The present invention relates in a first aspect to a valve insert for a liquid flow valve comprising a differential pressure regulator, the valve insert comprising:

a valve housing having a bottom, an open top and at least one outlet opening; and

a differential pressure regulator configured to maintain a substantially constant fluid flow through the valve insert,

the differential pressure regulator comprising a hollow valve element having an open bottom and an open top, said fluid flow being between said top and bottom, the valve element being movable within the valve housing along a longitudinal axis, L, of the valve insert between an open position, wherein the at least one outlet opening is uncovered, and a closed position, wherein the valve element at least partially covers the at least one outlet opening, and a spring device with a spring rate, the spring device extending substantially along the longitudinal axis, L, and being configured to bias the valve element towards said open position.

Flow regulation valves with such a valve insert are known for exam- pie from WO 03/036143 A1 (this document hereby being incorporated herein by reference in its entirety) and are used in heating or cooling systems. The valve insert implements a differential pressure regulator for maintaining a steady flow under fluctuating pressure conditions. Thus, pressure regulation is provided by a displaceable valve element that via a rolling diaphragm re- sponds to a differential pressure across an inlet opening against the force of a spring in order to set the size of an outlet opening, thereby maintaining the intended flow rate even under pressure fluctuations within the system. Such pressure fluctuations may arise due to fluctuations in the pump pressure or the operational pressure. Because the systems, where such valve inserts are implemented, often run continuously over extended periods of time, substantial energy savings can be attained by reducing the power required for opera- tion.

On this background it is an object of the invention to provide a valve insert with which reduced energy consumption and improved control are achieved.

According to the invention this is accomplished by means of a valve insert according to the introduction, wherein the spring rate of the spring device varies in discrete steps according to a compression distance of the spring device, such that the spring device in a first compression interval is compressed with a first substantially constant spring rate and in a subsequent compression interval is compressed with a second substantially constant spring rate, said second spring rate being greater than said first spring rate.

It has been recognized by the inventors that lowering the spring rate of a spring device, which biases the valve insert towards an open position, allows for the pump pumping liquid through the system to achieve an optimal flow through the valve at a lower pump pressure, thereby reducing the energy costs of running the system. However, this advantage comes at the cost of reduced stability in systems experiencing flow fluctuations since the pump pressure range, over which the valve insert is functional, depends on the force working against the fluid pressure. Because of this, implementing a spring with a lower spring rate will reduce the reliability of the valve insert.

The inventors have discovered that the advantages of using a spring with a greater spring rate and those of using a spring with a lower spring rate can be combined according to the invention by applying a spring device with two discrete spring rates. Hereby, a lower spring rate of the spring device works at lower pump pressures, and a higher spring rate works at higher pump pressures.

Thus, in a system, in which a valve with a valve insert according to the first aspect of the invention is inserted, reduced energy consumption of the pump and improved control are arrived at.

In the valve insert according to the first aspect of the invention the valve housing is preferably substantially cylindrical, and the valve element is similarly substantially cylindrical so as to be able to slide axially within the valve housing.

The inlet opening is typically provided at said top of the valve element, the inlet opening providing a flow inlet into the valve insert.

The valve insert may further comprise a flow presetting device com- prising a cover disc providing said inlet opening, the presetting device being adapted for being positioned in a use position, in which use position the size of the opening determines a preset maximum flow through the valve insert. The cover disc may be positioned at said top pf the valve element.

The spring device may be arranged within the valve element.

The first and second spring rates may each vary slightly during compression as may be the case with for example helical springs.

In an embodiment according of the first aspect of the invention said second spring rate is at least 1 .1 times, preferably at least 1 .4 times, more preferred at least 1 .7 times or 2 times greater than said first spring rate. Said second spring rate is preferably less than 5 times, preferably less than 4 times, more preferred less than 3 times greater than said first spring rate. These intervals provide an optimal ratio between the first and second spring rates in typical fluid systems in which a valve with a valve insert according to the first aspect of the invention are used.

In another embodiment the spring device comprises a helical spring

(i.e. a coil spring) providing the variable spring rate. Preferably, the spring device comprises one single helical spring. The spring may be substantially cylindrical, preferably circular-cylindrical. It is noted that the spring effect of the spring device may be provided using any other suitable type of spring.

In a development of this embodiment the helical spring comprises a first zone with a first spring rate and a second zone with a second spring rate greater than said first spring rate, said first zone substantially reaching full compression before said second zone during operation. Hereby, the spring device may be provided as one, single, integral helical spring integrating the two differerent spring rates. The spring rate may thus be varied by for example providing different thicknesses of and/or distance between the spring coils, i.e. the spring pitch, in the two zones, and/or varying the material used in the two zones. A person skilled in the art will be able to devise further ways of varying the spring rate of a helical spring as well as the spring rate of other types of springs.

