阅读说明：本技术 电隔离器 (Electrical isolator ) 是由 W.波利特 J.W.伯纳德 于 2019-12-13 设计创作，主要内容包括：描述一种电隔离器,其包括：第一流体载运构件和第二流体载运构件,第二流体载运构件与第一流体载运构件间隔开；电阻性、半导电或非导电部件,所述部件位于第一流体载运构件与第二流体载运构件之间,其中所述部件适于输送从第一流体载运构件流向第二流体载运构件的流体；其中第一流体载运构件包括沿径向向外延伸的第一环形突出部,并且第二流体载运构件包括沿径向向外延伸的第二环形突出部,使得在第一环形突出部与第二环形突出部之间形成环形空腔；其中电隔离器还包括：在环形空腔中的沿周向卷绕的纤维增强聚合物的层；以及螺旋状卷绕的纤维增强聚合物的层,螺旋状卷绕的纤维增强聚合物的层在第一环形突出部、环形空腔和第二环形突出部上方延伸。(An electrical isolator is described, comprising: a first fluid carrying member and a second fluid carrying member, the second fluid carrying member being spaced apart from the first fluid carrying member; a resistive, semi-conductive or non-conductive component, the component being located between the first fluid carrying means and the second fluid carrying means, wherein the component is adapted to transport fluid flowing from the first fluid carrying means to the second fluid carrying means; wherein the first fluid carrying member comprises a first annular protrusion extending radially outwardly and the second fluid carrying member comprises a second annular protrusion extending radially outwardly such that an annular cavity is formed between the first and second annular protrusions; wherein the electrical isolator further comprises: a layer of circumferentially wound fiber reinforced polymer in the annular cavity; and a layer of helically wound fiber reinforced polymer extending over the first annular protrusion, the annular cavity, and the second annular protrusion.)

1. An electrical isolator, comprising:

a first fluid carrying member and a second fluid carrying member, the second fluid carrying member being spaced apart from the first fluid carrying member;

a resistive, semi-conductive or non-conductive member located between the first fluid carrying means and the second fluid carrying means, wherein the resistive, semi-conductive or non-conductive member is adapted to convey fluid flowing from the first fluid carrying means to the second fluid carrying means;

wherein the first fluid carrying member comprises a first annular protrusion extending radially outwardly and the second fluid carrying member comprises a second annular protrusion extending radially outwardly such that an annular cavity is formed between the first and second annular protrusions;

wherein the electrical isolator further comprises:

a layer of circumferentially wound fiber reinforced polymer in the annular cavity; and

a layer of helically wound fiber reinforced polymer extending over the first annular protrusion, the annular cavity, and the second annular protrusion.

2. The electrical isolator of claim 1, wherein the layer of helically wound fiber reinforced polymer is partially electrically conductive.

3. The electrical isolator of claim 2, wherein the electrical conductivity of the helically wound layer of fiber reinforced polymer is controlled by the addition of a conductive additive.

4. The electrical isolator of claim 3, wherein the conductive additive is carbon black or carbon nanotubes.

5. The electrical isolator of any preceding claim, wherein the circumferentially wound layer of fibre reinforced polymer extends radially outwardly over at least a radial extent of the first and second annular projections.

6. An electrical isolator as claimed in any preceding claim, wherein the first and second annular projections taper from a relatively smaller thickness and/or outer diameter to a relatively larger thickness and/or outer diameter when moving towards the resistive, semi-conductive or non-conductive component.

7. The electrical isolator of claim 6, wherein the layer of helically wound fiber reinforced polymer extends axially past each of the first and second tapered annular protrusions of the first and second fluid carrying means when moving in a direction opposite the resistive, semi-conductive, or non-conductive component.

8. An electrical isolator as claimed in any preceding claim, wherein the resistive, semi-conductive or non-conductive member extends axially across the entire width of the annular cavity.

9. An electrical isolator as claimed in any preceding claim, further comprising:

a sacrificial layer of fiber reinforced polymer disposed radially outward of the helically wound layer of fiber reinforced polymer.

10. The electrical isolator of claim 9, wherein the sacrificial layer is formed from a circumferentially wound fiber reinforced polymer.

11. An electrical isolator as claimed in any preceding claim, wherein the first and second fluid-carrying members are metallic.

12. An electrical isolator as claimed in any preceding claim, wherein there is no air gap or other material between the layer of helically wound fibre reinforced polymer and the first and second fluid carrying members.

13. A hydraulic system for use in an aircraft, the hydraulic system comprising an electrical isolator as claimed in any preceding claim.

