VALVE The present invention relates to a valve for con- trolling a flow of fluid, comprising: a valve housing having an inlet and a first and a second outlet ; a first and a second valve member which are arranged in the valve housing, the first valve member having a first, passage- defining portion which faces a first, passage-defining portion of the second valve member, said portions defin- ing between themselves a passage for the flow of fluid ; and the first portion of said first valve member in a first open position being arranged upstream of the first portion of the second valve member for directing the flow of fluid from the inlet through said passage to the first outlet and in a second open position being arranged down- stream of the first portion of the second valve member for directing the flow of fluid from the inlet through said passage to the second outlet.

Field of the Invention and Background Art In recent years, there has been an increasing demand for so-called quick valves for controlling a flow of fluid. Conventional valves are usually limited to operat- ing frequencies of up to 500 Hz. By using quick valves, one hopes to be able to achieve operating frequencies of up to 1000 Hz and more. Such quick valves could be used, for instance, as pilot valves in servo valve assemblies for high frequency applications, as acoustically damping control valves for reducing variations in pressure in a flow of fluid and as control valves for quick control of the supply of cooling water in connection with continuous casting of thin steel wires. A further conceivable appli- cation is in connection with mechanical testing and load simulation at high frequencies.

The invention is based on fluidics technology.

Prior-art fluidic devices usually have two opposed guid-

ing ducts which are arranged approximately perpendicular to the main stream of fluid through the fluidic device, guiding streams from said guiding ducts making it pos- sible to control the direction of the main stream of fluid. Fluidic devices, however, suffer from certain drawbacks, inter alia, consumption of fluid in the guid- ing streams and the risk of the guiding ducts being blocked and especially difficulties in achieving effi- cient control at high frequencies and/or high pressures.

A prior-art device that solves some of these prob- lems is disclosed in US Patent 4,073,316. In this device, the guiding ducts are replaced by two valve flaps. When the flow of fluid flows between the flaps, a jet forms.

The jet is directed or deflected by moving one of the flaps upstream or downstream in relation to the other flap. The deflection depends essentially on the geometric shape of the passage formed, but also to some extent on the so-called Coanda effect which arises along the down- stream surface of the passage-defining portion of the flap positioned upstream. In this device, the degree of deflection of the jet increases or decreases continuously as one flap is displaced in relation to the other.

However, for applications at high frequencies and high working pressures, there are still several problems with the above prior-art devices.

The operation of the flaps causes obvious restric- tions to the working frequency. At high working pres- sures, extremely great forces are necessary to move the flaps. Prior-art devices which to some extent manage to handle these forces can only direct fluids at low and average frequencies, i. e. at frequencies up to 500 Hz at most. Moreover, the above device consumes energy also in the zero position, which is not desirable.

It is most important that the design and operation of the valve assembly is such that the pressure drop of the flow of fluid across the valve in an open position is as small as possible. It is also important, especial-

ly at high frequencies, that the pressure drop is low not only in the open position of the valve, but also in the partly open, successive or momentary positions which together constitute the opening and closing procedures of the valve.

In view of the speed at which a pressure wave propa- gates in a hydraulic oil, it is at high frequencies also very important that the valve is compact so that the phy- sical distance between a fluid-directing element, such as a valve member, and an element affected by the directing, such as a main slide of a servo valve, is small.

An object of the invention thus is to provide a valve of the type mentioned by way of introduction for directing a flow of fluid in applications at high fre- quencies and pressures.

A further object of the invention is to provide a valve of the type mentioned by way of introduction with a low pressure drop both in the open and in the partly open position.

A further object is to provide a compact valve of the type mentioned by way of introduction.

Summary of the Invention The inventive objects are achieved by a valve of the type mentioned by way of introduction and having the fea- tures defined in the appended claims.

Thus the invention is based on the understanding of the advantage that at least one of the valve members is operated with the aid of operating means which comprise a magnetostrictive of piezoelectric element and which effects a longitudinal change of said element, which in turn produces a force which is made to act on the valve member for operation thereof.

According to the invention, the valve members are thus operated by means of magnetrostrictive or piezoelec- tric materials. Magnetostrictive and piezoelectric mate- rials share the property that their dimensions depend on

magnetic or electric fields applied to the materials. The actuation can thus very well be effected with the aid of electric control means. The dimensional changes produce forces which are sufficient for advantageous use at very high hydraulic pressures. Moreover, the materials react very quickly to changes of the magnetic or electric fields, which is a very important property in applica- tions at high frequencies.

