WO2002087736A1

WO2002087736A1 - Device and method to add an additive to a fluid flow

Info

Publication number: WO2002087736A1
Application number: PCT/EP2001/012477
Authority: WO
Inventors: Stefano Bucci; Luca Aurola; Paolo Vielmo
Original assignee: Medical Clip S.R.L.
Priority date: 2001-05-02
Filing date: 2001-10-29
Publication date: 2002-11-07
Also published as: ITRM20010235A0; ITRM20010235A1

Abstract

Device (1) and related method to add an additive (V) to a fluid flow, in particular a liquid flow, comprising connection means (2), to connect the device to an inlet duct (C) and to an outlet duct (D) and having an inside lumen (5) apt to allow a passage of fluid between said ducts, pressure drop means (6), located at the lumen and apt to generate a pressure drop in the fluid flow, additive feeding means, apt to establish a communication between an additive tank (9) and a portion of the lumen downstream of the pressure drop means, comprising at least one substantially helical duct (11), and a piston structure (14) apt to slide in the additive tank as the additive level diminishes and having at least one channel (19) to put the helical duct in communication with a region of the tank containing the additive.

Description

DEVICE AND METHOD TO ADD AN ADDITIVE TO A FLUID FLOW

DESCRIPTION The present invention relates to a device, to a method and to a related apparatus to add an additive to a fluid flow, in particular a liquid flow. In several fields of the art there is the problem of treating the fluid of a flow by adding a certain additive thereto.

For example, the water of city waterworks needs to be purified of the saline ions, in particular of the Calcium salts, dissolved therein. In fact, such ions are prone to deposit onto surfaces lapped by the related waters, mostly at high temperatures. The latter, as it is known, promote the release of the carbon dioxide and the formation of insoluble carbonates.

Due to such deposition phenomena, white goods working with hot water are subjected to calcareous scale possibly prejudicing the operation thereof.

For example, steam jet electric irons are generally supplied with distilled water precisely in order to avoid scale-induced damages thereto. However, specific studies on the issue have demonstrated the distilled water to be too pure to provide an excellent ironing, since a certain grade of temporary hardness, though minimal, due to the water-dissolved Magnesium and Calcium bicarbonates, reduces the occurrence of the calefaction phenomenon, impedimental to the steam formation. Another example is provided by the electric percolators, which use untreated heated water that usually deposits Calcium and Magnesium carbonates in its pipes, seriously injuring the functionality thereof.

A further example is that of the electric washing machines, whose effectiveness considerably depends on the characteristics of the water from the washing water system. In particular, in this case an excessive hardness of the water inhibits the action of the surfactants present in the washing detergents, and, other conditions being equal, the amount of detergent required to attain the same washing results increases.

Further examples of machinery which commonly suffer from the problems associated to the use of untreated water are the dish washers, the kettles, the ice making machines, the boilers, the washing machines, the steam ovens, the thermal heaters and the heater members in general. The latter, in particular, require demineralized water.

At present, the machinery at issue requires periodical scaling treatments. Although several devices to add a decalcifier to a water flow are already known, these entail a number of relevant drawbacks.

One drawback lies in the fact that in the drawing of the saline solution employed as decalcifier states of vortical motion are generated, with the entailed extreme difficulty of proportional metering, not ensuring a perfect running under every operation mode.

In particular, the uncontrolled variation in the saline concentration added to the water does not allow attaining the qualitative standards required for drinkable waters.

Moreover, this could entail the provision of non-conditioned water, hence water unsuitable to the connected user, which might cause the aforementioned damage to the machinery and to the apparatuses supplied therewith.

A device that tries to overcome said problem associated with vorticity is described in Italian patent application BO2000A000132, wherein a metering device having a couple of concentric spiral channels for imputing a fluid to be additivated to an additive container and for outputting an additivated fluid from said container is disclosed. However, this device has the problem that, as the additive level in the container diminishes, the addition of the additive to the fluid changes. The technical problem underlying the present invention is that of providing a device, an apparatus and a method to add an additive to a fluid flow allowing to overcome the drawbacks hereto mentioned with reference to the known art.

