Proportional volumetric dosing unit

Abstract

A proportional volumetric dosing unit (1) is described, comprising: a motor (20) provided with an output shaft (31) movable along a respective sliding axis (X) between an upper dead centre position and a lower dead centre position, and a pump (25) fixed to the motor and adapted to be driven by said output shaft. Said pump comprising: a pump piston (362) fixed to an end of the output shaft, and a tubular body (300) coaxial with the output shaft and provided with an inner tubular surface (305), which comprises at least one contact section on which the pump piston slides in contact. Said tubular body (300), at least at the contact section, comprises a first annular portion (301) at least partially lined by a second annular portion (302), which second annular portion provides the inner tubular surface (305) at the contact section. Where the second annular portion is made of a polymeric material which is chemically more resistant to corrosion, against a predetermined corrosive agent, with respect to a polymeric or composite material of which the first annular portion is made, and / or the first annular portion is made of a polymeric or composite material which is mechanically more resistant than a polymeric material in which the second annular portion is made.

Description

[0001] PROPORTIONAL VOLUMETRIC DOSING UNIT

[0002] TECHNICAL FIELD OF THE INVENTION

[0003] The invention relates to a proportional volumetric dosing unit, in particular of the type which is driven solely by means of the energy provided by the flow of a first liquid into which the dosing unit must mix a predetermined amount of a second liquid.

[0004] PRIOR ART

[0005] As is well known, a proportional volumetric dosing unit is a device which allows a first liquid to be mixed with a second liquid, for example containing an additive or an active ingredient, for a variety of applications in all those sectors where it is necessary to mix a first liquid with an a second liquid or an additive in precise proportions. The main liquid may typically be water and the second liquid may be, according to the applications, oils, fertilizers, detergents, acids, chemical products or products intended for the pharmaceutical industry in solution or the like according to the application sector of the dosing unit. Said dosing units operate without the need to be connected to sources of electrical energy, but only due to the effect of the pressure and flow rate of the first liquid.

[0006] As for example disclosed in document EP3073112A1 , such dosing units have a hydraulic motor provided with a body inside which a piston is translated, slidably inserted in a cylinder of said body along a sliding axis, and which drives a pump of the dosing unit itself, which has the function of feeding inside the motor body, or in a by-pass conduit connected to an outlet conduit of the motor, the second liquid which mixes with the first liquid, sucking it from a source of the second liquid itself.

[0007] The pump comprises a tubular casing in which a pumping piston slides in contact with a motor output shaft. Such a tubular body is provided with an inner surface defining part of a pumping chamber of the pump.

[0008] One problem with the distributors of the prior art is that when the second liquid is a corrosive liquid, over time the inner surface of the tubular body is eroded and becomes gradually rougher. As a result, the pumping piston, in particular a gasket of the pumping piston sliding in contact with the inner surface, wears prematurely with respect to when the second liquid is non-corrosive.

[0009] Generally, a tubular body made of a material which is particularly resistant to a predetermined second corrosive liquid may result in high costs and may not ensure a long duration of the dosing unit, as it may occur that the materials best suited to resist certain corrosive agents are then not sufficiently resistant, when made in the thicknesses appropriate for these applications, from a mechanical viewpoint as regards the mechanical stresses to which the tubular body is subjected during installation and use.

[0010] An object of the present invention is to overcome the aforementioned constraints of the prior art by means of the features of the independent claim, which outlines an economical, robust and efficient solution. The dependent claims outline preferred and / or particularly advantageous aspects of the invention.

[0011] DISCLOSURE OF THE INVENTION

[0012] In particular, the invention provides a proportional volumetric dosing unit to reach such objects, comprising:

[0013] - a motor provided with an output shaft movable along a respective sliding axis between an upper dead centre position and a lower dead centre position,

[0014] - and a pump fixed to the motor and adapted to be driven by said output shaft, said pump comprising:

[0015] - a pumping piston fixed to an end of the output shaft,

[0016] - a tubular body coaxial with the output shaft and provided with an internal tubular surface, which comprises at least one contact section on which the pump piston slides, in which said tubular body, at least at the contact section, comprises a first annular portion at least partially covered by a second annular portion, which second annular portion provides (i.e. , makes, or in which is made) the inner tubular surface at the contact section, and in which the second annular portion is made of a polymeric material which is chemically more resistant to corrosion, against a predetermined corrosive agent, with respect to a polymeric or composite material of which the first annular portion is made, and / or the first annular portion is made of a polymeric or composite material which is mechanically more resistant (in particular, having a higher elastic modulus, e.g., measured in MPa) than a polymeric material of which the second annular portion is made.

[0017] Thereby a proportional volumetric dosing unit is provided which is particularly resistant both mechanically and with respect to corrosion, all in a compact, efficient and economical solution.

[0018] According to an aspect of the invention, the first annular portion and the second annular portion are co-moulded. Thanks to this solution, the tubular body is particularly compact and resistant.

[0019] Purely by way of non-limiting example, also in consideration of the fact that in the future new materials could be made or some existing materials could reach a cost suitable for volumetric dosing units, according to an aspect of the invention in which the material of which the second portion is made may be one among polyethylene, low-density polyethylene, high-density polyethylene, polypropylene, polyvinylidene fluoride and polyether ether ketone.

[0020] In the present discussion, the polyethylene is essentially medium-density polyethylene, whose mechanical features are intermediate between high-density and low-density polyethylene.

[0021] The material of which the first portion is made may be one among polyethylene, high- density polyethylene, fibre-reinforced polyethylene (glass or carbon fibres, e.g., between 20% and 60%), fibre-reinforced low- or high-density polyethylene (glass or carbon fibres, e.g., between 20% and 60%), polyvinylidene fluoride, fibre-reinforced polyvinylidene fluoride (glass or carbon fibres, e.g., between 20% and 60%), polyether ether ketone, fibre- reinforced polyether ether ketone (glass or carbon fibres, e.g., between 20% and 60%), polypropylene, fibre-reinforced polypropylene (glass or carbon fibres, e.g., between 20% and 60%), polyamide 12, fibre-reinforced polyamide 12 (glass or carbon fibres, e.g., between 20% and 60%).

[0022] Going into more detail, the material of the first portion may be one among high-density polyethylene, fibre-reinforced polyethylene (glass or carbon fibres, e.g., between 20% and 60%), fibre-reinforced low- or high-density polyethylene (glass or carbon fibres, e.g., between 20% and 60%), polyvinylidene fluoride, fibre-reinforced polyvinylidene fluoride (glass or carbon fibres, e.g., between 20% and 60%), polyether ether ketone, fibre-reinforced polyether ether ketone (glass or carbon fibres, e.g., between 20% and 60%), polypropylene, fibre-reinforced polypropylene (glass or carbon fibres, e.g., between 20% and 60%), polyamide 12, fibre-reinforced polyamide 12 (glass or carbon fibres, e.g., between 20% and 60%) when the material of the second portion is polyethylene, it may be one among polyethylene, high-density polyethylene, fibre-reinforced polyethylene (glass or carbon fibres, e.g., between 20% and 60%), fibre-reinforced low- or high- density polyethylene (glass or carbon fibres, e.g., between 20% and 60%), polyvinylidene fluoride, fibre-reinforced polyvinylidene fluoride (glass or carbon fibres, e.g., between 20% and 60%), polyether ether ketone, fibre-reinforced polyether ether ketone (glass or carbon fibres, e.g., between 20% and 60%), polypropylene, fibre-reinforced polypropylene (glass or carbon fibres, e.g., between 20% and 60%), polyamide 12, fibre-reinforced polyamide 12 (glass or carbon fibres, e.g., between 20% and 60%), when the material of the second portion is low-density polyethylene, it may be one among fibre-reinforced polyethylene (glass or carbon fibres, e.g., between 20% and 60%), fibre-reinforced low- or high-density polyethylene (glass or carbon fibres, e.g., between 20% and 60%), polyvinylidene fluoride, fibre-reinforced polyvinylidene fluoride (glass or carbon fibres, e.g., between 20% and 60%), polyether ether ketone, fibre- reinforced polyether ether ketone (glass or carbon fibres, e.g., between 20% and 60%), polypropylene, fibre-reinforced polypropylene (glass or carbon fibres, e.g., between 20% and 60%), polyamide 12, fibre-reinforced polyamide 12 (glass or carbon fibres, e.g., between 20% and 60%), when the material of the second portion is high-density polyethylene, it may be one among fibre-reinforced polyethylene (glass or carbon fibres, e.g., between 20% and 60%), fibre-reinforced low- or high-density polyethylene (glass or carbon fibres, e.g., between 20% and 60%), fibre-reinforced polyvinylidene fluoride (glass or carbon fibres, e.g., between 20% and 60%), polyether ether ketone, fibre-reinforced polyether ether ketone (glass or carbon fibres, e.g., between 20% and 60%), fibre-reinforced polypropylene (glass or carbon fibres, e.g., between 20% and 60%), polyamide 12, fibre-re- inforced polyamide 12 (glass or carbon fibres, e.g., between 20% and 60%), when the material of the second portion is polypropylene, it may be one among fibre-reinforced polyethylene (glass or carbon fibres, e.g., between 20% and 60%), fibre-reinforced high-density polyethylene (glass or carbon fibres, e.g., between 20% and 60%), fibre-reinforced polyvinylidene fluoride (glass or carbon fibres, e.g., between 20% and 60%), polyether ether ketone, fibre-reinforced polyether ether ketone (glass or carbon fibres, e.g., between 20% and 60%), fibre-reinforced polypropylene (glass or carbon fibres, e.g., between 20% and 60%), fibre-reinforced polyamide 12 (glass or carbon fibres, e.g., between 20% and 60%), when the material of the second portion is polyvinylidene fluoride, it may be one among fibre-reinforced high-density polyethylene (glass or carbon fibres, e.g., between 20% and 60%), fibre-reinforced polyvinylidene fluoride (glass or carbon fibres, e.g., between 20% and 60%), fibre-reinforced polyether ether ketone (glass or carbon fibres, e.g., between 20% and 60%), fibre-reinforced polypropylene (glass or carbon fibres, e.g., between 20% and 60%), fibre-reinforced polyamide 12 (glass or carbon fibres, e.g., between 20% and 60%), when the material of the second portion is polyether ether ketone.

