Patent Description:
In an aircraft engine, such as a gas turbine engine for example, there is sometimes a need to draw air from one air duct, for feeding downstream for other uses. Such an air duct may include an annular bypass duct that annularly surrounds a core of a turbofan gas turbine engine, for example. The core includes a compressor section, a combustor, and a turbine section. However, in some cases, the pipe used to draw the air from the bypass duct may induce undesired noises and/or vibrations. Improvements are therefore sought.

<CIT> discloses a gas turbine engine bleed duct.

<CIT> discloses an enhanced method and aircraft for pre-cooling an environmental control system using a two wheel turbo-machine with a supplemental heat exchanger.

<CIT> discloses a flush inlet scoop design for an aircraft bleed air system.

<CIT> discloses a bypass duct louver for noise mitigation.

According to an aspect of the present invention, there is provided an aircraft engine in accordance with claim <NUM>.

The aircraft engine as defined above and herein may further include, in whole or in part, and in any combination, one or more of the following additional features.

Optionally, and in accordance with the above, the duct includes an annular gaspath defined radially between the inner casing and the outer casing of the aircraft engine.

Optionally, and in accordance with any of the above, the second valve is a non-actuated valve, the non-actuated valve moving from the second closed configuration to the second open configuration following a pressure differential across the second valve greater than a pressure threshold.

Optionally, and in accordance with any of the above, the second valve is located at the bleed port.

Optionally, and in accordance with any of the above, the second valve includes at least one gate movable from a closed position in which the at least one gate blocks fluid communication between the duct and the bleed conduit through the second valve and an open position in which the at least one gate allows fluid communication through the second valve.

Optionally, and in accordance with any of the above, the at least one gate includes a plurality of gates circumferentially distributed about a valve axis.

Optionally, and in accordance with any of the above, each of the plurality of gates is pivotable from a closed position to an open position about a respective one of pivot axes being normal to the valve axis.

Optionally, and in accordance with any of the above, each of the plurality of gates has an edge pivotably connected to a peripheral wall of the bleed conduit or to a peripheral wall circumscribing the bleed port.

Optionally, and in accordance with any of the above, the at least one gate extends into the bleed conduit when the at least one gate is in the open position.

Optionally, and in accordance with any of the above, the plurality of gates are triangular, each of the plurality of gates having side edges sealingly engaged to side edges of adjacent gates of the plurality of gates.

Optionally, and in accordance with any of the above, the plurality of gates are circumferentially distributed around the valve axis, each of the plurality of gates partially overlapping a circumferentially adjacent one of the plurality of gates.

Optionally, and in accordance with any of the above, the at least one gate is biased in the closed position.

Optionally, and in accordance with any of the above, at least one biasing member is operatively connected to the at least one gate, the at least one biasing member exerting a force on the at least one gate to push the at least one gate in the closed position.

Optionally, and in accordance with any of the above, the at least one gate is free from engagement with an actuator.

<FIG> illustrates an aircraft powerplant (or simply "engine") <NUM> of a type preferably provided for use in subsonic flight. In this particular embodiment, such a powerplant may include a gas turbine engine that generally comprises in serial flow communication a fan <NUM> through which ambient air is propelled, a compressor section <NUM> for pressurizing the air, a combustor <NUM> in which the compressed air is mixed with fuel and ignited for generating an annular stream of hot combustion gases, and a turbine section <NUM> for extracting energy from the combustion gases. The fan <NUM>, the compressor section <NUM>, and the turbine section <NUM> are rotatable about a central axis <NUM> of the engine <NUM>.

The engine <NUM> includes an inner casing <NUM> that extends circumferentially around the compressor section <NUM>, the combustor <NUM>, and the turbine section <NUM>. The engine <NUM> has an outer casing <NUM> extending annularly around the inner casing <NUM>. A bypass duct <NUM> is defined radially relative to the central axis <NUM> between the inner casing <NUM> and the outer casing <NUM>. Struts <NUM> may extend in a direction having a radial component relative to the central axis <NUM>, such as to radially support the outer casing <NUM> relative to the inner casing <NUM>. The struts <NUM> may be circumferentially distributed around the central axis <NUM> and extend across the bypass duct <NUM>.