14. A fuel system for use in an aircraft, the fuel system comprising an electrical isolator as claimed in any one of claims 1 to 12.

15. A method of forming one or more electrical isolators, the method comprising:

connecting a first fluid carrying means to a second fluid carrying means using a resistive, semi-conductive or non-conductive member such that the resistive, semi-conductive or non-conductive member is capable of transporting fluid flowing from the first fluid carrying means to the second fluid carrying means;

winding a layer of circumferential fibers in an annular cavity formed between a first annular protrusion extending radially outward from the first fluid carrying member and a second annular protrusion extending radially outward from the second fluid carrying member;

winding a layer of helical fibers over the first annular protrusion, the annular cavity, and the second annular protrusion.

Technical Field

The present disclosure relates generally to electrical isolators, and more particularly to electrical isolators for use in hydraulic fluid lines of aircraft. The electrical isolator may be used to connect two fluid carrying members such as pipes, hoses or tubes, for example pipes carrying hydraulic fluid.

Background

Aircraft and other vehicles contain a large number of fluid conveyance systems, specifically hydraulic systems that include fluid conveyance components (such as pipes). Such components are typically metallic and have good electrical conductivity.

Devices are incorporated into such systems to form electrical isolators between the metal components. These isolators prevent the build-up of static charge by safely dissipating the static build-up and also prevent excessive current flow through the system, for example due to a lightning strike. Both of these events can lead to a fire hazard if no such isolator is present in the system.

When incorporated into a fluid delivery system, the electrical isolator also needs to serve as a safety passageway for the fluid. In certain systems, such as hydraulic systems or hydraulic fluid lines in aircraft, the isolator needs to be able to withstand high pressures, in addition to other loading and environmental factors.

The present disclosure is directed to balancing the above factors to provide electrical isolation functionality within a pressurized fluid system.

EP 3153756 describes such an electrical isolator in which a reinforcing composite material is provided over the top of the resistive component. The reinforced composite material is made partially conductive by adding conductive additives to the resin to control electrical conductivity within the electrical isolator so that the electrical isolator can dissipate static buildup without becoming a primary conductive path in the event of a lightning strike.

Disclosure of Invention

According to an aspect of the present disclosure, there is provided an electrical isolator comprising:

a first fluid carrying member and a second fluid carrying member, the second fluid carrying member being spaced apart from the first fluid carrying member;

a resistive, semi-conductive or non-conductive member located between the first fluid carrying means and the second fluid carrying means, wherein the resistive, semi-conductive or non-conductive member is adapted to convey fluid flowing from the first fluid carrying means to the second fluid carrying means;

wherein the first fluid carrying member comprises a first annular protrusion extending radially outwardly and the second fluid carrying member comprises a second annular protrusion extending radially outwardly such that an annular cavity is formed between the first and second annular protrusions;

wherein the electrical isolator further comprises:

a layer of circumferentially wound fiber reinforced polymer in the annular cavity; and

a layer of helically wound fiber reinforced polymer extending over the first annular protrusion, the annular cavity, and the second annular protrusion.

According to another aspect of the present disclosure, there is provided a method of forming one or more electrical isolators, the method comprising:

connecting a first fluid carrying means to a second fluid carrying means using a resistive, semi-conductive or non-conductive member such that the resistive, semi-conductive or non-conductive member is capable of transporting fluid flowing from the first fluid carrying means to the second fluid carrying means;

winding a layer of circumferential fibers in an annular cavity formed between a first annular protrusion extending radially outward from the first fluid carrying member and a second annular protrusion extending radially outward from the second fluid carrying member;

winding a layer of helical fibers over the first annular protrusion, the annular cavity, and the second annular protrusion.

The layer of circumferentially wound fibers (also referred to as "stirrup" fibers) provides additional pressure resistance to the joint. The stirrup fiber is wound at a large angle to the axis of the structure, so that it is wound in a very narrow helix (or in some cases even directly on itself, i.e. at ninety degrees to said axis). Thus, the stirrup fibers cannot be spread under radial pressure and can therefore withstand radial loads, i.e. they are pressure-resistant. Such electrical isolators with layers of hoop reinforcement fibers better accommodate the high pressures of hydraulic systems.

While circumferential fibers are well suited to provide pressure resistance, they are not well suited to holding the fitting together because they do not provide much strength in the axial direction. However, the layer of helically wound fibers disposed radially outward of the circumferential fibers provides axial strength. As this layer is wound over the annular projections provided on the first and second fluid carrying members, the layer of helical fibres provides axial compression to both projections and thus holds the two fluid carrying members and the resistive, semi-conductive or non-conductive component all tightly together.

