line <NUM>) is significantly better than the assembly <NUM> of <FIG> (line <NUM>), being closer to the data from the butterfly valve <NUM>.

Claim 1:
A valve assembly for an anti-ice system of an aircraft, comprising:
a valve body (<NUM>);
a first piston (<NUM>); and
a regulating piston (<NUM>);
wherein the valve body (<NUM>) defines a valve inlet (<NUM>), a valve outlet (<NUM>), a fluid passage between the valve inlet (<NUM>) and the valve outlet (<NUM>), and a core portion (<NUM>) defining a first chamber (<NUM>) by cooperation with the first piston (<NUM>) and a regulating chamber (<NUM>) by cooperation with the regulating piston (<NUM>);
wherein the first piston (<NUM>) is moveable between a first position and a second position and is disposed to open and/or close the valve inlet (<NUM>);
wherein the regulating piston (<NUM>) comprises an inlet port (<NUM>) arranged to permit fluid flow between the exterior and interior of the regulating piston (<NUM>), and an outlet (<NUM>) arranged to permit fluid flow from the interior of the regulating piston (<NUM>) to the valve outlet (<NUM>), the regulating piston (<NUM>) being movable between a first position in which the inlet port (<NUM>) permits fluid flow between the valve inlet (<NUM>) and the valve outlet (<NUM>) via the fluid passage and the interior of the regulating piston (<NUM>), and a second position in which the inlet port (<NUM>) is located within the core portion (<NUM>) of the valve body (<NUM>) so that the regulating piston (<NUM>) prevents fluid flow from the valve inlet (<NUM>) to the valve outlet (<NUM>); and
wherein the first piston (<NUM>) overlaps the regulating piston (<NUM>) when the first piston (<NUM>) is in its first position and the regulating piston (<NUM>) is in its second position.