GB2379726A

GB2379726A - Electro-magnetically operated device

Info

Publication number: GB2379726A
Application number: GB0227980A
Authority: GB
Inventors: Wladyslaw Wygnanski
Original assignee: Camcon Ltd
Current assignee: Silverwell Technology Ltd
Priority date: 2000-07-06
Filing date: 2001-07-05
Publication date: 2003-03-19
Anticipated expiration: 2021-07-05
Also published as: GB2379726B; GB2395362B; GB0227980D0; GB0403399D0; GB2395362A

Abstract

An electro-magnetically operated device is described in which a magnetisable armature 10 in the form of a length of thin naturally resilient mild steel, is sandwiched between, and extends from, two parts of a magnetic circuit which contains an air gap 28 into which the armature extends. An electromagnet polarizes the armature along its length so as to cause the end thereof in the air gap to be attracted to one or the other of the two poles 24,26 of the magnetic circuit defining the gap. The armature is designed so as to be capable of adopting a mid-position between the poles of the air gap if the current flowing in the electromagnet is reduced to zero. Equalising the air gaps and adjusting the size of the gap relative to the resilience of the armature will produce a bistable characteristic in which the armature will not remain in the mid-position, but will always remain in contact with one pole or the other, and is shifted from one to the other by a pulse of current of appropriate polarity. Adjustment of the size of the air gap on one side or the other of the armature introduces an out of balance in the magnetic circuit enabling the device to adopt a monostable characteristic instead of a bistable characteristic. Movement of the armature can open and/or close valves, controlling a flow of fluid.

Description

Title: Electro-magnetically operated device Field of Invention This invention concerns electromagnetically operative devices (actuators) of the type which use a magnetic field to move an armature from one position to another.

Background to the invention.

Such actuators can be used to control switch contacts and provide either a normally open, normally closed or changeover functionality, by attaching one or more contacts to the armature or using the movement of the armature to move another member carrying the contact (s). Similarly movement of the armature can open and/or close valves controlling a flow of fluid.

Many such devices require a continuous flow of electric current to hold the armature in one position or the other. This is wasteful of energy and can produce unwanted heat.

It is an object of the present invention to provide such a device with a bistable characteristic where the change in position of the armature is effected by means of a single pulse and the armature remains in the new position until a pulse of opposite polarity is received.

It is a further object of the invention to provide such a device in which the bistable operating characteristic can be converted to a monostable characteristic.

Summary of the invention The invention relates to an electromagnetically operable device comprising:

(a) a magnetic circuit having permanent N and S poles defining an air gap; (b) an armature assembly which extends into the air gap and at least a portion of which is magnetisable and is movable between two end positions adjacent the two permanent poles through an intermediate position towards which it is resiliently biased; and (c) an electromagnet which when energised by an electric current polarises the magnetisable portion of the armature assembly so that the part thereof in the air gap becomes a S or N pole and will thereby be attracted towards one of the permanent poles.

In a preferred arrangement which will possess a bistable characteristic, the residual permanent flux linking the magnetic part of the armature assembly and the relevant adjacent permanent pole after a current of a given magnitude and direction has flowed in the electromagnet and displaced the armature, is sufficient to generate a force of attraction which is greater than the resilient force acting to return the armature to its intermediate position so as to retain the armature in its displaced position, but which is less than the sum of the resilient force and the force of attraction created by the magnetic flux linking the magnetic part of the armature assembly and the other permanent pole, when a similar current, but flowing in the opposite direction, flows in the electromagnet.

In such an arrangement, a pulse of current in one direction will cause the armature assembly to move to, and remain at one end of its travel and a pulse of current of similar magnitude but opposite direction, will cause it to move to, and remain at, the other end of its travel.

According to the present invention the armature assembly is formed in part from a length of naturally resilient material, and the resilient force is generated by deflecting the resilient material from an undeflected condition, to one side or the other, and the naturally resilient magnetisable armature is sandwiched between two parts of a magnetic circuit which contains an air gap into which the armature extends, and an electromagnet is provided to

magnetically polarize the armature along its length to cause the end of the armature in the air gap to be attracted to one or the other of the two poles of the circuit defining the gap.

Preferably the armature is adapted to occupy the air gap with an equal distance between it and each of the two poles when relaxed, so that if the magnetic flux is reduced to zero the armature is equally spaced from both poles.

The closure of the gap by the movement of the armature towards one of the poles increases the flux linking the armature and that one pole, and by selecting the resilience of the armature material so that the tendency of the armature to resume a mid position between the poles is less than the magnetic force acting between it and the said one pole to which it has moved, the armature will remain in position near or in contact with the said one pole.