When the helical fibers are wound on top of the circumferential fibers, the helical fibers also tend to compress the underlying circumferential fibers as they are compacted in the radial direction as well as in the axial direction. If the circumferential fibres twist in the axial direction, the circumferential fibres lose their shape, which makes winding up the subsequent layers problematic. The arrangement of the circumferential fibres in the annular cavity formed between the two annular projections means that the circumferential fibres are received against axial expansion and are thus retained in the region of the joint in order to provide the desired pressure resistance using a sufficient number of circumferential fibres. This also ensures a consistent surface for the fibers to wrap around.

Circumferential fibres here mean fibres having a large winding angle (the angle which the fibre makes with the axis of the component (typically mounted on a mandrel) during winding)) which is typically 80 degrees up to 90 degrees, more preferably at least 85 degrees.

Helical fibres here mean fibres having a small winding angle, which is typically between 30 and 70 degrees. It is often difficult to wind the fiber at angles below about 30 degrees, while angles above 70 degrees do not provide the desired axial strength. However, lower angles as low as almost 0 degrees are still feasible if fiber placement can be achieved. Even though axial fibers may indeed be used instead of helical fibers (i.e. fibers at an angle of 0 degrees to the axis, i.e. parallel to the axis), the placement of such fibers is still difficult.

In some examples, the layer of helically wound fiber reinforced polymer may be partially conductive. This conductivity enables dissipation of static electricity, but the conductivity can be controlled such that the layer of helically wound fiber reinforced polymer does not provide a primary conductive path in the event of a lightning strike.

The conductivity of the layer of helically wound fiber reinforced polymer may be controlled by the addition of conductive additives. Any suitable conductive additive may be used. However, in some preferred examples, the conductive additive is carbon black or carbon nanotubes.

It will be appreciated that the axial fibre-reinforced polymer may also be made partially conductive. In some instances, this would not be necessary as the helical fibre reinforced polymer is in electrical contact with the first and second fluid carrying members and thus provides the desired electrically conductive path, so that there is no need to add any electrically conductive filler to the circumferential fibre reinforced polymer. In other instances, it may be preferable to add conductive fillers, for example, to achieve desired electrical properties.

Thus, such a separator uses a reinforced composite material to surround the first fluid carrying member, the second fluid carrying member and the non-conductive component while providing a conductive path through the reinforced composite material, rather than the component sealing the two fluid carrying members. This provides a device that effectively dissipates charge buildup and electrically isolates the junction between the two delivery devices while providing a strong junction that withstands high voltages.

The conductive additive may be present in the resin mixture in an amount up to or at least 30%, 20%, 10%, 5%, 2% or 1% by weight or volume of the resin mixture. The resin and/or fiber may be present in the reinforced composite in an amount up to or at least 30%, 40%, 50%, 60%, 70%, 80% or 90% by weight or volume of the reinforced composite.

In some examples, the circumferentially wound layer of fiber reinforced polymer extends radially outward for at least a radial extent of the first and second annular projections. While it will be appreciated that in some instances it may extend to a smaller radial extent than the projection, this may be accompanied by the creation of a void between the circumferentially wound fiber and the helical fiber wound over the projection. Thus, it is preferred that the circumferential fibre layer extends radially outwards at least as far as the protrusions. In most designs, it is desirable that the two projections be the same height. However, if there is a difference in height for any reason, it would be preferable to wind the circumferential fibers at least to the height (radial extent) of the higher projections. The circumferential fibers may be wound to a greater radial extent than the protrusions, for example to provide more pressure resistance.

The projections may have any suitable shape. However, in some examples, the first and second annular projections taper from a relatively smaller thickness and/or outer diameter to a relatively larger thickness and/or outer diameter when moving toward the resistive, semiconductive, or nonconductive component.

The layer of helically wound fiber reinforced polymer preferably extends axially past each of the tapered protrusions when moving in a direction opposite the resistive, semi-conductive or non-conductive member. This may provide a securing arrangement securing the first fluid carrying member, the second fluid carrying member and the resistive, semi-conductive or non-conductive component. As the helically wound fiber layer graduates from a small diameter (the outer diameter of the first fluid carrying member) at one end, through a larger diameter (the joint comprising the resistive, semi-conductive or non-conductive components and the stirrup fiber layer and the protrusion) and back to a small diameter (the outer diameter of the second fluid carrying member) at the other end, it holds the joint firmly together.