In a further development of this embodiment an outer diameter, d6, of the helical spring is less than 90 % of an inner diameter of the valve element. Hereby the advantages according to the second aspect of the invention may also be achieved, see further below. As is the case with the second aspect of the invention, the valve insert may further comprise an abutment projecting axially inwards from an inner surface of the valve element, this abut- ment potentially supporting a cover disc as described above in a use position of the cover disc, the abutment comprising an upper abutment surface potentially for supporting a lower abutment surface of the cover disc. The distance, D, is advantageously larger than a thickness of the abutment measured in a longitudinal direction of the valve insert. In embodiments comprising an abut- ment for supporting the cover disc, experiments have shown that it is preferable to arrange the upper spring support at a distance from the cover disc larger than a thickness of the abutment in order to effectively prevent the pressure losses that would otherwise occur over the upper spring support as is also explained further below. The distance, D, between the upper spring support and the cover disc is preferably at least 10 %, at least 25 % or at least 30 % of the inner diameter of the valve element. It is noted that generally the larger the distance between the upper spring support and the cover disc, the shorter the helical spring may be made and, in turn, the more cost efficient the helical spring and thus the valve insert will be. At least one rib element may be provided for attaching the upper spring support to the inner surface of the valve element. Thereby a particularly robust structure is provided for, which takes up very little space in the interior of the valve insert. The at least one rib element may comprise a leg part extending along an inner surface of the valve element and supporting or providing the abutment for supporting the cover disc. When the at least one rib element comprises a leg part extending along an inner surface of the valve element and providing the abutment for supporting the cover disc, it is possible to altogether omit the provision of a separate abutment for the cover disc, which in turn provides for a valve insert with a simpler and more robust structure. The upper spring support may comprise an at least partially circumferential leg part protruding in a direction away from the cover disc and comprising an inner diameter cor- responding to the diameter of the helical spring. Such a circumferential leg part provides for further support of the end of the helical spring supported by the upper spring support, and thereby in turn for a more robust and durable valve insert. The outer spring diameter, d6, of the helical spring is preferably less than 80 %, less than 70 % or less than 60 % of the inner diameter, d2, of the valve element. It is noted that, generally, the smaller the diameter of the helical spring, here expressed in a percentage of the inner diameter, d2, of the valve element, the smaller the helical spring may be made and, in turn, the more cost efficient the helical spring and thus the valve insert will be. However, the diameter should be large enough to allow the spring to fulfil its purpose.

In an alternative embodiment of the first aspect of the invention the spring device comprises two springs with different spring rates arranged in series such that one spring is fully compressed before the other to provide the variable spring rate. In a further alternative embodiment the spring device comprises two springs arranged in parallel such that one spring is substantially not engaged until after partial compression of the second spring to provide the variable spring rate. Hereby, two different springs, each with a substantially constant spring rate, may be used to provide the spring device. One or both springs of these embodiments may be helical springs. In this case, potentially, one or both helical springs comprise(s) a first zone with a first spring rate and a second zone with a second spring rate greater than said first spring rate.

In an embodiment the valve insert further comprises a guide element arranged at the top of the valve housing adjacent to an outer surface of the valve element to provide a guide during movement between the open and closed positions.

In an embodiment the differential pressure regulator further comprises a rolling diaphragm, which surrounds the valve element and extends be- tween an outer surface of the valve element and an inner surface of the valve housing or the guide element. In a development of this embodiment the valve insert further comprises means for fastening the rolling diaphragm at a first end to the valve element and at a second end to the valve housing or the guide element. In another or further development of this embodiment the force resulting from a differential pressure across the rolling diaphragm is exerted on the valve element, in a direction substantially parallel with the longitudinal axis, L, causing the valve element to move against the bias of the spring device towards the closed position.

The present invention in a second aspect relates to a valve insert for regulating a flow of a liquid through a valve, the valve insert comprising:

a valve housing with a closed bottom, an open top and at least one opening,

a hollow valve element with a top end and a bottom end and an inner diameter, d2, the valve element being arranged to be displaceable within the valve housing along a longitudinal axis, L, of the valve insert between an open position in which the at least one opening is uncovered and a closed position in which the valve element covers the at least one opening, the bottom of the valve housing providing a valve seat for the bottom end of the valve element,

a circumferential diaphragm extending between an outer surface of the valve element and an inner surface of the valve housing,

a helical spring extending substantially along the longitudinal axis, L, having an outer spring diameter, d6, and being arranged within the valve el- ement to bias the valve element towards the open position, the helical spring having a lower end supported by a lower spring support positioned at the bottom of and attached axially fixed to the valve housing and an opposite upper end supported by an upper spring support attached axially fixed to the valve element, and

a cover disc with a central inlet opening, the cover disc being adapted for being positioned in a use position at the top end of the valve element in which use position the size of the central inlet opening presets a max- imum flow through the valve insert.

In this context reference is made to the above mentioned WO 03/036143 A1 , which discloses such a valve insert. This valve insert is employed in applications as cooling or heating systems in which a cooling or heating liquid such as water is flowing. All parts of this known valve insert are made of a metal, such as steel.