The pole to which the armature is attracted is selected by causing a direct current to flow through the winding of the electromagnet coil in one direction or the other. Current in one direction will move the armature towards one of the poles and in the other direction it will move the armature towards the other of the two poles.

Typically the armature is a straight elongate strip of mild steel, part of the length of which is sandwiched between the two parts of the magnetic circuit and the unsupported remainder of which extends at least in part between the two poles.

Such an armature can be considered to hinge about a point along its length from where it protrudes from two parts between which it is secured and which make up the magnetic circuit, and the faces of the poles are preferably inclined so as to be parallel to the length of the armature which extends beyond the hinge point to its free end, and which by virtue of the hinging action, becomes angled relative to the remainder of the armature.

By ensuring good face to face contact between the armature and one of the two poles, and providing an opening in that pole which is covered by the armature when the latter is attracted to it, and opened when the armature either occupies its intermediate position or is

attracted to the other pole, the armature can be used to control the flow of fluid (liquid or gas) through the opening.

By providing an opening in the other pole, this other opening will be will be covered by the armature when it is attracted to this said other pole and vice versa.

If an opening is to be sealingly closed by the armature, an appropriate seal may be provided around the edge of the opening, to be engaged by the face of the armature. A suitable sealing material may instead, or in addition, be included on the face of the armature.

If a monostable characteristic is desired, means may be provided to increase the air gap between the armature and one of the pole faces, so that when a current flows through the electromagnet which would have attracted the armature to that pole, the flux linking the armature and that pole is insufficient even when combined with the resilient force, to generate the force of attraction needed the overcome the force of attraction between the armature and the other pole due to the residual permanent flux linking the armature and the said other pole.

The size of the air gap between the armature and each of the poles is preferably adjustable to enable the magnetic circuit to be balanced.

The adjustment may be by way of a movable insert which may be magnetisable and which can be adjusted so as to protrude to a greater or lesser extent from a pole face.

The device may be linked to a parameter sensing means for adjusting the position of one pole relative to the mid position of the armature, so as to increase the distance between the armature and that pole if the parameter sensed by the sensing means exceeds a predetermined value-eg. Temperature becomes elevated or pressure rises.

In each of the arrangements, movement of the or each armature assembly (or part thereof) can be arranged to cover or uncover openings, so as to permit or impede a fluid flow.

Since the armature will be attracted to opposite poles of the two V-shaped air gaps, the two armatures can be likened to opposite ends of a see-saw. Both can be adapted to cover and uncover ports to control fluid flow if desired. One or both may be visible in a window to indicate the position it has adopted in the slot.

One or both may for example be coloured and adapted to move relative to a window so as to present a different region in the window depending on its position, and two coloured regions may be provided on the or each armature.

In another arrangement one may be adapted to cover and uncover ports to control fluid flow and the other is merely employed as an indicator of the position of the former.

The invention also lies in a fluid flow control valve operated by movement of an armature in any device as herein described.

The invention will now be described by way of example with reference to the accompanying drawings, in which Fig I is a cross-section through a bistable electromagnetic drive embodying the invention; Fig 2 is a cross-section through a bistable electromagnetic drive modified to act as a safety valve; Fig 3 is a cross-section through the electromagnetic drive of Fig 2 in which the bistable

tn n 4inf-t ; nn b-,, f a function has been modified to a monostable function by operation of a bi-metal device ; Figs 4, 5 and 6 are a part sectioned plan view, side view and end view respectively of one Figs 4, 5 and 6 are a part sectioned plan view, side view and end view respectively of one embodiment of an electromagnetic drive embodying the invention ;

Figs 7 and 8 are force diagrams for when the coil current is =0 and > 0 for the device shown in Fig 1; Fig 9 is a section through another actuator embodying the invention; and Fig 10 is a section through a fluid flow control valve incorporating an actuator of the type shown in Figure 9.

In Fig 1 a linear armature of flat spring steel 10 is sandwiched between two internal pole pieces of mild steel 12,14 which are themselves sandwiched between two permanent magnets 16,18. Two external mild steel members 20,22 extend beyond the end of the sandwich of magnets and internal pole pieces 12-18 and armature 10, and at their remote ends provide two inwardly facing poles 24,26 defining an air gap 28 between which in its undeflected state the armature 10 extends equidistant from the two poles 24,26.

