Valve arrangement for a fuel system

Abstract

The disclosure relates to a valve for a fuel system having a body with at least one inlet and one outlet, the inlet fluidly connected to a pressurised fuel source in use. A shuttle is mounted within the body, the shuttle having a cavity of fixed volume and movable between a first position where fluid is permitted to flow through the inlet and is prevented from flowing through the outlet and a second position where fluid is prevented from flowing through the inlet and is permitted to flow through the outlet. A piston is configured to engage the fluid within the shuttle cavity to move the shuttle between the first and second position. A biasing mechanism biases the shuttle towards the first position and where the shuttle moves towards the second position when the fluid within the shuttle reaches a critical pressure.

Claims

1. A valve for a fuel delivery system, comprising: a valve body comprising an internal cavity, at least one inlet and one outlet, the inlet fluidly connected to a fuel source in use; a shuttle mounted within the body, the shuttle comprising a partition spanning the internal cavity and moveable relative to the inlet and outlet between a first position where the shuttle blocks the outlet whilst fluid is permitted to flow through the inlet and a second position whereby the outlet is opened whilst fluid is prevented from flowing through the inlet; a piston configured to engage the fluid within the internal cavity in order to move the shuttle between the first and second position; and a biasing mechanism arranged to bias the shuttle towards the first position; wherein the shuttle is moved towards the second position when the fluid within the cavity reaches a threshold pressure, and wherein the shuttle comprises the partition and a side wall having an open end so as to define an internal volume within the shuttle, wherein the internal volume defines a predetermined metered volume of fuel and the piston extends into the internal volume of the shuttle to expel the fluid therein when the shuttle is in the second position.

2. The valve according to claim 1, where the valve body has a longitudinal axis and the shuttle is translatable along said axis.

3. The valve according to claim 2, wherein the inlet and outlet are axially spaced.

4. The valve according to claim 1, where the shuttle comprises a side wall shaped to occlude the outlet in the first condition.

5. The valve according to claim 4, wherein the side wall comprises a discontinuity arranged to pass over the outlet as the shuttle moves to the second condition and thereby open the outlet in the second condition.

6. The valve according to claim 4, wherein the shuttle comprises an outlet, the shuttle outlet aligning with the housing outlet when the shuttle is in the second position.

7. The valve housing according to claim 4, wherein the shuttle side wall comprises an inlet, the shuttle inlet aligning with the housing inlet when the shuttle is in the first position.

8. The valve according to claim 7, where the shuttle inlet and the shuttle outlet are axially offset by a distance that is less than a stroke length of the piston and/or an axial spacing between the housing inlet and outlet.

9. The valve according to claim 1, where the piston is configured to extend into the cavity to expel the fluid therefrom.

10. The valve according to claim 1, where the piston comprises a solenoid actuator.

11. The valve according to claim 1, where the housing comprises a second inlet located on an opposing side of the partition from the first inlet and/or separated from the first inlet by the partition.

12. The valve according to claim 1, wherein the internal cavity is divided into two separate cavity portions by the partition, the two cavity portions being of variable volume according to the location of the shuttle.

13. The valve according to claim 1, wherein the piston extends fully into the internal volume into abutment with the partition when the shuttle is in the second position.

14. A fuel system for a gas turbine engine, the fuel system comprising the valve of claim 1.

15. A gas turbine engine comprising the fuel system of claim 14.

16. The gas turbine engine according to claim 15, further comprising: an engine core comprising a turbine, a compressor, and a core shaft connecting the turbine to the compressor; a fan located upstream of the engine core, the fan comprising a plurality of fan blades; a gearbox that receives an input from the core shaft and outputs drive to the fan so as to drive the fan at a lower rotational speed than the core shaft.