[0023] [when a percentage is indicated, this is meant in relation to weight

[0024] According to another aspect of the invention, when the predetermined corrosive agent is at least one among acetic acid, citric acid, formaldehyde, lactic acid, pure methanol phosphoric acid, potassium hydroxide, sodium ash, ethanol, ethylene glycol, glycerol and caustic soda, the material of which the second portion is made may be one among polyethylene, low-density polyethylene, high-density polyethylene, polypropylene, polyvinylidene fluoride and polyether ether ketone, in which when the predetermined corrosive agent is formic acid, the material of which the second portion is made may be one among polyethylene, low-density polyethylene, high- density polyethylene, polypropylene, polyvinylidene fluoride, in which when the predetermined corrosive agent is one among hydrogen peroxide and hydrochloric acid, the material of which the second portion is made may be one among polyethylene, low-density polyethylene, high-density polyethylene, polyvinylidene fluoride and polyether ether ketone, in which when the predetermined corrosive agent is paracetic acid, the material of which the second portion may be made is polyvinylidene fluoride, in which when the predetermined corrosive agent is one among sulphuric acid at a percentage greater than 80% and bleach, the material of which the second portion is made may be one among polyethylene, low-density polyethylene, high-density polyethylene, and polyvinylidene fluoride, in which when the predetermined corrosive agent is one among benzyl alcohol, gas oil and perchloric acid, the material of which the second portion is made may be one among polypropylene, polyvinylidene fluoride and polyether ether ketone, in which when the predetermined corrosive agent is butyric acid, the material of which the second portion may be made is one among polyvinylidene fluoride and polyether ether ketone in which when the predetermined corrosive agent is chloric acid, the material of which the second portion is made may be polyvinylidene fluoride. in which when the predetermined corrosive agent is sulphuric anhydride, the material of which the second portion is made may be polyether ether ketone.

[0025] Regardless of the specific materials, according to an aspect of the invention, the material of the first annular portion is a composite material containing reinforcing fibres and the material of the second annular portion does not comprise reinforcing fibres.

[0026] Thereby, the tubular body is particularly compact, as a particularly thick first position is not required to resist the mechanical forces due to the pumping of the liquid, given the high step forward in mechanical strength which polymer materials undergo when fibres are dispersed therein. The lack of fibres in the second portion is important because otherwise the fibres at the contact section would tend to scratch the pump piston, i.e., they would tend to scratch a sliding gasket of such a piston, causing premature wear thereof. According to a preferable aspect of the invention, the second portion may be made of polyethylene and the first portion may be made of a composite material comprising, i.e., consisting of, polypropylene and reinforcing fibres (glass fibres, e.g., in a proportion greater than 20%, preferably between 20% and 35%).

[0027] According to an aspect of the invention, the dosing unit may comprise a tubular sleeve provided with a first longitudinal end fixed to the motor and an opposite second longitudinal end, and in which the tubular body of the pump comprises a first longitudinal end inserted in the tubular sleeve and proximal to the motor, an opposite second longitudinal end opposite the first end at which a threaded portion is made, and a stop surface transverse to the sliding axis and facing the second longitudinal end of the tubular body, said volumetric dosing unit further comprising a ring nut mechanism configured to vary the relative position of the tubular body with respect to the motor along the sliding axis, which ring nut mechanism comprises a ring nut provided with an inner thread and a tubular containment body in which an outer thread which meshes with the inner thread of the ring nut, a first abutment surface adapted to be contacted by the abutment surface of the tubular body and a second abutment strike surface are made, said volumetric dosing unit also comprising a further tubular body, which comprises a thread adapted to screw onto the thread of the tubular body and a stop surface adapted to lie on the second abutment surface, so that by screwing said threads, a portion of the tubular containment body comprised between the first abutment surface and the second abutment surface is clamped between the stop surface of the tubular body and the stop surface of the further tubular body.

[0028] Thereby the dosing unit is quick to assemble.

[0029] The invention also provides, to solve the problems of the prior art, a proportional volumetric dosing unit comprising: a motor provided with an output shaft movable along a respective sliding axis between an upper dead centre position and a lower dead centre position, and a pump fixed to the motor and adapted to be driven by said output shaft, said pump comprising:

[0030] - a pumping piston fixed to an end of the output shaft,

[0031] - a tubular body coaxial with the output shaft and provided with an internal tubular surface, which comprises at least one contact section on which the pump piston slides, in which said tubular body, at least at the contact section, comprises a first annular portion at least partially covered (internally) by a second annular portion, which second annular portion provides the inner tubular surface at the contact section, and the first annular portion is made (solely) of a composite material, i.e. , comprising a polymer matrix in which reinforcing fibres are embedded, and the second annular portion is made (solely) of a polymer material not comprising reinforcing fibres.

[0032] The tubular body is overall made of polymer material and only the first portion comprises reinforcing fibres.

[0033] BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Further features and advantages of the invention will be more apparent after reading the following description provided by way of a non-limiting example, with the aid of the figures illustrated in the accompanying tables.

[0035] Figure 1 is a sectional view of a proportional volumetric dosing unit according to the invention depicted in an operating configuration, in which an output shaft of a motor of the piston is in an upper dead centre position.

[0036] Figure 2 is an enlargement of figure 1 , in which only one pump of the dosing unit is shown, which is connected to the motor of the dosing unit.

[0037] Figure 3 is an enlargement of the motor of the dosing unit of figure 1 .

[0038] BEST MODE TO IMPLEMENT THE INVENTION

[0039] With particular reference to such figures, a proportional (piston) volumetric dosing unit is indicated by 1 , which is capable of mixing a first liquid (main liquid) in input from an inlet mouth 11 of an inlet conduit 10 with a second liquid (auxiliary liquid) so as to provide in output, in an outlet mouth 16 of an outlet conduit 15, a mixed liquid, which is formed by a pre-set percentage of first liquid and a pre-set percentage of second liquid established by the volumetric dosing unit itself.

[0040] The proportional volumetric dosing unit 1 has a (hydraulic) motor 20, driven by the flow of the first liquid passing through the motor itself, and a delivery pump 25,25' of the second liquid, which is fixed to and driven by the motor so as to deliver said second liquid.

[0041] In particular, the motor comprises an output shaft 31 for driving the pump. As will become clearer below, such an output shaft is also part of the pump itself.

[0042] The motor 20 may comprise a tubular motor body 35, to which the pump is fixed and which is in fluid communication with the inlet conduit 10 and the outlet conduit 15.

[0043] The motor may further comprise a sliding piston 30 accommodated in the motor body along a sliding axis X and which is moved along said sliding axis by the force generated by the flow of first liquid between an upper dead centre position (abbreviated hereafter PMS and visible in figures 1 and 3) and a lower dead centre position (abbreviated hereafter PMI and not illustrated in the figures).

[0044] The output shaft 31 is coaxial with the sliding axis X, i.e., it is coaxial with the sliding axis X and extends longitudinally along said sliding axis, is integral in movement with the piston 30 between the lower dead centre position and the upper dead centre position (therefore, it too is movable between an upper dead centre position and a lower dead centre position) and has a first axial end (always) connected (directly) to the piston and an opposite second axial end which is (always) free inserted inside the pump 25,25'. In particular, the first axial end is fixed to the piston without residual degrees of freedom.

[0045] The tubular body 35 comprises a cylinder within which the piston 30 is slidably inserted (to size) along the sliding axis X. Such a cylinder thus has a central axis coaxial with the sliding axis X.

[0046] Furthermore, the motor body 35, at an end opposite an end to which the pump is fixed, may be closed (above) by a cover (or cap) 40. In the upper dead centre position the piston 30 is proximal to the cover and in the lower dead centre position the piston 30 is distal from the cover.

[0047] With particular reference to figure 13, said piston 30 may comprise a top 55 (facing the cover), e.g., an upper top.

[0048] The piston 30 is for example a differential-type piston, which therefore has a first cylindrical body 60, which provides the top 55, and a second cylindrical body 65 integral (without residual degrees of freedom) with the first cylindrical body sliding along the sliding axis X.

[0049] The second cylindrical body extends, from a face of the first cylindrical body (to which the first end of the output shaft 31 is fixed and from which said output shaft 31 rises towards the pump) which is transverse to the sliding axis X and opposite the top 55, i.e., facing the pump, coaxially with the first cylindrical body and in the direction of movement away from said face and from the top 55 (towards the pump and in the direction of movement away from the cap).