The internal pole pieces 12,14 extend beyond the permanent magnets 16,18 where they are surrounded by a coil former 30 on which a coil 32 is wound.

Two cylindrical inserts 34,36 are fitted in the poles 24,26 and the opposed inner ends of the inserts are closed except for orifices 38,40. The inserts are of magnetisable material.

The armature can be deflected under the magnetic field induced by a current flowing in the coil 32 and depending on the direction of current flow in the coil, the armature will be attracted towards the pole 26 and insert 36 as shown in solid outline, or towards the other pole 24 and insert 34, as shown in dashed outline.

The inserts 34,36 are mounted with their axes at an angle of less than 900 to the faces of the poles 24,26 so that the opposed end faces of the inserts are parallel to the armature when the latter is deflected towards the poles. In this way a flat face of the armature can

co-operate with the inwardly directed inclined face of insert 34 or 36, to close off orifice 38 or 40, respectively.

Each insert protrudes by a small distance beyond its pole face and is adjusted axially to create the desired air gap to the armature. The armature remains attracted to the pole towards which it was last deflected by the magnetic flux created by a current flowing in the coil, due to the closure of the gap concerned and the flux remaining due to the permanent magnets 16,18. The orifice in that pole insert thus remains closed off until such time as a current flows in the opposite sense in the coil, whereupon the armature will rapidly shift to the other pole, and in a similar manner remain attracted towards this other pole until a suitable current once again is caused to flow in the coil, to reverse the deflection of the armature once again. While deflected towards this other pole, the orifice in that pole-insert will be closed off by the armature, leaving the orifice in the insert in the first pole uncovered.

When constructed in this balanced way, the armature can be said to be bistable-in that it will remain in either position until prompted to adopt its other stable state. More importantly by selecting the strength of the magnets, the size of the air gaps between the armature and inserts as determined by the amount by which the inserts protrude beyond the faces of the pole pieces, and the resilience of the armature,-the armature will remain in its last deflected condition even after the current causing that deflection has ceased to flow in the coil. The device can therfore be switched from one state to the other (ie from one orifice closed and the other open to one in which the one orifice is open and the other is closed), by pulses of electric current of appropriate magnitude and polarity, as dictated by the number of turns in the coil and the direction in which the wire is wound to form the coil.

A The modification of Figs 2 and 3 allows this balanced form of condition to be changed in response to an external influence. This can be any device which alters the amount by which one of the inserts protrudes beyond the end of the pole piece in which it is mounted, relative to the other.

To this end insert 36 of Fig 1 is replaced by insert 42 (see Figs 2 and 3) which can be slid relative to the pole 26 within the limits defined by the engagement of a radial protrusion 44 into a cavity 46 in the wall of the bore in which the insert is fitted.

The actual position of the insert is governed by the condition of a bi-metal hairpin device 48 one limb of which is rigidly attached to the pole 26 and the other of which is hinged to the protruding end of the insert 36. At low temperatures the limbs of the bi-metal device remains tightly closed (as shown in Fig 2) but at elevated temperatures the limbs splay apart (as shown in Fig 3). In doing so, the insert 36 is moved axially relative to the pole 26 so that the internal end containing the orifice 40 is shifted into alignment with the end face of the pole 26.

In this condition the air gap between insert 36 and armature 20 is much greater than that between the armature and insert 34, and a current pulse normally able to shift the armature from pole 24 to pole 26, will not be able to generate sufficient flux in the larger air gap between 10 and 36 to overcome the magnetic attraction between 10 and 34. The device will thus remain with the armature deflected towards 24 and closing off orifice 38.

The device thus now has a fail safe characteristic in that at elevated temperatures, for example, a current pulse which would normally open orifice 38 is unable to attract the armature away from pole 24, so that orifice 38 remains closed, until the temperature of the bi-metal device 48 drops and allows the two limbs to close and shift the insert 36 back into its protruding position (similar to 34).

Figs 4,5 and 6 show how the component parts of the schematic arrangement of Fig 1 could be constructed and secured together in position-although it is to be understood these arrangements are illustrative only and the invention is not limited to the particular forms of construction shown. Thus the sandwich of the two permanent magnets 16,18 the internal pole pieces 12,14 and the external magnetic circuit members 20, 22 are secured within a two-part aluminium housing 54,56 each part of which is similar and includes a

tunnel section and two lateral flanges such as 58,60 (in the case of the upper part 54) and 62,64 (in the case of the lower part 56).