17. The gas turbine engine according to claim 16, wherein: the turbine is a first turbine, the compressor is a first compressor, and the core shaft is a first core shaft; the engine core further comprises a second turbine, a second compressor, and a second core shaft connecting the second turbine to the second compressor; and the second turbine, second compressor, and second core shaft are arranged to rotate at a higher rotational speed than the first core shaft.

18. A valve for a fuel delivery system, comprising: a valve body comprising an internal cavity, at least one inlet and one outlet, the inlet fluidly connected to a fuel source in use; a shuttle mounted within the body, the shuttle comprising a partition spanning the internal cavity and moveable relative to the inlet and outlet between a first position where the shuttle blocks the outlet whilst fluid is permitted to flow through the inlet and a second position whereby the outlet is opened whilst fluid is prevented from flowing through the inlet; a piston configured to engage the fluid within the internal cavity in order to move the shuttle between the first and second position; and a biasing mechanism arranged to bias the shuttle towards the first position; wherein the shuttle is moved towards the second position when the fluid within the cavity reaches a threshold pressure, and wherein the valve housing and shuttle comprise a first valve housing and a first shuttle, the valve comprising a further valve housing and a further shuttle sharing a common piston with the first valve housing and the first shuttle, and configured such that when the first shuttle is in the first position, the further shuttle is in the second position.

19. The valve according to claim 18, wherein opposing ends of the piston engage within the first and further valve housings respectively.

Description

DESCRIPTION OF THE DRAWINGS

(1) Embodiments will now be described by way of example only, with reference to the Figures, in which:

(2) FIG. 1 is a sectional side view of a gas turbine engine;

(3) FIG. 2 is a close up sectional side view of an upstream portion of a gas turbine engine;

(4) FIG. 3 is a partially cut-away view of a gearbox for a gas turbine engine;

(5) FIG. 4 is a close up of a valve arrangement in a first position

(6) FIG. 5 is a close up of a valve arrangement in a second position

(7) FIG. 6 is a close up of an arrangement comprising a first and second valve arrangement.

DETAILED DESCRIPTION

(8) Aspects and embodiments of the present disclosure will now be discussed with reference to the accompanying figures. Further aspects and embodiments will be apparent to those skilled in the art.

(9) FIG. 1 illustrates a gas turbine engine 10 having a principal rotational axis 9. The engine 10 comprises an air intake 12 and a propulsive fan 23 that generates two airflows: a core airflow A and a bypass airflow B. The gas turbine engine 10 comprises a core 11 that receives the core airflow A. The engine core 11 comprises, in axial flow series, a low pressure compressor 14, a high-pressure compressor 15, combustion equipment 16, a high-pressure turbine 17, a low pressure turbine 19 and a core exhaust nozzle 20. A nacelle 21 surrounds the gas turbine engine 10 and defines a bypass duct 22 and a bypass exhaust nozzle 18. The bypass airflow B flows through the bypass duct 22. The fan 23 is attached to and driven by the low pressure turbine 19 via a shaft 26 and an epicyclic gearbox 30.

(10) In use, the core airflow A is accelerated and compressed by the low pressure compressor 14 and directed into the high pressure compressor 15 where further compression takes place. The compressed air exhausted from the high pressure compressor 15 is directed into the combustion equipment 16 where it is mixed with fuel and the mixture is combusted. The resultant hot combustion products then expand through, and thereby drive, the high pressure and low pressure turbines 17, 19 before being exhausted through the nozzle 20 to provide some propulsive thrust. The high pressure turbine 17 drives the high pressure compressor 15 by a suitable interconnecting shaft 27. The fan 23 generally provides the majority of the propulsive thrust. The epicyclic gearbox 30 is a reduction gearbox.

