Electrical isolator

Abstract

There is described an electrical isolator comprising a first fluid-carrying member and a second fluid-carrying member spaced apart from said first fluid-carrying member, a resistive, semi-conductive or non-conductive component located between and sealed against said first and second fluid-carrying member, wherein said resistive, semi-conductive or non-conductive component is adapted to convey fluid flowing from said first fluid-carrying member to said second fluid-carrying member, a reinforcing composite encircling said first fluid-carrying member, said second fluid-carrying member and said resistive, semi-conductive or non-conductive component, wherein said reinforcing composite is continuous and provides a conductive path between said first fluid-carrying member and said second fluid-carrying member, wherein said reinforcing composite comprises fibre and a resin mixture, and said resin mixture comprises resin and a conductive additive.

Claims

1. A method of forming one or more electrical isolators, said method comprising: connecting a first fluid-carrying member to a second fluid-carrying member using a resistive, semi-conductive or non-conductive component; sealing said resistive, semi-conductive or non-conductive component against said first and second fluid-carrying member such that said resistive, semi-conductive or non-conductive component is able to convey fluid flowing from said first fluid-carrying member to said second fluid-carrying member; winding a fibre and resin mixture around said first fluid-carrying member, said resistive, semi-conductive or non-conductive component and said second fluid-carrying member so as to encircle said first fluid-carrying member, said second fluid-carrying member and said resistive, semi-conductive or non-conductive component, wherein said resin mixture comprises resin and a conductive additive; and curing said fibre and resin mixture; wherein the fibre and resin mixture is wound directly onto said first fluid-carrying member, said resistive, semi-conductive or non-conductive component and said second fluid-carrying member.

2. A method as claimed in claim 1, further comprising drawing a fibre through a resin bath to form said fibre and resin composite.

3. A method of forming one or more electrical isolators, said method comprising: connecting a first fluid-carrying member to a second fluid-carrying member using a resistive, semi-conductive or non-conductive component; sealing said resistive, semi-conductive or non-conductive component against said first and second fluid-carrying member such that said resistive, semi-conductive or non-conductive component is able to convey fluid flowing from said first fluid-carrying member to said second fluid-carrying member; winding a fibre and resin mixture around said first fluid-carrying member, said resistive, semi-conductive or non-conductive component and said second fluid-carrying member so as to encircle said first fluid-carrying member, said second fluid-carrying member and said resistive, semi-conductive or non-conductive component, wherein said resin mixture comprises resin and a conductive additive; curing said fibre and resin mixture; and applying a surface treatment to the first and second fluid-carrying members and the resistive, semi-conductive or non-conductive component, and then winding the fibre and resin mixture directly onto the surface treatment of the first fluid-carrying member, the resistive, semi-conductive or non-conductive component and the second fluid-carrying member.

4. A method of forming one or more electrical isolators, said method comprising: connecting a first fluid-carrying member to a second fluid-carrying member using a resistive, semi-conductive or non-conductive component; sealing said resistive, semi-conductive or non-conductive component against said first and second fluid-carrying member such that said resistive, semi-conductive or non-conductive component is able to convey fluid flowing from said first fluid-carrying member to said second fluid-carrying member; winding a fibre and resin mixture around said first fluid-carrying member, said resistive, semi-conductive or non-conductive component and said second fluid-carrying member so as to encircle said first fluid-carrying member, said second fluid-carrying member and said resistive, semi-conductive or non-conductive component, wherein said resin mixture comprises resin and a conductive additive; and curing said fibre and resin mixture; wherein each axial end of the resistive, semi-conductive or non-conductive component has an axially extending flange, and each of the first and second fluid-carrying members has an axially extending flange, the method comprises inserting the annular flanges of the first and second fluid-carrying members into or over a respective axially extending flange of the resistive, semi-conductive or non-conductive component, and the winding step involves winding the fibre and resin mixture around the annular flanges of the first and second fluid-carrying members and the resistive, semi-conductive or non-conductive component.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Various embodiments will now be described, by way of example only, and with reference to the accompanying drawings in which:

(2) The FIGURE shows a cross-section of an electrical isolator in accordance with an embodiment of the present disclosure.

DETAILED DESCRIPTION

(3) The present disclosure 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.

(4) The FIGURE shows a cross-section of an electrical isolator or fluid carrying element 10 according to an embodiment of the present disclosure.

(5) The electrical isolator 10 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 10 in the direction of arrow 100.

