TECHNICAL FIELD

The invention relates to separating magnetic and/or magnetizable particles from a fluid in general. The invention relates to a method and magnetic separator for separating magnetic and/or magnetizable particles from a fluid. More in particular the invention relates to separating magnetic and/or magnetizable particles in a system liquid of a heating or cooling system. These particles in system liquid can cause problems and heavy wear to components. Being able to separate magnetic and/or magnetizable particles from system liquid is crucial for prevention of further decay of the overall system efficiency and therefore reducing energy consumption, increasing efficiency, and preventing faults and failure.

BACKGROUND

Methods for separating magnetic and/or magnetizable particles from a fluid, and magnetic separators that separate magnetic and/or magnetizable particles from a fluid are known in the art.

Generally, magnet separators comprise a collection chamber, a fluid inlet, a fluid outlet, a fluid flow path, and means for providing a magnetic field across at least a part of the fluid flow path. Magnetic and/or magnetizable particles are retained or trapped in the magnetic field. In order to allow the retained or trapped magnetic and/or magnetizable particles to be flushed or removed from the collection chamber, the magnetic field across at least a part of the fluid flow path is preferably reducible or removable.

In one prior art embodiment, a magnet is placed inside the collection chamber. This is disadvantageous as magnets can be susceptible to corrosion, and the magnet itself must be physically removed from the collection chamber in order to reduce the magnetic field across at least part of the fluid flow path and to flush or remove the magnetic and/or magnetizable particles from the collection chamber.

WO 2009/125171 Al discloses a magnetic separator comprising a cylindrical vessel through which the liquid to be filtered may be passed, a magnetic filter device having one or more magnets suspended in the vessel, an inlet to allow liquid to flow into the vessel and an outlet to allow liquid to flow out of the vessel, wherein the magnets are mounted in sleeves. As part of the cleaning process the magnets are removed from the sleeves. This may facilitate removal of the accumulated magnetic and/or magnetizable particles from the sleeves. Therefore the magnetic field across at least part of the fluid flow path can only be reduced or removed by physically removing all of the magnets from the sleeves. Only then can the collection chamber be flushed. Furthermore constructing a collection chamber is difficult and expensive as the sleeves must be fluid tight. Sleeve construction could lead to structural weaknesses.

Moreover the number of suspended magnets can not be modified after construction of the collection chamber.

In a magnetic separator according to WO 2009/125171 Al, the magnetic field is concentrated in the area of the suspended magnets. This may only be in a small portion of the collection chamber. US 2001/0013491 Al discloses a magnetic separator comprising an inlet opening, a return feed, a collection chamber through which the fluid is arranged to flow, and a device for producing a magnetic field by means of which the particles are retained in a collector region of the collection chamber during a collection phase. The device for producing a magnetic field comprises at least one magnet element which is movable relative to the collection chamber. Specifically, the at least one movable magnet can be placed in a collection position or a removal position, e.g. by way of pivoting the magnet element relative to the collection chamber.

The disadvantage of a magnetic separator according to US 2001/0013491 Al is that even if the magnet elements are disposed on mounting plates of a ferromagnetic material, the strongest magnetic field is concentrated outside the collection chamber or at best around the edge of the collection chamber. This magnetic separator therefore inefficiently exploits the magnetic fields of the magnet elements resulting in poor coverage of the fluid flow path.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a method and magnetic separator for separating magnetic and/or magnetizable particles from a fluid. It is also an object of the invention to provide a magnetic separator that makes more efficient use of the magnet fields of the magnetic separator. It is a further object of the invention to provide a magnetic separator that improves control over the location of the highest magnitude portions of the magnetic field of the magnetic separator. More in general it is an object of the invention to provide an improved method and magnetic separator for separating magnetic and/or magnetizable particles from a fluid. The invention also relates to a method and magnetic separator for separating magnetic and/or magnetizable particles from a liquid such as water.

