Patent Description:
Aircraft and other vehicles contain a large number of fluid conveying systems, in particular hydraulic and fuel systems that comprise fluid conveying components such as pipes. Such components are typically metallic or a composite material and have good electrical conductivity.

Devices are incorporated into such systems to form electrical isolators between the metallic components thereof. These isolators prevent build-up of electrostatic charge by safely dissipating static build up, and also prevent excessive electrical current flowing through the system, for example due to a lightning strike. Both of these events may cause a fire hazard if such isolators were not present in the system.

When incorporated into a fluid conveying system, the electrical isolator also needs to act as a safe passage for fluid. In certain systems, for example hydraulic systems or hydraulic fluid lines in an aircraft, the isolator needs to be able to withstand high pressures, in addition to other load and environmental factors.

The present invention is aimed at balancing the above factors to provide an electrical isolation function within a pressurised fluid system.

When used in aircraft in particular although not exclusively, it is also desirable to make the electrical isolator as small and as light weight as possible.

<CIT> discloses an electrical isolator for use in a fluid conveying system. The electrical isolator comprises a first fluid-carrying member and a second fluid-carrying member spaced apart from the first fluid-carrying member; a resistive, semi-conductive or non-conductive component located between and sealed against the first and second fluid-carrying member, wherein the resistive, semi-conductive or non-conductive component is adapted to convey fluid flowing from the first fluid-carrying member to the second fluid-carrying member; a reinforcing composite encircling the first fluid-carrying member, the second fluid-carrying member and the resistive, semi-conductive or non-conductive component, wherein the reinforcing composite is continuous and may provide a conductive path between the first fluid-carrying member and the second fluid-carrying member, wherein the reinforcing composite comprises fibre and a resin mixture, and the resin mixture comprises resin and a conductive additive. O-ring seals provided in grooves machined into the first and second fluid-carrying members are used to seal the resistive, semi-conductive or non-conductive component to the first and second fluid-carrying members.

In a typical electrical isolator, costly multipart unidirectional seals are used to provide a seal between the fluid-carrying members and the resistive, semi-conductive or non-conductive component or liner.

<CIT> B discloses an electrically insulate pipe coupling in which a resilient annular seal portion is formed in an axial space between first and second sleeve members. The seal portion is chemically bonding to the end portions of the sleeve members and creates a low pressure coupling seal between the sleeve members.

<CIT>, over which claim <NUM> has been characterised, discloses an electrically insulating pipe coupling.

<CIT> discloses a connection between two pipes including coupling members with externally threaded ends advanced into opposite ends of an insulating sleeve.

In accordance with an aspect of the invention, there is provided an electrical isolator as claimed in claim <NUM>.

The above isolator uses a bond between the resistive, semi-conductive or non-conductive component and the first and second fluid-carrying members thereof to provide a fluid tight seal between the first fluid-carrying member and the resistive, semi-conductive or non-conductive component and between the second fluid-carrying member and the resistive, semi-conductive or non-conductive component so that in use, fluid may flow from the first fluid-carrying member to the second fluid-carrying member without leaking. In the isolator according to the invention, there is therefore no need to provide separate sealing members such as the traditional hydraulic seals used in known electrical isolators which require grooves to be machined into parts of the electrical isolator and which are typically expensive and time consuming to assemble. Further, the traditional hydraulic seals can sometimes be incorrectly fitted causing leaks which can only be detected after the isolator has been fully assembled, the reinforcing composite has been cured and the isolator is tested.

In addition to the above, as the resistive, semi-conductive or non-conductive component is bonded to the first and second fluid-carrying members in the electrical isolator according to the invention, the resistive, semi-conductive or non-conductive component and the first and second fluid-carrying members are fixed in place relative to each other such that no additional means are required to hold the resistive, semi-conductive or non-conductive component and the first and second fluid-carrying members in position while the reinforcing composite is being formed.

In addition to the above, in prior art arrangements using seals such as O-rings, internal fluid pressure in an electrical isolator may force the seal through a small gap, potentially causing the seal to be permanently deformed or extruded and so to fail. The seal provided by the bond of the isolator according to the invention can help to reduce deformation or extrusion of the seal by mechanically supporting some contact surfaces of the seal. By bonding to the resistive, semi-conductive or non-conductive component and the first and second fluid-carrying members, relative movement between the bond and the resistive, semi-conductive or non-conductive component and the first and second fluid-carrying members is reduced such that deformation or extrusion of the seal provided by the bond is less likely to occur.

In addition to the above, the electrical isolator according to the invention enables an electrical isolator which is fluid tight at the required pressures to be provided in a shorter axial length than has been previously possible. The electrical isolator of the invention is also lighter and less expensive to produce than known electrical isolators using traditional hydraulic seals.