This problem is overcome by a device to add an additive to a fluid flow, in particular a liquid flow, comprising: - connection means, to connect the device to an inlet duct of the fluid to be additivated and to an outlet duct of the additivated fluid, having an inside lumen apt to allow a passage of fluid between such ducts; pressure drop means, located at said lumen and apt to generate a pressure drop in the fluid flow; - additive feeding means, apt to establish a communication between an additive tank and a portion of said lumen downstream of said pressure drop means, comprising at least one substantially helical duct; and a piston structure apt to slide in the additive tank as the additive level diminishes and having at least one channel to put said at least one helical duct in communication with a region of the tank containing the additive.

According to the same inventive concept, the present invention further relates to a kit to add an additive to a fluid flow, comprising a device as defined above, and at least one additive tank.

The present invention further provides an apparatus to add an additive to a fluid flow, comprising a plurality of devices as hereto defined arranged in sequence or in parallel.

The invention further provides a method to add an additive contained in an additive tank to a fluid flow, comprising the steps of: generating a pressure drop in said flow; and feeding said additive towards said flow, downstream of said pressure drop, via a first substantially helical run having an inlet end at the free surface of the additive, wherein said inlet end of said helical run lowers as the additive level in the tank diminishes.

The present invention provides several relevant advantages.

One of the main advantages lies in the fact that said helical run promotes a regular flow void of vorticity, and therefore a precise metering of the additive. Furthermore, the presence of a piston structure following the lowering of the additive level allows the device of the invention to ensure a constant and repeatable addition of the additive, regardless of the level thereof, to the fluid to be additivated.

Other advantages, features, and the operation modes of the present invention will be made apparent in the following detailed description of some embodiments thereof, given by way of example and without limitative purposes. Reference will be made to the Figs, of the attached drawings, wherein:

Fig. 1 is a longitudinal sectional view of a first embodiment of a device to add an additive to a fluid flow according to the present invention, in a full additive tank condition;

Fig. 2 is a longitudinal sectional view of the device of Fig. 1, in a near-emptied additive tank condition;

Fig. 3 is a cross sectional view of a detail of the device of Fig. 1; Fig. 4 is a longitudinal sectional view of another detail of the device of Fig. 1; Fig. 5 is a longitudinal sectional view of a second embodiment of the device of the invention;

Fig. 6 is a longitudinal sectional view of a third embodiment of the device of the invention;

Fig. 7 is a longitudinal sectional view of a fourth embodiment of the device of the invention; and

Fig. 8 is a longitudinal sectional view of a fifth embodiment of the device of the invention.

In the following description, terms such as 'side', 'upper' 'lower' will be used for clarity's sake and purely by way of example, with reference to the orientation of the device of the invention shown in the Figures.

Likewise, words like 'upstream' and 'downstream' should be related to the sense of said fluid flow, indicated with arrows in the related Figures. With initial reference to Fig. 1, a device to add an additive V to a fluid flow is globally indicated with 1.

The device 1 can be used for any application and in association with any machinery requiring the treatment of a fluid, in particular of a liquid like, e.g., waterworks water, with a suitable additive. As additives, e.g., deionizing mixtures or liquid solutions, in particular decalcifiers, hardness abaters at large, disinfectants, scales removers, detergents, antiscales agents, perfumes and so on, can be provided.

For example, the device can be arranged in series with an electric percolator to soften the water fed thereto. In order not to overburden the Figures mentioned above, the members and the apparatuses co-operating with the device of the invention were not depicted and will not be described hereinafter as already known. Thus, e.g., neither the water mains nor the possible tap valves along the pipes were shown.

According to the invention, the device 1 comprises connection means 2 to connect the device to a inlet duct C of fluid to be additivated and to an outlet duct D of additivated fluid.

The direction and the sense of the fluid flow within such ducts C and D are indicated with respective arrows in Fig. 1.

In the present embodiment, the connection means 2 comprises a shaped union body, it also indicated with 2, having two dowel-shaped side portions, 3 and 4, respectively. Such dowel portions 3 e 4 are apt to insert each within a respective duct

C or D and, in order to attain a reliable seal, have an outer profile similar to that of the so called 'nipple' type unions.

According to the invention, the union body 2 has an inside lumen 5, extending according to a substantially rectilinear development from side to side of the body 2 itself, thereby allowing a passage of fluid between the ducts C and D.