The flanges are bolted or otherwise secured together as shown best in Fig 6, and in so doing the two tunnel sections of the housing parts 54,56 clamp the stacked sandwich of magnets etc.

The elongate thin mild steel armature 10 is itself sandwiched in the middle of the stack as can be seen in Figs 5 and 6, and two elongate spacers 66,68 are provided between the internal faces of the two tunnel sections and the internal pole pieces 12,14. The spacers are formed from non-magnetic material, preferably soft material such as copper or brass or plastics, to allow for lateral positioning and alignment of the pole pieces 12,14.

The opposed faces of the pole-pieces which are to engage the upper and lower faces of the armature are partly cut away t form two aligned shallow channels into which the upper and lower parts of the armature cross-section partly fit. In this way alignment of the armature is ensured.

The alignment of the two housing parts 58,60 is best achieved by close fitting sleeves such as 70,72 as shown in Fig 6, which extend through the aligned holes 74,76 and 78,80 respectively in the flanges 58 and 62, and 60 and 64. The bolts or other securing devices extend through the sleeves.

It is of course important not to bridge the gap between the permanent magnets 12,14 and the sleeves should therefore be formed from non-magnetic material such as copper, brass, aluminium or plastics.

At Ulle ou, Luoar'u ends oir the'.)-2 At the outboard ends of the external magnetic circuit members 20, 22 are fitted two blocks of magnetisable material such as mild steel 82,84 which contain through-bores to receive pole-piece inserts 86,88, also of mild steel or other magnetic material.

Each insert 86,88 is cylindrical and all but closed at the end protruding from the polepiece, except for a small orifice, only one of which is visible at 90 in Fig 5. The other insert 86 is constructed in a similar way to 88.

The ends of the members 20,22 are bifurcated to provide forks 92,94 (in the case of 20) and 96,98 (in the case of 22) and the blocks 82,84 are a tight fit between the respective forks and secured in place by hexagonal headed bolts such as shown at 100,102 and 104, 106.

The armature is magnetically polarised to effect changeover from one pole to the other, by energising a coil, some of the windings of which are denoted by reference number 108, wound on by a former 110-best seen in Fig 5. Connections to the coil are not shown in the drawings.

By using direct current and selecting the direction of current flow through the coil windings 108 so the armature 10 will be polarised N-S from left to right or vice versa. If the permanent magnets 16,18 are polarised as shown, then block 82 will be a North pole and block 84 will be a South pole. If in that event armature 10 is polarised so that its right hand end (as shown in Fig 5) is a North pole, then it will be attracted towards block 84, and if polarised as a South pole, it will be attracted towards the other block 82.

Figs 7 and 8 show the variation of the effective force acting on the armature 10-between the pole blocks 82,84 in the case of the current being zero in Fig 7 and for the current being > 0 in Fig 8.

In both cases the spring force (resilience) is the same and is denoted by the line of points 112. The net magnetic force acting on the armature is denoted by the line of points 114 and this will be seen to pass through zero in the same way and at the same position as does the spring force curve 112. The net force acting on the armature (magnetic force less spring force) is shown by the line of points 116 and again this passes through zero at the

same point as the other two curves, and follows the general shape of the magnetic force curve.

In the case of the current being zero the spring force curve 112 remains the same as in Fig 7, the magnetic force curve 114'starts at a higher value but never goes below zero and largely flattens out over the second half of the plot. The net force curve 116'is therefore always positive and is sufficient in all cases to overcome the spring force (resilience) of the armature 10, and will cause the latter to be deflected to one of the poles.

If the current is < 0 (ie flows in the opposite sense) then the curve 114'is the mirror image of that shown in Fig 8, and this time the net force curve will always remain below the zero line, so forcing the armature to be attracted to the other pole.

In Fig 9 an armature is formed in part from a short strip of resilient material 120 such as phosphor bronze held captive by a fixed mounting 122 so that it will normally extend midway between two pairs of poles 124,126 and 128,130 of two pole assemblies 132, 133 respectively. The resilient strip 120 is sandwiched between two longer lengths of flat strip material 134,135 to form the composite armature assembly. The strips 134,135 are of magnetisable material, such as silicon steel, and may be cut-away where they are to sandwich the phosphor bronze strip 120 so that the thickness of the latter is accommodated within the two cut-away regions of the strips 134,135. This refinement is shown in Fig 9A.

A permanent magnet 136 is mounted between two parallel faces of the two pole assemblies 132,134 being denoted by 138,140.