In addition to the above, the electrical isolator of the invention uses a reinforcing composite encircling the first fluid-carrying member, the second fluid-carrying member and the resistive, semi-conductive or non-conductive component, whilst providing a conductive path through the reinforcing composite, but not the gap between the first and second fluid-carrying members. This provides a device that effectively dissipates charge build-up and electrically isolates the junction between two fluid-conveying devices, whilst providing a fluid-tight joint.

The reinforcing composite encircles the first and second fluid-carrying members, but typically just the end portions thereof, e.g. closest to the resistive, semi-conductive or non-conductive component. The reinforcing composite may be a continuous tube that extends from the first fluid-carrying member (or an end portion thereof) and over the gap to the second fluid-carrying member (or an end portion thereof).

In any aspect of the invention, a material may be provided in the gap between the first and second fluid-carrying members and may be bonded to the resistive, semi-conductive or non-conductive component, and the first and second fluid-carrying members. The material may be bonded to the first and second fluid-carrying members and the resistive, semi-conductive or non-conductive component using an adhesive.

The material may have a low conductivity such that the material acts as an electrical isolator between the first and second fluid-carrying members.

Further, the material may act to minimise relative movement of the respective parts of the electrical isolator under pressure.

In any aspect of the invention, the material may be an elastomer, and more preferably the material may be a fluoro elastomer.

In any aspect of the invention, the first fluid-carrying member may terminate in a first flange extending radially outwardly therefrom, and the second fluid-carrying member may terminate in a second flange extending radially outwardly therefrom and the material may extend between the first flange and the second flange. The first and second flanges may provide a larger radial extent to support the material on either side thereof such that a greater volume of material may be provided between the first and second fluid-carrying members than would otherwise be possible.

According to the invention, the resistive, semi-conductive or non-conductive component is bonded to the first and second fluid-carrying members by a bonding material provided between the resistive, semi-conductive or non-conductive component and the first fluid-carrying member and between the resistive, semi-conductive or non-conductive component and the second fluid-carrying member. Thus, a seal may be provided by the bonding material extending over part or the full extent of mating surfaces of the resistive, semi-conductive or non-conductive component and the respective first and second fluid-carrying members.

In any aspect of the invention, the bonding material may be flexible so as to accommodate relative movement between the resistive, semi-conductive or non-conductive component and the first and second fluid-carrying members, for example due to different rates of thermal expansion and contraction thereof. The provision of a flexible bonding material may prevent delamination and increase the fatigue life of an isolator according to the invention.

In any aspect of the invention, the bonding material may comprise an adhesive, preferably a fuel resistant adhesive, or a flexible adhesive or a fuel resistant, flexible adhesive.

In any aspect of the invention, the bonding material may comprise a sealant material or an injection moulded elastomeric material.

In any aspect of the invention, a first cut-out portion may be formed in the first fluid-carrying member,.

In any aspect of the invention, the reinforcing composite may comprise:.

The layer of circumferentially wound fibre (also referred to as "hoop" fibre) provides additional pressure resistance to the electrical isolator. Hoop fibre is wound with a high angle to the axis of the structure such that it is wound in a very tight helix (or in some cases, even wound directly over itself, i.e. at ninety degrees to the axis). As such, hoop fibre cannot expand under radial pressure and is therefore strong against radial loads, i.e. it is pressure resistant. Such an electrical isolator with a layer of hoop fibre is better adapted to the high pressures of hydraulic systems.

While circumferential fibre is well-suited to providing pressure resistance, it is not well-suited to holding the electrical isolator together as it does not provide much strength in the axial direction. However, the layer of helical wound fibre (which may be provided radially outwardly of the circumferential fibre in one example) does provide axial strength.

Circumferential fibre here means fibre with a high winding angle (the angle that the fibre makes with the axis of the part (usually mounted on a mandrel) during winding), typically from <NUM> degrees up to <NUM> degrees, more preferably at least <NUM> degrees.

Helical fibre here means fibre with a low winding angle, typically between <NUM> degrees and <NUM> degrees. It is often difficult to wind fibre at angles below about <NUM> degrees, while angles above <NUM> degrees do not provide the required axial strength. Lower angles are however still viable, down to essentially <NUM> degrees if fibre placement can be achieved. Even true axial fibre can be used instead of helical fibre (i.e. fibre with an angle of <NUM> degrees to the axis, i.e. parallel to the axis), but placement of such fibre is difficult.

In some aspects of the invention, the first and second fluid-carrying members and the resistive, semi conductive or non-conductive component may comprise cylindrical components having a constant cross section along the axial extent thereof. The shape of the first and second fluid-carrying members and the resistive, semi conductive or non-conductive component may however be altered to optimise the weight of the electrical isolator in view of the internal stresses applied to it in use. In any aspect of the invention therefore, each of the first fluid-carrying member and the second fluid-carrying member may comprise a curved portion, such that the curved portions of the first and second fluid carrying members form a substantially ovoid shape or a bulge extending radially outwardly from the first and second fluid carrying members.