(11) An exemplary arrangement for a geared fan gas turbine engine 10 is shown in FIG. 2. The low pressure turbine 19 (see FIG. 1) drives the shaft 26, which is coupled to a sun wheel, or sun gear, 28 of the epicyclic gear arrangement 30. Radially outwardly of the sun gear 28 and intermeshing therewith is a plurality of planet gears 32 that are coupled together by a planet carrier 34. The planet carrier 34 constrains the planet gears 32 to precess around the sun gear 28 in synchronicity whilst enabling each planet gear 32 to rotate about its own axis. The planet carrier 34 is coupled via linkages 36 to the fan 23 in order to drive its rotation about the engine axis 9. Radially outwardly of the planet gears 32 and intermeshing therewith is an annulus or ring gear 38 that is coupled, via linkages 40, to a stationary supporting structure 24.

(12) Note that the terms “low pressure turbine” and “low pressure compressor” as used herein may be taken to mean the lowest pressure turbine stages and lowest pressure compressor stages (i.e. not including the fan 23) respectively and/or the turbine and compressor stages that are connected together by the interconnecting shaft 26 with the lowest rotational speed in the engine (i.e. not including the gearbox output shaft that drives the fan 23). In some literature, the “low pressure turbine” and “low pressure compressor” referred to herein may alternatively be known as the “intermediate pressure turbine” and “intermediate pressure compressor”. Where such alternative nomenclature is used, the fan 23 may be referred to as a first, or lowest pressure, compression stage.

(13) The epicyclic gearbox 30 is shown by way of example in greater detail in FIG. 3. Each of the sun gear 28, planet gears 32 and ring gear 38 comprise teeth about their periphery to intermesh with the other gears. However, for clarity only exemplary portions of the teeth are illustrated in FIG. 3. There are four planet gears 32 illustrated, although it will be apparent to the skilled reader that more or fewer planet gears 32 may be provided within the scope of the claimed invention. Practical applications of a planetary epicyclic gearbox 30 generally comprise at least three planet gears 32.

(14) The epicyclic gearbox 30 illustrated by way of example in FIGS. 2 and 3 is of the planetary type, in that the planet carrier 34 is coupled to an output shaft via linkages 36, with the ring gear 38 fixed. However, any other suitable type of epicyclic gearbox 30 may be used. By way of further example, the epicyclic gearbox 30 may be a star arrangement, in which the planet carrier 34 is held fixed, with the ring (or annulus) gear 38 allowed to rotate. In such an arrangement the fan 23 is driven by the ring gear 38. By way of further alternative example, the gearbox 30 may be a differential gearbox in which the ring gear 38 and the planet carrier 34 are both allowed to rotate.

(15) It will be appreciated that the arrangement shown in FIGS. 2 and 3 is by way of example only, and various alternatives are within the scope of the present disclosure. Purely by way of example, any suitable arrangement may be used for locating the gearbox 30 in the engine 10 and/or for connecting the gearbox 30 to the engine 10. By way of further example, the connections (such as the linkages 36, 40 in the FIG. 2 example) between the gearbox 30 and other parts of the engine 10 (such as the input shaft 26, the output shaft and the fixed structure 24) may have any desired degree of stiffness or flexibility. By way of further example, any suitable arrangement of the bearings between rotating and stationary parts of the engine (for example between the input and output shafts from the gearbox and the fixed structures, such as the gearbox casing) may be used, and the disclosure is not limited to the exemplary arrangement of FIG. 2. For example, where the gearbox 30 has a star arrangement (described above), the skilled person would readily understand that the arrangement of output and support linkages and bearing locations would typically be different to that shown by way of example in FIG. 2.

(16) Accordingly, the present disclosure extends to a gas turbine engine having any arrangement of gearbox styles (for example star or planetary), support structures, input and output shaft arrangement, and bearing locations.

(17) Optionally, the gearbox may drive additional and/or alternative components (e.g. the intermediate pressure compressor and/or a booster compressor).