[0050] The second cylindrical body has a smaller diameter with respect to the diameter of the first cylindrical body. In particular, the first cylindrical body comprises a cylindrical lateral outer surface 70 (coaxial with the sliding axis X) and the second cylindrical body comprises a cylindrical lateral outer surface 75 coaxial with that of the first cylindrical body (and extending from the face of the first cylindrical body opposite the top) having a smaller diameter with respect to the cylindrical lateral outer surface 70. Thus, there is an annular surface opposite the top, transverse to the sliding axis X and extending between an end of the cylindrical lateral outer surface 70 proximal to the second cylindrical body at an end of the cylindrical lateral outer surface 75 proximal to the first cylindrical body 60.

[0051] The second cylindrical body 65 is preferably a cylindrical tubular body (thin-walled) provided with a cylindrical lateral outer surface 75 and an opposite tubular lateral inner surface defining an inner axial cavity (arranged concordant with the sliding axis X) of the piston in direct fluid communication with the inlet conduit 10.

[0052] When the cylinder is of the differential type, the motor body 35 comprises a first (outer) tubular body 100 comprising a cylindrical inner surface 110 which accommodates to size (with reduced clearance) the first cylindrical body 60 of the piston in sliding, guiding it along the sliding axis X, and a second (inner) tubular body 105 at least partially accommodated in the first tubular body 100 comprising a cylindrical inner surface 115 which accommodates to size (with reduced clearance) the second cylindrical body 65 of the piston, guiding it in sliding along the sliding axis X.

[0053] The cap 40, which closes an end of the first tubular body distal from the pump, is fixed to the first tubular body.

[0054] At an end of the first tubular body opposite the cap, the first tubular body is joined to the second tubular body, e.g., near an end of the second tubular body proximal to the pump. The second tubular body 105 is spaced by a non-zero amount from the cap 40, such that it is not closed by the cap. In particular, the second tubular body 105 has a longitudinal extension along the sliding axis X which is smaller with respect to a longitudinal extension of the first tubular body 100. In further detail, the second tubular body 105 has a greater minimum distance from the cover than the first tubular body (which, for example, directly contacts the cover).

[0055] The second tubular body 105 is internally coaxial with the first tubular body 100 with respect to the sliding axis X and is sized so that there is an annular gap between a portion of the inner cylindrical surface 110 of the first cylinder 100 and a (cylindrical) outer lateral surface 120 of the second tubular body itself. Such an annular gap is in direct fluid communication with the outlet conduit 15. The inlet conduit 10 is instead isolated from such a gap; more in particular, such a conduit does not communicate directly with the gap.

[0056] Furthermore the cylindrical inner surface 115 defines an axial cavity 116 in direct fluid communication with the inlet conduit 10 and along which the piston, i.e., the second cylindrical body of the piston, slides. Such a cylindrical inner surface 115 is crossed by the inlet conduit 10, while the cylindrical inner surface 105 of the first tubular body 1 10 is crossed by the outlet conduit. The outlet conduit does not intersect the second tubular body, thus it does not communicate directly with axial cavity 116.

[0057] The axial cavity 116 and the inner axial cavity of the first cylindrical body of the piston are always in direct fluid communication with each other. Consequently, the inner axial cavity of the first cylindrical body of the piston is always in direct fluid communication with the inlet conduit 10.

[0058] The axial cavity 1 16 is entirely crossed by the output shaft 31 , and the second tubular body, at an end thereof proximal to the pump and distal from the cover 40, has an opening (which is never occluded by the piston) which is crossed by the output shaft, e.g., such an opening has a diameter which is at least 4 times larger with respect to a diameter of the output shaft, so that there is a large annular gap between output shaft and opening. The first tubular body 100, or its inner surface 110, together with the cover 40 and the first cylindrical body 60 of the piston delimits (entirely) a first chamber 45 of the motor, while the first tubular body 100, or its inner surface 110, together with the first cylindrical body 60, the second cylindrical body 65 i.e. , its outer surface 75, and the second tubular body 105, i.e., its outer surface 120, delimits (entirely) a second chamber 50 of the motor, where said chambers are separated from the piston and may be put in communication with each other (and with the cavity 116) in a manner which will be described in detail below.

[0059] A volume of the annular gap is part of the second chamber 50 (in particular when the piston is at lower dead centre, the volume of the second chamber 50 corresponds to the volume of the gap).

[0060] The first chamber 45 is in indirect fluid communication with the inlet conduit (as will become clearer below by means of appropriate valves and drive mechanisms of said valves) and the second chamber 50 is in direct fluid communication with the outlet conduit.

[0061] When the piston is at upper dead centre the volume of the first chamber 45 is minimum and the volume of the second chamber 50 is maximum, and in the lower dead centre position the volume of the first chamber is maximum and the volume of the second chamber is minimum.

[0062] The cavity 116, the face of the first cylindrical body from which the second cylindrical body rises, and the inner cavity of the second cylindrical body of the piston (entirely) delimit a third chamber, which is in direct fluid communication with the outlet conduit and in indirect fluid communication with the first chamber (and thus with the second chamber).

[0063] When the piston is at upper dead centre the volume of the third chamber is maximum, when it is at lower dead centre the volume of the third chamber is minimum.

[0064] The piston 30 has the top 55, e.g., made available from the first cylindrical body (and facing the cover), and also has an annular sealing lip 80 which rises from the top of the piston (or from the cylindrical outer lateral surface 70 of the first cylindrical body 60, or from both), in particular which rises from an outer annular peripheral edge of the top of the piston, and which lies in contact on the cylinder of the motor body, i.e., on the inner cylindrical surface 110 of the first tubular body, making a fluid seal between the first chamber and the second chamber. If the annular sealing lip were not present, the fluid could flow laterally to the piston in the gap between the cylinder and the piston due to the coupling clearance between said two elements. The annular sealing lip 80 is in contact with the cylinder at least along a continuous circumference, i.e., without interruption.

[0065] The piston 30 may comprise a further annular sealing lip 125, with a substantially similar shape to the annular sealing lip 80 which slides in contact with the cylindrical inner surface 115 of the second cylinder 105 so as to create a fluid seal separating the axial cavity 116 and the inner axial cavity of the second cylindrical body, i.e., the third chamber, from the second chamber 50.

[0066] The volumetric dosing unit may comprise an elastic element which pushes the annular sealing lip 80, i.e., the (free) end portion of the annular sealing lip against the cylinder, i.e., the first cylinder 100, even more in detail against the inner cylindrical surface 110 of the first cylinder 100.

[0067] The axial cavity of the second cylinder 105, i.e., the third chamber, is in communication with the outlet conduit 15 by means of a valve system. In particular, the axial cavity of the second cylinder 105, i.e., the third chamber, is in communication with the first chamber (only) by means of at least one valve and the first chamber is in communication with the second chamber (only) by means of a second valve.

[0068] For a detailed description of such a valve system, please refer to US201916423366, which is incorporated herein for reference purposes.

[0069] Such a valve system comprises at least one inner valve 130 and an outer valve 135, where the expression inner valve means a proximal valve with respect to the sliding axis X along a radial direction and the expression outer valve means a radially more distant valve from the sliding axis X with respect to the inner valve.

[0070] The inner valve 130 is interposed between the axial cavity of the second cylindrical body 65 and the first chamber 45, i.e., between the third chamber and the first chamber, and for example comprises a shutter 175 adapted to be engaged in a relative valve seat 180 made in the first cylindrical body 65, at a through hole (parallel to and eccentric with the sliding axis X) which places the axial cavity of the second cylindrical body and the first chamber 45 in fluid communication.

[0071] The outer valve 135 instead controls the opening and closing of a through hole made in the first cylindrical body, which places the first chamber 45 in fluid communication with the second chamber 50. The outer valve comprises a shutter adapted to be engaged in a valve seat made at such a through hole. The valves are associated with a rocker 185 which is articulated, at an end, to the top of the piston so as to perform small oscillations, about an articulation pin thereof, alternatively between a first position, in which the inner valve 130 is closed and the outer valve 135 is open, and a second position, in which the inner valve is open and the outer valve is closed. In particular, the inner valve 130 is constrained to the rocker by a portion thereof, so that when the rocker rotates from the second to the first position, the portion of the inner valve 130 is moved upwards and causes the shutter to close the valve seat. On the other hand, the shutter of the outer valve 135 is directly supported by the rocker and, by rotating from the second to the first position, the rocker brings the shutter to a position distal from the valve seat, opening the corresponding outer valve 135.

[0072] The movement of the rocker, which determines the respective opening and closing positions of the inner and outer valves, is delegated to a spring activation mechanism.

[0073] In the embodiment illustrated the spring activation mechanism is configured to be engaged in a slot 190, provided with a lower surface and an upper surface, e.g., opposite each other and aligned along a direction parallel to the direction of the sliding axis X, obtained in a body of the shutter 175 of the inner valve.

[0074] Such a spring activation mechanism comprises a pair of connecting rods 195, where each connecting rod is associated with a respective spring 200.

[0075] Each connecting rod is fixed to a respective hinge 205 placed on the piston 30 and, through a hinge 210, which is housed in the slot 190, at a first end of the respective spring 200.

[0076] In turn the springs 200 are fixed in a second end thereof to a hinge 215 placed on a rod 220 slidably associated with the piston 30 i.e., which is constrained to the piston 30 so as to be able to translate with respect to the piston itself.