As shown in <FIG>, the fan <NUM> creates an airflow that is divided into a core flow F1 and an annular flow F2; the annular flow F2 extending around the core flow F1. The inner casing <NUM> has a leading edge that divides the flow exiting the fan <NUM> into the core flow F1 and the annular flow F2. The annular flow F2 flows in the bypass duct <NUM> defined between the inner casing <NUM> and the outer casing <NUM>. The annular flow F2 is re-united with the core flow F1 at an exhaust of the engine <NUM>.

In some cases, it may be desirable to draw fluid (e.g. air) from a first or main passage or duct, which in this case is the bypass duct <NUM>, to supply the withdrawn or bled fluid to different systems S of the engine <NUM> and/or to supply air to different systems S of an aircraft equipped with the engine <NUM>. For instance, the air drawn from the bypass duct <NUM> may be used to supply an environmental control system (ECS) of an aircraft with fresh air. In some cases, the air drawn from the bypass duct <NUM> may be used in a heat exchanger of the aircraft for cooling aircraft components. Therefore, in some cases, the drawing of the air from the bypass duct <NUM> is driven by requirements of external systems outside of the engine <NUM>.

As shown in <FIG>, a bleed pipe <NUM>, which may also be referred to as a bleed conduit or bleed duct, is pneumatically connected to the bypass duct <NUM> and stems from the bypass duct <NUM> between inlet and outlet of the bypass duct <NUM>. Specifically, the outer casing <NUM> defines a bleed port <NUM>; the bleed pipe <NUM> having a bleed inlet <NUM> pneumatically connected to the bleed port <NUM>. The bleed pipe <NUM> has a bleed outlet <NUM> pneumatically connected to the system S, which may be the ECS or any other suitable system(s) S in need of fresh air.

A first valve <NUM>, also referred to as a master valve, is pneumatically connected to the bleed pipe <NUM> between the bleed inlet <NUM> and the bleed outlet <NUM>. The first valve <NUM> has a first open configuration in which the bleed inlet <NUM> is pneumatically connected to the bleed outlet <NUM> through the first valve <NUM> and a first closed configuration in which the bleed inlet <NUM> is disconnected from the bleed outlet <NUM> by the first valve <NUM>. The first valve <NUM> may be a butterfly valve or any other types of valve having regulating functions. The first valve <NUM> may be operable to regulate an air flow flowing in to the bleed pipe <NUM> as a function of flight conditions and/or as a function of air requirements of the system(s) S. In other words, the first valve <NUM> may have at least one intermediate configuration or position between the open configuration and the closed configuration. At given conditions (e.g., speed, altitude, etc.), a mass flow rate of the air flowing in the bleed pipe <NUM> is greater when the first valve <NUM> is at the open configuration than a mass flow rate into the bleed pipe <NUM> when the first valve <NUM> is at any of the at least one intermediate configuration.

It has been observed that, in some operating conditions, the bleed pipe <NUM> may exhibit tonal noise when the first valve <NUM> is in the first closed configuration. This tonal noise may be an indicator of acoustic instability in the bleed pipe <NUM>, which may damage some components of the engine <NUM>. This tonal noise may also result in cabin or external noises, which may be unpleasant for passengers. This tonal noise may be the result of a resonating closed-ended cavity defined by the bleed pipe <NUM> from the bleed inlet <NUM> or bleed port <NUM> to the first valve <NUM>; this closed-ended cavity may resonate as a result of air flowing into the bypass duct <NUM> passed the bleed port <NUM>. Specifically, flow instabilities may be created when the annular flow F2 flows past the bleed port <NUM>.