(18) Other gas turbine engines to which the present disclosure may be applied may have alternative configurations. For example, such engines may have an alternative number of compressors and/or turbines and/or an alternative number of interconnecting shafts. By way of further example, the gas turbine engine shown in FIG. 1 has a split flow nozzle 18, 20 meaning that the flow through the bypass duct 22 has its own nozzle 18 that is separate to and radially outside the core exhaust nozzle 20. However, this is not limiting, and any aspect of the present disclosure may also apply to engines in which the flow through the bypass duct 22 and the flow through the core 11 are mixed, or combined, before (or upstream of) a single nozzle, which may be referred to as a mixed flow nozzle. One or both nozzles (whether mixed or split flow) may have a fixed or variable area. Whilst the described example relates to a turbofan engine, the disclosure may apply, for example, to any type of gas turbine engine, such as an open rotor (in which the fan stage is not surrounded by a nacelle) or turboprop engine, for example. In some arrangements, the gas turbine engine 10 may not comprise a gearbox 30.

(19) The geometry of the gas turbine engine 10, and components thereof, is defined by a conventional axis system, comprising an axial direction (which is aligned with the rotational axis 9), a radial direction (in the bottom-to-top direction in FIG. 1), and a circumferential direction (perpendicular to the page in the FIG. 1 view). The axial, radial and circumferential directions are mutually perpendicular.

(20) FIGS. 4 and 5 illustrate a valve arrangement 42. In an example, the valve arrangement 42 is fora fuel system in the combustion equipment 16 of a gas turbine engine 10. However, the valve arrangement could potentially be used in other fuel delivery systems, e.g. for other types of engine.

(21) The valve arrangement 42 is provided between a fuel supply and one or more fuel spray nozzles within the combustion chamber of the engine. The valve arrangement 42 provides selective actuation of the fuel supply to the one or more fuel spray nozzles (i.e. provides a state where fuel flows to the fuel spray nozzles and provides a state where fuel does not flow to the fuel spray nozzles). The valve arrangement 42 may further provide a metered dose of fuel to the one or more fuel spray nozzles.

(22) The valve arrangement 42 may be located in close proximity to the fuel spray nozzles. The valve arrangement 42 may be an integral part of the fuel spray nozzle assembly. Alternatively, the valve arrangement 42 may be part of the fuel control system of the gas turbine engine, e.g. further upstream of a fuel spray nozzle.

(23) The valve arrangement 42 comprises a valve body 44. The valve body 44 comprises a hollow profile, such that a valve member 46, an actuator 48 and a biasing mechanism 50 may be located therein. The valve body 44 may comprise a substantially circular cross-sectional profile to form a substantially cylindrical/tubular body. Alternatively, the valve body 44 may comprise, inter alia, a rectangular, triangular, elliptical, or polygonal cross-sectional profile. The valve body 44 comprises a closed end 52, and an open end (not shown) in which the actuator 48 may be located.

(24) The valve body 44 may comprise a corrosion resistant and/or heat resistant material. The valve may comprise a metallic material. The metallic material may be nickel and/or steel. The skilled person may be able to determine other suitable conventional materials.

(25) The valve body 44 comprises a valve seat 54. The valve seat 54 is provided on the inner surface of the valve body 44. The valve seat 54 may extend fully or partially around the circumference of the valve body 44. The valve seat 54 may be annular in form.

(26) The valve seat may comprise an abutment, against which a valve member 46, to be described below can abut when biased into a first operative condition, e.g. to fill the valve body.

(27) The valve body 44 comprises a first inlet 56 fluidly connected to a fuel supply. The first inlet 56 may comprise an aperture. The first inlet 56 may comprise a valve and/or nozzle.

(28) The first inlet 56 is disposed toward the open end of the valve body 44, i.e. spaced from the closed end 52. The first inlet 56 is disposed in a portion of the valve body 44 comprising the valve member 46. The valve body 44 may comprise one, or more further, first inlets. The one, or more further, first inlets may be spaced circumferentially around the valve body 44 and/or may be spaced axially along the valve body 44.