An electromagnet winding 142 on a former 144 surrounds the central region of the armature with connections 146, 148. Energising the electromagnet by direct current flowing in one direction from 146 to 148 will produce a N pole at the left hand end, and a S pole at the right hand end of 144 and this will induce similar magnetic polarity in the

armature so that in that event the LH end of 134,135 between 128,130 will become a N pole and the RH end between 124,126 will become a S pole.

Consequent on this polarisation of 134,135, the composite armature will twist relative to the mounting 122 to enable the LH end to move towards face 128 and the RH end to move towards face 126.

If the current flows in an opposite sense, the LH end of 134,135 will become a S pole, and the RH end a N pole, and the movement will be reversed, ie the LH end will move towards 130 and the RH end towards 124.

The resilience of the strip 120 and the strength of the magnet 136 are selected so that when deflected either one way or the other, the residual flux linking the adjacent ends of the armature components 134,135 and the poles 128 (130) and 126 (128) (depending on the last direction of the current in 142), due to the permanent magnet 136, after the current flow in 142 has ceased, is greater than the restoring force exerted on 134,135 by the twist of 120, relative to 122. The armature will thus remain in that position until an opposite current flows in the winding 142.

It is of course necessary to ensure that the magnetic flux created by the current generates a sufficiently powerful magnet of the armature components 134,135 for the forces of attraction and repulsion in the air gaps between 128,130 at one end, and between 124,126 and the other, to overcome the stiffness of the resilient strip 120 and fixed mounting 122.

Fig 10 shows how such an actuator can be enclosed within a housing 150 and the poles defining faces 124,126 modified, to form fluid flow control valves.

To this end the RH end of the armature assembly forms a valve closure and in its deflected position either closes off a port 152 (and leaves open a port 154) or closes of 154 and opens 152. The ports are formed by sleeves 156,158 screwed or otherwise secured in bores 160,162 formed in the pole assemblies 132,133 respectively. The bores

communicate with openings 164,166 respectively in the wall of the housing 150 and 0ring seals 168,170 prevent fluid loss between the inside surface of the housing and the pole assemblies 132,133. Similar 0-ring seals 172,174 are fitted around the inboard ends of the sleeves 156 and 158 respectively, to form a good seal with the face of the armature components 134,135.

Claims

CLAIMS 1. A electromagnetically operated device comprising a naturally resilient magnetisable elongate armature sandwiched over part of its length between two parts of a magnetic circuit which contains an air gap into which the armature extends, and an electromagnet is provided to magnetically polarize the armature along its length to cause the end of the armature in the air gap to be attracted to one or the other of the two poles of the magnetic circuit defining the gap.
2. A device as claimed in claim 1, wherein the armature is adapted to occupy the air gap with an equal distance between it and each of the two poles when relaxed, so that if all the magnetic flux is reduced to zero the armature is equally spaced from both poles.
3. A device as claimed in claim 1 or 2, wherein closure of the gap by the movement of the armature towards one of the poles increases the flux linking the armature and that one pole, and the resilience of the armature material is selected so that the tendency of the armature to resume a mid position between the poles is less than the magnetic force acting between it and the said one pole to which it has moved so that the armature will remain in position near or in contact with the said one pole.
4. A device as claimed in claim 3, wherein the pole to which the armature is attracted is selected by causing a direct current to flow through the electromagnet coil in one direction or the other.
5. A device as claimed in any of claims 1 to 4, wherein the armature is a straight elongate strip of steel.

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6. A device as claimed in any of claims 1 to 5 in which the elongate armature hinges about a point along its length from where it protrudes from the two parts between which it is secured.
7. A device as claimed in any of claims 1 to 6, wherein the faces of the poles are inclined so as to be parallel to the inclination of the armature portion which extends beyond the hinge point to its free end, and which by virtue of the hinging action, becomes angled relative to the fixed part of the armature.
8. A device as claimed in any of claims 1 to 7, wherein an opening is provided in at least one of the poles which is covered by the armature when the latter is attracted to it, and opened when the armature either occupies its intermediate position or is attracted to the other pole, whereby movement of the armature controls the flow of a fluid (liquid or gas) through the opening.
9. A device as claimed in claim 8, wherein there is also an opening in the other pole, and this other opening is covered by the armature when it is attracted to this said other pole.
10. A device as claimed in claim 8 or 9, wherein a seal is provided around the edge of the or each opening, to be covered by the armature.
11. A device as claimed in claim 8,9 or 10, wherein a sealing material is provided on the or each face of the armature which is to cover an opening.
12. A device as claimed in any of claims 1 to 11, further comprising a device for increasing the air gap between the armature and one of the pole faces, so that when a current flows through the electromagnet which would have attracted the armature to that pole, the residual flux linking the armature and that pole is insufficient to overcome the resilient biasing of the armature so that the armature is only attracted to that pole while the current flows.