Thereto, according to the invention is provided a magnetic separator for separating particles from a fluid, the magnetic separator comprising a housing including a collection chamber, a fluid inlet, a fluid outlet, a fluid flow path, and at least one removable magnet. The fluid inlet is in fluid

communication with the collection chamber and the fluid outlet is in fluid communication with the collection chamber. The fluid flow path extends from the fluid inlet, through at least a part of the collection chamber to the fluid outlet. A magnetizable element is positioned inside the collection chamber, and the at least one removable magnet is arranged outside the collection chamber such that at least a part of a magnetic field of the at least one removable magnet extends from the at least one removable magnet to the magnetizable element across at least a part of the fluid flow path in the collection chamber. By placing a magnetizable element in the collection chamber, at least a part of the magnetic field of the at least one removable magnet outside the collection chamber is directed towards the magnetizable element, hereby allowing one to control the extent of the part of the magnetic field of the at least one removable magnet across the fluid flow path. Naturally, if the part of the magnetic field extends across a larger part of the fluid flow path, more magnetic and/or magnetizable particles can be retained or trapped. This is a direct result of more efficient use of the magnetic field of the at least one removable magnet.

The magnetic separator provided according to the invention is versatile. If the part of the magnetic field is not capable of retaining or trapping the desired magnetic or magnetizable particles, the magnetic separator can easily be adapted to include more removable magnets.

Optionally, the at least one removable magnet is in either a first situation or a second situation, wherein in the first situation the part of the magnetic field extending from the at least one removable magnet to the magnetizable element across at least a part of the fluid flow path in the collection chamber has a first magnetic field magnitude such that said part of the magnetic field is substantially capable of retaining magnetic and/or magnetizable particles in the collection chamber, and wherein in the second situation the part of the magnetic field extending from the at least one removable magnet to the magnetizable element across at least a part of the fluid flow path in the collection chamber has a second magnetic field magnitude smaller than the first magnetic field magnitude, and is preferably negligible, more preferably zero, such that said part of the magnetic field has a reduced capability of retaining magnetic and/or magnetizable particles in the collection chamber. It is preferable that said part of the magnetic field is unable to retain magnetic and/or magnetizable particles in the collection chamber. It shall be understood that magnetic field magnitude is used interchangeably with the strength of the magnetic field and both refer the capability of the magnetic field to retain or trap magnetic or magnetizable particles. It will be appreciated that the magnetic field magnitude or strength, e.g. a minimum magnetic field magnitude or strength, required for retaining or trapping magnetic and/or magnetizable particles can easily be determined by simple experimentation. Similarly, the magnetic field magnitude or strength, e.g. a maximum magnetic field magnitude or strength allowed, for allowing magnetic and/or magnetizable particles to pass through the magnetic field can also easily be determined by simple experimentation. Moreover it is desirable that these parameters are experimentally determined as the system properties may vary for different applications.

Hence, it is possible to control the extent of the magnetic field across the fluid flow path, and still be able to easily flush the collected magnetic and/or magnetizable particles from the collection chamber. In the presence of a reduced or absent magnetic field of the at least one removable magnet, the magnetizable element becomes demagnetized, loses its magnetic properties, and the particles that were retained or trapped can easily be flushed from the collection chamber. Typically, the magnetic and/or magnetizable particles fall by gravity or are taken by fluid flow towards a collection area and/or drain valve when the at least one removable magnet is in the second situation.

Owing to the magnetizable element, the magnetic separator according to the invention benefits from a magnetized element inside the collection chamber in the first situation, and yet in the second situation by simply removing the at least one removable magnet the magnetic field extending across the fluid flow path is for all practical purposes removed. Therefore the improvements of the invention are twofold. According to the invention, an improved capability for retaining or trapping magnetic and/or magnetizable particles is achieved in the first situation, and flushing is facilitated in the second situation. Optionally, the at least one removable magnet is arranged on a mounting unit comprising a magnetizable material for conducting a part of the magnetic field of the at least one removable magnet. This has the advantage that a part of the magnetic field of the at least one removable magnet can be controlled, i.e. conducted by the magnetizable material of the mounting unit.