A drawback of magnetostrictive and piezoelectric materials is that the dimensional changes that can be achieved with these materials are very small in relation to the movement which is frequently necessary for an ope- rable, closing and opening valve member of a valve. It is therefore desirable to achieve some sort of ratio between the magnetostrictive or piezoelectric element and the valve member, so that the limited longitudinal extension of the element is converted into a considerably greater movement of the valve member.

A drawback of conventional ratio-producing mecha- nisms is that they would amplify to a corresponding degree the inertial forces that must be overcome to pro- duce a movement of a valve member. At high frequencies, a very great inertia would thus act on the piezoelectric or magnetostrictive element that is used in a valve accord- ing to the invention.

According to preferred embodiments of the invention, this problem is solved by at least one valve member being turnable about an axis, and by said force being adapted to act preferably in an at least essentially linear man- ner on said valve member to produce a torque which re- sults in a turning motion of the valve member. Moreover, said operating means and said valve member are advan- tageously arranged to make said force act in a direction whose perpendicular distance to said axis is essentially smaller than a distance between said axis and the first, passage-defining portion of said valve member, whereby the movement, caused by said turning, of the first por-

tion of the valve member becomes great in relation to the longitudinal extension of said element.

By the fact that the longitudinal change of the mag- netostrictive or piezoelectric rod produces a force which is made to act on the respective valve members in a direction whose perpendicular distance to the axis is small, said preferred ratio between the longitudinal change of the rod and the motion of the valve member is produced by the actual turning motion of the valve mem- ber.

It will be appreciated that the perpendicular dis- tance between the direction of the force and the axis is not necessarily a constant distance and can be chang- ed momentarily or successively during the turning motion.

The essential thing is that the momentary distance is small in relation to the distance between the axis and the passage-defining portion of the valve member.

It will also be appreciated that it is not necessary for both valve members to be operated by means of a mag- netostrictive or piezoelectric rod. For instance, one flap can be operated by more conventional methods, like in the above-mentioned US Patent 4,073,316, or it can even be fixedly arranged in the valve housing.

According to one more preferred embodiment of the invention, the valve housing has at least a first portion which together with a second portion of the first valve member defines a first duct for the flow of fluid from the passage to the first outlet in the first open posi- tion, said duct being designed as a diffuser.

This construction thus has the advantage that a dif- fuser is formed as an integrated element of the central parts of the valve. This means that the total size of the valve can be reduced compared with a construction where a valve member and a diffuser are made of separate parts.

The diffuser shape of the duct also means that the occur- rence of turbulence at the valve and pressure drops across the valve is counteracted also in the successive

or momentary positions which all in all form the displac- ing movement of the valve members in relation to each other.

Brief Description of the Drawings The present invention will now be described by way of exemplifying embodiments with reference to the accom- panying drawings, in which Fig. 1 is a schematic cross-sectional view of a valve in a first position according to a first embodiment of the present invention ; Fig. 2 is a schematic cross-sectional view of the valve in Fig. 1 in a second position; Fig. 3 is a schematic cross-sectional view of the valve in Fig. 1 in a third position ; Fig. 4 is a schematic cross-sectional view of a valve in a first position according to a second embodi- ment of the present invention; Fig. 5 is a schematic cross-sectional view of the valve in Fig. 4 in a different position; Fig. 6 is a schematic cross-sectional view of a valve according to a third embodiment of the present invention; Fig. 7A is a schematic cross-sectional view, on a larger scale, of the central pivot portions of the valve member in Fig. 6 in a first position; Fig. 7B is a schematic cross-sectional view, on a larger scale, of the central pivot portions of the valve member in Fig. 6 in a second position; Fig. 8A is a schematic cross-sectional view along line I-I in Fig. 3; and Fig. 8B is a schematic cross-sectional view along line II-II in Fig. 6.

Detailed Description of Preferred Embodiments Figs 1,2 and 3 are schematic cross-sectional views of a valve 10 for directing a flow of fluid in three dif-

ferent positions according to an embodiment of the pre- sent invention. A section along line I-I in Fig. 3 will later be described with reference to Fig. 8A.