The device 1 further has pressure drop means to generate a pressure drop in said fluid flow, which in the present embodiment is implemented with a narrowing or neck 6 of the lumen 5. The shaped body 2 further has a first and a second channel, 7 and 8 respectively, substantially orthogonal to the lumen 5 and apt to put the latter, respectively upstream and downstream of the neck 6, in communication with a lower additive tank 9. In particular, the first channel 7 has an inlet section substantially in a maximal pressure thrust region, and the second channel 8 has a section, in this case an outlet one as it will be made apparent hereinafter, substantially in a minimal pressure region.

The first and the second channel 7 and 8 have cross sections substantially smaller than that of the lumen 5.

Said channels 7 and 8 of the union body 2 are partially engaged by respective ducts, in particular elastic tubular members indicated with 10 and 11, respectively, which will be further detailed later on. Such tubular members 10 and 11 are secured, e.g., by adhesive, inside of the respective channels 7 and 8 at the side wall of a first end portion thereof.

The union body 2 further provides a third channel 81, substantially parallel to the first two channels and located upstream of the neck 6. Such third channel 81 has a cross section which is smaller than that of the two channels 7 and 8 and is also apt to feed the fluid to be additivated from the lumen 5 to the tank 9.

The shaped body 2 also comprises a flange-shaped lower portion 12 for the coupling to said additive tank 9. Such coupling may be implemented by any traditional technology, and in particular by a joint or weld. In the present embodiment also the interposition of a seal 13 of the 'O-ring' type, housed in a seat obtained at the top edge of the tank 9, is provided.

The aforementioned tubular members 10 and 11 implement, together with the respective channels 7 and 8 and to a piston structure 14 which will be disclosed later on, additive feeding means, as it will be better understood with reference to the operation modes of the device of the invention. In particular, the first tubular member 10 is apt to feed the fluid to be additivated from the lumen 5 to the tank 9, whereas the second tubular member 11 is apt to feed the additivated fluid from the tank 9 to the lumen 5.

The tubular members 10 and 11 extend bottomwise of the union body 2 and are secured, at respective second end portions opposite to those connected to the body 2 itself, to the piston structure 14 mentioned above.

According to the invention, in the portion comprised between the aforementioned first and second end portions, the tubular members 10 and 11 are deformable, having a substantially helical path and being in particular being helically wound. This path favours a regular flow, and in particular a substantially laminar flow of the fluid therein.

In the present embodiment, the tubular members 10 and 11 have, both by virtue of the material of which they are made, e.g., a plastic material, and of the convoluted shape thereof, an intrinsic elastic strainability enabling them to assume a plurality of configurations, ranging from a contracted configuration, shown in Fig. 1, wherein adjacent coils of the helix are substantially side-by-side, and an extended configuration, analogous to that shown in Fig. 2, wherein the tubular members 10 and 11 are extended and the related coils more spread out. Always with reference to Fig. 1, according to the invention device 1 comprises said piston structure 14, which in the present embodiment has a substantially cylindrical outer profile, with a cross section of extension somewhat smaller than that of the inside cross section of the tank 9, thereby being capable of sliding inside the latter. Preferably, the gap between such cross sections does not exceed a few tenths of square millimetre.

The piston structure 14 of the present embodiment comprises a piston main body

15 and a lower bottom portion 16 secured to the body 15 at respective peripheral edges. Between the main body 15 and the bottom portion 16 there lies a region 17, which will be referred to as mixing region for reasons that will be made apparent hereinafter.

The main body 15 has a lower bottom wall 151 and a side wall 152 of cylindrical profile defining a top-opened chamber 153. Inside of the latter, the helical median portion of the tubular members 10 and 11 is partially or totally housed. In the bottom wall 151 two piston channels, 18 and 19 respectively, substantially aligned to the channels 7 and 8 obtained into the shaped body 2, are obtained. Such piston channels 18 and 19 cross lengthwise, from side to side, said bottom wall 151, bottomwise ending at said mixing region 17. Each piston channel 18, 19 houses a respective end portion of the first or second tubular member 10 or 11, the side wall of which being secured within the respective channel 18 or 19.

Between the two channels 18 and 19 the shaped body has a substantially wedge- shaped portion 20 facing said mixing region 17.