Optionally, a magnetic axis of the at least one removable magnet intersects the magnetizable element. It is known in the art that the magnetic axis is a virtual axis extending through the two poles of a magnet. This implies that a single pole of one of the at least one removable magnet is directed towards the magnetizable element while the other pole faces away from the magnetizable element. Arranging the at least one removable magnet in this fashion increases the control over the extent and strength of the part of the magnetic field across the fluid flow path.

Optionally, the at least one removable magnet comprises a first removable magnet and a second removable magnet, and the part of the magnetic field comprises at least a part of the magnetic field extending from the first removable magnet to the magnetizable element across at least part of the fluid flow path in the collection chamber, and at least a part of the magnetic field extending from the second removable magnet to the

magnetizable element across at least part of the fluid flow path in the collection chamber. Optionally, the magnetic axis of the first removable magnet and the magnetic axis of the second removable magnet include an angle between 60 and 120 degrees. Herein the angle is defined in plan view. It is conceivable that the first and second removable magnets could be provided anywhere outside the collection chamber, and it is found that when the magnetic axis of the first removable magnet and the magnetic axis of the second removable magnet include an include an angle between 60 and 120 degrees, e.g. 90 degrees, the capability of the first and second parts of the magnetic field to retain or trap magnetic and/or magnetizable particles is increased. Optionally, the at least one removable magnet includes at least one additional removable magnet. It is found that in order to retain or trap larger or additional magnetic and/or magnetizable particles, the use of additional magnets is advantageous.

Optionally, the collection chamber comprises a fluid flow restrictor arranged for forming an area of reduced fluid flow speed, and the fluid flow path includes at least part of said area. Providing the fluid flow restrictor forms an area of reduced fluid flow speed. If the part of the fluid flow path that the part of the magnetic field crosses also includes at least a part of the area of reduced fluid flow speed, magnetic and/or magnetizable particles are easier to retain or trap as their speed relative to their speed in the rest of the magnetic separator is slower.

Optionally, the magnetizable element comprises a magnetizable material with a low magnetic remanence such as soft iron, steel, laminated silicon steel, carbonyl iron, or soft ferrites. It is known in the art that magnetic remanence is the magnetization remaining in a material after an external magnetic field is removed or sufficiently reduced. In a material of low magnetic remanence the amount of residual magnetization is small. In the invention, this is a desired property of the magnetizable element. In the first situation the part of the magnetic field across the fluid flow path is controlled by the magnetizable element. However, in the second situation when the magnetic field magnitude is reduced or zero it is advantageous that the magnetic element does not remain magnetized, as this facilitates the step of flushing the retained or trapped magnetic and/or magnetizable particles.

Optionally, the magnetizable element comprises a magnetizable material with a low coercivity. It is known in the art that magnetic coercivity is the intensity of an applied magnetic field required to reduce the

magnetization of a material to zero after the material has been magnetized. Magnetic coercivity essentially defines the resistance of a material to becoming demagnetized. Sometimes low coercivity materials are also referred to as being magnetically soft. In the invention, this is a desired property of the

magnetizable element. In the first situation the part of the magnetic field across the fluid flow path is controlled by the magnetizable element. However, in the second situation when the magnetic field magnitude extending from the at least one removable magnet to the magnetizable element across at least a part of the fluid flow path is reduced or zero it is advantageous that the magnetic element quickly becomes demagnetized, as this enhances efficiency of the step of flushing the retained or trapped magnetic and/or magnetizable particles.

Optionally, the magnetizable element comprises a magnetizable material with a low remanence and a low coercivity.

Optionally, the at least one removable magnet is a permanent magnet. Optionally, the at least one removable magnet is a rare earth magnet such as a neodymium magnet.

