Proportional metering pump and associated metering method

Abstract

The present invention relates to a method and a proportional metering pump for introducing a liquid additive into a main liquid stream flowing in a conduit, the pump being of the reciprocating differential piston type for withdrawing the additive from a container and metering it, the pump including a first inlet (E) for receiving a main liquid flow which drives the pump, a second inlet for withdrawing the additive and an outlet(S) for the mixture of additive and liquid, characterised in that the method and the pump use a device (3) for controlling the pressure losses of the pump, which is adjustable as a function of the flow at the inlet of the pump.

Description

TECHNICAL FIELD

[0001] The present invention relates to a method and a proportional metering pump for introducing a liquid additive into a main liquid stream flowing in a conduit, the pump being of the reciprocating differential piston type for withdrawing the additive from a container and metering it, the pump including a first inlet for receiving a main liquid flow which drives a hydraulic machine, a second inlet for withdrawing the additive and an outlet for the mixture of additive and liquid.BACKGROUND

[0002] In a metering pump, the differential piston performs a reciprocating movement and causes a plunger piston to withdraw the additive to be metered during a rise stroke and to inject this additive into the main liquid or driving liquid during a fall stroke. The pressure loss between the first inlet of the pump and the outlet is variable according to the operating phases of the pump.

[0003] For a good energy efficiency of the pump, it is advantageous, as proposed in the prior art documents EP 1773479 and EP 1151196, to use a venturi to create a pressure loss between its inlet and the neck, substantially equal to the pressure loss in the pump.

[0004] However, when the dosages of the liquid additive are large, in particular greater than 2% in the diverted flow to obtain 0.2% in the total flow, or 10% in the diverted flow to obtain 1% in the total flow, the difference in pressure loss between the rise phase of the differential piston and the fall phase becomes large.

[0005] This phenomenon is all the more present when the pressure in the metering system is large and the metering of the by-pass metering device is large, since the pressure loss during the rise has to compensate for the pressure applied to the metering piston which serves to meter the additive.

[0006] This results in a reduction in the precision, or in it being impossible to create the pressure loss necessary for the operation of the metering pump over a large flow range, typically by a ratio of 6 to 10 between the minimum and the maximum of the main flow.

[0007] For this reason, document WO2014 / 111770 A1 proposes to introduce a means that is sensitive to the pressure loss in the pump and that is capable of controlling the constriction means of the neck of the venturi to reduce the passage cross-section when the pressure loss in the pump increases, and to increase the passage cross-section when the pressure loss in the pump decreases.

[0008] For relatively low dosages of additive, in particular less than 1% of additive in the main liquid, in particular when placing in by-pass by a factor of 10 metering pumps metering up to 0.3% in the diverted flow to obtain 0.03% in the total flow, metering devices of the type defined above are satisfactory for large flows, and in particular greater than 6000 l / h.

[0009] It is particularly for high flows that the differences in pressure loss between rise and fall of the differential piston are not too large, since the pressure loss between the neck of the venturi and its inlet is not too different from the pressure loss of the pump during the rise and fall of the differential piston.

[0010] On the other hand, for low flows, the pressure differences that act on the means for regulating the pressure losses are small since the Venturi effect depends on the square of the flow speed. As a result, the closing-off means no longer has sufficient lift and tends to close off the neck of the venturi.

[0011] This results in greater diversion toward the hydraulic machine and consequently an over-metering.