In any aspect of the invention, the gap may be located at the radially outermost portion of the ovoid shape or bulge.

In any aspect of the invention, the resistive, semi conductive or non conductive component may be shaped so as to follow the shape of the first and second fluid-carrying members.

In some examples of the invention as discussed above, electrical isolation between the first a second fluid-carrying members may be provided by an elastomer. In an alternative example, the resistive, semi conductive or non-conductive component may further comprise a radial protrusion extending radially outwardly therefrom into the gap. Thus, the radial protrusion may provide electrical isolation between the first and second fluid-carrying members.

In another alternative example, a composite material having a low conductivity may be provided in the gap extending between the first and second fluid-carrying members. The composite material may act to provide electrical isolation between the first and second fluid-carrying members and to resist movement between them.

In another alternative example, the resistive, semi conductive or non conductive component may extend radially externally of the first and second fluid-carrying members such that no isolating material is provided in the gap extending between the first and second fluid-carrying members.

From a further aspect of the invention, a hydraulic or fuel system comprising an electrical isolator of any of the above examples is provided.

From a still further aspect of the invention, a method of making an electrical isolator as claimed in claim <NUM> is provided.

Using the method of the invention provides a simple and cost effective method of making an electrical isolator. As the first fluid-carrying member and the second fluid-carrying member are bonded into position relative to the resistive, semi-conductive or non-conductive component prior to forming the reinforcing composite, there is no need to use an external compressive force or other means to hold the parts of the electrical isolator in place while forming the reinforcing composite. In contrast, in a prior art isolator using hydraulic seals, a compressive force is required to hold the parts of the isolator in place until after the reinforcing composite is fully formed.

In addition, the method of bonding the first fluid-carrying member and the second fluid-carrying member to the resistive, semi-conductive or non-conductive component provides a simpler, less expensive and less time consuming method of forming a seal between the components than in the prior art isolators using hydraulic seals.

In any aspect of the method of the invention, forming the reinforcing composite may comprise:.

In the method of the invention, as a seal is provided by the bond between the first fluid-carrying member and the resistive, semi-conductive or non-conductive component and the second fluid-carrying member and the resistive, semi-conductive or non-conductive component, resin may not leak from the reinforcing composite provided radially externally of the first and second fluid-carrying members into the first and second fluid-carrying members prior to the curing step. Thus, there is no need to provide separate environmental seals between the first fluid-carrying member and the resistive, semi-conductive or non-conductive component and the second fluid-carrying member and the resistive, semi-conductive or non-conductive component as in known electrical isolators using hydraulic seals.

In any aspect of the method of the invention, the winding fibre-reinforced polymer around the first fluid-carrying member, the second fluid-carrying member and the resistive, semi-conductive or non-conductive component may comprise:.

It will be understood that the circumferentially wound fibre-reinforced polymer and the helical wound fibre-reinforced polymer could be provided in various different arrangements including but not limited to: the circumferentially wound fibre-reinforced polymer being provided in a first layer and the helical wound fibre-reinforced polymer being provided in a second layer extending around the first layer; or the helical wound fibre-reinforced polymer being provided in a first layer and the circumferentially wound fibre-reinforced polymer being provided in a second layer extending around the first layer.

Various non-limiting examples will now be described, by way of example only, and with reference to the accompanying drawings in which:.

The present invention relates to electrical isolators, which may be used in aircraft hydraulic systems or hydraulic fluid lines in order to provide a strong fluid carrying structure whilst controlling induced electric current (e.g. by lightning) and dissipation of electrostatic charge. It will be understood that the drawings show cross sections through example electrical isolators above the centreline thereof. The cross sections through the example electrical isolators of the drawings below the centreline thereof (not shown) would be a mirror image of that shown above the centreline.

<FIG> shows an electrical isolator or fluid carrying element <NUM> according to an example of the present invention.

The electrical isolator <NUM> forms part of a fluid conveying network, such as a hydraulic fluid network in an aircraft. Fluid, for example hydraulic fluid, may flow through the electrical isolator <NUM> in the direction of arrow <NUM>.

The electrical isolator <NUM> comprises a first fluid-carrying member or pipe <NUM> and a second fluid-carrying member or pipe <NUM>. Both the first pipe <NUM> and the second pipe <NUM> may be metallic and may comprise end fittings for attachment to other tubular members in a fluid-carrying system. In the illustrated example the first pipe <NUM> and the second pipe <NUM> have the same structure. The first and second pipes <NUM>, <NUM> are opposed and spaced apart from one another to provide a gap G there between.

In the illustrated example the first pipe <NUM> and second pipe <NUM> are tubular, i.e. cylindrical in shape and having a circular cross-section. Other shapes and cross-sections are possible. Whilst in <FIG> the first pipe <NUM> and second pipe <NUM> are shown as coaxial extending about an axis A-A, this is not essential and examples are envisaged in which the axes of the first pipe <NUM> and second pipe <NUM> are at an angle with respect to each other. The angle may be less than <NUM>, <NUM>, <NUM>, <NUM>, <NUM> or <NUM> degrees, for example.