(29) The valve body 44 comprises a second inlet 58 fluidly connected to a fuel supply. The second inlet 58 may comprise an aperture. The second inlet 58 may comprise a valve and/or nozzle. The second inlet 58 is disposed toward the closed end of the valve body 44.

(30) The second inlet 58 is disposed in a portion of the valve body 44 comprising the biasing mechanism 50. That is to say the second inlet may open into a portion of the valve body 44 in which the biasing spring is mounted.

(31) The first 56 and second 58 inlets are spaced by the valve member 46. The valve member 46 may block flow communication from the first inlet 56 to the second inlet 58 through the valve body interior.

(32) The valve body 44 may comprise one, or more, further second inlets. The one, or more further, second inlets may be spaced circumferentially around the valve body 44 and/or may be spaced axially along the valve body 44.

(33) The valve body 44 comprises an outlet 60, which in this example may be fluidly connected to a fuel spray nozzle.

(34) The outlet 60 may comprise an aperture. The outlet 60 may comprise a valve and/or nozzle.

(35) The outlet is located closer to the closed end 52 of the valve body 44 than the first inlet 56. The outlet may be located at a location along the valve body 44 that is between the first 56 and second 58 inlets.

(36) The outlet 60 is disposed in a portion of the valve body 44 comprising the valve member 46 and/or biasing member 50.

(37) The valve body 44 may comprise one, or more further, outlets. The one or more further outlets may be spaced circumferentially around the valve body 44 and/or may be spaced axially along the valve body 44.

(38) The outlet 60 is axially displaced with respect to the first inlet 56. Whilst in this example, the outlet 60 is axially displaced toward the closed end 52 of the valve body 44, the outlet 60 could otherwise be axially displaced toward the open end of the valve body 44.

(39) The outlet 60 may be circumferentially displaced with respect to the first inlet 56. The outlet 60 may be circumferentially displaced by 180 degrees. The outlet 60 may be circumferentially displaced by 90 degrees. The outlet 60 may be circumferentially displaced by between 0 degrees and 180 degrees.

(40) In this example, the valve outlet is on the opposing side of the valve body from the inlet 56.

(41) The valve arrangement 42 comprises a valve member 46. The valve member 46 is movably mounted within the valve body 44. The valve member 46 comprises side walls 60 to provide a substantially hollow profile. The valve member 46 may comprise a substantially circular cross-sectional profile to form a substantially cylindrical body. Alternatively, the valve member 46 may comprise, inter alia, a rectangular, triangular, elliptical, or polygonal cross-sectional profile. The cross-sectional profile of the valve member may substantially match that of the interior of the valve body 44.

(42) The side walls 60 of the valve member form a close fit and/or liquid-tight seal between the valve member 46 and the interior of the valve body 44.

(43) The valve member 46 comprises a panel or partition wall 62 extending between the side wall 61. The partition spans the internal/cavity area of the valve body 44 so as to fluidly isolate the interior of the valve body into two cavities, one on each side of the partition 62.

(44) The partition 62 engages the side wall 61 to define a first cavity 64 extending toward the open end of the valve body 44. A second cavity 66 is defined as extending from the other side of the partition 62 towards the closed end 52 of the valve body 44. The partition may be disposed at the end of the valve member adjacent the biasing mechanism. Alternatively, the partition 62 may be disposed part way along the valve member 46 to define a minimum volume of the second cavity 66

(45) The valve member 46 comprises an inlet 68. The inlet 68 may comprise an aperture. The aperture is configured for selective alignment with the first inlet 56 in an open condition. The aperture may be configured to correspond to the shape and/or size of the first inlet 56 provided on the valve body 44.

(46) The inlet 68 may comprise a valve and/or nozzle. The valve and/or nozzle may be configured to engage a valve and/or nozzle provided by the first inlet 56 provided on the valve body 44

(47) The valve member 46 may comprise one, or more further, inlets. The one or more further inlets may be disposed circumferentially around the valve member 46 and/or may be disposed axially along the valve member 46, e.g. to correspond with a plurality of first inlets 56 of the valve body.