In the embodiment shown, a second valve <NUM>, which may be referred to as a slave valve, is located upstream of the first valve <NUM> relative to a bleed flow F3 flowing into the bleed pipe <NUM>. This second valve <NUM> may therefore decrease a volume of this closed-ended cavity and may prevent the noise phenomenon described above. This second valve <NUM> may sit flush with the bleed port <NUM>. The second valve <NUM> is located at or proximate the port <NUM>. In some cases not forming part of the invention, this second valve <NUM> may be located downstream of the port <NUM> into the bleed pipe <NUM>. In some other cases not forming part of the invention, second valve <NUM> may be located anywhere inside the bleed pipe <NUM>. In some embodiments, the second valve <NUM> is located at the bleed inlet <NUM> since this may avoid creating any cavities in the bypass duct <NUM>. However, this may not be possible in some embodiments due to the design of bleed pipe entrance. In such cases, the second valve <NUM> may be placed further downstream of the bleed port <NUM>. In some examples not forming part of the invention, second valve <NUM> may be located anywhere upstream of the first valve <NUM> such that it may change the frequency of tone/resonance inside the bleed pipe <NUM>.

In some embodiments, for instance, when the bleed pipe <NUM> is used to provide air to a system S of an aircraft, the control/actuation of the first valve <NUM> may be controlled by a controller of the aircraft. In other words, a controller of the engine <NUM> may have no control over actuation of the first valve <NUM>. In the embodiment shown, the second valve <NUM> has a second open configuration and a second closed configuration. In the second open configuration, the bleed inlet <NUM> is pneumatically connected to the bleed outlet <NUM> through the second valve <NUM> and through the first valve <NUM>. In the second closed configuration, the bleed inlet <NUM> is pneumatically disconnected from the first valve <NUM> by the second valve <NUM>. The second valve <NUM>, in the second closed configuration, fluidly isolates a portion of the bleed pipe <NUM> from the bypass duct <NUM>; the portion of the bleed pipe <NUM> located between the first valve <NUM> and the second valve <NUM>. The second valve <NUM> is in the second closed configuration when the first valve <NUM> is in the first closed configuration. The second valve <NUM> is in the second open configuration when the first valve <NUM> is in the first open configuration. In other words, switching the first valve <NUM> from the first closed configuration to the first open configuration indirectly switches the second valve <NUM> from the second closed configuration to the second open configuration. Hence, controlling the first valve <NUM> may indirectly control the second valve <NUM>.

This indirect opening of the second valve <NUM> may be triggered by air being drawn by the system S from the bypass duct F2 thereby causing a pressure drop across the second valve <NUM>. This pressure drop may exert a pressure on the second valve <NUM> to push a valve body of the second valve <NUM> out of the flow path to allow air to flow through the second valve <NUM>. In some cases, the first valve <NUM> and the second valve <NUM> may be operatively connected to one another such that, sending a signal to the first valve <NUM> using, for instance, an aircraft controller sends a signal to the second valve <NUM> to open the second valve at the same time than the first valve <NUM>. In some cases, the aircraft controller is operatively connected to both of the first and second valves <NUM>, <NUM> to control them independently. In some other cases, the first valve <NUM> may be operatively connected to the aircraft controller and the second valve <NUM> may be operatively connected to an engine controller; the aircraft and engine controllers may be operatively connected to one another such that, when a signal is sent by the aircraft controller to open the first valve <NUM>, a signal is sent to the engine controller by the aircraft controller, and the engine controller sends a signal to the second valve <NUM>.