Optionally, the at least one removable magnet is a switchable permanent magnet The switchable permanent magnet comprises a rotatable permanent magnet, a first and a second layer of magnetizable material, and one layer of un-magnetizable material sandwiched between the two sections of magnetizable material wherein the permanent magnet is substantially embedded in the layer of un-magentizable material. When switched on, i.e. in a first situation, the magnetic axis of the permanent magnet substantially extends from the first layer of magnetizable material to the second layer of magnetizable material, so that the first and second layers of magnetizable material guide the magnetic field of the permanent magnet to the

magnetizable element of the magnetic separator. When switched off, i.e. in a second situation, the permanent magnet is in a position that the magnetic axis substantially extends within the layer of un-magnetizable material so that the first and second layers of magnetizable material effectively short out the permanent magnet. Optionally, the at least one removable magnet is an electromagnet. Optionally, the housing comprises a material with a relative magnetic permeability substantially close to 1. Optionally, the housing is made of a material with a relative magnetic permeability substantially close to 1. Optionally, at least a portion of the housing in proximity to the collection chamber is made of a material with a relative magnetic permeability substantially close to 1. Optionally, the housing comprises a magnetically non- permeable material. Optionally, the housing is made of a magnetically non- permeable material. Optionally, at least a portion of the housing in proximity to the collection chamber is made of a magnetically non-permeable material. Whereby the material essentially acts as free space and has a negligible effect on the magnetic field passing though it.

Optionally, the at least one removable magnet or mounting unit is provided in the first situation by a fixing or mounting means such as snap system, click system, screws or the like.

Optionally, the fluid flow restrictor comprises a magnetizable material. Optionally, the fluid flow restrictor is made of a magnetizable material. The flow restrictor can e.g. be designed as a spirally wound wire extending around a core and held at a distance from the core by spokes. The core can comprise or be made of magnetizable material. Alternatively, or additionally, the wire and/or the spokes can comprise or be made of

magnetizable material. Optionally, the fluid flow restrictor comprises a material with a relative magnetic permeability substantially close to 1.

Optionally, the fluid flow restrictor is made of a material with a relative magnetic permeability substantially close to 1. Optionally, the fluid flow restrictor comprises a magnetically non-permeable material. Optionally, the fluid flow restrictor is made of a magnetically non-permeable material.

According to the invention is also provided a method for separating magnetic or magnetizable particles from a fluid, the method comprising the steps of: providing a fluid flow through at least a part of a collection chamber, providing a magnetizable element inside the collection chamber, providing at least one removable magnet outside the collection chamber, such that at least a part of a magnetic field of the at least one removable magnet extends from the at least one removable magnet to the magnetizable element across at least a part of the fluid flow in the collection chamber.

Optionally, the method further comprises selectively providing the at least one removable magnet in either a first situation or a second situation, wherein in the first situation the part of the magnetic field extending from the at least one removable magnet to the magnetizable element across at least a part of the fluid flow path in the collection chamber has a first magnetic field magnitude such that said part of the magnetic field is substantially capable of retaining magnetic and/or magnetizable particles in the collection chamber, and wherein in the second situation the part of the magnetic field extending from the at least one removable magnet to the magnetizable element across at least a part of the fluid flow path in the collection chamber has a second magnetic field magnitude smaller than the first magnetic field magnitude, and is preferably negligible, more preferably zero, such that said part of the magnetic field has a reduced capability of retaining magnetic and/or magnetizable particles in the collection chamber. It is preferable that said part of the magnetic field is unable to retain magnetic and/or magnetizable particles in the collection chamber.

Optionally, the method provides the collection chamber included in a housing, and wherein in the first situation the at least one removable magnet is at or near the housing, and wherein in the second situation the at least one removable magnet is remote from the housing. When the at least one removable magnet is at or near the housing, a part of the magnetic field of the at least one removable magnet extends from the at least one removable magnet to the magnetizable element. When the removable magnet is remote from the housing, the part of the magnetic field of the at least one removable magnet extending from the at least one removable magnet to the magnetizable element is negligible. This is a simple method for realizing the two situations. Optionally, the method further comprises a flushing step wherein, a drain valve is provided, the at least one removable magnet is provided in the second situation, and the retained magnetic and/or magnetizable particles are removed from the collection chamber by opening the drain valve and flushing the fluid from the collection chamber. Again owing to the magnetizable element, the magnetic separator according to the invention benefits from a magnetized element inside the collection chamber in the first situation, and yet in the second situation by simply removing the at least one removable magnet the magnetic field extending across the fluid flow path is negligible and flushing is facilitated.