However, it is desired to employ such a valve insert also in flow systems on board off-shore vessels, in which the liquid flowing in the system comprises sea water. Due to the more corrosive nature of sea water, corro- sion of the metal parts takes place which lowers the life time of the valve insert.

One possible solution would be to make the metal parts of a highly corrosion resistant metal. However, corrosion resistant metals and consequently also corrosion resistant metal parts in general and corrosion resistant springs in particular are very expensive.

It is therefore the object of the second aspect of the invention to provide a valve insert which is corrosion resistant while simultaneously being cost efficient in production and transport.

According to the second aspect of the invention, this is obtained by means of a valve insert as described above, wherein the outer spring diameter, d6, is less than 90 % of the inner diameter, d2, of the valve element, and the upper spring support is arranged at a distance, D, from a bottom of the cover disc in the use position of the cover disc.

By providing such a valve insert it becomes possible to use a helical spring which has a smaller diameter than those used in the prior art valve inserts, and which is therefore more cost efficient due to a smaller amount of corrosion resistant metal being needed. Thereby, a valve insert, which is cost efficient in production and transport, is provided. At the same time the arrangement of the upper spring support at a distance from the cover disc has the effect of alleviating or preventing a pressure loss that would otherwise occur over the upper support element since this is positioned in the flow path. Furthermore, the arrangement of the upper spring support at a distance from the cover disc also has the effect of separating the spring support from the cover disc, and thereby of enabling the use of cover discs with an opening having a diameter larger than the diameter of the helical spring.

The diaphragm may act together with the other elements of the valve insert to provide a differential pressure regulator similar to that described above in the context of the first aspect of the invention.

In an embodiment of the second aspect of the invention the valve insert further comprises an abutment projecting axially inwards from an inner surface of the valve element for supporting the cover disc in the use position, the abutment comprising an upper abutment surface for supporting a lower abutment surface of the cover disc, and wherein the distance, D, is larger than a thickness of the abutment measured in a longitudinal direction of the valve insert. In embodiments comprising an abutment for supporting the cover disc, experiments have shown that it is preferable to arrange the upper spring support at a distance from the cover disc larger than a thickness of the abutment in order to effectively prevent the pressure losses that would otherwise occur over the upper spring support.

In an embodiment the distance, D, between the upper spring support and the cover disc is at least 10 %, at least 25 % or at least 30 % of the inner diameter of the valve element. It is noted that generally the larger the distance between the upper spring support and the cover disc, the shorter the helical spring may be made and, in turn, the more cost efficient the helical spring and thus the valve insert will be.

In an embodiment at least one rib element is provided for attaching the upper spring support to the inner surface of the valve element. Thereby a particularly robust structure is provided for, which takes up very little space in the interior of the valve insert.

In a development of this embodiment the at least one rib element comprises a leg part extending along an inner surface of the valve element and supporting or providing the abutment for supporting the cover disc.

Embodiments in which the at least one rib element comprises a leg part extending along an inner surface of the valve element and providing the abutment for supporting the cover disc makes it possible to altogether omit the provision of a separate abutment for the cover disc, which in turn provides for a valve insert with a simpler and more robust structure.

In an embodiment the upper spring support comprises an at least partially circumferential leg part protruding in a direction away from the cover disc and comprising an inner diameter corresponding to the diameter of the helical spring. Such a circumferential leg part provides for further support of the end of the helical spring supported by the upper spring support, and thereby in turn for a more robust and durable valve insert.

In an embodiment the outer spring diameter, d6, of the helical spring is less than 80 %, less than 70 % or less than 60 % of the inner diameter, d2, of the valve element. It is noted that, generally, the smaller the diameter of the helical spring, here expressed in a percentage of the inner diameter, d2, of the valve element, the smaller the helical spring may be made and, in turn, the more cost efficient the helical spring and thus the valve insert will be. However, the diameter should be large enough to allow the spring to fulfil its purpose.

In an embodiment the valve insert further comprises a guide element arranged between the valve element and the valve housing adjacent the open end of the valve housing. The guide element may be a separate element or it may be provided as an integral part of the valve housing. This provides for a valve insert in which the pressure on the inlet side of the valve insert may be transferred to a surface of the diaphragm, thus providing the differential pressure across the diaphragm in a particularly simple way.

In an optional further development of this embodiment the guide element is adapted for fastening one of a first and a second circumferential end of the diaphragm to the outer surface of the valve element and/or for fastening the other of the first and second circumferential end of the diaphragm to the inner surface of the valve housing. This provides for a further simplified structure of the valve insert.

In an embodiment the force resulting from a differential pressure across the diaphragm is exerted in a direction substantially parallel with the longitudinal axis, L, of the valve insert, this direction being coincident with a plane of a circumferential contact surface provided between the valve element and the valve housing at the top end of the valve element. Thereby, a particularly smooth movement of the valve element with respect to the valve housing is provided for, which in turn provides for a particularly well functioning valve insert.