The first pipe <NUM> and the second pipe <NUM> comprise a radially inner axial surface <NUM> and a radially outer axial surface <NUM> spaced therefrom in a radial direction to form a wall thickness of the first and second pipes <NUM>, <NUM>. Both the first pipe <NUM> and the second pipe <NUM> terminate in a flange <NUM> extending radially away from the axis A-A and beyond the radially outer axial surface <NUM>. Thus, the flanges <NUM> provide a radial surface <NUM> as the end face of the first and second pipes <NUM>, <NUM>.

A cut-out portion is formed in the radially inner axial surface <NUM> of the first pipe <NUM> and the second pipe <NUM> extending from the open end thereof and away from the opposing pipe and extending around the circumference of the pipe so as to form a substantially annular cut-out portion. A radial surface <NUM> defines the end of the cut-out portion and joins with the radially inner axial surface <NUM>.

An annular liner <NUM> formed from a resistive, semi-conductive or non-conductive material is provided to fit within the cut-out portions in the first and second pipes <NUM>, <NUM> so that a radially inner surface <NUM> of the annular liner <NUM> extends substantially flush with the radially inner axial surface <NUM> of the first and second pipes <NUM>, <NUM>. It will be appreciated that the annular liner <NUM> extends between the first and second pipes <NUM>, <NUM> to maintain the gap G there between. The size of the gap G between the first and second pipes <NUM>, <NUM> is determined to provide electrical isolation between the first and second pipes <NUM>, <NUM>. In one example, the size of the gap G may be defined by the expected static and electrical requirements of an isolator. In one preferred example, the gap G between the first and second metallic pipes <NUM>, <NUM> should be at least <NUM>.

A minimum gap between the first and second pipes at the wet surfaces thereof is also required. This may typically be provided by an axial length of the annular liner <NUM> extending between the wet surface of the respective first and second pipes <NUM>, <NUM> and may be about <NUM> (<NUM> inches). It will be appreciated however that the gap required will be dependent on the dimensions and intended use of a particular isolator and may be defined by the expected static and electrical requirements thereof. Thus, in an alternative example of the invention, the minimum gap between the first and second pipes at the wet surfaces thereof may be about <NUM> to about <NUM> (about <NUM> inches to about <NUM> inch).

In the example shown in <FIG>, the minimum gap between the first and second pipes at the wet surfaces thereof is defined by the axial length of the annular liner <NUM>. It will therefore be appreciated that the electrical isolator of the example may be made significantly shorter in an axial direction than has been possible in the past as the moulded fluoro elastomer seal and a reinforcing composite <NUM> can be provided to extend over less than the axial extent of the annular liner <NUM>. Further the electrical isolator of the example may have a reduced weight and be less expensive and time consuming to produce than previously known electrical isolators.

A material (for example, a fluoro elastomer <NUM>) is moulded to fill the gap G between the flanges <NUM> of the first and second pipes <NUM>,<NUM>. Many rigid or flexible materials could be provided in place of the fluoro elastomer if the material provides appropriate electrical isolation properties and if the material does not react with a fluid medium flowing through the isolator. In one example, a material similar to Dow Corning®<NUM> FS Solvent Resistant Sealant Arc Resistance = <NUM> can be used. Moulded materials like PEEK or Nitrile may be used when chemically compatible with the other materials used in the isolator. In another preferred example, PR-<NUM> Class A Fuel Tank Sealant may be used.

When in situ, the material or fluoro elastomer <NUM> forms an annular shape and is bonded to the radially outer surface of the annular liner <NUM> and the radial surfaces <NUM> defined by the respective flanges16 of the first and second pipes <NUM>, <NUM>. It will be understood that the moulded fluoro elastomer acts to hold together the first and second pipes <NUM>, <NUM> and to hold the annular liner <NUM> to the first and second pipes <NUM>, <NUM>. Thus, the moulded fluoro elastomer <NUM> provides a fluid tight seal between the annular liner <NUM> and the first and second pipes <NUM>, <NUM>.

The moulded fluoro elastomer typically also has a hardness and rigidity appropriate to minimise movement and the radial or hoop stresses experienced between the first pipe <NUM>, the second pipe <NUM> and the annular liner <NUM>.

In accordance with the present invention, a reinforcing composite <NUM> is located around the first pipe <NUM>, the second pipe <NUM> and the fluoro elastomer <NUM>. The reinforcing composite <NUM> may consist of, or consist essentially of the fibre and resin mixture. The fibre may be glass fibre, carbon fibre or aramid fibre. The resin mixture may comprise a resin that may be of thermoset (e.g. epoxy) or thermoplastic (e.g. polyether ether ketone - "PEEK") construction.