Referring now to <FIG>, the second valve <NUM> is described in more detail. The second valve <NUM> is shown in the second closed configuration in <FIG> and in the second open configuration in <FIG>. In the embodiment shown, the second valve <NUM> may be a passive, or non-actuated, valve that is switched from its second closed configuration to its second open configuration as a result of a pressure differential between the bleed inlet <NUM> and the bleed outlet <NUM> greater than a given pressure threshold. This pressure differential may be imparted by the switching of the first valve <NUM> from its first closed configuration to its first open configuration. Namely, opening the first valve <NUM> connects the bleed pipe <NUM> to a system S in need of fresh air. A pressure in this system S may be lower than a pressure in the bypass duct <NUM>, either as a result of operating conditions and/or because this system S uses a pump to draw air. Consequently, the pressure differential which is thereby created may suction air from the bypass duct <NUM> via the bleed port <NUM>. The second valve <NUM> may therefore move from its second closed configuration to its second open configuration as a result of a pressure imbalance created on opposite upstream and downstream sides of the second valve <NUM>. Hence, actuation of the second valve <NUM> may be triggered by engine flow conditions and may not require external power.

The expression "passive" or "non-actuated" refers to a valve that is not coupled to an actuator for its moving between open and closed configurations. In other words, a passive or non-actuated valve cannot be directly controlled by an actuator. A passive or non-actuated valve may be free from connection to a controller and may be free from engagement with an actuator. The second valves disclosed herein include at least one gate; the at least one gate may be free from engagement with an actuator.

As shown in <FIG>, the second valve <NUM> includes a plurality of gates 34a that are circumferentially distributed about a valve central axis V. Eight gates 34a are provided in the embodiment shown. It is however understood that only one gate may be used. In some cases, from two to eight gates or more than eight gates may be used without departing from the scope of the present disclosure.

In the embodiment shown, each of the gates 34a is triangular and has having a first edge 34b secured to a wall of the bleed pipe <NUM> and to a wall circumscribing the bleed port <NUM> of the outer casing <NUM>. The first edge 34b of each of the gates 34a defines a pivot axis P about which the gates 34a may pivot from a closed position shown in <FIG> to an open position shown in <FIG>. It will be appreciated that any other suitable shapes of the gates may be sued without departing from the scope of the present disclosure. Each of the gates 34a has opposed side edges 34c. In the closed position shown in <FIG>, the side edges 34c of the gates 34a are in abutment against neighbouring side edges 34c of adjacent gates 34a. A sealing engagement may be defined between the side edges 34c. In some cases, a seal may be disposed on the side edges 34c to provide this sealing engagement.

In an alternate embodiments, the gates may pivot about axes that are substantially radial relative to the valve axis V. In other words, each of the gates may pivot about one of its opposed side edges 34c. Alternate positions of the pivot axes are shown at P' in <FIG>.

In the embodiment shown, each of the gates 34a is engaged by a biasing member 34d (only one shown for clarity) disposed between the first edges 34b of the gates 34a and the wall of the bleed pipe <NUM> or the wall of the bleed port <NUM>. The biasing members 34d are operable to bias the gates 34a in their closed position shown in <FIG>. The biasing members 34d may be torsional spring, a compression spring, an extension spring, or any other suitable means operable to exert a force maintaining the gates 34a in their closed position. In some embodiments, constant force/torque springs may be used to bias the gates 34a in their closed position. Any types of actuators such as hydraulic, pneumatic, electric, magnetic, electromechanical, electrohydraulic, electrostatic, electromagnetic, thermal expansion, piezoelectric actuators or a combination of above may be used. In some embodiments, the biasing members 34d are omitted since a weight of the gates 34a may be sufficient to maintain them in their closed position. A center of gravity of each of the gates 34a may remain offset from the pivot axis P when the gates 34a are in their open position such that the gates 34a may revert back to their closed position as a result of their own weight when the first valve <NUM> is closed. In some cases, back pressure accumulated inside the bleed pipe <NUM> may help keeping the gates 34a in their closed position. The gates 34a may be designed to cover the entire cross-section of the bleed pipe <NUM> to block-off the flow when the first valve <NUM> is closed. The gates 34a may be designed to have non-uniform weight along their surfaces to facilitate the movement between the open and closed positions.

