Filter retaining plug

Abstract

A plug for retaining a filter screen in a fluid port of a servovalve, comprises an annular body, the annular body comprising: opposed first and second axial end surfaces, a radially inner surface extending between the first and second axial end surfaces, a radially outer surface extending between the first and second axial end surfaces and at least one recess formed in the radially inner surface for receiving a tool for removing the plug from the port. A tool for removing the plug comprises a pair of handles pivotally mounted to one another about a pivot, each handle having a plug gripping portion extending therefrom beyond the pivot, each plug gripping portion comprising an outwardly projecting tooth for engaging in the recess of the plug when the plug gripping portions are moved apart by operation of the handles.

Claims

1. A plug for retaining a filter screen in a fluid port of a servovalve, the plug comprising an annular body, the annular body comprising: opposed first and second axial end surfaces; a radially inner surface extending between the first and second axial end surfaces; a radially outer surface extending between the first and second axial end surfaces; and at least one recess formed in the radially inner surface for receiving a tool for removing the plug from the port, wherein the at least one recess is an annular recess extending around the entire radially inner surface and having opposed axial surfaces and a base surface.

2. A plug as claimed in claim 1, wherein the at least one recess extends perpendicularly to the radially inner surface.

3. A plug as claimed in claim 1, wherein the opposed axial surfaces are parallel to at least one of the first and second axial end surfaces.

4. A plug as claimed in claim 1, wherein the base surface is parallel to at least one of the radially inner surface and radially outer surface.

5. A plug as claimed in claim 1, wherein the recess extends radially into the plug body from the radially inner surface to a depth of from 30-50% of the thickness of the plug body measured between the radially inner and radially outer surfaces of the plug body.

6. A plug as claimed in claim 1, wherein the recess has a height (H) measured in a direction between the first and second axial end surfaces of 0.25 to 0.43 of the height Hp of the plug body measured in the direction between the first and second axial end surfaces.

7. A plug as claimed in claim 1, wherein the plug body is made from aluminium.

8. A servovalve comprising: a plug as claimed in claim 1, a port for receiving a working fluid, wherein the filter screen is mounted in a bore of the port and received on an annular shoulder at a base of the bore, and wherein the plug is interference fitted in the port to retain the filter screen on the annular shoulder in the port.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 shows a cross-section through a servovalve in accordance with the disclosure;

(2) FIG. 2 shows an exploded view of the servovalve of FIG. 1;

(3) FIG. 3 shows a cross-sectional view of a plug in accordance with the disclosure;

(4) FIG. 4 shows a perspective cross-sectional view of the plug of FIG. 3;

(5) FIG. 5 shows a plug removal tool in accordance with the disclosure;

(6) FIG. 6 shows the tool of FIG. 5 in a preliminary stage of removing a plug from a servovalve;

(7) FIG. 7 shows a partial cross-sectional view of the tool in a removal configuration engaged with the plug; and

(8) FIG. 8 shows the tool holding the removed plug.

DETAILED DESCRIPTION

(9) With reference to FIGS. 1 and 2, a servovalve 2 comprises a servovalve housing 4 which houses a pair of nozzles 6 and a flapper element 8. As is known in the art, the flapper element 8 is deflected in a direction along the axes of the nozzles 6 by an actuator, not shown, in order to meter a working fluid which passes through the nozzles 6.

(10) The servovalve housing 4 comprises has three ports 10, which allow communication of the working fluid to the nozzles 6. The central port 10 is typically called a control port and its function is to communicate fluid to an actuator (not shown). This type of servovalve is well known in the art, being used in a wide variety of aircraft control systems, for example in fuel and air management systems for operating engine fuel metering valves, active clearance control valves, bleed valves and so on.

(11) Since, as is discussed above, the distances moved by the flapper element 8 may be relatively small, in order to prevent operation of the flapper element 8 being compromised by contamination, particle filters 14 are arranged in one or more of the ports 10. As can be seen in FIG. 1, in an embodiment of the disclosure, the filters 14 are received within a bore 16 of the respective ports 10 and are received on an annular shoulder 18 at the base of each bore 16.

(12) The filter 14 may be a screen or mesh structure as is known in the art, with an appropriate mesh size. For example, in some embodiments the filter 14 may be configured to filter particles having a nominal size larger than 0.07 mm. The filter 14 may be made from any suitable material, for example a metal or a plastics material.