Thus, in a preferred example, the layer of helically wound fibre reinforced polymer extends axially past each of the first and second tapered annular protrusions of the first and second fluid carrying means when moving in a direction facing away from the resistive, semi-conductive or non-conductive component.

The surface within the annular air on which the circumferential fibres are to be wound may be formed by a combination of the first and second fluid-carrying members and the resistive, semi-conductive or non-conductive component. However, in some examples, it will be convenient for the winding surface between the projections to be formed entirely by the outer diameter of the resistive, semiconductive or nonconductive member. Thus, in certain preferred examples, the resistive, semiconductive or nonconductive component extends axially across the entire width of the annular cavity. This provides a uniform and consistent surface upon which the circumferential fibers will be wound. In addition, since a certain zone of the resistive, semiconductive or nonconductive component generally requires the maximum strength from the circumferential fibres, it is effective, in terms of material and therefore weight, to have the width of the layer of circumferential fibres the same as the width of said resistive, semiconductive or nonconductive component. In addition, this arrangement also minimizes the overall axial extent of the joint and thus also minimizes material and weight, since the projections preferably form the side walls of the cavity and since the projections also define the axial extent of the over-wound helical fiber layer.

In some examples, the side of the protrusion forming the sidewall of the cavity (i.e., the side closest to the resistive, semi-conductive or non-conductive component and thus the side opposite the aforementioned tapered side) is formed perpendicular to the axis of the fluid carrying means and the resistive, semi-conductive or non-conductive component (i.e., substantially perpendicular to the outer diameter of the resistive, semi-conductive or non-conductive component forming the bottom of the annular cavity).

In a preferred example, the electrical isolator further comprises: a sacrificial layer of fiber reinforced polymer disposed radially outward of the helically wound layer of fiber reinforced polymer. The sacrificial layer provides an outer surface that can be machined to shape the isolator for attachment to other structures (e.g., support structures within an aircraft). The sacrificial layer ensures that such machining does not damage the underlying helical fibers, which could reduce the axial strength of the joint. The sacrificial layer may furthermore optionally be made of a circumferentially wound fibre reinforced polymer and it may optionally be partially electrically conductive, for example by including electrically conductive fillers as discussed above.

The first and second fluid carrying members may be metallic.

The first and/or second fluid-carrying means and/or resistive, semi-conductive or non-conductive components and/or reinforced composite material may be tubular. The first and/or second fluid-carrying means and/or resistive, semiconductive or nonconductive components and/or reinforced composite material may each have substantially the same cross-section, for example a circular cross-section.

Alternatively, the first and/or second fluid carrying means and/or resistive, semi-conductive or non-conductive components and/or composite layers (spiral and circumferential) may each have other shapes and cross-sections, such as square, rectangular, triangular or irregular cross-sections.

The diameter of the first and/or second fluid-carrying means and/or resistive, semi-conductive or non-conductive component and/or fibre-reinforced polymer layer may be at least or no greater than 5mm, 10mm, 15 mm, 20 mm, 25mm, 30 mm, 35 mm, 40 mm, 45 mm, 50 mm, 60 mm, 70 mm, 80 mm, 90 mm or 100 mm.

The thickness of the first and/or second fluid-carrying means and/or resistive, semiconductive or nonconductive means and/or fibre-reinforced polymer layer may be at least or not greater than 1 mm, 2 mm, 3 mm, 4 mm, 5mm or 10 mm.

The first fluid carrying means, the second fluid carrying means and the resistive, semi-conductive or non-conductive component may have a substantially constant inner diameter. This may reduce the amount of sloshing experienced by the fluid as it flows through the isolator, which in turn reduces the accumulation of static charge.

In a preferred example, there is no air gap or other material between the helically wound fibre reinforced polymer and the first and second fluid carrying members. This ensures that the helically wound fibers contact and press the first and second fluid carrying components directly onto the resistive, semi-conductive or non-conductive component for good joint strength and stability.

According to an aspect of the present disclosure, there is provided a hydraulic system or hydraulic fluid line, for example for use in an aircraft, comprising an electrical isolator as described above. It has been found that the techniques disclosed herein are particularly suitable for electrically isolating components that are under high pressure, for example, high pressures experienced in hydraulic systems, such as greater than 1000, 2000, or 3000 psi. In other aspects, a fuel system or fuel line, for example for use in an aircraft, is provided, comprising an electrical isolator as described above.