(48) The valve member 46 comprises an outlet 70. The outlet 70 may comprise an aperture. The aperture is configured for selective alignment with the outlet 60 when in an open condition. The aperture may be configured to correspond to the shape and/or size of the outlet 60 provided on the valve body 44

(49) The outlet 70 may comprise a valve and/or nozzle. The valve and/or nozzle may be configured to engage a valve and/or nozzle provided by the outlet 60 provided on the valve body 44

(50) The valve member 46 may comprise one, or more further, outlets. The one or more further outlets may be disposed circumferentially around the valve member 46 and/or may be disposed axially along the valve member 46, e.g. to correspond with a plurality of outlets 60 of the valve body.

(51) The outlet 70 is axially spaced/displaced with respect to the inlet 68. The outlet 70 may be axially displaced toward the closed end 52 of the valve body 44. In an alternative configuration, the outlet 70 may be axially located closer to the open end of the valve body 44.

(52) The inlet 68 and outlet 70 of the valve member are both located to the same side of the partition 62, i.e. within the same cavity within the valve body.

(53) The axial spacing between the inlet 68 and outlet 70 of the valve member 46 is different from the spacing between the inlet 56 and outlet 60 of the valve body. This ensures that the inlet and outlet cannot both be open at the same time. In this example, the axial spacing between the inlet 68 and outlet 70 of the valve member is less the axial spacing between the inlet 56 and outlet 60 of the valve body.

(54) The outlet 70 may be circumferentially displaced with respect to the inlet 68. The outlet 70 may be circumferentially displaced by 180 degrees. The outlet 60 may be circumferentially displaced by 90 degrees. The outlet 60 may be circumferentially displaced by between 0 degrees and 180 degrees. The circumferential spacing may match the spacing between the inlet 56 and outlet 60 of the valve body.

(55) In this example, the outlet 70 is on the opposing side of the valve member from the inlet 68.

(56) The valve arrangement 42 comprises an actuator 48. The actuator comprises an arm or piston 72. The piston 72 is provided at the open end of the valve body 44 and extends into the open end of the valve body 44. In the condition shown, the piston terminates, e.g. at an end face, adjacent inlet 56 of the valve body.

(57) The piston 72 is shaped to correspond to the profile of the valve body 44 interior. The outer surface of the piston 72 forms a close fit and/or liquid-tight seal with the interior of the valve member 46/valve seat 54.

(58) The piston 72 is shaped so as to extend into/through the valve seat 54. The piston 72 is further shaped so as to extend into the first cavity 64 and along the side wall 61 of the valve member 46. The end profile of the piston 48 may match that of the partition 62.

(59) The piston 72 is actuatable within the valve arrangement in a linear/axial direction. The piston 72 is configured to move towards and away from the closed end 52 of the valve body 44.

(60) The actuator 48 may comprise a linear actuator, such as an electrical solenoid configured to move the piston 72. Alternatively, the actuator 48 may comprise, inter alia, a hydraulic actuator, a pneumatic actuator or a mechanical actuator.

(61) The valve arrangement 42 comprises a biasing mechanism 50. The biasing mechanism 50 is configured to bias the valve member 46 away from the closed end.

(62) The biasing mechanism 50 is disposed between the closed end 52 of the valve body 44 and the valve member 46. The biasing mechanism 50 engages the valve member 46, e.g. on the opposing side of the partition wall 62 from the piston 72.

(63) The biasing mechanism 50 may be affixed to the valve member 46 or may engage the valve member 46 without fixation. In one example, the biasing mechanism 50 engages the partition 62 provided on the valve member 46. The biasing mechanism 50 may extend into cavity 66, if present. In an alternative example, the biasing mechanism 50 engages the side walls 61 of the valve member 46.