(13) The filter 14 is retained on the shoulder 18 within the bore 16 by a plug 20 which is press fitted into the bore 16. As can be seen in FIGS. 3 and 4, the plug 20 has an annular body 22 having opposed first and second axial end surfaces 24, 26, a radially inner surface 28 extending between the first and second axial end surfaces 24, 26 and a radially outer surface 30 extending between the first and second axial end surfaces 24. The first and second axial end surfaces 24, 26 are generally parallel to one another and perpendicular to the central axis A of the plug 20. The radially inner and outer surfaces 28, 30 are also generally parallel to one another and extend parallel to the central axis A of the plug 20.

(14) An annular recess 36 is formed in the radially inner surface 28. In this embodiment, the recess 36 extends entirely around the circumference of the inner surface 28. In other embodiments, however, one or more pairs of diametrically opposed recesses may be provided instead. However, an annular recess 36 may be more easily manufactured and may facilitate removal of the plug 20.

(15) The recess 36 extends into the plug body 22 generally perpendicularly to the radially inner surface 28. In the disclosed embodiment, the recess 36 has opposed axial surfaces 38, 40 and a base surface 42. The axial surfaces 38, 40 may, as shown, be parallel to the axial end surfaces 24, 26 of the plug body 22. The base surface 42 may be parallel to the radially inner and outer surfaces 28, 30 of the plug body 22.

(16) The recess 36 may extend radially into the plug body 22 from the radially inner surface 28 to a depth D of from 30-50% of the thickness T of the plug body 22 measured between the radially inner and radially outer surfaces 28, 30 of the plug body 22.

(17) The recess 36 may have a height HR measured in the direction between its opposed axial surfaces 38, 40 of from 0.25 to 0.43 of the height HP of the plug body 22 measured between the first and second axial end surfaces 28, 30 of the plug body 22.

(18) In a typical embodiment, the plug body 22 may have an outer diameter DPO of 7.5 mm and an inner diameter DPI of 4.7 mm and the recess 36 have an outer diameter DR of 6 mm. The inner diameter DPI of the plug body 22 will need to be large enough to allow the flow of working fluid through the respective ports 10, 12. The height HP of the plug body 22 may typically be 2.7 mm and the height HR of the recess 36 22 may typically be 1 mm.

(19) As can be seen, for example FIG. 3, in embodiments, the plug 20 may be symmetrical about an axial centreline B defined equidistant between the first and second axial end surfaces 24, 26 of the plug 20 such that it may be inserted into the bore 16 in either orientation, thereby facilitating assembly. Also, as can be seen in FIG. 3, the corners 32, 34 between the first and second axial end surfaces 24, 26 and the radially outer surface 30 may be chamfered or rounded in order to facilitate insertion of the plug 20 into the bore 16.

(20) The plug body 22 may be made from any suitable material. In certain embodiments, the plug body 22 may be made from aluminium for example. This will provide sufficient rigidity and strength for the plug body 22.

(21) As discussed above, the plug body 22 is press fitted into the bore 16 in order to retain the filter 14 in position. The recess 36 facilitates removal of the plug 20 from the bore 16 as will be discussed further below.

(22) FIG. 5 illustrates a tool 50 which may be used in removing the plug 20 from a bore 16.

(23) The tool 50 comprises a pair of handles 52a, 52b pivotally mounted to one another about a pivot 54. The pivot 54 may take any suitable form, for example a pin extending through respective openings (not shown) on the handles 52a, 52b. Each handle 52a, 52b has a respective plug gripping portion 56a, 56b extending therefrom beyond the pivot 54.

(24) Each plug gripping portion 56a, 56b comprises an outwardly projecting tooth 58a, 58b at its distal end for engaging in the recess 36 of the plug 20 when the plug gripping portions 56a, 56b are moved apart by operation of the handles 52a, 52b.