[0012] For this reason, the aim of the invention is, above all, to propose a proportional metering pump that no longer or to a lesser degree has the disadvantages mentioned above and that makes it possible to optimize the operation of the pump, in particular in the case where the flows of the main liquid are low.SUMMARY

[0013] The invention relates in particular to a pump for proportional metering of an additive into a main liquid, provided with an inlet and an outlet, and comprising

[0014] a metering mechanism equipped with means for drawing in an additive stored in a reservoir,

[0015] a hydraulic machine provided with an inlet and an outlet connected respectively to the inlet and to the outlet of the pump, and containing a member capable of performing a reciprocating movement, the supplying of the pump with main liquid at the inlet triggering the reciprocating movement of the member, this movement alternately causing an aspiration of the additive into the hydraulic machine with opening of the aspiration means and then an expulsion of the mixture constituted by the main liquid and the additive, at the outlet of the hydraulic machine with closure of the aspiration means,

[0016] a device for controlling the pressure losses of the pump, as a function of the flow at the inlet of the pump,

[0017] said device being provided with a first venturi connected, in parallel with the hydraulic machine, to the inlet and to the outlet of the pump,

[0018] said device further including a means for closing off the neck of the first venturi mounted slidingly in said neck to control the passage cross-section thereof, means that are sensitive to the pressure loss in the pump and that are capable of controlling the sliding of the closing-off means to reduce the passage cross-section when the pressure loss in the pump increases and / or the flow decreases, and to increase the passage cross-section when the pressure loss in the pump decreases and / or the flow increases,

[0019] characterized in that the closing-off means extends inside the neck while defining a first surface referred to as “downstream”, substantially perpendicular to the geometric axis of the first venturi, a second surface referred to as “upstream” and a third surface connecting the first and second surfaces.

[0020] Optional, complementary or substitute features of the invention are set out below.

[0021] Advantageously, the third surface connects the first and second surfaces in a beveled manner so as to form with said geometric axis an acute angle, the vertex of which is at the free end of the first surface.

[0022] According to one aspect of the invention, the means sensitive to the pressure loss in the pump include a second venturi installed on a first pipe connecting the inlet of the pump to the inlet of the hydraulic machine, and comparison means between the pressure at the neck of the first venturi, and the pressure at the neck of the second venturi.

[0023] According to another aspect of the invention, the pressure comparison means include a first chamber and a second chamber, the first chamber being in fluid communication with the neck of the first venturi, and separated in a sealed manner from the second chamber by movable separation means, said second chamber being in fluid communication with the neck of the second venturi, the closing-off means being integral with said movable separation means, so that their deformation causes said closing-off means to slide over a stroke making it possible to enlarge or decrease the passage cross-section of the neck of the first venturi.

[0024] Preferably, the movable separation means comprise a membrane.

[0025] According to an embodiment of the invention, the closing-off means comprise a base from which the first and second surfaces extend.

[0026] According to another embodiment of the invention, the first and second surfaces are planar so as to form a blade.

[0027] Advantageously, reinforcing means are provided on at least one of the first and second surfaces.

[0028] Even more advantageously, reinforcing means comprise a rib extending over all or part of the length of the second surface.

[0029] According to another embodiment of the invention, all of the first, second and third surfaces form a bevelled cylinder.

[0030] According to another embodiment of the invention, all of the first, second and third surfaces form a bevelled half-tube.

[0031] Preferably, the acute angle is between 25 and 75 degrees.

[0032] Preferably, at least one of the surfaces has one or more recesses.

[0033] Preferably, the first surface has one or more recesses.

[0034] Preferably, the first and the second venturi extend substantially parallel to one another, preferably in a direction substantially perpendicular to the longitudinal axis of the hydraulic machine.

[0035] The invention relates also to a method for metering an additive into a main liquid flow using a proportional metering pump in accordance with an embodiment of the invention.BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Other advantages and features of the invention will become apparent upon reading the detailed description of non-limiting implementations and embodiments, which are by no means limiting, and the following accompanying drawings:

[0037] FIG. 1 This figure depicts a schematic view of a proportional metering pump in accordance with an embodiment of the invention.

[0038] FIG. 2 This figure depicts a perspective longitudinal section of a hydraulic machine used in an embodiment of the invention.

[0039] FIG. 3 This figure depicts a cross-section of a proportional metering pump in accordance with another embodiment of the invention.