It will be appreciated that any suitable fiber placement technique may be used to form the circumferentially (stirrup) -wound fiber layer and the helically or axially wound fiber layer. Examples of suitable techniques include filament winding, braiding, advanced fiber placement, resin transfer molding, and the like.

It will also be appreciated that any suitable type of fibre may be used. For example, the fibers may include glass fibers, carbon fibers, or aramid fibers.

The fibre-reinforced polymer may be formed from a polymer matrix (such as a resin) in which fibres are embedded. The resin mixture may include a resin, which may be a thermosetting polymer (e.g., an epoxy resin) or a thermoplastic polymer (e.g., polyetheretherketone- "PEEK").

It will also be appreciated that the fiber placement technique may include adding resin to the fibers at any suitable time (e.g., before, during, or after placement of the fibers).

Additionally, while it will be appreciated that different resins may be used for different fiber layers, it is preferred in some instances to use the same resin to improve bonding between the layers. In addition, while the different layers may be cured separately, it is preferred that the two layers be cured together simultaneously so that the two layers are chemically bonded by polymeric crosslinking.

In any aspect of the embodiments described herein, the first and second fluid-carrying members may be configured to carry or transport a fluid and are not limited to any particular geometry or cross-section. The first fluid carrying means, the second fluid carrying means and the resistive, semi-conductive or non-conductive component may be coaxial with one another.

The helical fibre reinforced polymer layer surrounds the first and second fluid carrying members but is typically only an end portion thereof, for example, closest to the resistive, semi-conductive or non-conductive component. The helical fibre reinforced polymer layer may be a continuous tube extending from the first fluid carrying member (or an end portion thereof) and extending across the resistive, semi-conductive or non-conductive component (and circumferentially wound fibre reinforced polymer layer) to the second fluid carrying member (or an end portion thereof).

The helical fibre-reinforced polymer layer may have a varying cross-sectional area and/or inner and/or outer diameter. Optionally, the helical fibre-reinforced polymer layer may have a constant or substantially constant cross-sectional area and/or inner diameter and/or outer diameter and/or thickness. The cross-sectional area of the helical fibre-reinforced polymer layer varies by no more than 5%, 10%, 15%, 20%, 30%, 40%, 50%, 100%, 200%, 300%, 400% or 500% over its length.

The electrical isolator may further comprise one or more first seals between a cooperating surface of the first fluid carrying member and a cooperating surface of the first end of the resistive, semi-conductive or non-conductive member. The electrical isolator may further comprise one or more second seals between a cooperating surface of the second fluid carrying member and a cooperating surface of the second end of the resistive, semi-conductive or non-conductive member. The cooperating surface may be formed by overlapping the fluid carrying means with the resistive, semi-conductive or non-conductive component (e.g. by partially inserting one of the components inside the other). The cooperating surfaces may thus be an outer facing surface (i.e. an outer diameter) of the first (or second) fluid carrying member and an inner facing surface (i.e. an inner diameter) of the first (or second) end of the resistive, semi-conductive or non-conductive member. In such an arrangement, the resistive, semi-conductive or non-conductive member partially surrounds each of the first and second fluid-carrying members. Likewise, the cooperating surfaces may be an inward facing surface (i.e. inner diameter) of the first (or second) fluid carrying member and an outward facing surface (i.e. outer diameter) of the first (or second) end of the resistive, semi-conductive or non-conductive member. In such an arrangement, the resistive, semi-conductive or non-conductive member is partially surrounded by each of the first and second fluid-carrying members.

Positioning the seal between the surfaces as described above may provide an optimal location for the seal assembly. The cooperating surfaces may be dimensioned such that, on assembly, one or more of the first and second seals are pressed against the opposing surface.

The one or more first and second seals may be configured to fluidly isolate the resistive, semi-conductive or non-conductive component from the first and second fluid-carrying members.

Drawings

Certain preferred examples will now be described, by way of example only, and with reference to the accompanying drawings, in which:

FIG. 1 illustrates a cross-sectional view of an electrical isolator according to one example of the present disclosure;

FIG. 2 illustrates the problem of wrapping around stirrup fibers; and

fig. 3 shows a perspective view of the electrical isolator of fig. 1.

Detailed Description

The present disclosure relates to electrical isolators that may be used in aircraft hydraulic systems or hydraulic fluid lines to provide a robust fluid-carrying structure while controlling induced electrical currents (e.g., induced by lightning) and dissipation of static electrical charges. Such electrical isolators may also be used in fuel lines in, for example, aircraft.