The hinges about which the gates 34a pivot may allow solely rotation of the gates 34a toward the bleed pipe <NUM> and may prevent rotation of the gates 34a toward the bypass duct <NUM> such that the second valve <NUM> acts as a one way valve preventing air from exiting the bleed pipe <NUM> toward the bypass duct <NUM>. The gates 34a may interlock one another at their side edges 34c to prevent this rotation of the gates 34a toward the bypass duct <NUM>.

In some embodiments, preventing gates to rotate backwards, that is, inside the bypass duct <NUM>, may be achieved by using support rods/frames <NUM> (<FIG>) along the side edges 34c of the gates 34a, such that the gates 34a abut on the frames and are prevented from moving backward. This may provide structural stability for the gates 34a as well. A support structure may extend across the bleed pipe <NUM> for supporting the gates in their closed position.

As shown in <FIG>, when the first valve <NUM> is switched from its first closed configuration to its first open configuration, the bleed flow F3 is allowed to flow through the first valve <NUM>. The first valve <NUM> being in its first open configuration results in air being drawn from the bleed pipe <NUM> and results in a pressure in the bleed pipe <NUM> being less than that in the bypass duct <NUM>. As pressure wants to equilibrate, a pressure on a first side of the gates 34a that faces the bypass duct <NUM> becomes greater than a pressure on a second side of the gates 34a that faces the bleed pipe <NUM> thereby pushing the gates 34a from their closed position of <FIG> to their open position of <FIG> to pneumatically connect the portion of the bleed pipe <NUM> that extends from the second valve <NUM> to the first valve <NUM> to the system S in need of air.

Referring now to <FIG>, another exemplary second valve is shown at <NUM>. The second valve <NUM> includes a plurality of gates 134a that are rectangular-shaped. The gates 134a include twelve gates, but as low as two or three gates may be used. The gates 134a are distributed around the valve axis V. Each of the gates 134a has a first edge 134b pivotably mounted to the wall of the bleed pipe <NUM> or the wall of the bleed port <NUM>. The gates 134a are pivotable about respective pivot axes P defined between the first edges 134b and the wall of the bleed pipe <NUM> or the wall of the bleed port <NUM>. Each of the gates 134a may extend substantially perpendicularly from the wall of the bleed port <NUM> or the wall of the bleed pipe <NUM> across the bleed pipe <NUM>. Stated differently, each of the gates 134a may extend along an axis intersecting the valve axis V. Alternatively, the gates 134a may be angled such that each of the gates 134a extend along an axis free of intersection with the valve axis V.

In the embodiment shown, each of the gates 134a partially overlaps a circumferentially adjacent one of the gates 134a. For instance, a first gate 134a1 of the gates 134a partially overlaps a second gate 134a2 of the gates 134a; the second gate 134a2 being immediately circumferentially adjacent the first gate 134a1 of the gates 134a. Then, the second gate 134a2 partially overlaps a third gate 134a3 of the gate 134a; the third gate 134a3 being immediately circumferentially adjacent the second gate 134a2 of the gates 134a. This goes on and on until a last one of the gates 134a. Consequently, because of the overlapping of the circumferentially adjacent gates 134a, a sealing engagement may be provided by the contacting surfaces of the circumferentially adjacent gates 134a. Each of the gates 134a, but the first gate 134a1 and the last one of the gates 134a, is partially sandwiched between two neighbouring gates 134a.

The hinges about which the gates 134a pivot may allow solely rotation of the gates 134a toward the bleed pipe <NUM> and may prevent rotation of the gates 134a toward the bypass duct <NUM> such that the second valve <NUM> acts as a one way valve preventing air from exiting the bleed pipe <NUM> toward the bypass duct <NUM>.