The reinforcing composite <NUM> may be continuous and cover all of the first pipe <NUM>, second pipe <NUM> and fluoro elastomer <NUM> with no air gap and/or other material in between. The first pipe <NUM> and second pipe <NUM> may comprise a surface coating or treatment, and the surface coating or treatment may be the only material between the first pipe <NUM> or second pipe <NUM> and the reinforcing composite <NUM>.

The reinforcing composite <NUM> extends axially past the flanges <NUM> of the first pipe <NUM> and the second pipe <NUM>. As such, the internal diameter of the reinforcing composite <NUM> gradually decreases as the reinforcing composite <NUM> extends over and beyond the flanges <NUM> to provide a domed outer profile which may be optimised for internal pressures experienced by the isolator. In some examples, an isolator may have an outer profile comprising a parallel centre section radially outward of the gap G, the outer profile tapering away at either end thereof.

The resin mixture comprises a conductive additive, for example carbon black and/or carbon nanotubes, and this can be incorporated into the resin mixture in varying amounts to achieve the desired conductivity for a particular application.

The reinforcing composite allows the electrical isolator to withstand the high internal pressures to which it will be subjected when used in a hydraulic system without leaking. To achieve the best resistance to both the radial and axial forces exerted on the electrical isolator, the reinforcing composite may comprise fibres wound circumferentially around the pipes and the fluoro elastomer (for the radial forces) and fibres wound helically around the pipes and the fluoro elastomer (for the axial forces and some radial force). In one example of the invention, the reinforcing composite comprises a layer or a plurality of layers of circumferentially wound fibre-reinforced polymer extending circumferentially around the first fluid-carrying member, the second fluid-carrying member and the resistive, semi-conductive or non-conductive component and a layer or a plurality of layers of helical wound fibre-reinforced polymer extending helically around the layer of circumferentially wound fibre-reinforced polymer, the first fluid-carrying member, the second fluid-carrying member and the resistive, semi-conductive or non-conductive component.

The layers of circumferentially wound fibre (also referred to as "hoop" fibre) provide additional pressure resistance to the electrical isolator. Hoop fibre is wound with a high angle to the axis of the structure such that it is wound in a very tight helix (or in some cases, even wound directly over itself, i.e. at ninety degrees to the axis). As such, hoop fibre cannot expand under radial pressure and is therefore strong against radial loads, i.e. it is pressure resistant. Such an electrical isolator with a layer of hoop fibre is better adapted to the high pressures of hydraulic systems.

While circumferential fibre is well-suited to providing pressure resistance, it is not well-suited to holding the electrical isolator together as it does not provide much strength in the axial direction. However, the layer of helical wound fibre does provide axial strength.

A method of forming the electrical isolator of <FIG> will now be described.

The first pipe <NUM> and the second pipe <NUM> may be provided. The first pipe <NUM> and/or second pipe <NUM> may form part of a pipe network, or each comprise the end portion of a larger pipe. The electrical isolator <NUM> may be part of a hydraulic pipe network operating at greater than about <NUM>, <NUM> or <NUM> MPa (about <NUM>, <NUM> or <NUM> psi), for example a hydraulic system or hydraulic fluid pipe in an aircraft.

The annular liner is inserted into the cut-out portions of the first and second pipes <NUM>, <NUM> so as to extend along and between the first and second pipes <NUM>, <NUM> and to provide a gap G between the first and second pipes <NUM>, <NUM>. A fluoro elastomer <NUM> is then moulded into the gap G between the flanges <NUM> of the first and second pipes <NUM>,<NUM>. Thus, when in situ, the fluoro elastomer <NUM> forms an annular shape and is bonded to the radially outer surface <NUM> of the annular liner <NUM> and the radial surfaces <NUM> defined by the respective flanges16 of the first and second pipes <NUM>, <NUM>. In one preferred example, the fluoro elastomer is injection moulded and adhesive is applied to the radially outer surface <NUM> of the annular liner <NUM> and the radial surfaces <NUM> defined by the respective flanges16 of the first and second pipes <NUM>, <NUM> to bond the fluoro elastomer thereto.

In order to provide a reinforcement, a reinforcing composite <NUM> is located around the first pipe <NUM>, the second pipe <NUM>, the annular liner <NUM> and the fluoro elastomer <NUM>.

To form the composite <NUM>, a fibre (e.g. a polymer fibre) may be drawn through a bath containing the resin mixture, and then the fibre and resin mixture may be wound around the first pipe <NUM>, the second pipe <NUM>, the annular liner <NUM> and the fluoro elastomer <NUM> until the fibre and resin mixture exhibits a sufficient thickness and covers the required axial extent of the first pipe <NUM>, the fluoro elastomer <NUM> and the second pipe <NUM>. The orientation of the fibres may be controlled, for example using an automated layup method. The resin mixture comprises a conductive additive. This can be added and mixed into the resin contained in the bath in varying amounts, to alter or change the conductivity of the reinforcing composite <NUM>.