(6) The electrical isolator 10 comprises a first pipe 12 and a second pipe 14. Both the first pipe 12 and the second pipe 14 may be metallic. In the illustrated example the first pipe 12 and the second pipe 14 have the same structure. The first and second pipes 12, 14 are opposed and spaced apart from one another to provide a gap therebetween.

(7) In the illustrated embodiment the first pipe 12 and second pipe 14 are tubular, i.e. cylindrical in shape and having a circular cross-section. Other shapes and cross-sections are possible. Whilst in the FIGURE the first pipe 12 and second pipe 14 are shown as coaxial, this is not essential and embodiments are envisaged in which the axes of the first pipe 12 and second pipe 14 are at an angle with respect to each other. The angle may be less than 90, 60, 30, 15, 10 or 5 degrees, for example.

(8) Both the first pipe 12 and the second pipe 14 terminate in a shoulder portion 11. The shoulder portion 11 has an increased outer diameter and/or thickness compared to the portion of the respective pipe 12, 14 that is adjacent to it. The shoulder portion 11 comprises a radial surface 15 and an annular flange 13 extending axially from the radial surface 15. Each annular flange 13 terminates at a respective radial surface 17.

(9) A resistive, semi-conductive or non-conductive component or liner 16 is located between the first pipe 12 and the second pipe 14. The liner 16 connects the first pipe 12 to the second pipe 14 and maintains a fluid path (see arrow 100) therebetween. The liner is shown as tubular in the FIGURE, and coaxial with the first pipe 12 and second pipe 14. Other configurations are possible, for example if the axes of the first pipe 12 and second pipe 14 are at an angle with respect to each other as discussed above. The liner 16 is resistive, semi-conductive or non-conductive such that it does not itself conduct or transfer electric current between the first pipe 12 and the second pipe 14.

(10) Each axial end of the liner 16 comprises a radial surface 19 and an annular flange 18 extending axially from the radial surface 19. The annular flanges 18 of the liner 16 terminate at radial surfaces 20.

(11) The respective flanges 13 of the first pipe 12 and second pipe 14 are configured to fit and/or slide into respective flanges 18 of the liner 16. Alternatively, the respective flanges 18 of the liner 16 may be configured to fit and/or slide into the respective flanges 13 of the first pipe 12 and the second pipe 14. As such, the radial surfaces 17 of the first pipe 12 and second pipe 14 contact and oppose the radial surfaces 19 of the liner 16. Similarly, the radial surfaces 15 of the shoulder portion 11 contact and oppose the radial surfaces 20 of the annular flanges 18 of the liner 16.

(12) The inner diameter of the liner 16 may be the same as that of the first pipe 12 and the second pipe 14. This can assist in reducing disturbances to fluid flowing through the electrical isolator 10.

(13) The shoulder portions 11 of the first pipe 12 and/or second pipe 14 may be shaped so as to taper from a relatively small outer diameter to a relatively large outer diameter, when moving towards the end of the respective pipe 12, 14 (or towards the liner 16). The shoulder portions 11 thus comprise a ramp whose outer diameter increases when moving towards the end of the respective pipe 12, 14 (or towards the liner 16). The ramp may terminate at the radial surface 15, which may define the point at which the shoulder portions 11 have the largest outer diameter.

(14) The outer diameter of the liner 16 may be the same as that of the shoulder portions 11 of the first pipe 12 and second pipe 14, for example where the ramp terminates at the radial surface 15. This creates a smooth transition from the outer surface of the liner 16 to the outer surface of the first pipe 12 and second pipe 14.

(15) The liner 16 is fluidly sealed against both the first pipe 12 and the second pipe 14 using one or more sealing members 25. In the illustrated embodiment, the sealing members 25 are annular “0” rings and two are provided for sealing each of the first pipe 12 and the second pipe 14. The annular rings sit within respective grooves on the annular flanges 13 of the first pipe 12 and second pipe 14. It would be possible to use other amounts or types of seal and in other arrangements, for example provide the grooves on the annular flanges 18 of the liner 16 instead.

(16) In accordance with the present disclosure, a reinforcing composite 30 is located around the first pipe 12, the second pipe 14 and the liner 16. The reinforcing composite comprises fibre and a 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.

(17) The reinforcing composite 30 may consist of, or consist essentially of the fibre and resin mixture. The reinforcing composite 30 may be continuous and cover all of the first pipe 12, second pipe 14 and liner 16 with no air gap and/or other material in between. The first pipe 12 and second pipe 14 may comprise a surface coating or treatment, and the surface coating or treatment may be the only material between the first pipe 12 or second pipe 14 and the reinforcing composite 30.