[0077] In particular, the rod 220 can slide vertically inside a through hole 26a obtained in the body of the piston 30 itself.

[0078] Furthermore, the rod 220 has a raised element constrained to slide within a guide 52 of the piston 30 which terminates at an end with a lower abutment element and at the opposite end with an upper abutment element, where said abutment elements can alternatively engage with the raised element of the rod to determine the respective stroke ends thereof along the translation axis of the rod, an axis which is parallel to the sliding axis X. The position of the rod 220 with respect to the piston 30 determines the activation of the spring activation mechanism and regulates the upward and downward stroke of the piston.

[0079] The pump 25 is fixed below the motor body 20, which as mentioned, has the function of feeding a second liquid to the motor.

[0080] The dosing unit may be of the type with by-pass or without by-pass, such as the embodiment illustrated, in which the second liquid is pumped into cavity 116, i.e., into the third chamber.

[0081] The pump 25 comprises a piston 362 which is mechanically connected and rigidly connected to the output shaft, i.e., at its distal end from the motor piston, so that the stroke of the piston 362 is the same as that of the motor piston.

[0082] The piston 362 comprises a plurality of openings 362a, arranged radially with respect to the sliding axis X, for the outflow of the second liquid which is pumped towards the motor or the bypass conduit (in particular towards an internal volume of a pump sleeve, as will become clearer below). Associated with said openings 362a is a friction gasket 364 (annular and coaxial with the sliding axis X) which selectively allows or prevents the passage of the second liquid through the openings 362a. Such a friction gasket 364 is housed in an annular groove of the piston 362. As will become clearer below, the friction gasket 364, during the movement of the piston from PMS to PMI, rubbing along an inner surface of a tubular body, moves to a position in which it allows the outflow of the auxiliary fluid, previously aspirated, through the openings 362a, while during the movement of the piston from PMI to PMS, rubbing along said inner surface, the gasket 364 moves to a position in which it prevents the passage of the auxiliary fluid through the openings 362a, instantly producing a vacuum in the pumping chamber 112.

[0083] The pump 25 comprises a (rigid) tubular body 300, e.g., cylindrical, coaxial with the output shaft 31 , i.e., the sliding axis X, and comprising an inner tubular surface 305 (at least partially cylindrical, e.g., also smooth) coaxial with the output shaft 31 , i.e., the sliding axis X.

[0084] In its stroke between PMI and PMS, the piston 362 is always at least partially housed in an internal volume of the tubular body (partially) defined by the inner tubular surface 305. In particular, the friction gasket 362 is always entirely housed in the internal volume of the tubular body and is always in contact with a (cylindrical) contact section of the inner tubular surface 305. Such internal volume together with the piston 362 at least partially defines a pumping chamber 310 of the second liquid

[0085] The tubular body 300 comprises a first longitudinal end, distal from the motor, near or at which the inner tubular surface 305 provides an inlet mouth 315 of the second liquid to be pumped, and an opposite second longitudinal end, proximal to the motor, and near or at which the inner tubular surface provides an outlet mouth 320 of the second liquid. For example, the contact section is proximal to the second longitudinal end of the tubular body 300.

[0086] The inner tubular surface 305 is, for example, seamlessly continuous along its entire extension, and in particular, there are no holes in the tubular body 300 at the inner tubular surface 305 which cross the inner tubular surface transverse to the sliding axis X and which place the inner volume in connection with an external environment.

[0087] The tubular body may comprise an outer tubular surface 325 opposite the inner tubular surface, e.g., coaxial with the sliding axis X, which is distant by a non-zero amount from the surface 305 defining a (non-zero) thickness of the tubular body itself.

[0088] At the first longitudinal end, the inlet mouth 315 is in direct fluid communication with a one-way valve 395, e.g., of the automatic type (governed by the difference in pressures), which governs the passage of the second liquid through the inlet mouth 315, allowing only the entry of the second liquid into the internal volume, i.e., into the pumping chamber, and not the exit therefrom. Such a one-way valve 395 is thus movable between an open position, in which it allows the second liquid to enter the internal volume, and a closed position, in which it isolates and closes the pumping chamber. In the embodiment illustrated, the one-way valve 395 comprises a shutter acting on said through hole and a spring placed abuttingly at the housing seat and pushing the shutter into the closed position of the through hole.

[0089] The one-way valve could be (only) partially housed in a seat in the tubular body 300 made at the first longitudinal end of the tubular body 300 itself or, as illustrated in the figures, it may be outside the tubular body 300 and rest at the first longitudinal end.

[0090] For example, the pumping chamber is delimited by the piston, the inner surface of the tubular body 300 and the one-way valve 395.

[0091] Regardless of the exact position of the one-way valve, it is held in place by means of a further tubular body 400 which is removably fixed to the tubular body 300 by clamping the one-way valve between itself and the tubular body. For example, the further tubular body, at a longitudinal end thereof proximal to the first end of the tubular body 300, comprises a thread 401 adapted to screw onto a thread 303 of the tubular body 300. At an opposite longitudinal end, the further tubular body comprises an inlet mouth for the second liquid surrounded by means for fixing a tube for transporting the second liquid to the pump. Such a further tubular body 400 is crossed from one to the other by a through hole originating from the inlet mouth and which is in fluid communication with the pumping chamber when the one-way valve 395 is open.

[0092] The tubular body 400 then comprises means, e.g., threaded or quick-release, for connecting a tube conveying the second liquid to the through hole.

[0093] The further tubular body 400 comprises a stop surface 402 (e.g., annular) facing the motor 20, for example placed near the second longitudinal end of the further tubular body 400. It is not excluded that in an alternative embodiment not illustrated, the one-way valve could be part of a tube connected to the tubular body.

[0094] With particular reference to the enlargement of figure 2, the tubular body 300 comprises a threaded portion at the first longitudinal end. In particular, such a threaded portion comprises an outer thread 303 made in the outer surface of the tubular body.

[0095] The tubular body, between the first longitudinal end and the second longitudinal end, in particular between the contact section and the aforesaid threaded portion, comprises a stop surface 304 (annular, e.g., a circular crown) transverse to the sliding axis of the output shaft and facing the first longitudinal end. The stop surface 304 is preferably radially more external with respect to the sliding axis X with respect to the first longitudinal end of the tubular body, in particular with respect to the threaded portion 303 at the first longitudinal end of the tubular body.

[0096] In the embodiment illustrated, the stop surface 304 is made available by an (annular) protrusion rising from the outer surface of the tubular body 300. However, it is not excluded that in an alternative embodiment not illustrated, the stop surface 304 could be made available by a groove made in the outer surface of the tubular body.

[0097] The tubular body may comprise, between the first and the second end of the body itself, a portion with a restricted passage section. In particular, at such a portion, both the inner and the outer surface of the tubular body have a reduced transverse section (with respect to the sliding axis X) with respect to a transverse section measured near the second longitudinal end of the tubular body.

[0098] In particular, the tubular body comprises a first sector, starting from the second longitudinal end (and at which there is the contact section) which is substantially cylindrical, which is followed by a second sector in which there is the restricted section, which in turn is followed by a third sector which that goes from the restricted section to the first longitudinal end and which is substantially cylindrical in shape, with a smaller diameter with respect to the first sector.

[0099] The stop surface 304 is preferably placed near (at) the portion with restricted passage section.

[0100] The tubular body may also comprise, at the second longitudinal end, a housing seat for an annular sealing gasket 306, which seat is made in the outer surface of the tubular body 300.

[0101] The pump then comprises a (tubular and rigid) sleeve 330 coaxial with the output shaft 31 , i.e., the sliding axis X, which connects the tubular body 300 to the motor, i.e., to the motor body 35. For example, the sleeve 330 comprises a portion thereof fixed by means of connection members threaded to the motor, i.e., the motor body 35. In particular, the sleeve is fixed to the motor body 35 from a high opposite the cover 40.

[0102] The sleeve 330 defines an internal volume 335, inside the sleeve 330 itself, in fluid communication (mediated by the pump piston) with the internal volume of the tubular body 300, i.e., with the pumping chamber 310.

[0103] Such an internal volume 335 partially accommodates the tubular body 300. In particular, the sleeve comprises a (cylindrical) inner tubular surface 340 defining the internal volume 335. The internal volume 335 is delimited at an end of the sleeve by the tubular body 300 and the piston, and at an opposite end by the motor body.

[0104] Said internal volume 335, depending on the embodiment of the dosing unit with or without by-pass, may be in direct fluid communication either with the axial cavity 1 16, i.e., with the third chamber of the motor, e.g., by means of the opening of the second tubular body 110 proximal to the pump, or it may be in direct fluid communication with the by-pass conduit, which makes an inlet opening in said sleeve, or in its inner surface 340. In the last bypass case, the internal volume of the sleeve 330 is partly delimited by a stopper which closes the opening of the second tubular body 110. The sleeve is substantially shaped like a tubular body from an end fixed to the motor to an opposite end and its inner tubular surface has a diameter at least greater than the diameter of the outer tubular surface 325 of the tubular body 300.