In an embodiment the diaphragm is a roller diaphragm.

In an embodiment the valve insert further comprises a fastening element adapted for fastening one of a first and a second circumferential end of the diaphragm to the outer surface of the valve element.

In an embodiment the valve insert further comprises a fastening element adapted for fastening the other of the first and second circumferential ends of the diaphragm to the inner surface of the valve housing. Thereby a particularly robust valve insert is provided for as the diaphragm is secured to the valve element and/or the valve housing in a particularly robust manner.

In an embodiment the distance, D, is at least 3 %, at least 5 %, at least 8 %, or at least 10 % of a length of the helical spring along the longitudinal axis, L, when measured in the open position of the valve insert, and or the distance, D, is less than 60 %, less than 70 %, or less than 80 % of a length of the helical spring along the longitudinal axis, L, when measured in the open position of the valve insert. This provides for an upper spring support positioned sufficiently far from the inlet opening to minimize the pressure loss across the upper spring support while providing a length of the spring sufficient to allow for the spring to vary out its intended function. Optimally, the distance, D, is 10 to 20 % of the length of the helical spring along the longitudinal axis, L, when measured in the open position of the valve insert.

In an embodiment the valve insert further comprises a releasable locking element adapted for locking the cover disc to the valve element. Thereby, the cover disc is held firmly and safely in place during transport and use of the valve insert, which in turn ensures that the cover disc is not lost during transport and does not fall off or shift position during use. Also, the cover disc can be readily exchanged to shift the inlet opening size and thus the preset maxi- mum flow through the valve insert.

In an embodiment the valve insert further comprises a dampening element adapted for dampening oscillations of the helical spring inflicted by a liquid flowing through the valve insert. Thereby a valve insert is provided which is durable and stable in use, and in which excess wear of the helical spring is avoided.

In an embodiment the at least the valve housing and the valve element are made of a plastic material. Thereby a valve insert is provided which is cost efficient to produce, low in weight and thus also cost efficient to trans- port and which is furthermore very resistant towards corrosion, and in particular corrosion inflicted by sea water and like liquids.

The helical spring is preferably made of a corrosion resistant spring metal. Non-limiting examples are a galvanized spring metal, a painted spring metal, a stainless spring steel, phosphor bronze and beryllium copper. Other corrosion resistant spring metals are known within the art of springs.

In an embodiment according to any one of the above embodiments of the second aspect of the invention, the valve insert is also according to any one of the above embodiments according to the first aspect of the invention. Hereby, the advantages of both the first and the second aspects of the inven- tion may be achieved.

The invention will be described in more detail below by means of non-limiting examples of presently preferred embodiments and with reference to the schematic drawings, in which:

Fig. 1 shows a perspective view of an embodiment of a valve insert according to the second aspect of the invention,

Fig. 2 shows a cross sectional side view of the valve insert according to Fig. 1 ,

Fig. 3 shows a perspective cross sectional view of the valve insert according to Fig. 1 ,

Fig. 4 shows a top view of the valve insert according to Fig. 1 with the cover disc removed,

Fig. 5 shows an exploded perspective view of the valve insert ac- cording to Fig. 1 ,

Fig. 6 shows a view similar to that of Fig. 2 of an embodiment of a valve insert according to the first aspect of the invention,

Fig. 7 shows a diagram with flow rate as a function of differential pressure for the valve insert according to Fig. 6, and

Fig. 8 shows a view similar to that of Fig. 2 of a valve insert according to both the second and first aspects of the invention.

Figs 1 to 5 show a valve insert 1 according to the second aspect of the invention for regulating a flow of a liquid through a valve. The liquid may in principle be any type of liquid. For instance a valve insert according to the second aspect (or the first aspect) of the invention may be used in on-shore or off-shore hot water or cold water installations leading or circulating fresh water or sea water. The valve insert may even be used in installations involving transport of corrosive liquids.

The valve insert 1 comprises a valve housing 3, a valve element 2 and a helical spring 6.

The valve housing 3 comprises a closed bottom 13, an open top, an inner surface 31 , an outer surface 32 and at least one opening 9.

The openings 9 of the valve housing 3 form an outlet of the valve in- sert 1 for leading liquid out of the valve insert to an outlet side 20. The openings 9 are arranged adjacent the closed bottom 13 of the housing 3 and extend along the periphery of the circular cylindrical valve housing 3. The openings 9 are in the embodiment shown provided as a row of rectangular openings - cf. particularly Fig. 2. However, the openings 9 may be provided with any feasible shape.

For instance the openings 9 may be provided as longitudinal, slot- shaped openings with a cross-section decreasing in a direction towards the closed bottom of the valve housing 3.

Alternatively, the openings 9 may be provided as round openings or as partly parabolic openings with an apex pointing away from a central inlet opening 5 in a cover disc 4 or in other words towards the closed bottom 13 of the valve housing 3. The openings 9 may also have different sizes and/or be arranged along the periphery of the valve housing 3 in accordance with increasing or decreasing size.