Optionally, the method comprises using a magnetic separator according to the invention.

According to the invention is also provided a heating and/or cooling system including a magnetic separator according to claim 1. The magnetic separator according to the invention is ideal for use in a heating and or cooling system. System liquid, such as water, contains dirt that can cause problem and heavy wear to components. The dirt is inherent to the system as it comes from components such as radiators. Typically, the dirt comprises magnetic and/or magnetizable particles, sometimes referred to a magnetite. These magnetic and/or magnetizable particles are generally range from 1 micron to 100 microns. It is noted that magnetic and/or magnetisable particles larger than 100 microns may be present, e.g. formed by installation debris (e.g. steel filings). BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be further elucidated by means of non-limiting examples referring to the drawings, in which

Fig. 1 is a schematic representation of a magnetic separator with the at least one removable magnet removed; Fig. 2 is a schematic representation in top plan view of a magnetic separator according to a first embodiment of the invention with one removable magnet;

Fig. 3 is a schematic representation in top plan view of a magnetic separator according to a second embodiment of the invention with two removable magnets;

Fig. 4 is a schematic representation in top plan view of a magnetic separator according to the second embodiment with the two removable magnets and mounting unit in the second situation;

Fig. 5 is a schematic representation in top plan view of a magnetic separator according to a third embodiment of the invention with two removable magnets;

Fig. 6 is a schematic representation in top plan view of a magnetic separator according to the third embodiment according to the second embodiment with the two removable magnets and mounting unit in the second situation; and

Fig. 7 is a schematic representation in perspective view of a fluid flow restrictor. DETAILED DESCRIPTION

In this section, three embodiments of the invention will be described in detail. The first embodiment is a magnetic separator with one removable magnet. The second embodiment is a magnetic separator with two magnets arranged on a mounting unit comprising a magnetizable material wherein the axis of the first removable magnet and the axis of the second removable magnet include an angle of approximately 90 degrees. The third embodiment is a magnetic separator with two magnets arranged on a mounting unit comprising a magnetizable material wherein the axis of the first removable magnet and the axis of the second removable magnet include an angle of approximately 180 degrees. Figure 1 depicts a magnetic separator 1 comprising a housing 2, in this example made from brass. The housing 2 includes a collection chamber 3, a fluid inlet 4, a fluid outlet 5, and a fluid flow path 6. In this example, the magnetic separator also comprises a fluid flow restrictor 7 made from a magnetically non-permeable material such as brass. In this example, the magnetic separator 1 also includes a closable drain port or drain valve 8. The magnetic separator 1 further includes a magnetizable element 9. In this example the magnetizable element is made from steel 9. The at least one removable magnet is not pictured in Figure 1. Figure 1 forms the basis for all three embodiments. The number of removable magnets used and how they are arranged differs in the three embodiments. Typically, the magnetic separator is mounted such that the drain valve 8 is pointed downwards so as to allow draining of magnetic or magnetizable particles by simple gravity, or by flow into a container such as a bucket.

Figure 2 shows a schematic representation in top plan view of a magnetic separator according to a first embodiment of the invention. The general description given with respect to Figure 1 also applies to the embodiment shown in Figure 2. In this first embodiment the magnetic separator 1 is provided with a removable magnet 10. In this example, the removable magnet 10 is a permanent magnet, e.g. a neodymium magnet. In the situation shown in Figure 2, the removable magnet 10 is mounted to the housing 2 of the magnetic separator. The magnetic axis 11 of the removable magnet 10 intersects the magnetizable element 9. A part of a magnetic field of the removable magnet 10 extends across the fluid flow path 6 from the removable magnet 10 to the magnetizable element 9. It will be appreciated that magnetizable element 9 acts to focus this part of the magnetic field so as to efficiently extend across the fluid flow path 6. Magnetic and/or magnetizable particles are retained or trapped in this magnetic field.