Fig. 1 illustrates a cross-sectional view of an electrical isolator or fluid carrying element 10 according to one embodiment of the present disclosure.

The electrical isolator 10 forms part of a fluid carrying network, such as a hydraulic fluid network in an aircraft. Fluid (e.g., hydraulic fluid) may flow through electrical isolator 10 in the direction of arrow 100.

Electrical isolator 10 includes a first conduit 12 and a second conduit 14. The first conduit 12 and the second conduit 14 may be metallic. In the example shown, the first conduit 12 and the second conduit 14 have the same structure. The first and second conduits 12, 14 are opposed to and spaced apart from each other to provide a gap therebetween.

In the illustrated embodiment, the first conduit 12 and the second conduit 14 are tubular, i.e., cylindrical in shape and have a circular cross-section. Other shapes and cross-sections are possible. Although the first conduit 12 and the second conduit 14 are shown as being coaxial in fig. 1, this is not required and embodiments are contemplated in which the axes of the first conduit 12 and the second conduit 14 are at an angle relative to each other. The angle may be, for example, less than 90, 60, 30, 15, 10, or 5 degrees.

The first and second conduits 12, 14 terminate in a shoulder portion 11. The shoulder portion 11 has an increased outer diameter and/or thickness compared to the portions of the respective pipe 12, 14 adjacent thereto. The shoulder portion 11 comprises a radially extending surface 15 perpendicular to the axis a of the pipe and an annular flange 13 extending axially from the radially extending surface 15. Each annular flange 13 terminates in a respective radially extending surface 17.

A resistive, semiconductive or nonconductive member or liner 16 is positioned between first conduit 12 and second conduit 14. The liner 16 connects the first conduit 12 to the second conduit 14 and maintains a fluid path therebetween (see arrows 100). The liner is shown in fig. 1 as being tubular and coaxial with the first conduit 12 and the second conduit 14. Other configurations are possible, for example if the axes of the first and second conduits 12, 14 are angled with respect to each other as discussed above. Liner 16 is resistive, semi-conductive, or non-conductive such that it does not itself conduct or carry current between first conduit 12 and second conduit 14.

Each axial end of the liner 16 includes a radial surface 19 and an annular flange 18 extending axially (i.e., perpendicular to the axis a of the liner 16) from the radially extending surface 19. The annular flange 18 of the liner 16 terminates in a radially extending surface 20.

The respective flanges 13 of the first and second conduits 12, 14 are configured to fit and/or slide into the respective flanges 18 of the liner 16. Optionally, the respective flanges 18 of the liner 16 may be configured to fit and/or slide into the respective flanges 13 of the first and second pipes 12, 14. Thus, the radially extending surfaces 17 of the first and second conduits 12, 14 contact and are opposite the radially extending surfaces 19 of the liner 16. Similarly, the radially extending surface 15 of the shoulder portion 11 contacts and is opposite the radially extending surface 20 of the annular flange 18 of the liner 16.

The inner diameter of the liner 16 may be the same as the inner diameter of the first conduit 12 and the second conduit 14. This may help reduce turbulence to the fluid flowing through electrical isolator 10.

Shoulder portions 11 of first and/or second conduits 12, 14 may be shaped to taper from a relatively smaller outer diameter to a relatively larger outer diameter moving toward the end of the respective conduit 12, 14 (or toward liner 16). The shoulder portion 11 thus forms a tapered projection comprising a ramp of increasing outer diameter when moving towards the end of the respective pipe 12, 14 (or towards the liner 16). The ramp may terminate in a radially extending surface 15, which may define the point at which the shoulder portion 11 has the greatest outer diameter.

The liner 16 is fluidly isolated from the first and second conduits 12, 14 using one or more sealing members 25. In the illustrated embodiment, the sealing member 25 is an annular "O" ring, and two sealing members are provided to seal each of the first and second conduits 12, 14. The annular rings are seated in corresponding grooves on the annular flanges 13 of the first and second pipes 12, 14. Other amounts or types of seals would be possible and in other arrangements, such as instead providing a groove on the annular flange 18 of the liner 16.

Two opposite radially extending surfaces 15 form the walls of an annular cavity 30, the bottom of which is formed by the radially outer surface 31 of the liner 16. In this example, the liner 16 extends across the entire width of the annular cavity 30 and thus provides a single continuous surface on which the circumferentially wound layer 32 of fibre reinforced polymer is wound.