Referring now to <FIG>, another exemplary second valve is shown at <NUM>. The second valve <NUM> includes two gates 234a pivotably mounted to a central rib <NUM> extending across the bleed pipe <NUM> or the bleed port <NUM>. The central rib <NUM> may intersect the valve axis V. The two gates 234a may be hingedly connected to each other at their central edges 234b and supported by the central rib <NUM>. The central rib <NUM> need not extend all the way across the bleed pipe <NUM> or bleed port <NUM> and may include only two rib members secured to the wall of the bleed pipe <NUM> or the wall of the bleed port <NUM> at diametrically opposed locations across the pipe <NUM> or port <NUM>. In some cases, the pivot axis P may be off-centered.

When the first valve <NUM> is switched to the open configuration, the pressure difference causes the two gates 234a to rotate about the pivot axis P, which, in this embodiment, extends across the port <NUM> or pipe <NUM> and intersects the valve axis V. The two gates 234a therefore rotate toward one another until they become substantially parallel to the valve axis V and substantially parallel to the bleed flow F3 flowing inside the bleed pipe <NUM>. Once the first valve <NUM> is switched to its closed configuration, the two gates 234a may fall back toward their closed position shown in <FIG>, either by the result of their own weight or by a biasing member connected to the two gates 234a.

The hinge(s) about which the gates 234a pivot may allow solely rotation of the gates 234a toward the bleed pipe <NUM> and may prevent rotation of the gates 234a toward the bypass duct <NUM> such that the second valve <NUM> acts as a one way valve preventing air from exiting the bleed pipe <NUM> toward the bypass duct <NUM>. A cleat or shoulder may be defined by the bleed port <NUM> or bleed pipe <NUM> for abutment with the gates 234a to prevent them from moving into the bypass duct <NUM>.

Referring now to <FIG>, another exemplary second valve is shown at <NUM>. In the embodiment shown, the bleed pipe <NUM> and the bleed port <NUM> have rectangular or square cross-sections. The second valve <NUM> includes single gate 334a pivotably mounted via one of its edges 334b to a wall of the bleed pipe <NUM> or a wall of the bleed port <NUM>. The single gate 334a is therefore rotatable between its closed in open positions about a pivot axis P that, in the present embodiment, registers with the one of the edges 334b of the single gate 334a. It will be appreciated that the pivot axis P may be offset from the edges 334b of the single gate 334a; the pivot axis P being off-centered relative to the single gate 334a such as to allow the pressure differential to create a moment about the pivot axis P to rotate the single gate 334a between the closed and opened positions.

The hinge about which the single gate 334a pivots may allow solely rotation of the gate 334a toward the bleed pipe <NUM> and may prevent rotation of the gate 334a toward the bypass duct <NUM> such that the second valve <NUM> acts as a one way valve preventing air from exiting the bleed pipe <NUM> toward the bypass duct <NUM>. A cleat or shoulder may be defined by the bleed port <NUM> or bleed pipe <NUM> for abutment with the gate 334a to prevent them from moving into the bypass duct <NUM>.

The disclosed second valves <NUM>, <NUM>, <NUM>, <NUM> may allow to attenuate the noise phenomenon described above by closing the bleed pipe <NUM> proximate to the bleed port <NUM> when the first valve <NUM> is in the closed configuration. The second valves <NUM>, <NUM>, <NUM>, <NUM>, and their respective gates, may rotate to close/block the bleed pipe <NUM> and stop the flow from the bypass duct <NUM> from entering the bleed pipe <NUM>. The second valves <NUM>, <NUM>, <NUM>, <NUM> may allow air to enter the bleed pipe <NUM> when the first valve <NUM> is in the open configuration. Their respective gates may rotate in the open position to allow air to pass through the second valves <NUM>, <NUM>, <NUM>, <NUM>. The second valves <NUM>, <NUM>, <NUM>, <NUM> may disconnect the portion of the bleed pipe <NUM>, <NUM> that extends from the bleed port <NUM>, <NUM> to the first valve <NUM>. This may prevent or at least partially alleviate the acoustic tone/noise phenomenon described above. The second valves <NUM>, <NUM>, <NUM>, <NUM> may act as check valve or one-way valve since air may flow through them solely from the bleed inlet <NUM> to the bleed outlet <NUM>. Hence, when the first valve <NUM> is closed, a pressure difference between the bleed pipe <NUM> and the bypass duct <NUM> may not force the second valves to open. Means may be provided to preclude the gates 34a, 134a, 234a, 334a from pivoting toward the bypass duct <NUM>. These means may include, for instance, cleats, locking members and so on.