The composite <NUM> may also be formed using a fibre material that has been impregnated with a resin, rather than drawing the fibre through a resin bath as described above.

The fibre and resin mixture is cured to form the reinforcing composite <NUM>. Once cured, the reinforcing composite acts to hold the components of the electrical insulator <NUM> together to provide strength and resistance when high pressure fluids are passed through the electrical isolator <NUM>.

The method may further comprise passing fluid through the electrical isolator <NUM>, i.e. from the first pipe <NUM> to the second pipe <NUM> via the annular liner <NUM>, at a pressure of greater than about <NUM>, <NUM> or <NUM> MPa (<NUM>, <NUM> or <NUM> psi). The method may further comprise passing fluid through the electrical isolator <NUM>, i.e. from the first pipe <NUM> to the second pipe <NUM> via the annular liner <NUM>, at a test pressure of about <NUM> MPa (<NUM>,<NUM> psi) or more.

<FIG> shows an electrical isolator or fluid carrying element <NUM> according to an alternative example of the present invention in which the shape thereof has been altered to reduce internal stresses in the components of the electrical isolator and the weight thereof.

In the illustrated example the first pipe <NUM> and second pipe <NUM> are tubular, i.e. cylindrical in shape and having a circular cross-section.

The first pipe <NUM> and the second pipe <NUM> comprise a radially inner axial surface <NUM> and a radially outer axial surface <NUM> spaced therefrom in a radial direction to form a wall thickness of the first and second pipes <NUM>, <NUM>. Both the first pipe <NUM> and the second pipe <NUM> comprise an end portion <NUM> which forms a curved shape in cross section, extending radially outwardly away from the axis A-A along which the first and second pipes <NUM>, <NUM> extend. When assembled so that the first pipe <NUM> opposes the second pipe <NUM> with the gap G there between, the curved end portions <NUM> of the first and second pipes <NUM>, <NUM> form an arc in cross section as seen in <FIG>. Thus, the end portions of the first annular pipe <NUM> and the second annular pipe <NUM> extend towards each other and form a substantially ovoid shape or a bulge extending radially outwardly from the first and second annular pipes <NUM>, <NUM>.

A cut-out portion is formed in the radially inner axial surface <NUM> of the first pipe <NUM> and the second pipe <NUM> extending from the open ends thereof and away from the opposing pipe. A radial surface <NUM> defines the end of the cut-out portion in each of the first and second pipes <NUM>, <NUM> and joins with the radially inner axial surface <NUM>.

An annular liner <NUM> formed from a resistive, semi-conductive or non-conductive material is provided to fit within the cut-out portions in the first and second pipes <NUM>, <NUM> and to extend between the first and second pipes <NUM>, <NUM> to maintain the gap G there between. As seen in <FIG>, the annular liner <NUM> of this example is shaped to conform with the curved shape of the end portions of the first and second pipes <NUM>, <NUM>. In one preferred example, the gap G between the first and second pipes <NUM>, <NUM> should be at least <NUM>.

A fluoro elastomer <NUM> is moulded to fill the gap G between the opposing end faces <NUM> of the first and second pipes <NUM>, <NUM>. Thus, when in situ, the fluoro elastomer <NUM> forms an annular shape and is bonded to the radially outer surface of the annular liner <NUM> and the end faces <NUM> of the first and second pipes <NUM>, <NUM>. It will be understood that the moulded fluoro elastomer acts to hold together the first and second pipes <NUM>, <NUM> and to hold the annular liner <NUM> to the first and second pipes <NUM>, <NUM>. Thus, the moulded fluoro elastomer <NUM> provides a fluid tight seal between the annular liner <NUM> and the first and second pipes <NUM>, <NUM>. The moulded fluoro elastomer typically has a hardness and rigidity appropriate to minimise movement and hoop stresses experienced between the first pipe <NUM>, the second pipe <NUM> and the annular liner <NUM>. In one non-limiting example the moulded fluoro elastomer may comprise Dow Corning <NUM> Solvent Resistant Sealant White <NUM> Tube. This material cures to a tough, flexible rubber, has good adhesion to many substrates, is stable and flexible from -<NUM> (-<NUM>°F) to <NUM> (<NUM>°F). It retains its properties under exposure to fuels, oils and solvents. The material properties are as follows:.

In an alternative example, DAIKIN's DAI-EL fluoro elastomer or Greene Tweed FPH Seal material may be used.

In accordance with the present invention, a reinforcing composite <NUM> is located around the first pipe <NUM>, the second pipe <NUM> and the fluoro elastomer <NUM> in a manner similar to that described in relation to <FIG>.