Although not strictly essential, it will be appreciated that the fluid flow restrictor 7 pictured in Figure 1 will increase the efficiency with which magnetic and/or magnetizable particles are retained or trapped in the magnetic field extending across the fluid flow path. Due to the flow restrictor 7, the fluid flowing locally has a lower speed than fluid flowing in the rest of the separator. Therefore magnetic and/or magnetizable particles are easily retained or trapped in the magnetic field extending across the fluid flow path 6.

For draining or flushing the magnetic separator 1, the removable magnet 10 is removed from the housing 2 of the magnetic separator 1 and kept at a distance such that the magnetic field magnitude of the part of the magnetic field extending across the fluid 6 flow path is negligible. The magnetic field extending across the fluid flow path 6 is then unable to retain the magnetic and/or magnetizable particles. The magnetizable element 9 becomes demagnetized, loses its magnetic properties, and the magnetic and/or magnetizable particles fall by gravity towards the bottom of the collection chamber 3 and the drain valve 8. When the drain valve 8 is opened the magnetic and/or magnetizable particles are drained or flushed from the magnetic separator 1. The fluid flow need not necessarily be shut off before opening the drain valve 8.

After draining or flushing the removable magnet 10 is re-mounted on the housing 2 of magnetic separator 1. Hence, for retaining or trapping the magnetic and/or magnetizable particles, the removable magnet 10 is in a first position, or first situation, close to the collection chamber 3, e.g. at or near the housing 2. For allowing the magnetic and/or magnetzable particles to be drained or flushed the removable magnet 10 is in a second position, or second situation, remote form the collection chamber 3, e.g. remote from the housing 2.

Figure 3 shows a schematic representation in top plan view of a magnetic separator according to a second embodiment of the invention. The general description given with respect to Figure 1 also applies to the embodiment shown in Figure 3. In this second embodiment, the magnetic separator 1 is provided with two removable magnets 20, 21. In this example the removable magnets 20, 21 are permanent magnets, e.g. neodymium magnets. In the example of Figure 3 the removable magnets 20, 21 are mounted on a mounting unit 25 such that a first magnetic axis 22 of the first removable magnet 20 and a second magnetic axis 23 of the second removable magnet 21 include an angle of approximately 90 degrees. In Figure 3, the magnets are mounted such that the pole of the first removable magnet 20 closest to the magnetizable element 9 along the first magnetic axis 22 is the magnetic opposite of the pole of the second removable magnet 21 closest to the magnetizable element 9 along second magnetic axis 23. The mounting unit 25 comprises a magnetizable material, in this embodiment iron, connecting the pole of the first removable magnet 20 away from the magnetizable element 9 along the first magnetic axis 22 to the pole of the second removable magnet 21 away from the magnetizable element 9 along the second magnetic axis 23. Hence, the mounting unit 25 comprising the magnetizable material acts as a magnetic "short circuit" and the strongest magnetic field forms along the first magnetic axis 22 between the first removable magnet 20 and the magnetizable element 9, along the second magnetic axis 23 between the second removable magnet 21 and the magnetizable element 9, and along the mounting unit 25.