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13. A device as claimed in any of claims 1 to 12, wherein the size of the air gap between the armature and each of the poles is adjustable to enable the balance of the magnetic circuit to be adjusted.
14. A device as claimed in claim 13, wherein the adjustment is by way of a movable insert which can be adjusted so as to protrude to a greater or lesser extent from a pole face.
15. A device as claimed in claim 14 wherein the insert is of magnetisable material
16. A device as claimed in any of claims 1 to 15, adapted to be linked to a parameter sensing device, which is adapted to adjust the position of one pole or a part thereof relative to the mid position of the armature, so as to increase the distance between the armature and that pole if the parameter sensed by the sensing device exceeds a predetermined value.
17. An electromagnetically operable device as claimed in claim 1 wherein the electric current polarises the magnetisable portion of the armature assembly so that the part thereof in the air gap becomes a S or N pole and will thereby be attracted towards one of the permanent poles, further comprising a device by which the air gap between the armature and one of the pole faces can be increased, so that the residual flux linking the armature and that pole after the current ceases to flow is insufficient to overcome the resilient biasing of the armature, so that the armature is only attracted to that pole while an appropriate current flows.
18. A device as claimed in claim 17, wherein the residual permanent flux linking the magnetic part of the armature assembly and the relevant adjacent permanent pole after a current of a given magnitude and direction has flowed in the electromagnet and displaced the armature, is sufficient to generate a force of attraction which is greater than the resilient force acting to return the armature to its intermediate position so as to retain the armature in its displaced position, but which is less than the sum of the

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resilient force and the force of attraction created by the magnetic flux linking the magnetic part of the armature assembly and the other permanent pole, when a similar current, but flowing in the opposite direction, flows in the electromagnet, so as to impart a bistable characteristic to the device.
19. A device as claimed in claim 17 or 18, wherein the armature assembly is formed in part from a length of resilient material and the resilient force is generated by deflecting the resilient material from an undeflected condition, to one side or the other.
20. A device as claimed in any of claims 17 to 19, wherein the faces of the poles are inclined so as to be parallel to the inclination of the armature portion which extends beyond the hinge point to its free end, and which by virtue of the hinging action, becomes angled relative to the fixed part of the armature.
21. A device as claimed in any of claims 17 to 20, wherein an opening is provided in at least one of the poles which is covered by the armature when the latter is attracted to it, and opened when the armature either occupies its intermediate position or is attracted to the other pole, whereby movement of the armature controls the flow of a fluid (liquid or gas) through the opening.
22. A device as claimed in claim 21, wherein there is also an opening in the other pole, and this other opening is covered by the armature when it is attracted to this said other pole.
23. A device as claimed in claim 21 or 22, wherein a seal is provided around the edge of the or each opening, to be covered by the armature.
24. A device as claimed in claim 21, 22 or 23, wherein a sealing material is provided on the or each face of the armature which is to cover an opening.

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25. A device as claimed in any of claims 17 to 24, wherein the size of the air gap between the armature and each of the poles is adjustable to enable the balance of the magnetic circuit to be adjusted.
26. A device as claimed in claim 25, wherein the adjustment is by way of a movable insert which may be magnetisable and which can be adjusted so as to protrude to a greater or lesser extent from a pole face.
27. A device as claimed in any of claims 17 to 26, adapted to be linked to a parameter sensing device, which is adapted to adjust the position of one pole or a part thereof relative to the mid position of the armature, so as to increase the distance between the armature and that pole if the parameter sensed by the sensing device exceeds a predetermined value.
28. A fluid flow control valve having at least one inlet and at least one outlet comprising an electromagnetically operated device as claimed in any of the preceding claims, wherein the movable armature acts on or comprises at least part of a movable device for controlling the flow of fluid from the inlet to the outlet.
29. A valve as claimed in claim 16, having one inlet and two outlets.
30. A valve as claimed in claim 16 having two inlets and one outlet.
31. Electromagnetically operable devices (actuators) constructed, arranged and adapted to operate substantially as herein described and/or with reference to Figs 1 to 10 of the accompanying drawings.
32. Electromagnetically operable fluid flow control valves constructed, arranged and adapted to operate substantially as herein described and/or with reference to Figs 1 to 10 of the accompanying drawings.