The layer 32 of circumferentially wound fibre reinforced polymer provides good pressure resistance at the joint between the liner 16 and the two pipes 12, 14. In particular, the layer 32 of circumferentially wound fibre-reinforced polymer is located within the annular cavity 30, being confined to the radially extending surface 15 forming the wall of the cavity 30. The circumferentially wound fibre-reinforced polymer layer 32 is thus axially constrained within the cavity 30, thereby maintaining its shape and quality of pressure resistance.

In the example shown in fig. 1, the layer 32 of circumferentially wound fibers extends radially to the same height as the top of the radially extending surface 15. Thus, the outer diameter of the layer 32 is the same as the outer diameter of the shoulder portions 11 of the first and second conduits 12, 14, e.g. with a ramp (conical projection) terminating in the radially extending surface 15. This creates a smooth transition from the outer diameter of the layer 32 to the outer surface of the first pipe 12 and the second pipe 14 and thus provides a good surface on which the layer 33 of axial or helical fibre reinforced polymer is laid. In other examples, layer 32 may have a greater height than shoulder portion 11. In such cases, overwinding of layer 33 may result in some displacement of the circumferential fibers of layer 32, but a substantial portion of layer 32 remains constrained within annular cavity 30.

The fiber displacement problem caused by winding over the top of the circumferential fiber is illustrated in fig. 2. This figure illustrates what would occur if the circumferential fiber layers 32 were not constrained within the annular cavity as shown in figure 1. Thus, in fig. 2, the liner 16 occupies the entire cavity 30 such that the outer diameter of the liner 16 is flush with the height of the shoulder portion 11. As shown, if in this arrangement the circumferential fibre layer 32 would wind beyond the shoulder 11 and liner 16 and therefore the axial or helical fibre 33 would wind beyond the top of the circumferential fibre 32, then the compression caused by the axial or helical fibre 33 would cause the axial fibre 32 to unwind in the axial direction. This problem is exacerbated by the presence of the ramp on the shoulder portion 11, as the circumferential fibres 32 are pressed down by the ramp. When this occurs, the thickness and uniformity of the circumferential fiber layer 32 is compromised, which in turn compromises its strength and pressure resistance. At the same time, the axial or helical fibers 33 are not in direct contact with the ramped surfaces on the shoulder portion 11 and therefore the compressive force of the layer 33 is not effectively transferred without compressing the joint and holding it together in its entirety.

In contrast, turning back to fig. 1, it can be seen that the axial or helical fiber layer 33 directly contacts the ramp and thus serves directly to compress the pipes 12, 14 and liner 16 together to form a strong and stable joint. Since this arrangement is more efficient in terms of the fibrous layers 32, 33 providing corresponding forces in the desired direction, the amount of material required for those layers 32, 33 can be minimized, thereby reducing the weight of the component parts.

It will be appreciated that in the example shown in figure 1, the shoulder portion 11 is formed by a conical ramp of increasing diameter towards the liner 16 and a radially extending wall 15, the shoulder portion forming an annular projection which in turn forms a wall of the annular cavity 30. The radially extending wall 15 provides a good constraint for the layer 32, while the tapered ramp provides a good surface on which the layer 33 will be wound. However, in other examples, a different profile of the annular protrusion may be used, such as having a tapered surface on the side facing layer 32 and thus constraining layer 32 and/or having a radially extending surface on the side facing away from layer 32.

The fibers used in either or both of layers 32 and 33 may be glass, carbon, or aramid fibers. The resin mixture may include a thermosetting resin (e.g., epoxy resin) or a thermoplastic resin (e.g., polyetheretherketone- "PEEK").

The fiber-reinforced polymer layers 32, 33 may consist of or consist essentially of a fiber and resin mixture. The axial or helical fiber-reinforced layer 33 may be continuous and cover all of the first conduit 12, the second conduit 14, and the circumferential fiber layer 32, without air gaps and/or other materials therebetween. The first conduit 12 and the second conduit 14 may include a surface coating or treatment, and the surface coating or treatment may be the only material between the first conduit 12 or the second conduit 14 and the fiber reinforced layer 33.

An axial or helical fibre-reinforced polymer layer 33 extends axially over the shoulder portions 11 of the first and second tubes 12, 14. Thus, the inner diameter of the axial or helical fibre reinforced polymer layer 33 decreases as the layer 33 extends over and abuts the tapered surfaces of the first and second tubes 12, 14 at the shoulder portion 11.