(18) The reinforcing composite 30 extends axially past the shoulder portions 11 of the first pipe 12 and the second pipe 14. As such, the internal diameter of the reinforcing composite 30 decreases as the reinforcing composted 30 extends over and hugs the tapering surface of the first and second pipes 12,14 at the shoulder portion 11.

(19) Due to the reinforcing composite 30 extending axially past the shoulder portion 11, the smallest internal diameter of the reinforcing composite 30 (i.e. past the shoulder portion 11) may be less than the largest outer diameter of the first pipe 12 and the second pipe 14 (i.e. at the shoulder portion 11). In this manner, the first pipe 12, second pipe 14 and the liner 16 may be held captive by the reinforcing composite 30.

(20) Alternatively, or additionally the shoulder portion 11 of the first pipe 12 and/or the second pipe 14 may comprise a protrusion, over which the reinforcing composite extends.

(21) 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.

(22) Alternatively, or additionally the desired conductivity could be achieved by varying the amount of fibre or resin mixture in the composite 30. It will be appreciated that the conductivity of the composite 30 is a function of the relative amounts of fibre, resin and additive and these amounts could be varied to provide any desired conductivity. The conductive additive may be present in the resin mixture in an amount between 0-10 wt. %.

(23) The features discussed above provide an electrical isolator achieving a balance of controlling electric current and dissipating electric charge, whilst also being capable of withstanding high pressures. The issue of high fluid pressure is particularly important when incorporating an electrical isolator in a hydraulic fluid line, for example that of an aircraft, which typically operate at a higher pressure, for example greater than 3000 psi, than for example fuel lines, which operate at pressures of about 100 psi.

(24) This can be used in pressurised fluid systems that require controlled electrical resistance. The electrical isolators described herein achieve robust static sealing, resilience to fatigue, electrical continuity.

(25) Use of a conductive reinforcing composite as disclosed herein removes the need for conductive leads that are exhibited in conventional arrangements. At the same time, the arrangements of the present disclosure remove the need for adhesive and surface preparation, unlike adhered bonds which can be hard to manufacture. Using a conductive additive in the resin also means that the resistivity (or conductivity) of the electrical isolator can be tuned during production, by simply varying the amount of conductive additive in the resin.

(26) A method of forming the electrical isolator 10 of the FIGURE will now be described.

(27) The first pipe 12 and the second pipe 14 may be provided. The first pipe 12 and/or second pipe 14 may form part of a pipe network, or each comprise the end portion of a larger pipe. The electrical isolator 10 may be part of a hydraulic pipe network operating at greater than 1000, 2000 or 3000 psi, for example a hydraulic system or hydraulic fluid pipe in an aircraft.

(28) Ring seals 25 are inserted into respective grooves on the first pipe 12 and second pipe 14. The ends of the first pipe 12 and the second pipe 14 may then be brought close to one another, and the resistive, semi-conductive or non-conductive component or liner 16 may be placed therebetween. The annular flanges 13 of the first pipe 12 and second pipe 14 may be inserted into (or over) the corresponding annular flanges 18 of the liner 16. This forms a connection between the first pipe 12 and the second pipe 14.

(29) Due to the presence of seals 25, the liner 16 is fluidly sealed against the first pipe 12 and the second pipe 14. This allows fluid to flow or be conveyed from the first pipe 12 to the second pipe 14.

(30) In order to provide reinforcement, a reinforcing composite 30 is located around the first pipe 12, the second pipe 14 and the liner 16. The composite 30 may be continuous and contact all of the first pipe 12, second pipe 14 and the liner 16.

(31) To form the composite 30, a fibre (e.g. a glass 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 12, liner 16, and second pipe 14 until the fibre and resin mixture composite exhibits a sufficient thickness and covers all of the first pipe 12, second pipe 14 and liner 16. The orientation of the fibres may be controlled, for example using an automated layup method. As discussed above, 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 composite 30.

(32) The composite 30 may also be formed using a fibre material that has been impregnated with a resin, rather than drawing the resin through a resin bath as described above.

(33) The glass fibre and resin mixture is cured to form the reinforcing composite 30 that is located around and contacts the first pipe 12, second pipe 14 and liner 16. Once cured, the reinforcing composite acts to hold the components of the electrical insulator 10 together to provide strength and resistance when high pressure fluids are passed through the electrical insulator 10.

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

(35) Although 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 detail may be made without departing from the scope of the disclosure as set forth in the accompanying claims.