(64) The biasing mechanism 50 may comprise a resilient biasing means. The resilient biasing means may comprise a spring. The spring may comprise, inter alia, a compression spring, an extension spring, a torsion spring, a constant force spring, or a Belleville spring. Alternatively, the resilient biasing means may comprise a pneumatic device.

(65) In a further example, a plurality of valve arrangements are operated using a common actuator 48 and/or piston 72.

(66) As shown in FIG. 6, a first valve arrangement 42 and a second valve arrangement 43 are operated using a common actuator 48. The valve arrangements 42,43 are substantially identical and are provided about a mirror axis 74.

(67) Two valve members 46 are provided at opposing ends of the piston 72. The two valve members 46 are provided in a mirror arrangement about the piston 72.

(68) A single valve body 44 may be provided, or alternatively, separate valve bodies for each end of the piston may be provided.

(69) Operation of the Valve Arrangement

(70) FIG. 4 shows the valve arrangement in a first position to provide a filling cycle. In the first position the piston 72 of the actuator 48 is in a retracted position relative to the end wall 52 and/or cavity 64. The piston end is retracted behind the opening 56 and opening 68.

(71) The valve member 46 is biased by the biasing mechanism 50 towards the open end of the valve body 44 and rests against the valve seat 54.

(72) The first inlet 56 provided on the valve body 44 and the inlet 68 provided on the valve member are aligned. This permits fuel from the fuel supply to flow into the cavity 64. The cavity 64 provides a fixed volume and therefore holds a fixed, or metered, volume of fuel in this condition.

(73) The outlet 60 provided on the valve body 44 and the outlet 70 provided on the valve member 46 are misaligned. The outlet 70 provided on the valve member 46 overlies a wall portion of the valve body 44, preventing egress of fuel from the cavity 64.

(74) Fuel may freely enter/leave the second inlet 58 provided on the valve body 44 and the volume to the left-hand side of partition 62 (i.e. surrounding the biasing mechanism 50 and cavity 66) may be flooded.

(75) The biasing force provided by the biasing mechanism 50 may be sufficient to prevent movement of the valve member 46 from this condition under the operational fluid pressure alone.

(76) Once an appropriate amount of fuel enters the valve member, an emptying cycle is performed by actuation of the piston.

(77) FIG. 5 shows the valve arrangement in a second position to provide the emptying cycle.

(78) At the beginning of the emptying cycle, the actuator is activated and the piston 72 begins to extend into the cavity 64 towards the partition 62. The piston 72 moves to a position that overlies the inlet 68 provided on the valve member 46 and prevents further fuel from entering.

(79) Further extension of piston increases the pressure of the fuel within the cavity 64. The biasing force of the mechanism 50 opposes the fluid pressure in the cavity 64. Once the pressure reaches/exceeds a threshold level, the force provided by pressure onto the valve member will be greater than the biasing force provided by the biasing mechanism 50. This will result in the valve member 46 moving against the biasing mechanism 50 towards the closed end 52 of the valve body 44. As a result of the movement of the valve member, the first inlet 56 provided on the valve body 44 and the inlet 68 provided on the valve member become misaligned, further preventing flow of fuel into the cavity 64.

(80) At the same time, fuel is also ejected from the area surrounding the biasing mechanism 50 and cavity 66 through the second inlet 58. This can prevent excessive pressure build up on the opposing side of the partition 62 from the piston 72.

(81) The valve member 46 is further moved by the actuator 48 to a second position where the outlet 60 provided on the valve body 44 is aligned with the outlet 70 provided on the valve member 46. This permits fuel to egress from the cavity 64, e.g. to flow towards the combustion equipment 16, e.g. the burner head or nozzle, in this example.

(82) The piston 72 is further driven by the actuator 48 into the cavity 64 to eject fuel from the cavity 64. The piston 72 fully occupies the cavity 64 and ejects all of the fuel contained within the cavity. The piston 72 may then be retracted.