[0105] Irrespective of the exact shape of the tubular body, it comprises (solely), i.e., is made (solely) of, a first annular portion 301 (i.e., an outer annular portion) at least partially lined (internally, i.e., only on one face of the first portion facing the sliding axis X) by a second annular portion 302 (i.e., an inner annular portion), where the materials of such portions are different. The liner in the contact section of the pump piston gasket is total, i.e., the piston seal only touches the second portion.

[0106] The second portion has a thickness of at least 0.3 mm, preferably at least 1 mm, and less than 10 mm, e.g., less than 3 mm.

[0107] The second portion forms a liner of non-zero thickness for the entire extension of the second portion itself.

[0108] The first annular portion and the second annular portion are both made as tubular bodies, e.g., coaxial with the X-axis.

[0109] The first portion and the second portion are rigidly fixed to each other, with no residual degrees of freedom, together forming a rigid body. For example, they may be fixed to each other by adhesives, or by welding (of polymers) or because, preferably, the sleeve is made by co-moulding the first and the second portion.

[0110] The second annular portion 302 provides a portion of the inner tubular surface 305 at the contact section. In particular, only the second annular portion 302 makes such a portion of the surface available. In further detail, the second annular portion 302, at least at the contact section, has no surface coating.

[0111] The first annular portion extends along the sliding axis substantially from the second longitudinal end of the tubular body 300, or near thereto, to the first longitudinal end of the tubular body 300.

[0112] In particular, the first annular portion provides the threading near the first longitudinal end and the stop surface of the tubular body 300. Additionally, the first portion provides the second and the third sector of the tubular body 300. In further detail, the first annular portion provides the protrusion in which the stop surface of the tubular body 300 is obtained. The second annular portion is for example essentially shaped like an axially hollow cylindrical tubular body, the axial cavity of which is cylindrical.

[0113] The second annular portion forms together with the first only the first sector of the tubular body 300.

[0114] Regardless of the exact shape and extension of the portions, the second annular portion comprises an outer annular surface opposite the inner annular surface 305 which has a plurality of depressions and protrusions, e.g., in the form of a roughness evident to the touch or protrusions greater than one millimetre, adapted to allow a better relative fixing of the first portion to the second portion.

[0115] Such a roughness may be achieved by knurling or shot-peening.

[0116] The second portion is made of a (single) polymeric material which is chemically more resistant to corrosion, against a predetermined corrosive agent, with respect to a polymeric or composite material (where composite in this discussion is preferably intended as a material formed from a polymer matrix into which reinforcing fibres are embedded, in an ordered or disordered manner) in which the first portion is made,

[0117] Alternatively or additionally, the first portion is made of a (single) polymeric or composite material which is mechanically more resistant than the polymeric material in which the second portion is made (the material of the first portion and the material of the second portion in this case could have substantially the same or similar resistance to a predetermined corrosive agent).

[0118] Resistance to a corrosive agent is intended as the consumption of material due to the corrosive agent, usually expressed as a linear length over a time interval, e.g., in mm / year, which, for a material to be chemically resistant, must be a consumption which is substantially irrelevant over the life of the dosing unit. In the present case, the consumption is essentially zero over the life of the dosing unit, otherwise abnormal consumption of the pump piston gasket would occur. The service life of the body 300 is generally a few years.

[0119] Therefore, a material with a higher chemical resistance has a lower consumption in terms of mm / year with respect to a less chemically resistant material.

[0120] With regard to mechanical strength, for example, the yardstick may be the elastic modulus, generally measured in Pa, i.e., in MPa. Therefore, a mechanically more resistant material has a higher elastic modulus in Pa with respect to a mechanically less resistant material.

[0121] It is obviously intended that the resistance is measured under similar, if not identical conditions, e.g., for mechanical resistance, values are generally measured at a temperature of 23°c and 50% humidity.

[0122] By way of example and not as an exhaustive list, the following describes certain polymeric and composite materials, and combinations of polymeric and composite materials (combination to be understood as pairing of a material of the first portion with a material of the second portion), that are particularly suitable for use in proportional volumetric dosing units, in particular in the body 300 of such dosing units.

[0123] For example, the material of which the second portion is made may be one among polyethylene (abbreviation PE), low-density polyethylene (abbreviation LDPE), high-density polyethylene (abbreviation HDPE), polypropylene (abbreviation PP), polyvinylidene fluoride (abbreviation PVDF) and polyether ether ketone (abbreviation PEEK).

[0124] More in detail, again not exhaustively, when the predetermined corrosive agent is at least one among acetic acid, citric acid, formaldehyde, lactic acid, pure methanol phosphoric acid, potassium hydroxide, sodium carbonate, ethanol ethylene glycol, glycerol and caustic soda, the material of which the second portion is made is one among polyethylene, low-density polyethylene, high-density polyethylene, polypropylene, polyvinylidene fluoride and polyether ether ketone.

[0125] Alternatively or additionally, when the predetermined corrosive agent is formic acid, the material of which the second portion is made is one among polyethylene, low-density polyethylene, high-density polyethylene, polypropylene, polyvinylidene fluoride.

[0126] Alternatively or additionally, when the predetermined corrosive agent is one among hydrogen peroxide and hydrochloric acid, the material of which the second portion is made is one among polyethylene, low-density polyethylene, high-density polyethylene, polyvinylidene fluoride and polyether ether ketone.

[0127] Alternatively or additionally, when the predetermined corrosive agent is paracetic acid, the material of which the second portion is made is polyvinylidene fluoride. in which when the predetermined corrosive agent is one among sulphuric acid at a percentage greater than 80% and bleach, the material of which the second portion is made is one among polyethylene, low-density polyethylene, high-density polyethylene, and polyvinylidene fluoride, Alternatively or additionally, when the predetermined corrosive agent is one among benzyl alcohol, gas oil and perchloric acid, the material of which the second portion is made is one among polypropylene, polyvinylidene fluoride and polyether ether ketone.

[0128] Alternatively or additionally, when the predetermined corrosive agent is butyric acid, the material of which the second portion is made is one among polyvinylidene fluoride and polyether ether ketone.

[0129] Alternatively or additionally, when the predetermined corrosive agent is chloric acid, the material of which the second portion is made is polyvinylidene fluoride.

[0130] Alternatively or additionally, when the predetermined corrosive agent is sulphur dioxide, the material of which the second portion is made is polyether ether ketone.

[0131] In the present discussion, polyethylene is essentially medium-density polyethylene, whose mechanical properties are intermediate between high-density and low-density polyethylene, i.e., it has an intermediate elastic modulus.

[0132] Generally, low-density polyethylene has an elastic modulus of about 130-300 MPa, polyethylene has an elastic modulus of about 500 MPa, high-density polyethylene has an elastic modulus of 600-1100 MPa, polyvinylidene fluoride has an elastic modulus of about 2200 MPa and polyether ether ketone has an elastic modulus of about 3600 MPa.

[0133] Given these materials for the second portion, following the principle asserted in claim 1 , the polymeric, or composite, material of the first portion must at least have either a higher mechanical resistance, i.e., a higher elastic modulus, or a lower resistance (and generally a lower cost) to corrosion of such a chemical agent. The corrosion resistance of the first portion matters little, as it is not in contact with the liquid pumped by the pump of the dosing unit.

[0134] By way of non-limiting example, following the principle that the material of the first portion must be mechanically more resistant, for example, when the material of the second portion is polyethylene, the material of the first portion may be one among high-density polyethylene, fibre-reinforced polyethylene (glass or carbon fibres, e.g., between 20% and 60%), fibre-reinforced low or high-density polyethylene (glass or carbon fibres, e.g., between 20% and 60%), polyvinylidene fluoride, fibre-reinforced polyvinylidene fluoride (glass or carbon fibres, e.g., between 20% and 60%), polyether ether ketone, fibre-reinforced polyether ether ketone (glass or carbon fibres, e.g., between 20% and 60%), polypropylene, fibre-reinforced polypropylene (glass or carbon fibres, e.g., between 20% and 60%), polyamide 12, fibre-reinforced polyamide 12 (glass or carbon fibres, e.g., between 20% and 60%).

[0135] When the material of the second portion is low-density polyethylene, the material of the first portion may be one among polyethylene, high-density polyethylene, fibre-reinforced polyethylene (glass or carbon fibres, e.g., between 20% and 60%), fibre-reinforced low- density or high-density polyethylene (glass or carbon fibres, e.g., between 20% and 60%), polyvinylidene fluoride, fibre-reinforced polyvinylidene fluoride (glass or carbon fibres, e.g., between 20% and 60%), polyether ether ketone, fibre-reinforced polyether ether ketone (glass or carbon fibres, e.g., between 20% and 60%), polypropylene, fibre-reinforced polypropylene (glass or carbon fibres, e.g., between 20% and 60%), polyamide 12, fibre- reinforced polyamide 12 (glass or carbon fibres, e.g., between 20% and 60%).

[0136] When the material of the second portion is high-density polyethylene, the material of the first portion may be one among polyethylene, high-density polyethylene, fibre-reinforced polyethylene (glass or carbon fibres, e.g., between 20% and 60%), fibre-reinforced low- or high-density polyethylene (glass or carbon fibres, e.g., between 20% and 60%), polyvinylidene fluoride, fibre-reinforced polyvinylidene fluoride (glass or carbon fibres, e.g., between 20% and 60%), polyether ether ketone, fibre-reinforced polyether ether ketone (glass or carbon fibres, e.g., between 20% and 60%), polypropylene, fibre-reinforced polypropylene (glass or carbon fibres, e.g., between 20% and 60%), polyamide 12, fibre- reinforced polyamide 12 (glass or carbon fibres, e.g., between 20% and 60%).