In yet another alternative, the openings 9 may have a cross-section which seen in a direction towards and starting away from the closed bottom first is increasing and then is decreasing.

The valve element 2 comprises a top end 2a, a bottom end 2b and an inner diameter d2. The valve element 2 is hollow.

The valve element 2 is arranged to be telescopically displaceable in the valve housing 3 between an open position in which the at least one opening 9 is uncovered and a closed position in which the valve element 2 covers the at least one opening 9 partially or completely. Put in other words, the valve element 2 is arranged to be displaceable within the valve housing 3 along a longitudinal axis, L, of the valve insert 1 between the open position and the closed position. The valve element 2 comprises an inner surface 21 and an outer surface 22.

In a not shown embodiment, the edge of the valve element 2 facing the closed bottom 13 of the valve housing 3 may be formed in an irregular manner. Thereby a too abrupt closing of the openings 9 which may in turn cause a partly unstable movement of the valve element towards its closed position may be avoided.

The helical spring 6 comprises an upper end 6a, a lower end 6b and an outer spring diameter d6. The helical spring 6 is adapted for biasing the valve element 2 towards the open position. The helical spring 6 is made of a corrosion resistant material such as a metal, a non-limiting example being a corrosion resistant spring steel.

With reference particularly to Fig. 2, the valve insert 1 further comprises a circumferential diaphragm 8.

The circumferential diaphragm 8 comprises an upper side 81 , a lower side 82, a first circumferential end 83 and a second circumferential end 84. One of the first and second circumferential end 83 and 84, in the embodiment shown the first circumferential end 83, is attached to an outer surface 22 of the valve element 2. The other of the first and second circumferential end 83 and 84, in the embodiment shown the second circumferential end 84, is attached to an inner surface 31 of the valve housing 3.

The cover disc 4 is in a use position arranged at the top end 2a of the valve element 2 facing away from the closed end 13 of the valve housing 3. The central inlet opening 5 provided in the cover disc 4 may have any shape. The central inlet opening 5 is provided with a size suitable for the application in which the valve insert is to be used. The size of the central inlet opening 5 presets a maximum flow through the valve insert 1 . Thus, the cover disc 4 may be exchangeable such as to provide for changing the size of the central inlet opening 5 and thereby a presetting of the maximum flow through the valve insert 1 in a simple and straight forward manner. Alternatively, the size of the central inlet opening 5 of one cover disc 4 may be directly adjustable.

Furthermore, the valve insert comprises an upper spring support 7 adapted for supporting one end, particularly the upper end 6a, of the helical spring 6. Generally, the upper spring support 7 is arranged in a distance, D, (cf. Fig. 2) from the cover disc.

Hence, the helical spring 6 is arranged such that it extends between the upper spring support 7 and the closed bottom 13 of the valve housing 3. In some embodiments the closed bottom 13 of the valve housing may furthermore comprise a lower spring support 14 adapted for supporting an end, particularly the lower end 6b, of the helical spring 6. The lower spring support 14 may for instance be a recess provided in the closed bottom 13.

In some embodiments the valve insert 1 comprises an abutment 23 for supporting the cover disc 4. In such embodiments the distance, D, is larger than a thickness of the abutment 23 measured in a longitudinal direction of the valve insert 1 . The abutment 23 projects axially inwards from the inner surface 21 of the valve element 2 and comprises an upper abutment surface 23a for supporting a lower abutment surface 4a of the cover disc 4 - cf. Fig. 2.

Generally, at least one rib element 72 is provided for attaching the upper spring support 7 to the inner surface 21 of the valve element 2. In the embodiment shown six such rib elements 72-76 are provided - cf. Fig. 4. However, any other number of rib elements, such as one through five or more than six may be provided.

The at least one rib element 72 is generally made as thin as possible, such as for instance with a thickness of below 2 mm, below 1 ,5 mm, below 1 mm or even below 0,5 mm.

The upper spring support 7, the at least one rib element 72 and the valve element 3 may be provided as one integrally shaped or cast element.

As shown on Fig. 2, each rib element 72, 73 comprise a leg part 722, 723, respectively, extending along the inner surface 21 of the valve element. The leg part 722, 723 comprises an upper surface 723, 733, respectively.

The leg part 722, 723 and particularly the upper surface 723, 733 may in some embodiments and as indicated on Fig. 3 support or even provide the abutment 23 and/or the upper abutment surface 23a for supporting the cover disc 4.

Furthermore, the upper spring support 7 comprises an at least partially circumferential leg part 78 protruding in a direction away from the cover disc 4 and comprising an inner diameter corresponding to the diameter, d6, of the helical spring 6. In the embodiment shown the leg part 78 is provided as a surface 721 , 731 of the respective rib elements 72, 73.

It is noted that the leg parts 722, 723 of the rib elements 72, 73, the upper surface 723, 733 and the leg part 78 are all optional elements.