(83) Upon retraction of the piston 72, the biasing mechanism 50 acts to bias the valve member 46 away from the closed end 52 of the valve body. The valve member moves towards the open end of the valve body and the outlet 60 provided on the valve body 44 becomes misaligned with the outlet 70 provided on the valve member 46, and any further egress of fuel is prevented. This closure of the outlet is achieved before the inlet is opened on the return stroke.

(84) The piston 72 is retracted fully to allow the valve member 46 to return to the first position. Once again, the first inlet 56 provided on the valve body 44 and the inlet 68 provided on the valve member are aligned. The outlet 60 provided on the valve body 44 and the outlet 70 provided on the valve member 46 are again misaligned.

(85) The filling and emptying cycle is then repeated. Then number of cycles may be monitored to determine the fuel consumption based on the metered volume of fuel provided at each cycle. Metered fuel delivery can thus be controlled using the valve arrangement, e.g. by controlling the frequency/speed of the filling and emptying cycle. A conventional engine or fuel delivery controller may be used for this purpose, in communication with the actuator 48 so as to send control instructions thereto.

(86) The first inlet 56 and the outlet 60 of the valve body 44 and the inlet 68 and the outlet 70 of the valve member 46 are configured such that at most one fluid pathway in or out of the cavity 64 is provided at a given time. At no point in the cycle can fuel flow into the valve arrangement and out of the valve arrangement 42 simultaneously. Throughout the majority of the cycle fuel can neither flow into the valve arrangement 42 nor out of the fuel arrangement 42.

(87) Where a plurality of valve arrangements are provided using a common actuator, operation of the valve arrangements remains substantially the same as described above, save that both advancing and retracting strokes of the piston can be used simultaneously to meter/control fluid flow through two valve arrangements simultaneously.

(88) As shown the FIG. 6, the first valve arrangement 42 and the second valve arrangement 43 are configured so that when the first valve arrangement 42 is in the first position (i.e. the filling cycle), the second valve arrangement 43 is in the second position (i.e. the emptying cycle).

(89) The piston 72 is then moved toward the first valve arrangement 42, so that the first valve arrangement 42 is in the second position (i.e. the emptying cycle) and the second valve arrangement 43 is in the first position (i.e. the filling cycle).

(90) The piston 72 is then moved back toward the second valve arrangement 43 and the cycle is repeated. Thus equivalent operation of two valve arrangements is achieved but each valve being out of phase with respect to the operation of the other.

(91) Advantages of the Valve AArrangement:

(92) The valve arrangement prevents unrestricted flow of fuel through the valve in case of failure of the actuator.

(93) The valve arrangement prevents excess fuel entering the engine and damaging the turbine.

(94) The valve arrangement provides a fail-safe to prevent leakage of fuel.

(95) The valve arrangement permits each cycle of the arrangement to provide a metered dose of fuel.

(96) The valve arrangement permits efficient fuel consumption of the gas turbine engine.

(97) The dual valve arrangement allows double the rate of fuel delivery for a single stroke of the actuator. This can reduce the number/weigh of actuators and/or allow greater variation in volumetric flow rate through the metering valve.

(98) Whilst the present disclosure has been discussed in terms of a gas turbine engine, the valve arrangement 42 may be used in any field where the controlled transmission of a fuel/fluid is required. The valve arrangement 42 may be used with any suitable fluids, including liquids and/or gasses.

(99) The valve arrangement 42 may comprise gas tight seals between the valve member 46 and the valve body 44. The valve arrangement 42 may comprise gas tight seals between the actuator 48 and the valve body 44/valve seat 54.

(100) It will be understood that the invention is not limited to the embodiments above-described and various modifications and improvements can be made without departing from the concepts described herein. Except where mutually exclusive, any of the features may be employed separately or in combination with any other features and the disclosure extends to and includes all combinations and sub-combinations of one or more features described herein.