Fig. 3 shows a cross sectional view of the bottom portion 16. With reference also to the latter Figure, such bottom portion 16 has, in a position substantially centred with respect to the channels 18 and 19, a substantially rectangular opening 21. The latter puts the mixing region 17 in communication with a bottom region of the tank 9 containing the additive V.

In the present embodiment, the piston structure 14 is made in a material having a density lower than that of the additive V, so that the structure 14 itself can substantially float thereon.

Preferably, the structure 14 also has a density higher than that of the fluid to be additivated, for reasons that will be made apparent later on.

The aforementioned additive tank 9 has a substantially cylinder-shaped body 91, completed upward by a coupling flange 92 for the connection to the union body 2. As mentioned above, according to the invention the piston structure 14 is housed inside of the tank 9 in slidadable coupling. The bottom portion 16 of such structure

14 substantially lies onto the free surface of the additive V. Therefore, the structure 14 partitions the inside space of the tank 9 itself into two regions, a lower one for the containment of the additive and an upper one apt to be filled by the fluid coming from the inlet duct C, as it will hereinafter be better illustrated.

Another variant embodiment provides that the tank 9 be revertably connected to the connection means 2, in order to be easily replaceable upon exhaustion of the additive V, with no need to uninstall the entire device 1.

According to the same logic, the device 1 can also be provided to the final user as a kit comprising several interchangeable tanks, each containing a different additive.

The operation modes of the device 1 will hereinafter be illustrated with reference to Figs. 1, 2 and 4.

Firstly, to install the device 1 it suffices to connect the union body 2 to the inlet C and outlet D ducts at the side dowel portions 3 and 4.

During the normal flow of the fluid to be additivated in the inlet duct C, by virtue of its delivery pressure a fraction of such fluid flows into the first channel 7 of the union body 2, and therefrom into the first tubular member 10. Then the fluid exits at the opposite end thereof, in the first piston channel 18, and therefrom, also by virtue of the state of motion given by the helical path of the tubular member 10, it transversally crosses the mixing region 17 flowing up to the mouthpiece of the second piston channel 19, as indicated by the arrows of Fig. 4. In particular, during said flowing into the mixing region 17, the fluid is induced by the wedge-shaped portion 20 of the piston main body 15 to lap against the underlying additive V, onto which the structure 14 floats, so as to drag a fraction of such additive V in the flowing towards the second piston channel 19. Upon entering said channel 19, the additivated fluid is conveyed by the second tubular member 11 towards the second channel 8 of the union body 2 and therefrom once more into the lumen 5, downstream of the neck 6.

It will be understood that the suction of the additivated fluid towards the lumen 5 is determined not merely by the initial state of motion of the fluid and by the capillarity of the second tubular member 11, but above all by the depression that, due to the pressure drop generated by the neck 6, ensues downstream of the latter at the outlet section of the second channel 8.

Therefore, the device 1 determines a 'washing' of the fluid to be additivated in the region of the tank 9 containing the additive V.

Hence, the metering of the additive is controlled by the difference in pressure between upstream and downstream of the neck 6 and by the pressure drop in the tubular members 10 and 11, said drop of course being adjustable by varying the length, the shape and the inside diameter of members 10 and 11 themselves. According to a further variant embodiment, at the neck 6, adjustment means, e.g., of the screw type, to modify the section of the neck itself and therefore the pressure drop associated thereto, is provided.

As it is shown in Fig. 2, as the level of the additive V diminishes, the piston structure 14, floating substantially thereon, lowers, thus inducing an unwinding and a gradual lengthening of the tubular members 10 and 11. The latter, by virtue of the elasticity and of the helical path thereof, follow the lowering of the piston structure

14 with no substantial altering of the state of motion of the fluid therein.

The sinking of the piston structure 14 and the fact that the latter be always maintained in contact with the additive V are also ensured by the presence of the third channel 81 of the union body 2. In fact, as the level of additive V lowers, the fluid to be additivated flows through such third channel 81, by virtue of the delivery pressure thereof so entering into the region of the tank 9 comprised between the shaped body 2 itself and the piston body 15. Hence, the fluid gradually flowed in such region exerts a pressure onto the piston structure 14 so as to have the latter lower evenly, following the lowering in the level of additive V in the tank 9.