The reinforcing composite <NUM> extends axially past the bulge formed by the first pipe <NUM> and the second pipe <NUM> so as to meet the radially outer axial surface <NUM> of the first pipe <NUM> and the radially outer axial surface <NUM> of the second pipe <NUM>. As such, the internal diameter of the reinforcing composite <NUM> gradually decreases as the reinforcing composite <NUM> extends over and beyond the bulge.

As seen in <FIG>, the radially outer surface <NUM> of the fluoro elastomer <NUM> may be concave due to natural shrinkage of the fluoro elastomer away from the surfaces against which it is bonded during the production process. The concave surface <NUM> of the fluoro elastomer <NUM> may reduce the accuracy with which reinforcing fibres may be wound around the pipes and the fluoro elastomer when forming the reinforcing composite <NUM>. To allow for this, the radially outer surface <NUM> of the fluoro elastomer <NUM> may be built up to provide a substantially flat surface.

It will be understood that the electrical isolator of <FIG> may be formed by the method described above in relation to <FIG>.

<FIG> shows an electrical isolator or fluid carrying element <NUM> according to an alternative example of the present invention in which the shape thereof has been altered to reduce internal stresses in the components of the electrical isolator and the weight thereof in a manner similar to the example of <FIG>.

The first pipe <NUM> and the second pipe <NUM> comprise a radially inner axial surface <NUM> and a radially outer axial surface <NUM> spaced therefrom in a radial direction to form a wall thickness of the first and second pipes <NUM>, <NUM>. Both the first pipe <NUM> and the second pipe <NUM> comprise an end portion <NUM> shaped in a similar manner as in the example of <FIG>. In contrast to the example of <FIG> however, the end faces <NUM> of the first and second pipes <NUM>, <NUM> are angled, extending inwardly towards one another as they approach the radially inner surface of the respective first and second pipes <NUM>, <NUM>.

A cut-out portion is again formed in the radially inner axial surface <NUM> of the first pipe <NUM> and the second pipe <NUM>.

An annular liner <NUM> formed from a resistive, semi-conductive or non-conductive material is provided to fit within the cut-out portions in the first and second pipes <NUM>, <NUM> as in the example of <FIG>.

As seen in <FIG>, the seal between the first pipe <NUM>, the annular liner <NUM> and the second pipe <NUM> is formed by bonding the radially outer surface <NUM> of the annular liner <NUM> to the radially inner surface <NUM> of the cut-out portions in the first and second pipes <NUM>, <NUM>. In one example, the annular liner may be coated with a film of adhesive then over wound with composite such that the adhesive bonds to the liner and the composite during curing.

A low conductivity glass composite material <NUM> is formed in the gap between the end faces <NUM> of the first and second pipes <NUM> and the radially inner surface of the low conductivity glass composite material <NUM> is bonded to the radially outer surface <NUM> of the annular liner <NUM>. In one example, the glass fibres may be wound around the annular liner <NUM> in the gap so as to form a first few layers of hoop glass fibre in non-conductive (low carbon) resin. The fibres can then be overwound with conductive glass fibre and then the fibres and resin may be cured. If necessary to avoid carbon resin bleed, a partial cure may be carried out for the first few layers of hoop glass fibre in non-conductive (low carbon) resin, before over winding and then providing a final cure.

A reinforcing composite <NUM> is again located around the first pipe <NUM>, the second pipe <NUM> and the low conductivity glass composite material <NUM> in a manner similar to that described in relation to <FIG>.

The first pipe <NUM> and the second pipe <NUM> may be provided. The first pipe <NUM> and/or second pipe <NUM> may form part of a pipe network, or each comprise the end portion of a larger pipe. The electrical isolator <NUM> may be part of a hydraulic pipe network operating at greater than about <NUM>, <NUM> or <NUM> MPa (<NUM>, <NUM> or <NUM> psi), for example a hydraulic system or hydraulic fluid pipe in an aircraft.

A bonding material such as an adhesive, sealant material or injection moulded elastomeric material is applied to the radially outer surface <NUM> of the annular liner <NUM> and the annular liner is then inserted into the cut-out portions of the first and second pipes <NUM>, <NUM> so as to provide a gap between the first and second pipes <NUM>, <NUM> and to form the seal between the first pipe <NUM>, the annular liner <NUM> and the second pipe <NUM>.

A glass composite material <NUM> is then formed in the gap G between the ends of the first and second pipes <NUM>, <NUM>.

In order to provide a reinforcement, a reinforcing composite <NUM> is located around the first pipe <NUM>, the second pipe <NUM>, the annular liner <NUM> and the glass composite material <NUM> in the manner described in relation to <FIG>.

The method may further comprise passing fluid through the electrical isolator <NUM>, i.e. from the first pipe <NUM> to the second pipe <NUM> via the annular liner <NUM>, at a pressure of greater than about <NUM>, <NUM> or <NUM> MPa (<NUM>, <NUM> or <NUM> psi).