The valve 10 comprises a valve housing 11 with an inlet 12 and two outlets 13,13'. In the valve housing, two plate-shaped wings, turning slides or valve mem- bers 20,20'are arranged turnably and opposite to each other, said valve members having respective first, passage-defining edge portions 21,21'which define a gap or passage 17 for a flow of fluid between the valve members.

Moreover, the valve housing 11 has an essentially flat first portion 15 which together with an essentially flat second portion 22, which extends from said first portion 21, of the first valve member 20 defines a first duct 16 which extends from a point immediately obliquely downstream of said passage 17 to the first outlet 13. The first wall portion 15 of the valve housing and the second portion 22 of the first valve member are designed in such manner that the first duct 16 forms a diffuser.

Correspondingly, the valve housing 11 also has an essentially flat second portion 15'which together with an essentially flat second portion 22', which extends from said first portion 21', of the second valve member 20'defines a second duct 16'which extends from a point immediately obliquely downstream of said passage 17 to the second outlet 13'. Also the second wall portion 15' of the valve housing and the second portion 22'of the second valve member are designed in such manner that the second duct 16'has the form of a diffuser.

As is evident from Figs 1-3, the upper opening of the first duct 16 and the upper opening of the second duct 16'thus are arranged side by side just downstream of said passage 17.

Preferably, the ducts 16,16'each have an opening angle of between 4° and 10°, preferably 8°. However, it will be appreciated that the opening angle of the ducts

will vary depending on the turning position of the valve members 20,20'.

When one valve member or both are turned so that the edge portion 21 of the left first valve member 20 is arranged upstream in relation to the edge portion 21'of the right second valve member 20'as shown in Fig. 1, the geometric shape of the passage 17 defined by the valve members has the effect of making the flow of fluid through the passage 17 directed, diverted or deflected to the left, so that the flow of fluid is conducted into the first duct 16 and further to the first outlet 13.

Correspondingly, the flow of fluid is directed through the passage 17 to the right to the second duct 16'in the direction of the second outlet 13'when the edge portion 21 of the left first valve member 20 is arranged downstream in relation to the edge portion 21' of the right second valve member 20', as illustrated in Fig. 2.

Thus, the flow of fluid is directed from the inlet 12 through the passage 17 and the respective ducts 16, 16'to the outlet 13 or 13'depending on the position of the edge portions 21,21'of the valve members 20,20' relative to each other.

In the Figures, the valve members 20 and 20'are arranged turnable about the respective fixed axes 30, 30'which are perpendicular to the turning plane of the valve members and, thus, are directed perpendicular to the direction of the flow of fluid through the valve housing 11. In this embodiment, the valve members 20, 20'are turnable by means of needle bearings 36,36'on circular-cylindrical pivots 31,31'.

When the flow of fluid passes between the passage- defining edge portions 21,21'of the valve members 20, 20', i. e. through the passage 17, the flow of fluid changes partly into a jet or into a more turbulent flow.

In this connection, the pressure produced by the fluid upstream of the passage 17 is partly converted into kine-

tic energy of the jet, and thus a pressure drop arises.

The diffuser, which is formed of the second portion 22, 22'of the respective valve members and the respective wall portions 15,15'of the valve housing, then has the effect of again converting the kinetic energy of the jet into a pressure of the fluid at the respective outlets 13,13'. Thus the pressure drop across the valve becomes relatively low.

Fig. 3 illustrates the valve according to the first embodiment in a third, essentially closed position. In this closed position, the edge portion 21 of the first valve member 20 and the edge portion 21'of the second valve member 20'are arranged close to each other and thus block said passage. In this fashion, the flow of fluid is prevented from passing through the valve in the closed position. This does not, however, exclude the possibility of a limited leakage flow also in the closed position since, for practical reasons, it is difficult and involves a risk to arrange the valve members so that the edge portions are contacted with each other and com- pletely close said passage.

The combination of bringing the edge portions of the valve members close to each other in the closed position and designing the ducts as a diffuser results in a device which has a small consumption of energy in the zero posi- tion but which all the same has a small pressure drop.

A result of the fact that the valve members 20, 20'are arranged so as to be practically in contact with each other in the closed position is that the continuous- ly increasing or decreasing deflection of the jet, which depends on the relative displacement of the edge por- tions 21,21', is lost. A so-called bistable behaviour is obtained instead, in which the flow of fluid in the open positions is deflected either completely to the left or completely to the right. This depends mainly on a combi- nation of the geometric design of the passage 17 and

the Coanda effect on the flow of fluid at the respective edge and duct portion surfaces 21,22,21', 22'.