Since the axial or helical layer 33 extends axially past the shoulder portion 11, the minimum inner diameter of the layer 33 (i.e., past the shoulder portion 11) may be less than the maximum outer diameter of the first and second conduits 12, 14 (i.e., at the shoulder portion 11). In this manner, the first pipe 12, the second pipe 14, and the liner 16 may be secured by the axial or helical layer 33.

As discussed above, alternatively or additionally, the shoulder portion 11 of the first conduit 12 and/or the second conduit 14 may include a protrusion over which the layer 33 extends.

The resin mixture of layer 33 includes conductive additives, such as carbon black and/or carbon nanotubes, and this may be incorporated into the resin mixture in varying amounts to achieve the desired conductivity for a particular application.

Alternatively or additionally, the desired conductivity may be achieved by varying the amount of fiber or resin mixture in the layer 33. It will be appreciated that the conductivity of the layer 33 varies with the relative amounts of fibers, resin and additives and that these amounts may be varied to provide any desired conductivity. The conductive additive may be present in the resin mixture in an amount of 0 to 10 wt.%.

The above discussed features provide an electrical isolator that achieves a balance of controlling current and dissipating charge while also being able to withstand high voltages. The problem of high fluid pressure is particularly important when incorporating electrical isolation into a hydraulic fluid line (e.g., an aircraft's hydraulic fluid line), which typically operates at a higher pressure than, for example, a fuel line operating at a pressure of about 100 psi, e.g., greater than 3000 psi.

The electrical isolator may be used in any fluid system where a controlled electrical resistance is desired. The electrical isolator described herein achieves robust static sealing, fatigue resistance, and electrical continuity.

The use of a conductive composite layer as disclosed herein removes the need for conductive lines found in conventional arrangements. Also, unlike bonds that may be difficult to manufacture, the arrangement of the present disclosure eliminates the need for adhesives and surface preparation. The use of a conductive additive in the resin also means that the resistivity (or conductivity) of the electrical isolator can be adjusted during manufacture by simply changing the amount of conductive additive in the resin.

A method of forming electrical isolator 10 of fig. 1 will now be described.

A first conduit 12 and a second conduit 14 may be provided. The first conduit 12 and/or the second conduit 14 may form part of a network of conduits, or each comprise an end portion of a larger conduit. The electrical isolator 10 may be part of a hydraulic conduit network (e.g., a hydraulic system or hydraulic fluid conduit in an aircraft) that operates at pressures greater than 1000, 2000, or 3000 psi.

The annular seal 25 is inserted into corresponding grooves on the first and second pipes 12, 14. The ends of the first and second pipes 12, 14 may then be drawn close to each other and resistive, semi-conductive or non-missile components or liners 16 may be placed therebetween. The annular flanges 13 of the first and second conduits 12, 14 may be inserted into (or onto) the corresponding annular flanges 18 of the liner 16. This forms a connection between the first conduit 12 and the second conduit 14.

Due to the presence of the seal 25, the liner 16 is fluidly isolated from the first and second conduits 12, 14. This allows fluid to flow or be conveyed from the first conduit 12 to the second conduit 14.

A layer 32 of circumferential (hoop) fibre reinforced polymer is wound onto the outer diameter 31 of the liner 16 up to the level of the height (radial extent) of the outer diameter of the shoulder portion 11. The shoulder portions (annular projections) form, with the liner, an annular cavity that confines the layer 32 in an axially expanded orientation. The resin may be applied with the fibers (e.g., using prepreg fibers) or may be applied before or after the fibers.

After winding the layer 32 of circumferential fibers, a layer 33 of axial or helical fibers is placed (typically wound) on top of the first pipe 12, the layer 32, and the second pipe 14. The layer 33 extends in the axial direction such that it completely surrounds the conical slope of the annular projection of the shoulder portion 11 on each of the first and second conduits 12, 14. Likewise, the resin may be applied with the fibers, or may be applied before or after the fibers.

As discussed above, the resin mixture includes a conductive additive. This may be added and mixed into the resin in varying amounts to alter or change the conductivity of the composite layer 33 (and optionally also layer 32).

Finally, the two layers 32, 33 of fibre-reinforced polymer are cured. This stiffens the joint and secures the two pipes 12, 14 and the liner 16 together via the compressive force of the axial or helical fibre layer 33 acting directly on the tapered ramp of the shoulder portion 11.

The method may further include passing fluid through the electrical isolator 10, i.e., from the first conduit 12 to the second conduit 14 via the liner 16, at a pressure greater than 1000, 2000, or 3000 psi.

While the present disclosure has been described with reference to various embodiments, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the present disclosure as set forth in the appended claims.