The valve insert 1 further comprises a guide element 10 arranged between the valve element 2 and the valve housing 3 adjacent the open end of the valve housing 3.

In some embodiments the guide element 10 may be adapted for fastening one of the first and second circumferential end 83, 84 of the diaphragm 8 to the outer surface 22 of the valve element 2 and/or for fastening the other of the first and second circumferential end 83, 84 of the diaphragm 8 to the inner surface 31 of the valve housing 3.

Furthermore, the guide element 10 is provided as a separate element (cf. e.g. Fig. 5) but may in other embodiments be provided in one piece with the valve housing 3.

The guide element 10 is shaped in such a way that a circumferential spacing or channel 1 1 is formed between the valve element 2 and the guide element 10. The dampening of the movement of the valve element 2 may be adjusted by adjusting the size of the circumferential spacing or channel 1 1. This may for instance be done by replacing the guide element 10 with a guide element having a different shape providing a circumferential spacing or channel of a different size.

The valve insert furthermore comprises a fastening element 15 adapted for fastening the first circumferential end 83 of the diaphragm 8 to the outer surface 22 of the valve element 2 and a fastening element 17 adapted for fastening the second circumferential end 84 of the diaphragm 8 to the inner surface 31 of the valve housing 3 and/or to the guide element 10.

The fastening elements 15 and 17 may be any suitable type of fas- tening element, non-limiting examples being a clamping ring, a number of fastening elements arranged along the periphery of the valve element 2 or valve housing 3 or even a suitable adhesive. In the embodiment shown the fastening element 15 is a clamping ring (cf. Fig. 5), while the fastening element 17 forms an integral part of the guide element 10.

The valve insert 1 further comprises a locking element 40, 41 adapted for locking the cover disc 4 to the valve element 2. In the embodiment shown, the locking element 40, 41 is a snap-locking mechanism provided as a resilient protrusion 41 on the cover disc 4 (cf. Fig. 3) and a corresponding recess 42 in the valve element 2 (cf. Fig. 1 ). In other embodiments the locking element may be a locking ring.

The valve insert 1 further comprises a dampening element 18 adapted for dampening oscillations of the helical spring inflicted by a fluid or liquid flowing through the valve insert 1 . The dampening element 18 is in the non-limiting embodiment shown cylindrical and is arranged inside the helical spring 6 such as to extend from the closed bottom 13 of the valve housing in the longitudinal axis, L, of the valve insert 1 .

It is noted that the fastening elements 15 and 17, the locking element 40, 41 and particularly the dampening element 18 are all optional elements.

The valve insert 1 according to the second aspect of the invention works as follows.

The valve insert 1 is intended for insertion in a valve forming part of a system in which a fluid or liquid flows, e.g. as described in the applicant's WO 03/036143 A1 .

In order to ensure that the fluid or liquid flowing in the system may not flow along the outer surface 32 of the valve housing 3 a sealing element 16 may in some embodiments be provided such as to seal the valve housing 3 against a wall of the valve of the system in which the valve insert 1 is inserted. Thereby the fluid or liquid flowing in the system is forced to flow though the valve insert 1 .

Furthermore, an annular projection (not shown) may be provided at the closed bottom 13 of the valve housing 3 such as to secure the valve insert 1 in place by engaging the annular projection in a corresponding recess in the valve of the system in which the valve insert 1 is inserted.

The valve insert 1 may also be inserted directly into a straight piece of piping forming part of a system in which a fluid or liquid flows. In this case the piece of piping is of such a dimension that it is possible for the flowing fluid or liquid to pass between the inner wall of the piece of piping and the outer surface 22 of the valve element 2 of the valve insert 1 . Between the inner wall of the piece of piping and the valve insert 1 a sealing element 16 may be provided such as to seal the valve housing 3 against the inner wall of the piece of piping. Thereby the fluid or liquid flowing in the system is forced to flow though the valve insert 1 .

The fluid or liquid flowing in the system will enter the valve insert 1 at the inlet side 19 through the central inlet opening 5 in the cover disc 4, flow though the valve insert 1 and exit at the outlet side 20 through the at least one opening 9 adjacent the closed bottom 13 of the valve housing 3.

An inlet pressure exerted by the fluid or liquid flowing in the system prevails on the inlet side 19 of the valve insert 1. As a small amount of the fluid or liquid may enter and flow through the channel 1 1 , the channel 1 1 serves to ensure that the upper surface 81 of the diaphragm 8 is subjected to the inlet pressure prevailing on the inlet side 19 of the valve insert 1 .

Simultaneously, the lower surface 82 of the diaphragm 8 is subjected to a pressure being different from, and predominantly smaller than, the inlet pressure. Thereby a differential pressure is created across the diaphragm 8.

The diaphragm 8 is arranged in the valve insert 1 such that the force resulting from the differential pressure across the diaphragm 8 is exerted or directed in a direction being substantially parallel with a longitudinal axis, L, (cf. Fig. 1 ) of the valve insert 1 .