It will be understood that the substantially equivalent dimensions of the cross sections of the piston structure 14 and of the tank 9 ensure that the amount of additive V ascending sideways to the structure 14 itself and spreading in the upper region of the tank 9 is practically nil.

Moreover, the general states of motion of the fluid into the mixing region 17 minimise the amount thereof remaining in the region of the tank 9 containing the additive V.

It will be now better appreciated that the aforementioned gradual lowering of the piston structure 14 allows the device 1 to ensure a constant and repeatable addition of the additive V, regardless of the level thereof, to the fluid in the inlet duct C.

Hereinafter, further preferred embodiments of the device of the invention will be illustrated. In order not to overburden the description, such further embodiments will be disclosed merely with reference to the members differentiating them one from the other and from the first embodiment hereto disclosed. Hence, analogous components will be indicated with the same reference number.

Fig. 5 shows a second embodiment of the device of the invention, in this case globally indicated with 22.

The device 22 provides a piston structure 23 comprising a piston main body 24 and a bottom portion 25 secured thereto, a mixing region 26 being defined therebetween.

Unlike the first embodiment, the piston body 24 has a substantially flat bottom face facing the mixing region 26, without any wedge-shaped projection.

Moreover, the bottom portion 25 has a plurality of side-by-side openings 27, in particular three, formed in a position substantially centred with respect to two piston channels 18 and 19 analogous to the ones already described. Preferably, such openings 27 have a slanting development with respect to a longitudinal axis of symmetry 28 of the structure 23 and of the related tank 9.

Hence, in this second embodiment the additive V is sucked by the fluid flow into the mixing region 26, as indicated by the arrows in Fig. 5, through the openings 27.

The slanting profile of the latter reduces the possible inflow of the fluid to be additivated in the lower region of the tank 9 containing the additive V and therefore a possible progressive dilution of the latter.

Fig. 6 relates to a third embodiment of the device of the invention, in this case globally indicated with 29.

According to the invention, the device 29 provides additive feeding means, in this case comprising a single duct shaped as an helically wound elastic tubular member

11 , analogous to the one disclosed with reference to the first embodiment. Therefore, the device 29 provides a shaped union body 30 comprising a single channel 8 to establish a communication between a lumen 5, downstream of a neck 6, and a region of a tank 9 containing an additive V. The device 29 further comprises a flat-bottomed piece-formed piston structure 31.

The latter has a central piston channel 32 crossing it lengthwise from side to side.

Such piston channel 32 houses an end portion of the tubular member 11 and establishes a direct communication between such member 11 and said region of the tank 9 containing the additive V, without the mediation of a mixing region as instead in the preceding embodiments.

Therefore, in this third embodiment the additive V is sucked within the lumen 5 by virtue of both the pressure drop generated by the neck 6 and capillarity of the tubular member 11.

It will be appreciated that this third embodiment is further simplified with respect to the other ones.

Fig. 7 relates to a fourth embodiment of the device of the invention, in this case generally indicated with 33.

Such device 33 differs from that of the above-disclosed third embodiment in the shape of the piston structure, in this case indicated with 34, and of the related tank, in this case indicated with 35. In fact, they both have a respective bottom wall, 36 and

37, respectively, having a substantially cone-shaped profile. The latter shape facilitates the insertion of the structure 34 in the tank 35 and further allows an improved suction of the additive V in a tubular member 11 even when the level of such additive V into the tank 35 be minimal.

Moreover, the piston structure 34 has a shaped rather than straight side wall 38. In particular, topwise the latter ends with a membrane collar 39 apt to establish a minimal friction slidadable seal with the inside wall of the tank 35. Thus, the aforementioned phenomenon of the diffusion of the additive V in the upper region of the tank 35 is totally eliminated. This entails also that fewer constraints subsist in selecting the density of the material constituting the piston structure.

Figure 8 relates to a fifth embodiment of the device of the invention, globally indicated by 40. Device 40 comprises, as pressure dropping means according to the invention, a substantially eccentric neck 42 obtained in a lumen 5, associated with screw-type adjustment means 43. The latter allows a micrometric adjustment of the section of the lumen of the neck 42, and it is of course susceptible of several embodiments alternative to the hereto disclosed one. It will be understood that acting onto the adjustment means 43 the pressure difference between the upstream and the downstream of the eccentric neck 42 can be changed.