[0137] When the material of the second portion is polypropylene, the material of the first portion may be one among fibre-reinforced polyethylene (glass or carbon fibres, e.g., between 20% and 60%), fibre-reinforced low- or high-density polyethylene (glass or carbon fibres, e.g., between 20% and 60%), fibre-reinforced polyvinylidene fluoride (glass or carbon fibres, e.g., between 20% and 60%), polyether ether ketone, fibre-reinforced polyether ether ketone (glass or carbon fibres, e.g., between 20% and 60%), fibre-reinforced polypropylene (glass or carbon fibres, e.g., between 20% and 60%), polyamide 12, fibre-re- inforced polyamide 12 (glass or carbon fibres, e.g., between 20% and 60%).

[0138] When the material of the second portion is polyvinylidene fluoride, the material of the first portion may be one among fibre-reinforced polyethylene or fibre-reinforced high-density polyethylene (glass or carbon fibres, e.g., between 20% and 60%), fibre-reinforced polyvinylidene fluoride (glass or carbon fibres, e.g., between 20% and 60%), fibre-reinforced polyether ether ketone (glass or carbon fibres, e.g., between 20% and 60%), fibre-reinforced polypropylene (glass or carbon fibres, e.g., between 20% and 60%), fibre-reinforced polyamide 12 (glass or carbon fibres, e.g., between 20% and 60%).

[0139] When the material of the second portion is polyether ether ketone, the material of the first portion may be one among fibre-reinforced high-density polyethylene (glass or carbon fibres, e.g., between 20% and 60%), fibre-reinforced polyvinylidene fluoride (glass or carbon fibres, e.g., between 20% and 60%), fibre-reinforced polyether ether ketone (glass or carbon fibres, e.g., between 20% and 60%), fibre-reinforced polypropylene (glass or carbon fibres, e.g., between 20% and 60%), fibre-reinforced polyamide 12 (glass or carbon fibres, e.g., between 20% and 60%).

[0140] Instead, following the principle that the material of the second portion is more chemically resistant with respect to a material of the second portion, irrespective of the mechanical resistance of the materials of the two portions, when the predetermined corrosive agent is at least one among acetic acid, citric acid, formaldehyde, lactic acid, pure methanol phosphoric acid potassium hydroxide, sodium carbonate, ethanol, ethylene glycol, glycerol and caustic soda, the material of which the second portion is made is one among polyethylene, low-density polyethylene, high-density polyethylene, polypropylene, polyvinylidene fluoride and polyether ether ketone, and the material of which the first portion is made is polyamide 12.

[0141] Alternatively or additionally, when the predetermined corrosive agent is formic acid, the material of which the second portion is made is one among polyethylene, low-density polyethylene, high-density polyethylene, polypropylene, polyvinylidene fluoride, and the material of which the first portion is made is one among polyamide 12 and polyether ether ketone.

[0142] Alternatively or additionally, when the predetermined corrosive agent is one among hydrogen peroxide and hydrochloric acid, the material of which the second portion is made is one among polyethylene, low-density polyethylene, high-density polyethylene, polyvinylidene fluoride and polyether ether ketone, and the material of which the first portion is made is one among polyamide 12 and polypropylene.

[0143] Alternatively or additionally, when the predetermined corrosive agent is paracetic acid, the material of which the second portion is made is polyvinylidene fluoride, and the ma- terial of which the first portion is made is one among polyamide 12, polypropylene, polyethylene, low-density polyethylene or high-density polyethylene.

[0144] Alternatively or additionally, when the predetermined corrosive agent is one among sulphuric acid at a percentage greater than 80% and bleach, the material of which the second portion is made is one among polyethylene, low-density polyethylene, high-density polyethylene, and polyvinylidene fluoride, and the material of which the first portion is made is one among polyamide 12, polypropylene, and polyether ether ketone.

[0145] Alternatively or additionally, when the predetermined corrosive agent is one among benzyl alcohol, gas oil and perchloric acid, the material of which the second portion is made is one among polypropylene, polyvinylidene fluoride and polyether ether ketone, and the material of which the first portion is made is one among polyamide 12, polyethylene, low- density polyethylene or high-density polyethylene.

[0146] Alternatively or additionally, when the predetermined corrosive agent is butyric acid, the material of which the second portion is made is one among polyvinylidene fluoride and polyether ether ketone, and the material of which the first portion is made is one among polyamide 12, polyethylene, low-density or high-density polyethylene, and polypropylene. Alternatively or additionally, when the predetermined corrosive agent is chloric acid, the material of which the second portion is made is polyvinylidene fluoride, and the material of which the first portion is made is one among polyamide 12, polyethylene, low-density or high-density polyethylene, and polypropylene.

[0147] Alternatively or additionally, when the predetermined corrosive agent is sulphuric anhydride, the material of which the second portion is made is polyether ether ketone, and the material of which the first portion is made is one among polyamide 12 , polyethylene, low- density or high-density polyethylene, polypropylene and polyvinylidene fluoride.

[0148] Additionally, as an alternative to the chemically less resistant materials in the latter list, any of the fibre-reinforced composite materials listed above may be used, as the fibres cause uneven wear of the surface in contact with the corrosive agent when the material begins to corrode, resulting in an uneven surface which leads to an early end of service life of the composite element, as the material consumption is high due to corrosion, the composite materials are therefore considered poorly resistant to corrosion by chemical agents, as the surface undergoes deformation, to be intended as an increase in irregularity, such that the piece in composite material becomes useless in little time. Generally, low-density polyethylene reinforced with 20%-30% (glass) fibres has an elastic modulus of approx. 2700 MPa (in the case of carbon, the elastic modulus will be even higher), polyethylene reinforced with 20%-30% (glass) fibres has an elastic modulus of approx. 3500 MPa, high-density polyethylene reinforced with 20% (glass) fibres has an elastic modulus of more than 4500 MPa, polypropylene with 20% glass fibre has an elastic modulus of approx. 4500 MPa, polyamide 12 has an elastic modulus of approx. 1800 MPa, polyamide 12 reinforced with 30% glass fibre has an elastic modulus of approx. 4000 MPa, has an elastic modulus of approx. 2200 MPa and polyether ether ketone has an elastic modulus of approx. 3600 MPa.

[0149] Fibre-reinforced polymers (glass or carbon, but preferably glass) are the composite materials mentioned above, in which the specific polymer forms the matrix. The fibre percentage given is the weight percentage of the fibres in relation to the total weight. Preferably, the fibres of all the materials indicated are of the non-orderly type.

[0150] Obviously, there may be variations based on the specific supply of each manufacturer, and obviously variations of materials and their combinations are within the reach of the person skilled in the art as long as the correlation between the material of the first portion and the material of the second portion indicated in claim 1 is respected.

[0151] Apart from the possible examples made of the specific materials, in the preferred embodiment, the material of the first annular portion 301 is a composite material containing reinforcing fibres (e.g., glass) and the material of the second annular portion 302 is a polymeric material and does not comprise reinforcing fibres (it is a non-composite polymeric material). The fact of not comprising fibres in the second portion is explained by the fact that the fibres at the contact section would tend to scratch the piston, i.e., the piston gasket, eventually causing premature wear of such an element.

[0152] Further, again apart from possible examples in specific materials, it may be preferable for the polymeric or composite material of the first portion to have an elastic modulus greater than 2000 MPa, preferably greater than 4000 MPa.

[0153] Furthermore, the optimal solution in terms of weight, space and cost is the use of high- density polyethylene for the second portion and fibre-reinforced polypropylene (glass, e.g., 20%-30%) for the first portion.

[0154] The tubular body 300 is inserted at least partially, e.g., almost entirely, into a tubular containment body 425, and is retained therein by means of the further tubular body 400, which is screwed to the thread of the tubular body, clamping a portion of the tubular containment body 425 between itself and the tubular body 300. The tubular containment body 425 is itself partially inserted in the tubular sleeve and protrudes therefrom in the direction away from the motor.

[0155] In particular, the tubular containment body 425 comprises a first longitudinal end near the motor, which has an opening into which the tubular body 300 may be inserted (to size), and an opposite second longitudinal end distal from the motor, into which the further tubular body 400 may be at least partially inserted.

[0156] The tubular containment body 425 further comprises a first abutment surface 426 (facing the motor) adapted to be contacted by the stop surface 304 of the tubular body 300, and a second abutment surface 427 (facing the opposite direction with respect to the motor), for example provided by the second longitudinal end of the tubular containment body itself, adapted to be contacted by the stop surface of the further tubular body.

[0157] When the thread of the further tubular body is screwed to the thread of the tubular body, a portion of the tubular containment body between the first abutment surface and the second abutment surface is clamped between the stop surface of the tubular body and the stop surface of the further tubular body, thus fixing such tubular bodies in relative position to each other, and for example retaining the one-way valve 395 in position.

[0158] The tubular containment body comprises an inner tubular surface facing the tubular body and an opposite outer tubular surface which extend from a longitudinal end of the tubular containment body itself to the other. For example, such surfaces are cylindrical at least near the longitudinal ends.