More particularly, the diaphragm 8 is arranged in the valve insert 1 such that the force resulting from a differential pressure across the diaphragm 8 is exerted or directed in a direction being substantially parallel with the longitudinal axis, L, of the valve insert 1 and extending in the plane of a contact surface 12 provided between the valve element 2 and the valve housing 3 at an end of the valve element 2 facing the closed end 13 of the valve housing 3.

Thereby, the force resulting from the differential pressure across the diaphragm 8 causes the valve element 2 to be displaced along the longitudinal axis, L, towards the closed position.

Simultaneously the spring force exerted by the helical spring 6 as well as the force exerted by the fluid or liquid flowing downstream of the cover disc 4 on the valve element 2 is directed in a direction opposite to the force resulting from the differential pressure across the diaphragm 8.

Thereby a constant pressure difference across the central inlet open- ing 5 in the cover disc 4 is obtained which in turn ensures that a constant flow through the valve insert 1 is maintained at all times.

In order to ensure a constant flow at an increasing differential pressure across the diaphragm 8 one may change the spring characteristics of the helical spring 6 and/or the size of the central inlet opening 5. Alternatively or in addition thereto it is also possible during manufacture of the valve insert 1 to take into account the piston area of the valve element 2, and thereby to produce a valve insert 1 with a constant flow at increasing differential pres- sure across the diaphragm 8, at least when operating above a lower threshold of the pump pressure or operational pressure of the system in which the valve insert 1 is employed.

It is noted that all elements of the valve insert 1 except the dia- phragm 8 and the helical spring 6 are in the embodiment shown made of a plastic material, particularly a rigid plastic material, such as reinforced Poly- phenylene Sulfide, Polyphthalamide or the like. Such materials are generally preferred in embodiments according to both the second and first aspects of the invention.

Fig. 6 shows a valve insert 1 according to the first aspect of the invention. The valve insert shown in Fig. 6 is generally identical or similar to the valve insert shown in Figs 1 to 5 except for the differences that will be explained in the following. Elements that are identical to or of similar function or purpose as the elements of Figs 1 to 5 are generally denoted with identical reference numerals in Fig. 6 and may not be described in detail in the following unless pertinent differences exist. For a description of these elements, reference is generally made to the above description related to Figs 1 to 5.

The valve insert 1 of Fig. 6 is similarly able to maintain a substantially constant flow rate of a liquid flowing through a valve, the valve being position- able in a system that may experience fluctuations of the pump pressure or operational pressure.

Both the valve insert of Fig. 6 and that of Figs 1 to 5 comprise a differential pressure regulator comprising the hollow valve element 2. The valve element 2 is formed to fit through the open top of the valve housing 3 and to be displaceable within the valve housing 3 along the longitudinal axis, L, of the valve insert 1 , between an open position, wherein the outlet opening 9 is uncovered, and a closed position, wherein the outlet opening 9 is partially or fully covered, such that during use the valve element 2 defines the cross- sectional area of the outlet opening 9, thereby regulating the differential pres- sure across the inlet opening 5.

The differential pressure regulator further comprises a helical spring 6, which in the present embodiment embodies the spring device according to the first aspect of the invention. The spring 6 extends substantially along the longitudinal axis L. The differential pressure regulator also comprises the rolling diaphragm 8 arranged around the valve element 2.

The valve housing 3 and valve element 2 are both substantially circu- lar-cylindrical in shape. However, in other embodiments both elements may be shaped arbitrarily, as long as the intended function can be performed.

In the embodiment of Figs 1 to 5 the spring 6 has a substantially constant spring rate in relation to a degree of compression of the spring 6, the spring rate during operation biasing the valve element 2 towards the open position. In contrast, in the present embodiment shown in Fig. 6 the spring device or spring 6 has a variable spring rate. Furthermore, the spring 6 of Fig. 6 has an outer diameter that substantially corresponds to or is only slightly smaller than an inner diameter of the valve element 2. Otherwise, the spring 6 of Fig. 6 is largely similar to the spring 6 of the valve insert 1 shown in Figs 1 to 5. In the embodiment of Fig. 6, since the spring 6 is of a large diameter, no rib elements and leg parts are provided, an upper spring support simply being embodied as a circumferentially extending rim 7 forming part of the abutment 23.

Thus, the spring rate of the spring device or spring 6 of the present embodiment varies in discrete steps according to a compression distance of the spring device 6, such that the spring device 6 in a first compression interval is compressed with a first substantially constant spring rate and in a subsequent compression interval is compressed with a second substantially constant spring rate, said second spring rate being greater than said first spring rate.

With the spring 6 of the present embodiment, the magnitude of the response by the differential pressure regulator is dependent of the size of the differential pressure as this determines the compression distance of the spring device and thereby the spring rate. Therefore, the differential pressure regulator will be more sensitive at a smaller differential pressure, and the valve element 2 will be displaced farther, causing a greater reduction of the cross-sectional area of the outlet opening 9 than at a larger differential pres- sure, when the spring 6 is compressed into its second interval, increasing the resistance against further displacement.