<FIG> shows an electrical isolator or fluid carrying element <NUM> according to an alternative example of the present invention in which the shape thereof has been altered to reduce internal stresses in the components of the electrical isolator and the weight thereof in a manner similar to the examples of <FIG> and <FIG>.

The first pipe <NUM> and the second pipe <NUM> comprise a radially inner axial surface <NUM> and a radially outer axial surface <NUM> spaced therefrom in a radial direction to form a wall thickness of the first and second pipes <NUM>, <NUM>. Both the first pipe <NUM> and the second pipe <NUM> comprise an end portion <NUM> shaped in a similar manner as in the example of <FIG>.

An annular liner <NUM> formed from a resistive, semi-conductive or non-conductive material is provided to fit within the cut-out portions in the first and second pipes <NUM>, <NUM> as in the example of <FIG>. In the example shown in <FIG>, the axially central part of the annular liner <NUM> forms an arc in cross section so as to form an ovoid shape or bulge portion <NUM> extending radially outwardly from a first cylindrical portion <NUM> provided at one end of the annular liner <NUM>. A second cylindrical portion <NUM> is provided adjacent the bulge portion <NUM> at the other end of the annular liner <NUM>. The annular liner <NUM> further comprises a radial protrusion <NUM> extending radially outwardly from the radially outermost part of the bulge portion <NUM>. The radial protrusion <NUM> is shaped so as to fill the gap between the end portions <NUM> of the first and second pipes <NUM>, <NUM>. Thus, in this example, the radial protrusion <NUM> provides the required isolation between the first and second pipes <NUM>, <NUM>.

As seen in <FIG>, the seal between the first pipe <NUM>, the annular liner <NUM> and the second pipe <NUM> is formed by bonding the radially outer surface <NUM> of the annular liner <NUM> to the radially inner surface <NUM> of the cut-out portions in the first and second pipes <NUM>, <NUM>. PR-<NUM> Class A Fuel Tank Sealant or similar may be used. The end faces <NUM> of the first and second pipes are also bonded to the corresponding surfaces of the radial protrusion <NUM>.

A reinforcing composite <NUM> is again located around the first pipe <NUM>, the second pipe <NUM> and the annular liner <NUM> in a manner similar to that described in relation to <FIG>.

A bonding material such as an adhesive, sealant material or injection moulded elastomeric material is applied to the radially outer surface <NUM> of the annular liner <NUM> and the side surfaces of the radial protrusion <NUM>. The annular liner <NUM> is then inserted into the cut-out portions of the first and second pipes <NUM>, <NUM> so as to provide a gap (filled by the radial protrusion <NUM>) between the first and second pipes <NUM>, <NUM> and to form the seal between the first pipe <NUM>, the annular liner <NUM> and the second pipe <NUM>.

In order to provide a reinforcement, a reinforcing composite <NUM> is located around the first pipe <NUM>, the second pipe <NUM> and the annular liner <NUM> in the manner described in relation to <FIG>.

Claim 1:
An electrical isolator (<NUM>; <NUM>; <NUM>; <NUM>) comprising:
a first fluid-carrying member (<NUM>; <NUM>; <NUM>; <NUM>);
a second fluid-carrying member (<NUM>; <NUM>; <NUM>; <NUM>) spaced apart from the first fluid-carrying member (<NUM>; <NUM>; <NUM>; <NUM>) to form a gap;
a resistive, semi-conductive or non-conductive component (<NUM>; <NUM>; <NUM>; <NUM>) extending across the gap and bonded to the first and second fluid-carrying members so as to provide a fluid tight seal between the first fluid-carrying member (<NUM>; <NUM>; <NUM>; <NUM>) and the resistive, semi-conductive or non-conductive component (<NUM>; <NUM>; <NUM>; <NUM>) and between the second fluid-carrying member (<NUM>; <NUM>; <NUM>; <NUM>) and the resistive, semi-conductive or non-conductive component (<NUM>; <NUM>; <NUM>; <NUM>); and
a reinforcing composite (<NUM>; <NUM>; <NUM>; <NUM>) encircling the first fluid-carrying member, the second fluid-carrying member (<NUM>; <NUM>; <NUM>; <NUM>) and the resistive, semi-conductive or non-conductive component (<NUM>; <NUM>; <NUM>; <NUM>),
wherein the resistive, semi-conductive or non-conductive component comprises an annular liner extending coaxially with and between respective wet surfaces of the first and second fluid-carrying members,
characterised in that the resistive, semi-conductive or non-conductive component is bonded to the first and second fluid-carrying members by a bonding material (<NUM>) provided between the resistive, semi-conductive or non-conductive component and the first fluid-carrying member (<NUM>; <NUM>; <NUM>; <NUM>) and between the resistive, semi-conductive or non-conductive component (<NUM>; <NUM>; <NUM>; <NUM>) and the second fluid-carrying member (<NUM>; <NUM>; <NUM>; <NUM>).