(25) The teeth 58a, 58b may have any suitable profile as long as they can be received within the recess 36. In this embodiment, each tooth 58a, 58b tapers in an outward direction. Thus, as shown, the upper surface 59 of each tooth 58a, 58b may be angled. This may facilitate positioning of the tooth 58a, 58b in the recess 36, as can be seen from FIG. 7 for example. Of course other shapes of tooth 58a, 58b are possible within the scope of the disclosure

(26) In the disclosed embodiment, the plug gripping portions 56a, 56b are configured such that as the handles 52a, 52b are moved towards one another the plug gripping portions 56a, 56b are moved apart. This facilitates removal of the plug 20 as it is possible to engage the tool 50 with the plug 20 using just one hand.

(27) Each handle 52a, 52b further comprises a stop 60a, 60b for limiting the movement of the handles 52a, 52b and therefore the movement apart of the plug gripping portions 56a, 56b. The stops 60a, 60b therefore determine how far the teeth 58a, 58b will extend into the recess 36 and indicate to a user that the teeth 58a, 58b are properly located in the recess 36 when the stops 60a, 60b engage.

(28) In the embodiment described, each stop 60a, 60b is generally L-shaped, having opposed distal surfaces 62a, 62b which will engage with each other in the closed position. Of course, different forms of stop may be provided. In this embodiment, both stops 60a, 60b extend from a respective handle 52a, 52b. In other embodiments, only one stop may extend from a handle 52a, 52b, the other stop being formed as a stop surface on the handle 52a, 52b.

(29) As can be seen from FIG. 5, in this embodiment each handle 52a, 52b comprises a first section 64a, 64b arranged generally parallel to the first section 64a, 64b of the other handle 52a, 52b and an angled section 66a, 66b extending therefrom to the pivot 54. The stops 60a, 60b extend from the angle sections 66a, 66b and are cranked such that the stop surfaces 62a, 62b thereof are generally parallel when they engage one another.

(30) As can also be seen from FIG. 5, each plug gripping portion 56a, 56b comprises a proximal portion 68a, 68b attached to its respective handle 52a, 52b at the pivot 54 and a distal portion 70a, 70b comprising the outwardly projecting tooth 58a, 58b. As the handles 52a, 52b are spaced laterally along the pivot axis P, the plug gripping portions 56a, 56b are shaped such that the proximal portions 68a, 68b and distal portions 70a, 70 b are offset laterally from one another in the opposite direction so that the distal portions 70a, 70b of the plug gripping portions 56a, 56b align back to back when the handles 52a, 52b are spaced apart, thereby assuring that the teeth 58a, 58b are aligned. The proximal portions 68a, 68b and 70a, 70b may therefore, as shown, be joined by an angled section 72a, 72b.

(31) Having described the plug 20 and tool 50, removal of a plug 20 from a bore 16 will now be described.

(32) Firstly, with the tool 50 in the “closed” position shown in FIG. 5, the plug engaging portions 56a, 56b are inserted into the plug 20 as shown in FIG. 6. The tool 50 is inserted to such a depth that the teeth 58a, 58b lie opposite the recess 36.

(33) The handles 52a, 52b are then moved together as indicated by arrow A in FIG. 6. This will cause the plug gripping portions 56a, 56b to pivot apart from one another, as shown schematically by the arrow B in FIG. 7. This moves the teeth 58a, 58b into the recess 36 as shown in FIG. 7. The movement of the teeth 58a, 58b is limited by the stops 60a, 60b coming into engagement with each other. This will indicate to the user that the teeth 58a, 58b are fully engaged in the recess 36 and that the plug 20 may then be removed.

(34) To remove the plug 20, the user pulls on the handles 52a, 52b, and possibly also twists the tool to loosen the plug 20. Once the plug 20 has been removed (as shown in FIG. 8) it may be discarded. The filter 14 may then be removed, for example using a hook-like tool and the relevant port 10, 12 cleaned if necessary. A new filter 14 may then be placed in the bore 16 and a new plug 20 press fitted into the bore 16 to retain the filter 14.

(35) The above described embodiments arrangement offers significant advantages. Firstly, they may allow easy replacement of a filter 14 without the need to return the servovalve 2 to the manufacturer. This is both attractive in terms of time and cost. The tool 50 also allows easy and consistent gripping of a plug 20 to facilitate its removal. The use of an annular recess 36 is potentially advantageous as it will allow the tool 50 to be engaged in the recess in any angular orientation, facilitating removal of the plug 20.

(36) It will be appreciated that the above embodiments are exemplary only and that modifications thereto may be made within the scope of the disclosure.