[0159] In order to obtain a fluid seal with the tubular containment body, a sealing (static) gasket x, e.g., annular, preferably housed in a housing seat made in the tubular body 300, is present between the outer surface of the tubular containment body and the inner surface of the tubular containment body. In the embodiment illustrated, such a sealing gasket is housed in a seat obtained in an annular protrusion of the tubular body 300 which protrudes with respect to adjacent outer surface portions of the tubular body 300.

[0160] The tubular containment body may also comprise an outer thread 428 made in the outer surface of the tubular containment body itself, in particular made near the first longitudinal end near the motor.

[0161] The tubular body 300 may be movably associated with the motor, i.e., the sleeve 330, sliding along the sliding axis X, and for example the pump 25 may comprise a mechanism for varying the position of the tubular body 300, configured to allow the sliding of the tubular body 300 along the sliding axis with respect to the sleeve 330 and the positioning, i.e. , (stable) locking of the tubular body 300 in a plurality of positions along the sliding axis X.

[0162] In particular, the tubular body 300 is slidably movable along the sliding axis X between a maximum dosing position of the pump, in which the distance of the tubular body 300, i.e., of the second end of the tubular body 300 (i.e., from the end of the sleeve 330 fixed to the motor), from the motor is minimum and a percentage of the internal volume of the tubular body 300 occupied by the output shaft (when the output shaft is at the PMI) is maximum, and a minimum dosing position, in which the distance of the tubular body 300 (i.e., from the end of the sleeve 330 fixed to the motor), or of the second end of the tubular body 300, from the motor is maximum and a percentage of the internal volume of the tubular body 300 occupied by the output shaft (when the output shaft is at the PMI) is minimum.

[0163] The stroke of the output shaft between the PMI and the PMS does not vary, i.e., it is constant.

[0164] The position variation mechanism allows the tubular body to be moved along the sliding axis and to lock the sliding in a plurality (infinite to continuous) of positions between the maximum dosing position and the minimum dosing position.

[0165] The position variation mechanism comprises a ring nut mechanism provided with a ring nut 430 rotatably associated with the sleeve and coaxial with the sliding axis X. In particular, said ring nut 430 is provided with a single residual degree of freedom in rotation about the sliding axis and is provided with an inner thread 435 which meshes with the outer thread 428 of the tubular containment body. Thereby, a rotation of the ring nut 430 corresponds to a translation of the tubular body along the sliding axis.

[0166] The ring nut may have an enlarged end 450 (radially enlarged) which is housed in a conjugate annular groove obtained in an enlarged portion of the sleeve 330 at the end of the sleeve which is distal from the motor.

[0167] Such an end of the sleeve 330 is then associated with an closing cover 455 configured to hold the enlarged end of the ring nut 430 in the annular groove. Thanks to this configuration, the ring nut is associated with the sleeve with only one residual degree of freedom in rotation about the sliding axis X.

[0168] The sleeve 330 may comprise a locking system configured to selectively mechanically lock the tubular body 300, i . e . , the further tubular body, in a reached position, with respect to the sleeve 330.

[0169] For example, the locking system is configured to mechanically lock, making a shape constraint, i.e., making an obstruction connection.

[0170] Preferably, the shape constraint, i.e., the obstruction connection, which blocks the relative movement between the tubular body 300, i.e., the further tubular body, and the sleeve is obtained by acting radially on an outer surface of the ring nut, in particular its enlarged portion.

[0171] Such a locking system comprises a lever, which is housed in a seat at the enlarged portion of the sleeve and which is constrained to the seat of the sleeve thanks to an articulation hinge with an axis parallel to the sliding axis of the output shaft.

[0172] The lever has, at one end, a portion provided with reliefs and / or grooves, e.g., provided with a notching, adapted to engage with said outer portion of the ring nut 430 provided with reliefs and / or grooves configured to create a shape constraint with the reliefs and / or grooves of the portion.

[0173] In the preferred embodiment illustrated, the tubular body has both the shape in which the portion of the tubular containment body 425 comprised between the first abutment surface and the second abutment surface is clamped between the stop surface of the tubular body and the stop surface of the further tubular body, and the creation in the first portion and second portion in different materials. So that the peculiar assembly shape, which has ease and speed of assembly, is also particularly resistant despite the tensile stresses to which the portion of the body 300 is subjected between the surface 304 and the end of the body 300 itself distal from the motor.

[0174] The operation of the proportional volumetric dosing unit 10 occurs according to the following methods.

[0175] When the first liquid is supplied to the motor through the inlet conduit, the piston is at a PMI thereof and is pushed by the first liquid towards a PMS thereof. In fact, in this position the inner valve of the piston is closed and the outer valve is open, and the first liquid exerts a pressure on part of the first face of the cylindrical body of the piston, which translates towards the PMS.

[0176] The movement towards the upper dead centre of the piston also draws rod 220 therewith, the relief element of which is kept in abutment against the upper abutment element of the guide of the piston.

[0177] The ascent movement of the rod 220 continues until the rod meets an abutment stroke end placed in the lower portion of the cover of the motor body.

[0178] At this point, the rod stops but the piston continues its stroke upwards for a short stretch as said piston can continue to slide upwards thanks to the through hole in which the rod slides.

[0179] Since the springs 200 are fixed on one side to the pin on the rod, and on the other side to the hinge, they are placed in traction and are inclined gradually downwards assuming a greater inclination than that of the connecting rods.

[0180] At that point the spring mechanism is triggered and the connecting rods are brought from the position in which they were in contact with the upper surface of the hole of the slot to a position in which they come into contact with the lower surface of the hole of the slot.

[0181] Thus the connecting rods open the inner valve, because the shutter of the inner valve moves away from the valve seat and simultaneously, causing the rotation of the rocker, close the outer valve.

[0182] Therefore, in the first place the thrust of the first liquid on the first face of the first cylindrical body 60 of the piston fails, and at the same time the first chamber also fills with the first liquid which passes through the open inner valve.

[0183] The piston therefore starts to descend towards the bottom dead centre until the rod comes into contact with the shank.

[0184] The movement towards the lower dead centre of the piston is also transmitted to the pump piston and the friction gasket reaches the open position of the openings so as to let the second liquid flow through.

[0185] At this point, the rod stops but the piston continues its descent for a short stretch as said piston can still slide with respect to the rod making use of the through hole.

[0186] The springs 200 are again placed in traction and are inclined, this time upwards, gradually assuming a greater inclination than that of the connecting rods.

[0187] At that point the spring mechanism is triggered again and the connecting rods are snapped from the position in which they were in contact with the lower surface of the slot to a position in which they come into contact with the upper surface of the slot.

[0188] They thus close the inner valve and simultaneously open the outer valve and the cycle starts again with the methods previously seen.

[0189] The movement towards upper dead centre of the motor piston is also transmitted to the pump piston, and the friction gasket moves to the closed position of the openings so as to push the second liquid towards the motor, particularly into the internal volume of the sleeve.

[0190] It should be noted that in the present discussion, rigid is intended as not noticeably deformable, i.e., appreciably deformable, under the normal working loads to which it is subjected. In other words, a rigid element does not carry out its function for which it was designed by also means of its own deformation.

[0191] Elastic element is instead intended as a body which is shaped so as to deform (only) elastically under the normal working loads to which it is subjected and therefore also (or only) carries out its function by means of its own elastic deformation. It should be noted that the definition 'elastic deformation' is to be understood as opposed to 'plastic deformation', where plastic deformation is the type of deformation in which the body subjected to deformation does not return to its original shape once it is no longer subjected to the deforming force.

[0192] In the present case a gasket is elastically deformed to adhere to given surfaces so as to generate a possibly hermetic seal.

[0193] Further, it should be noted that a monolithic body is intended as a body obtained from the solidification of a single casting, or injection, of (a single) material into a mould and eventually by a subsequent processing of said solidified body by means of the removal of material.

[0194] The terms 'to size' and 'reduced clearance' means that the elements with such a coupling can slide with respect to each other without any particular effort, i.e., with low friction, and without tilting appreciably with respect to the sliding direction. If, on the other hand, there is a large amount of clearance, the elements could tilt significantly in the feed direction and become stuck.

[0195] The invention thus conceived is susceptible to many modifications and variants, all falling within the same inventive concept. Moreover, all details may be replaced by other technically equivalent elements.

[0196] In practice, the materials used, as well as the contingent shapes and sizes, may be whatever according to the requirements without for this reason departing from the scope of protection of the following claims.

Claims

CLAIMS1. Proportional volumetric dosing unit (1 ), comprising: a motor (20) provided with an output shaft (31 ) movable along a respective sliding axis (X) between an upper dead centre position and a lower dead centre position, and a pump (25) fixed to the motor and adapted to be driven by said output shaft, said pump comprising:- a pumping piston (362) fixed to an end of the output shaft,- a tubular body (300) coaxial with the output shaft and provided with an inner tubular surface (305), which comprises at least one contact section on which the pump piston slides in contact, wherein said tubular body (300), at least at the contact section, comprises a first annular portion (301 ) at least partially lined by a second annular portion (302), which second annular portion provides the inner tubular surface (305) at the contact section, characterised by the fact that the second annular portion is made of a polymeric material which is chemically more resistant to corrosion, against a predetermined corrosive agent, with respect to a polymeric or composite material of which the first annular portion is made, and / or that the first annular portion is made of a polymeric or composite material which is mechanically more resistant than a polymeric material of which the second annular portion is made.