The present invention also provides an apparatus incorporating several devices according to the invention. In particular, several devices according to one of the above-disclosed embodiments can be set in a sequence or in parallel to add to a fluid flow, at three different stages, the same additive or different additives.

It will now be understood that the present invention also provides a method to add an additive to a fluid flow, e.g., a water flow, implementable by a device according to any one of the hereto disclosed embodiments. In particular, in its most general definition the invention relates to a method to add an additive contained in an additive tank comprising the steps of: generating a pressure drop in the flow; and feeding the additive towards the flow, downstream of the pressure drop and preferably in a minimal pressure region, via a first substantially helical run having an inlet end at the free surface of the additive, which end lowers as the additive level in the tank diminishes.

In light of the above-reported description of the device of the invention, it will further be understood that said step of feeding the additive towards the flow in turn preferably provides the steps of: - drawing a volume of fluid to be additivated upstream of the pressure drop, preferably at a maximal pressure region, and driving it towards the additive through a second substantially helical run; and lapping the volume of drawn fluid against the free surface of the additive, so that a fraction of the latter be dragged by the volume of fluid to be additivated, thus generating an additivated fluid volume.

Always according to a preferred embodiment, concomitantly to the step of drawing the volume of fluid to be additivated, a substantially equivalent volume of additivated fluid is fed towards the flow by said first substantially helical run.

Of course, it is understood that the invention applies to all cases, regardless of the actual fluid-additive miscibility.

It will be better appreciated at this point that the present invention provides a device and a method to treat a fluid, and in particular to purify water, which allow a restrained use of additive for the regeneration, and that perform the additive regeneration operations automatically at the operator's will.

It will also be appreciated that the device and the method of the invention allow to produce decalcified water so as to maintain a minimal residual hardness in view of the uses thereof in the various water-supplied apparatuses.

Furthermore, the device of the invention is easy to use, hence suitable to an unskilled operator as well.

Moreover, the device of the invention is compact in size, thereby being easy to fit in the small spaces available to house or industrial appliances. Moreover, the device is apt to be implemented at low costs and with simple and reliable components, it further being of simple installation and use.

The present invention has hereto been described with reference to specific embodiments thereof. It is understood that there may be other embodiments afferent to the same inventive concept, all however falling within the protective scope of the annexed claims.

Claims

1. A device (1; 22; 29; 33) to add an additive (V) to a fluid flow, in particular a liquid flow, comprising: connection means (2; 30), to connect the device to an inlet duct (C) of the fluid to be additivated and to an outlet duct (D) of additivated fluid, having an inside lumen (5) apt to allow a passage of fluid between such ducts; pressure drop means (6), located at said lumen and apt to generate a pressure drop in the fluid flow; additive feeding means, apt to establish a communication between an additive tank (9; 35) and a portion of said lumen downstream of said pressure drop means, comprising at least one substantially helical duct (11); and a piston structure (14; 23; 31 ; 34) apt to slide in the additive tank as the additive level diminishes and having at least one channel (19; 32) to put said at least one helical duct in communication with a region of the tank containing the additive.

2. The device (1; 22; 29; 33) according to claim 1, wherein said pressure drop means comprises a neck (6) of said lumen (5).

3. The device (40) according to the preceding claim, wherein said neck (42) is substantially eccentric.

4. The device (1; 40) according to claim 2 or 3, comprising adjustment means (43) to change the section of said neck (6; 42).

5. The device (1; 40) according to the preceding claim, wherein said adjustment means is of a screw-type (43).

6. The device (1; 22; 29; 33) according to any one of the preceding claims, wherein said at least one helical duct (11) has an outlet section communicating with a minimal pressure region of said lumen (5).

7. The device (1; 22; 29; 33) according to any one of the preceding claims, wherein said at least one helical duct is a helically wound tubular member (11).

8. The device (1; 22; 29; 33) according to the preceding claim, wherein said tubular member is a capillary pipe (11).

9. The device (1; 22; 29; 33) according to claim 7 or 8, wherein said tubular member (11) is elastically strainable.

10. The device (1; 22) according to any one of the preceding claims, wherein said additive feeding means comprises a first (10) and a second (11) substantially helical duct, each apt to put in communication the additive tank (9) with a respective portion of said lumen (5) respectively upstream and downstream of said pressure drop means (6).