In the shown embodiment this is achieved by providing a single, dual-rate helical spring 6. Hereby, the spring 6 according to the present em- bodiment comprises two zones 61 , 62, each with a different spring rate and individual free length, the free length of the zone 62 with the lower spring rate being such that the zone 62 reaches full compression before full compression of the spring device 6, i.e. the first compression interval, at which point the number of active coils in the spring device 6 is reduced to those providing the greater spring rate, i.e. the second compression interval zone 61 .

In the present embodiment the different spring rates of the zones 61 , 62 of the spring 6 are provided by changing a pitch 61 p, 62p of the coils so as to become different for each zone. The different spring rates may alternatively be provided by for example changing the coil thickness and/or the materials from of the coils of each zone.

Furthermore, the variable spring rate may alternatively be provided by a spring device 6 comprising two separate springs with different spring rates and arranged in series (not shown), such that the spring with the lower spring rate reaches full compression before the spring with the higher spring rate.

In another alternative embodiment (not shown), the variable spring rate may be provided by a spring device comprising two springs with different free lengths arranged co-axially and in parallel, such that one spring is disengaged during initial compression of the other spring and is activated during further compression of the spring device.

The inlet opening 5 of the above embodiments can be provided by the opening at the open top 2a of the valve element 2, i.e. without use of the cover disc 4. However, it is preferred that the inlet opening 5 is provided as an aperture in the cover disc 4. In some embodiments the cover disc 4 may be securely fastened by means of a seal 43 and/or a locking ring 41 .

The valve insert 1 according to Fig. 6 generally works in a similar manner as the valve insert 1 according to Figs 1 to 5, the main difference be- ing that the spring force acting against the fluid pressure changes according to the compression distance of the spring device 6. Because of this, the valve element 2 is displaced more at lower differential pressures than it is at larger differential pressures.

Fig. 7 is included herein to further illustrate the advantages of the first aspect of the invention. Thus, Fig. 7 schematically shows a diagram with three different graphs illustrating flow rate Q through a valve insert as a function of differential pressure ΔΡ across the valve insert 1 .

The dashed line A shows the flow characteristic of a valve insert 1 of the prior art type according to Fig. 6, except with a single-rate, high-rate spring replacing the spring 6. Such a valve insert 1 has the advantage of having good stability, i.e. it achieves a substantially constant flow rate at larger differential pressures. However, because of the large spring force acting against the differential pressure, the differential pressure, which is needed to achieve the desired flow rate through the valve insert 1 , requires the pump operating the system to consume large amounts of power.

A lower start up differential pressure can be achieved by using a valve insert with a single-rate, low-rate spring replacing the spring, as shown by the dashed-dotted curve B. However, a valve insert with such a spring to some extent loses the ability to maintain the desired flow rate at higher differential pressures.

The solid line C shows the flow regulation characteristics of the valve insert 1 shown in Fig. 6 (or that of Fig. 8, this line generally being characteristic for valve inserts according to the first aspect of the invention). Since the variable spring rate of the spring device 6 is lower upon initial compression, with a valve insert according of the first aspect of the invention a flow rate line is achieved with which the flow rate at low differential pressure allows the system to be driven at favourable pump power. When the spring device 6 reaches the second interval of compression, wherein the spring rate is greater than the initial spring rate, the valve insert 1 performs similar one with a spring of high rate, achieving superior stability. Thus, the valve insert 1 in this case allows the system to be operated reliably in a large range of differential pressure, while maintaining a low pump power-consumption.

Fig. 8 shows a valve insert 1 according to both the second and first aspects of the invention. The shown embodiment is generally identical to the embodiment of the second aspect of the invention shown in Figs 1 to 5 except for the differences that will be explained in the following. Again, elements that are identical to or of similar function or purpose as the elements of Figs 1 to 5 are generally denoted with identical reference numerals in Fig. 8 and may not be described in the following unless pertinent differences exist. For a description of such elements, reference is made to the above description related to Figs 1 to 5.

Thus, in the valve insert 1 of Fig. 8 the spring device is a dual-rate helical spring 6 similar to the dual-rate helical spring used in the embodiment of Fig. 6, except the spring 6 of Fig. 8 has a smaller diameter similar to the spring of Figs 1 to 5.

The embodiment of Fig. 8 thus combines the first and second aspects of the invention to achieve the advantages of both, thereby providing a cost-efficient and corrosive-resistant valve insert, which enables reliable and energy-efficient flow regulation.

It should be noted that the above description of preferred embodi- ments serves only as examples, and that a person skilled in the art will know that numerous variations are possible without deviating from the scope of the claims.

The person skilled in the art realizes that the present invention by no means is limited to the preferred embodiments described above. On the con- trary, many modifications and variations are possible within the scope of the appended claims.