As shown in Figs 1-3, each valve member 20,20'is operated by a magnetostrictive or piezoelectric rod 50, 50'. The rod assemblies for the two valve members are usually identical and, for the sake of simplicity, therefore the operation of only one valve member will be described below.

In the Figures, the rod 50 is a magnetostrictive rod whose longitudinal extension thus is controlled by an electromagnetic field which is generated by an electro- magnetic coil 65, which in turn is supplied with voltage from a voltage source/control unit 60. The electromagne- tic coil 65 and the magnetostrictive rod 50 are arranged in a casing 18 in connection with the valve housing 11.

Since this type of rods is very sensitive to flexu- ral stress, the rod 30 is hingedly fixed to the housing 18 and to a link arm 55 by means of some sort of essen- tially frictionless, articulated connections, which in the Figures are exemplified in the form of balls 51 and 52. The link arm 55 transfers the longitudinal extension or longitudinal change of the rod 50 to the valve member 20 without any kind of ratio. As shown in the Figures, the magnetostrictive rod and the link arm 55 are axially aligned with each other and the link arm 55 extends through an opening in the valve housing.

In the above embodiment, operation of the valve mem- ber 20 is effected by said control means 60 generating a magnetic field which causes a longitudinal change of the rod 50. The longitudinal extension of the rod 50 results in a linearly acting force which via the link arm 55 is made to act upon the valve member 20 via a ball 53 in a point of application 25 on the valve member 20.

As shown in Fig. 2, the valve member 20 and the rod/ link arm 50,55 are designed so that the perpendicular distance a between the direction of the force and the axis 30 is small relative to the distance A between the

axis 30 and the passage-defining edge portion 21 of the valve member 20. This means that the longitudinal change of the rod 50 is small in relation to the displacement, caused by the turning motion of the valve member, of the first portion 21 of the valve member 20. It will be appreciated that a small distance a means that the linearly acting force is retained to an essential extent.

For instance, the ratio in the prototypes that have been developed so far by the inventors has typically been between 1: 5 and 1: 20, i. e. a longitudinal change of the magnetostrictive rod of 0.1 mm has resulted in a periphe- ral movement of the first portion 21 of the valve member 20 of between 0.5 and 2 mm.

The valve housing further comprises one or more seals 40,41,40'and 41'which are arranged between the circular rear part of the respective valve members 20, 20'and the valve housing 11 and which prevent the flow of fluid from flowing another way through the valve than through said passage 17 between the valve members 20,20' and further through the respective ducts 16,16'. It will be appreciated that the valve preferably also comprises seals between the valve housing and the valve member sur- faces which are plane-parallel with the cross-section as shown in the Figures.

Some magnetostrictive or piezoelectric materials have brittle properties, which especially is a problem at high frequencies when the accelerating power acting on the rods in such applications is particularly great.

Depending on the choice of material, it is therefore pre- ferred that the respective rods 50,50'are prestressed.

The prestress can be achieved either mechanically, with different types of springs, and/or hydraulically.

In the embodiment shown in Figs 1-3, the valve 10 advantageously comprises torsion springs (not shown) which act to turn the respective pivot 31,31'with a view to turning the valve member 20 clockwise and the valve member 20'counterclockwise in the Figure, whereby

the respective valve members 20,20'are pressed against the respective link arms 55,55', which in turn transfer this pressure load to the respective rods 50,50'.

According to this embodiment, hydraulic prestress of the magnetostrictive rods 50,55 is also achieved by the valve housing 11 and a portion 23,23'of the circumfe- rence of the respective valve members 20,20'being designed so that a distance B between the respective pivot axes 30,30'and the first edge portion 21,21'of the respective valve members is greater than a distance b between the respective pivot axes 30,30'and the respec- tive seals 41,41', as shown in Fig. 3. The fluid pres- sure from the inlet 12 then acts on said portions 23,23' between said first portions 21,21'and said seals 41, 41'. Owing to the difference in distance, the pressure acting on the portions 23,23'produces on the whole a moment that wants to turn the valve member 20 clockwise and the valve member 20'counterclockwise in the Figure.