11. The device (1; 22; 29; 33) according to any one of the preceding claims, wherein said additive feeding means comprises a channel (8) obtained in said connection means (2; 30) starting from said lumen portion downstream of said pressure drop means (6), said channel being in communication with at least one helical duct (11).

12. The device (1; 22; 29; 33) according to the any one of the preceding claims, wherein said piston structure (14; 23; 31 ; 34) is made of a material having a density which is lower than that of the additive (V).

13. The device (1; 22; 29; 33) according to any one of the preceding claims, wherein said piston structure ( 14; 23 ; 31 ; 34) is made of a material having a density which is greater than that of the fluid to be additivated.

14. The device (33) according to any one of the preceding claims, wherein said piston structure (34) has a side wall (38) comprising a membrane collar (39) apt to establish a sliding seal on an inside wall of the tank (35).

15. The device (33) according to any one of the preceding claims, wherein said piston structure (34) has a bottom wall (36) of substantially cone-shaped profile.

16. The device (1; 22; 29; 33) according to any one of the preceding claims, wherein said connection means (2; 30) comprises, upstream of said pressure drop means (6), a further channel (81) apt to put said lumen (5) into communication with a region of the tank (9; 35) comprised between said connection means and said piston structure (14; 23; 31; 34).

17. The device (1; 22) according to any one of the preceding claims, wherein said piston structure (14; 23) has a piston body (15; 24), wherein said at least one channel (19; 32) is obtained, and a bottom portion (16; 25) peripherally secured to said piston body and apt to lap the free surface of the additive (V), a mixing region (17; 26) being defined between said piston body and bottom portion, and wherein said bottom portion has at least one opening (21 ; 27) for communicating said mixing region with a region of the tank containing the additive (V).

18. The device (1) according to the preceding claim, wherein said piston body (15) has a wedge-shaped portion (20) partially engaging said at least one opening

(21).

19. The device (22) according to claim 17, wherein said bottom portion (25) has a plurality of openings (27) slanting with respect to an axis of symmetry (28) of said piston structure (23).

20. The device (1) according to any one of the preceding claims, wherein said connection means (2) is preset for a reversible connection to the additive tank (9).

21. A kit to add an additive (V) to a fluid flow, comprising a device (1; 22; 29; 33) according to any one of the preceding claims, and at least one additive tank (9; 35).

22. The kit according to the preceding claim, comprising a plurality of tanks containing different additives (V).

23. The kit according to claim 21 or 22 when dependent from claim 15, wherein said at least one tank (35) has a bottom wall (37) of substantially cone-shaped profile.

24. An apparatus to add an additive (V) to a fluid flow, comprising a plurality of devices (1; 22; 29; 33) according to any one of the claims 1 to 20 arranged in sequence or in parallel.

25. A method to add an additive (V) contained in an additive tank to a fluid flow, comprising the steps of: generating a pressure drop in said flow; feeding said additive towards the flow, downstream of said pressure drop, via a first substantially helical run having an inlet end at the free surface of the additive, wherein said inlet end of said helical run lowers as the additive level in the tank diminishes.

26. The method according to claim 25, wherein said step of feeding said additive towards the flow provides the additive to be conveyed towards a minimal pressure region.

27. The method according to claim 25 or 26, wherein said step of feeding said additive towards said flow in turn provides the steps of:

- drawing a volume of said fluid to be additivated upstream of said pressure drop and driving it towards said additive through a second substantially helical run; and

- lapping said volume of drawn fluid against the free surface of the additive, so that a fraction of the latter be dragged by said volume of fluid to be additivated thus generating an additivated fluid volume.

28. The method according to the preceding claim, wherein said step of drawing a volume of fluid to be additivated provides that the latter be taken at a maximal pressure region.

29. The method according to claim 17 or 28, wherein concomitantly to said step of drawing said volume of fluid to be additivated a volume of additivated fluid is fed towards said flow by said first helical run.

30. The method according to the preceding claim, wherein said volume of fluid to be additivated and the volume of additivated fluid are substantially equivalent.

31. The method according to any one of claims 25 to 30, wherein said fluid to be additivated is water.