In this embodiment, a part of the magnetic field of the first removable magnet 20 extends across the fluid flow path and a part of the magnetic field of the second removable magnet 20 extends across the fluid flow path. It will be appreciated that magnetizable element 9 acts to focus these parts of the magnetic fields of the first and second removable magnets 20, 21 so as to efficiently extend across the fluid flow path 6. Magnetic and/or magnetizable particles are retained or trapped by these magnetic fields. The removable magnets are in the first situation such that the magnet fields across the fluid flow path 6 retain or trap magnetic and/or magnetizable particles. As in the first embodiment this may be aided by use of the fluid flow restrictor 7 pictured in Figure 1. In Figure 4, the magnetic separator 1 according to the second embodiment is pictured in the second situation. In the second situation the magnetic field magnitude of the magnetic field extending from the two removable magnets 20, 21 to the magnetizable element 9 across a part of the fluid flow path 6 in the collection chamber 3 is smaller than the magnetic field magnitude of the magnetic field extending from the two removable magnets 20, 21 to the magnetizable element 9 across a part of the fluid flow path 6 in the collection chamber 3 in the first situation shown in Figure 3. When bringing the magnetic separator 1 from the first situation to the second situation, the mounting unit 25 and two removable magnets 20, 21 are removed as a unit and placed remote from the collection chamber 3. In the second situation, the magnetic separator 1 is unable to retain magnetic and/or magnetizable particles. The magnetizable element 9 becomes demagnetized, loses its magnetic properties, and the magnetic and/or magnetizable particles fall by gravity towards the bottom of the collection chamber 3 and the drain port or drain valve 8. When the drain valve 8 is opened the magnetic and/or magnetizable particles are drained or flushed from the magnetic separator 1. The fluid flow need not necessarily be shut off before opening the drain valve 8. After flushing, the two removable magnets 20, 21 and mounting unit 25 are re-mounted as a unit on the housing 2 of magnetic separator 1.

Hence, for retaining or trapping the magnetic and/or magnetizable particles, the removable magnets 20, 21 are in a first position, or first situation, close to the collection chamber 3, e.g. at or near the housing 2. For allowing the magnetic and/or magnetizable particles to be drained or flushed the removable magnets 20, 21 are in a second position, or second situation, remote form the collection chamber 3, e.g. remote from the housing 2.

Figure 5 shows a schematic representation in top plan view of a magnetic separator according to a third embodiment of the invention. The general description given with respect to Figure 1 also applies to the embodiment shown in Figure 5. In this third embodiment the magnetic separator 1 is provided with two removable magnets 30, 31. In this example the removable magnets 30, 31 are permanent magnets, e.g. neodymium magnets. In the example of Figure 5 the removable magnets 30, 31 are mounted on a mounting unit 35 such that a first magnetic axis 32 of the first removable magnet 30 and a second magnetic axis 33 of the second removable magnet 31 include an angle of approximately 180 degrees. In Figure 5, the magnets are mounted such that the pole of the first removable magnet 30 closest to the magnetizable element 9 along the first magnet axis 32 is the magnetic opposite of the pole of the second removable magnet 31 closest to the magnetizable element 9 along the second magnetic axis 33. The mounting unit 35 comprises a magnetizable material, in this embodiment iron, connecting the pole of the first removable magnet 30 away from the magnetizable element 9 along the first magnetic axis 32 to the pole of the second removable magnet 31 away from the magnetizable element 9 along the second magnetic axis 33. Hence the mounting unit comprising the magnetizable material acts as a magnetic "short circuit" and the strongest magnetic field forms along the first magnetic axis 32 between the first removable magnet 30 and the magnetizable element 9, along the second magnetic axis 33 between the second removable magnet 31 and the magnetizable element 9, and along the mounting unit 35.

In this embodiment, a part of the magnetic field of the first removable magnet 30 extends across the fluid flow path and a part of the magnetic field of the second removable magnet 31 extends across the fluid flow path. It will be appreciated that magnetizable element 9 acts to focus these parts of the magnetic fields of the first and second removable magnets 30, 31 so as to efficiently extend across the fluid flow path 6. Magnetic and/or particles are retained or trapped by these magnetic fields. The removable magnets are in the first situation such that the magnet fields across the fluid flow path 6 retain or trap magnetic and/or magnetizable particles. As in the first embodiment this may be aided by use of a fluid flow restrictor 7 pictured in Figure 1. In Figure 6, the magnetic separator 1 according to the third embodiment is pictured in the second situation. In the second situation the magnetic field magnitude of the magnetic field extending from the two removable magnets 30, 31 to the magnetizable element 9 across a part of the fluid flow path 6 in the collection chamber 3 is smaller than the magnetic field magnitude of the magnetic field extending from the two removable magnets 30, 31 to the magnetizable element 9 across a part of the fluid flow path 6 in the collection chamber 3 in the first situation shown in Figure 5. When bringing the magnetic separator 1 from the first situation to the second situation, the mounting unit 35 and two removable magnets 30, 31 are removed as a unit and placed remote from the collection chamber 3. In the second situation, the magnetic separator 1 is unable to retain magnetic and/or magnetizable particles. The magnetizable element 9 becomes demagnetized, loses its magnetic properties, and the magnetic and/or magnetizable particles fall by gravity towards the bottom of the collection chamber 3 and the drain port or drain valve 8. When the drain port or drain valve 8 is opened the magnetic and/or magnetizable particles are drained or flushed from the magnetic separator 1. The fluid flow need not necessarily be shut off before opening the drain valve 8. After flushing, the two removable magnets 30, 31 and mounting unit 35 are re-mounted as a unit on the housing 2 of magnetic separator 1.