This torque acts via the respective valve members on the link arms 55,55'which in turn transfer this pressure load to the magnetostrictive rod, whereby the above- mentioned prestress of the respective rods 50,50'is achieved by the fluid pressure and the actual design of the valve housing and the valve members.

Fig. 4 illustrates one more embodiment of the pre- sent invention, the outlets 13,13'from the valve 10 in Figs 1-3 being connected to a working loop 70,70', in which a working means 80, which can be, for instance, a cylinder piston or a main slide of a servo valve assembly as shown in the Figure, is arranged to be actuated and preferably displaced by the pressure applied by the flow of fluid through the valve.

Moreover, the assembly in Fig. 4 comprises one or more detectors 61 which preferably are arranged down- stream of the valves and preferably in the vicinity of the main slide. The detector 61 can be a pressure sensor or a mechanical detector which senses the pressure down-

stream of the valves or the position of the main slide and which feeds this information to the control unit 60".

This results in the feedback coupling to the control unit which in many cases is necessary for correct control and operation of the valve assembly.

In the embodiment in Fig. 4, the valve housing 11 of the valve in Figs 1-3 comprises a third outlet or a return connection 14 which is arranged between the por- tions 15 and 15'of the valve housing 11, i. e. between the upper openings of the ducts 16 and 16', immediately straight downstream of the passage 17.

When the valve members of the valve in Fig. 4 are moved to such a position as shown in Fig. 1, the fluid flows from the inlet 12 through the passage 17 and the first duct 16 to the outlet 13 and further to the working lcop portion 70 and makes the main slide 80 move to the right in the Figure. Fluid in the working loop portion 70'to the right of the main slide 80 is then pressed by the same towards the outlet 13'and further through the second duct 16'to the return connection 14.

Correspondingly, the fluid flows from the inlet 11 through the passage 17 and the first duct 16'to the out- let 13'and the working loop portion 70'when the valve members of the valve in Fig. 4 are moved to the position shown in Fig. 2. The flow of fluid then presses the main slide 80 to the left in Fig. 4, and fluid in the working loop portion 70 to the left of the main slide 80 is then pressed by the main slide towards the outlet 13 through the first duct 16 to the return connection 14.

The above-mentioned bistable behaviour prevents a considerable part of the flow of fluid in any position from flowing directly from the passage 17 to the return connection 14.

When the flow of fluid through the valve in Fig. 4 flows from the passage to the first duct 16, the flow of fluid causes a flow-dependent ejector action at the upper openings of the return connection 14 and the second

duct 16'. The ejector action produces a sucking action which on the one hand prevents part of the flow of fluid from the passage 17 from flowing to the duct 16'or to the return connection 14 by mistake and, on the other hand, assists in sucking fluid from the working loop por- tion 70'to the right of the main slide 80 through the outlet 13'and the duct 16'to the return connection 14 or into the flow of fluid to the duct 16. The displace- ment of the main slide to the right in Fig. 4 thus is facilitated since the relatively less pressurised fluid to the right of the main slide 80 is more easily dis- placed.

Correspondingly, the flow of fluid from the inlet 11 through the passage 17 to the second duct 16'in the position of the valve member in Fig. 2 causes a flow- dependent ejector action at the upper openings of the return connection 14 and the first duct 16. The ejector action then produces a sucking action which assists in sucking fluid from the working loop portion 70 to the left of the main slide 80 through the first outlet 13 and the first duct 16 to the return connection 14 or into the flow of fluid from the passage 17 to the second duct 16', thereby facilitating the displacement of the main slide 80 to the left in the Figure.

The valve in Fig. 4 is in Fig. 5 shown with the valve member in a different position, in which the area of the duct 16'is extended by the edge portions 20,21 of the two valve members being simultaneously displaced downstream, but to different degrees. Since the edge por- tion 21 of the first valve member 20 is arranged upstream in relation to the edge portion 21'of the second valve member 20', the fluid will essentially flow from the passage 17 to the first duct 16. The simultaneous, but slightly shorter downstream displacement of the edge portion 21'of the second valve member 20', however, increases the area of the return flow duct 16'so that

the return flow of fluid from the working loop portion 70'to the return connection 14 is further facilitated.