In some embodiments, the second valve may be an actuated valve. That is, either the gate(s) of the second valve are engaged by an actuator operable to move the gate(s) between the closed and open position. Or, the second valve may be servo valve having a servo mechanism engaged to a valve body of the valve to move the valve between open and closed positions. In some embodiments, a hydraulic, pneumatic, and/or electromagnetic mechanism may be engaged to the gate(s) to control rotation/movement of the gate(s). In some cases, the gate(s) may be curved to better conform with a shape of the bleed pipe <NUM> when the gate(s) is/are in the open position.

In the embodiments shown, the second valve <NUM>, <NUM>, <NUM>, <NUM> may be switched between their open and closed configurations without requiring external power and without being engaged by an actuator. The second valve <NUM>, <NUM>, <NUM>, <NUM> may be opened by the flow conditions inside the bleed pipe <NUM>, <NUM>. The second valve <NUM>, <NUM>, <NUM>, <NUM> may be closed by an external mechanisms, such as springs, pneumatics or electromagnetics (e.g., electromagnetic actuators, solenoids), or may be closed as a result of weight of their respective gates. Both the actuation and de-actuation motions of the second valve could be triggered by external mechanisms, which in-turn could be controlled by aircraft or engine control system via direct or remote protocols. The movement of the gate may be along the flow or at a specified direction to the flow.

In some embodiments, the second valve <NUM> as disclosed herein may allow to reduce and, in some cases, eliminate the noise associated to the pipe resonance. The second valve <NUM> may further allow to reduce vibrations and reduce structural instabilities.

Claim 1:
An aircraft engine (<NUM>), comprising:
an inner casing (<NUM>) extending circumferentially around a compressor section (<NUM>), a combustor (<NUM>), and a turbine section (<NUM>);
an outer casing (<NUM>) extending annularly around the inner casing (<NUM>);
a duct (<NUM>) defined radially relative to a central axis (<NUM>) between the inner casing (<NUM>) and the outer casing (<NUM>), the duct (<NUM>) having an inlet and an outlet, the duct (<NUM>) defining a bleed port (<NUM>) through the outer casing (<NUM>) between the inlet and the outlet;
a bleed conduit (<NUM>) stemming from the duct (<NUM>), the bleed conduit (<NUM>) having a bleed inlet (<NUM>) connected to the bleed port (<NUM>) and a bleed outlet (<NUM>) fluidly connectable to a fluid system (S);
a first valve (<NUM>) connected to the bleed conduit (<NUM>) between the bleed inlet (<NUM>) and the bleed outlet (<NUM>), the first valve (<NUM>) having an open configuration and a closed configuration; characterized in that it further comprises
a second valve (<NUM>) connected to the bleed conduit (<NUM>) upstream of the first valve (<NUM>) and at or proximate the bleed port (<NUM>), the second valve (<NUM>) having a second open configuration and a second closed configuration, and in that:
when in the second closed configuration, the second valve (<NUM>) blocks fluid communication between the bleed port (<NUM>) and the first valve (<NUM>) such that a portion of the bleed conduit (<NUM>) between the first valve (<NUM>) and the second valve (<NUM>) is fluidly isolated from the duct (<NUM>); and
the second valve (<NUM>) being in the second open configuration when the first valve (<NUM>) is in the open configuration to fluidly connect the bleed port (<NUM>) to the bleed outlet (<NUM>) through the first valve (<NUM>) and through the second valve (<NUM>).