Hence, for retaining or trapping the magnetic and/or magnetizable particles, the removable magnets 30, 31 are in a first position, or first situation, close to the collection chamber 3, e.g. at or near the housing 2. For allowing the magnetic and/or magnetizable particles to be drained or flushed the removable magnets 30, 31 are in a second position, or second situation, remote form the collection chamber 3, e.g. remote from the housing 2.

In the foregoing specification, the invention has been described with reference to specific examples of embodiments of the invention. It will, however, be evident that various modifications and changes may be made therein without departing from the broader spirit and scope of the invention as set forth in the appended claims.

In the example of Figure 1 the fluid inlet 4 and fluid outlet 5 are arranged concentrically with the fluid outlet 5 being located radially outward with respect to the fluid inlet 4 in an end plane of the housing 2. It is possible that the locations of the fluid inlet 4 and the fluid outlet 5 are reversed such that the fluid inlet 4 is located radially outward with respect to the fluid outlet 5. It is also possible that the fluid inlet 4 and fluid outlet 5 are placed side-by-side, and/or at at an angle with respect to each other (e.g. in top plan view).

Furthermore, in the figures the fluid flow path 6 is depicted by a curved line, it is also possible that the fluid flow path is straight line, such as a straight line through the collection chamber 3, a combination of straight and curved lines, or another form.

Additional embodiments can be formed by adding additional removable magnets to the mounting units 25, 35, of the second and third embodiment. This could result in a strengthening of the part of the magnetic field extending across the fluid flow path. Also this could result in additional focussing of the extent of the part of the magnetic field across the fluid flow path. Other embodiments can be imagined that exploit the ability to control the at least part of the magnetic field of the at least one removable magnet.

For example the magnetizable mounting as described with respect to the second and third embodiments could also be used in combination with a single removable magnet. In the described embodiments the magnet field across the fluid flow path is substantially horizontal. It is also possible that the magnetic field across the fluid flow path is substantially vertical, diagonal or directed in any direction. The magnetizable element in the above described embodiments is of a cylindrical form. In other embodiments the magnetizable element is rectangular or even a free form shape. It is possible that the fluid flow restrictor 7 forms or comprises the magnetizable element 9. The flow restrictor 7 can e.g. be designed as a spirally wound wire 36 extending around a core 38 and held at a distance from the core by spokes 40. An example of such a fluid flow restrictor 7 is pictured in Figure 7. The core 38 can comprise or be made of magnetizable material.

Alternatively, or additionally, the wire 36 and/or the spokes 40 can comprise or be made of magnetizable material.

However, other modifications, variations, and alternatives are also possible. The specifications, drawings and examples are, accordingly, to be regarded in an illustrative rather than in a restrictive sense.

In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The word 'comprising' does not exclude the presence of other features or steps than those listed in a claim.

Furthermore, the words 'a' and 'an' shall not be construed as limited to 'only one', but instead are used to mean 'at least one', and do not exclude a plurality. The mere fact that certain measures are recited in mutually different claims does not indicate that a combination of these measures cannot be used to advantage.