Fig. 6 shows one more embodiment of a valve accord- ing to the invention. The valve differs from the one shown in the previous Figures in two respects. The valve members 20,20'in Fig. 6 are formed with portions 27, 27'cut away all the way through the valve members. These cavities are designed for the purpose of reducing the inertia of the valve members and reducing the friction of the valve members against the valve housing, thereby facilitating the turning of the valve members. It goes without saying that this feature is not limited to the embodiment in Fig. 6 and can advantageously be used in the other embodiments as well. Moreover, the valve in Fig. 6 has an alternative form of action of the link arms 55 on the respective valve members.

In Fig. 6 the valve member 20 is turnable on a pivot 32 which has a cut-off portion defining a plane sliding surface which engages a corresponding plane sliding sur- face of a wedge 33. The wedge 33 is turnably arranged in relation to the valve member 20 in a recess therein in connection with the pivot 32. The wedge 33 is turnable in relation to the valve member 20 and displaceable in rela- tion to the pivot 32 along the plane surface thereof.

In this embodiment, the longitudinal change of the rod 50 produces a force which via the link arm 55 is made to act on the circularly curved side of the wedge 33 in a slidably engaging manner, the sliding movement of the wedge 33 in relation to the pivot 32 making the pivot 32 and the valve member 20 turn in the desired fashion about the axis 30 in the valve housing 11.

A section along line II-II in Fig. 6 which further explains the function of the wedge 33 will later be described with reference to Fig. 8B.

As appears from the Figures, the axis 30 is also in this embodiment essentially perpendicular to the direc- tion of flow through the valve.

By means of the wedge construction in Fig. 6, it is ensured that the distance a is kept constant during the entire turning motion, which thus prevents the link arm 55 from being laterally displaced during the turning motion. Such a lateral displacement of the link arm 55 would cause the ratio to change during the turning motion and give rise to certain construction difficulties.

Figs 7A and 7B illustrate schematically an enlarged cross-section of the central pivot portions of the valve member 20 in Fig. 6 in two positions. For better under- standing of the movement of the wedge 33 in relation to the pivot 32 and the valve member 20, the change of posi- tion shown in the Figures is somewhat exaggerated.

The valve member in Figs 7A and 7B is turnable on the pivot 32 which, as described above, has a cut-off portion defining a plane sliding surface which slidably engages a corresponding surface of the wedge 33. The wedge 33 is arranged in a recess in the valve member 20 in connection with the pivot 32. As mentioned above, the wedge 33 is turnable in relation to the valve member 20 and displaceable in relation to the pivot 32 along the surface thereof.

Fig. 8A is a cross-sectional view along line I-I in Fig. 3. Since the above-mentioned wedge 33 is missing in this embodiment and the pivot 31 is a"whole"circular- cylindrical pivot, the valve member 20 is here turnable in the valve housing 11 on the cylindrical pivot 31 by means of the needle bearing 36. The circular-cylindrical pivot 31 is in turn connected to the valve housing 11.

Fig. 8B is a cross-sectional view along line II-II in Fig. 6. Since the assembly which consists of the valve member 20, the pin 32 and the wedge 33 should be turnable in relation to the axis 30 in the valve housing 11, the pivot 32 extends into the valve housing 11 and is turn- ably connected to the valve housing 11 by means of bear- ings, such as needle bearings 36. The valve member 20,

the pivot 32 and the wedge 33 are also slidably or turn- ably arranged in relation to each other.

A person skilled in the art realises that the fea- tures which in this specification are presented in con- nection with specific embodiments are not restricted to the respective embodiments and that these can advanta- geously be combined in different ways depending on the field of application and the desired mode of function of the valve.

Although the valve member according to the various embodiments is turnable about a given axis, it will be appreciated that the turning motion can consist of a com- bined turning and translational motion, in which case the pivot is displaced momentarily during the translational motion in relation to the valve body or the valve hous- ing.

Although the passage-defining portions of the valve members have been described as"edge portions", it will be appreciated that they need not necessarily form sharp edges, but also more rounded, convex valve member por- tions can be employed to achieve the invention.

Although the embodiments described show a magneto- strictive element which is controlled by a magnetic field generated by a coil, it will be appreciated that the cor- responding operation is achieved by means of a piezoelec- tric element which is controlled by voltage applied to the element or an electric field generated in some suit- able manner.

Although a first and a second open position are mentioned in the various embodiments, it will be appre- ciated that the first and the second open position can comprise several positions with different degrees of opening which, to different extents, prevent or allow a flow of fluid through the valve.