2. Proportional volumetric dosing unit (1 ) according to claim 1 , wherein the first annular portion (301 ) and the second annular portion (302) are co-moulded.

3. Proportional volumetric dosing unit (1 ) according to any one of the preceding claims, wherein the material of the first annular portion (301 ) is provided with an elastic modulus greater than 1000 MPa.

4. Proportional volumetric dosing unit (1 ) according to any one of the preceding claims, wherein the material of which the second portion (302) is made is one among polyethylene, low-density polyethylene, high-density polyethylene, polypropylene, polyvinylidene fluoride and polyether ether ketone.

5. Proportional volumetric dosing unit (1 ) according to any one of the preceding claims, wherein the material of which the first portion (301 ) is made is one among polyethylene,high-density polyethylene, fibre-reinforced polyethylene (glass fibres or carbon fibres, for example between 20% and 60%), fibre-reinforced low- or high-density polyethylene (glass fibres or carbon fibres, for example between 20% and 60%), polyvinylidene fluoride, fibre-reinforced polyvinylidene fluoride (glass or carbon fibres, e.g., between 20% and 60%), polyether ether ketone, fibre-reinforced polyether ether ketone (glass or carbon fibres, e.g., between 20% and 60%), polypropylene, fibre-reinforced polypropylene (glass or carbon fibres, e.g., between 20% and 60%), polyamide 12, fibre-reinforced polyamide 12 (glass or carbon fibres, e.g., between 20% and 60%).

6. Proportional volumetric dosing unit (1 ) according to any of the preceding claims, wherein the material of the first portion (301 ): is one among high-density polyethylene, fibre-reinforced polyethylene (glass or carbon fibres, e.g., between 20% and 60%), fibre-reinforced low- or high-density polyethylene (glass or carbon fibres, e.g., between 20% and 60%), polyvinylidene fluoride, fibre-rein- forced polyvinylidene fluoride (glass or carbon fibres, e.g., between 20% and 60%), polyether ether ketone, fibre-reinforced polyether ether ketone (glass or carbon fibres, e.g., between 20% and 60%), polypropylene, fibre-reinforced polypropylene (glass or carbon fibres, e.g., between 20% and 60%), polyamide 12, fibre-reinforced polyamide 12 (glass or carbon fibres, e.g., between 20% and 60%) when the material of the second portion (302) is polyethylene, it is one among polyethylene, high-density polyethylene, fibre-reinforced polyethylene (glass or carbon fibres, e.g., between 20% and 60%), fibre-reinforced low- or high-density polyethylene (glass or carbon fibres, e.g., between 20% and 60%), polyvinylidene fluoride, fibre-reinforced polyvinylidene fluoride (glass or carbon fibres, e.g., between 20% and 60%), polyether ether ketone, fibre-reinforced polyether ether ketone (glass or carbon fibres, e.g., between 20% and 60%), polypropylene, fibre-reinforced polypropylene (glass or carbon fibres, e.g., between 20% and 60%), polyamide 12, fibre-reinforced polyamide 12 (glass or carbon fibres, e.g., between 20% and 60%), when the material of the second portion (302) is low-density polyethylene, it is one among fibre-reinforced polyethylene (glass or carbon fibres, e.g., between 20% and 60%), fibre-reinforced low- or high-density polyethylene (glass or carbon fibres, e.g., between 20% and 60%), polyvinylidene fluoride, fibre-reinforced polyvinylidene fluoride(glass or carbon fibres, e.g., between 20% and 60%), polyether ether ketone, fibre-reinforced polyether ether ketone (glass or carbon fibres, e.g., between 20% and 60%), polypropylene, fibre-reinforced polypropylene (glass or carbon fibres, e.g., between 20% and 60%), polyamide 12, fibre-reinforced polyamide 12 (glass or carbon fibres, e.g., between 20% and 60%), when the material of the second portion (302) is high-density polyethylene, it is one among fibre-reinforced polyethylene (glass or carbon fibres, e.g., between 20% and 60%), fibre-reinforced low- or high-density polyethylene (glass or carbon fibres, e.g., between 20% and 60%), fibre-reinforced polyvinylidene fluoride (glass or carbon fibres, e.g., between 20% and 60%), polyether ether ketone, fibre-reinforced polyether ether ketone (glass or carbon fibres, e.g., between 20% and 60%), fibre-reinforced polypropylene (glass or carbon fibres, e.g., between 20% and 60%), polyamide 12, fibre-reinforced polyamide 12 (glass or carbon fibres, e.g., between 20% and 60%), when the material of the second portion (302) is polypropylene, it is one among fibre-reinforced polyethylene (glass or carbon fibres, e.g., between 20% and 60%), fibre-reinforced high-density polyethylene (glass or carbon fibres, e.g., between 20% and 60%), fibre-reinforced polyvinylidene fluoride (glass or carbon fibres, e.g., between 20% and 60%), polyether ether ketone, fibre-reinforced polyether ether ketone (glass or carbon fibres, e.g., between 20% and 60%), fibre-reinforced polypropylene (glass or carbon fibres, e.g., between 20% and 60%), fibre-reinforced polyamide 12 (glass or carbon fibres, e.g., between 20% and 60%), when the material of the second portion (302) is polyvinylidene fluoride, it is one among fibre-reinforced high-density polyethylene (glass or carbon fibres, e.g., between 20% and 60%), fibre-reinforced polyvinylidene fluoride (glass or carbon fibres, e.g., between 20% and 60%), fibre-reinforced polyether ether ketone (glass or carbon fibres, e.g., between 20% and 60%), fibre-reinforced polypropylene (glass or carbon fibres, e.g., between 20% and 60%), fibre-reinforced polyamide 12 (glass or carbon fibres, e.g., between 20% and 60%), when the material of the second portion (302) is polyether ether ketone.

7. Proportional volumetric dosing unit (1 ) according to any one of the preceding claims, wherein when the predetermined corrosive agent is at least one among acetic acid, citricacid, formaldehyde, lactic acid, pure methanol phosphoric acid, potassium hydroxide sodium carbonate, ethanol, ethylene glycol, glycerol and caustic soda, the material of which the second portion (302) is made is one among polyethylene, low-density polyethylene, high-density polyethylene, polypropylene, polyvinylidene fluoride and polyether ether ketone, wherein when the predetermined corrosive agent is formic acid, the material of which the second portion (302) is made is one among polyethylene, low-density polyethylene, high- density polyethylene, polypropylene, polyvinylidene fluoride, wherein when the predetermined corrosive agent is one among hydrogen peroxide and hydrochloric acid, the material of which the second portion (302) is made is one among polyethylene, low-density polyethylene, high-density polyethylene, polyvinylidene fluoride and polyether ether ketone, wherein when the predetermined corrosive agent is paracetic acid, the material of which the second portion (302) is made is polyvinylidene fluoride, wherein when the predetermined corrosive agent is one among sulphuric acid at a percentage greater than 80% and bleach, the material of which the second portion (302) is made is one among polyethylene, low-density polyethylene, high-density polyethylene, and polyvinylidene fluoride, wherein when the predetermined corrosive agent is one among benzyl alcohol, gas oil and perchloric acid, the material of which the second portion (302) is made is one among polypropylene, polyvinylidene fluoride and polyether ether ketone, wherein when the predetermined corrosive agent is butyric acid, the material of which the second portion (302) is made is one among polyvinylidene fluoride and polyether ether ketone, wherein when the predetermined corrosive agent is chloric acid, the material of which the second portion (302) is made is polyvinylidene fluoride, wherein when the predetermined corrosive agent is sulphuric anhydride, the material of which the second portion (302) is made is polyether ether ketone.

8. Proportional volumetric dosing unit (1 ) according to any one of the preceding claims, wherein the material of the first annular portion (301 ) is a composite material containing reinforcing fibres and the material of the second annular portion (302) does not comprise reinforcing fibres.

9. Proportional volumetric dosing unit (1 ) according to the preceding claim, wherein the second portion (302) is made of polyethylene and the first portion (301 ) is made of a composite material comprising polypropylene and reinforcing fibres.

10. Proportional volumetric dosing unit (1 ) according to any one of the preceding claims, comprising a tubular sleeve (330) provided with a first longitudinal end fixed to the motor (20) and an opposite second longitudinal end, and wherein the tubular body (300) of the pump comprises a first longitudinal end inserted into the tubular sleeve and proximal to the motor, an opposite second longitudinal end opposite the first longitudinal end at which a threaded portion (303) is made, and a stop surface (304) transverse to the sliding axis (X) and facing the second longitudinal end of the tubular body (300), said volumetric dosing unit further comprising a nut mechanism configured to vary the relative position of the tubular body with respect to the motor along the sliding axis, wherein said ring nut mechanism comprises a ring nut (430) provided with an inner thread and a tubular containment body (425) in which an outer thread (428) which meshes with the inner thread of the ring nut, a first abutment surface (426) adapted to be contacted by the stop surface (304) of the tubular body and a second abutment surface (427) are made, said volumetric dosing unit further comprising a further tubular body (400), which comprises a thread (401 ) adapted to screw onto the thread of the tubular body and a stop surface (402) adapted to lie on the second abutment surface (426), so that by screwing said threads (303,401 ), a portion of the tubular containment body (425) between the first abutment surface and the second abutment surface is clamped between the stop surface of the tubular body and the stop surface of the further tubular body.

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