[0040] FIG. 4 This figure depicts a schematic detail of a prior art pump.

[0041] FIG. 5 This figure depicts another schematic detail of a prior art pump.

[0042] FIG. 6 This figure depicts a schematic detail of a pump in accordance with a certain embodiment of the invention.

[0043] FIG. 7 This figure depicts a schematic detail of a pump in accordance with another embodiment of the invention.

[0044] FIG. 8 and FIG. 9 These figures respectively depict a side and perspective view of a detail of a proportional metering pump in accordance with a certain embodiment of the invention.

[0045] FIG. 10 and FIG. 11 These figures respectively depict a side and perspective view of a detail of a proportional metering pump in accordance with another embodiment of the invention.DETAILED DESCRIPTION

[0046] Referring to FIG. 1 and then to FIG. 2, an example of a hydraulic machine 1 of the type that can be used in the proportional metering pump according to the invention can be seen.

[0047] This example is by no means limiting insofar as other machines operating on the principle of a supplying of the pump with main liquid at the inlet triggering the reciprocating movement of a member alternately causing an aspiration of additive, could also be suitable.

[0048] The hydraulic machine 1 comprises a reciprocating differential hydraulic piston 16 contained in a casing 190 consisting of a cylindrical body extending along an axis (z) and surmounted by a cover 191 assembled onto the body in a removable manner, in particular by screwing. The differential piston 16 is arranged in the casing 190 to slide in a reciprocating movement along the axis (z). The piston 16 comprises, in the upper part, an upper crown 160 of large section, the periphery of which bears in a sealed manner against the inner wall of the casing. The piston barrel, coaxial with the casing and of smaller diameter than the upper crown 160, is integral with this crown and extends downwards. The lower part of the piston barrel slides in a sealed manner in a cylindrical housing 17 coaxial with the casing. The barrel is closed in the lower part by a lower base 161. The piston 16 and the cylindrical housing 17 compartmentalize the interior of the casing according to a so-called “mixture” chamber 14 delimited by the cylindrical housing 17 and the lower base of the piston 161, a so-called “upper” chamber 13 delimited by the upper crown 16 and the cover 191 of the casing, and a so-called “lower” chamber 12, of substantially annular shape, delimited by the part beneath the upper crown 160, by the casing and by the cylindrical housing 17.

[0049] The hydraulic machine comprises a first inlet pipe 10 connecting the lower chamber 12 to the exterior, and a second outlet pipe 11 connecting the mixing chamber 14 to the exterior. A cylindrical sleeve 15 coaxial with the casing extends from the mixing chamber downwards to allow the connection of the mixing chamber to a suction device 2. This suction device is actuated by the hydraulic machine by means of a rod 162 of the piston, itself connected by a nozzle to a means for pumping the additive (not depicted in the figures). For more details concerning this type of device, reference can be made to documents EP0255791 and EP1151196.

[0050] Hydraulic switching means are provided for feeding and emptying the chambers 12, 13, 14 separated by the piston. These switching means are operated by the movements of the piston and include a connecting rod 180 acting on a distribution member capable of adopting two stable positions. More specifically, the distribution member comprises at least one valve holder 181 comprising at least one first, so-called “upper” valve 182 cooperating with a seat 163 formed in the upper crown of the piston, and at least one second, so-called “lower” valve 183 cooperating with a seat 164 formed in the lower base of the piston.

[0051] The hydraulic machine further includes triggering means comprising a pusher 185 capable of causing, at the end of the stroke of the piston, by coming to bear against a stop, a sudden change in the position of the switching means under the action of an elastic means 18, for the reversal of the stroke of the piston. The coming to bear against a stop (not depicted in the figures) is carried out in the vicinity of the cover 191 to allow the piston to change its upward stroke into a downward stroke. The coming to bear against a stop 184 is also carried out in the vicinity of the lower part of the casing to allow the piston to change its downward stroke into an upward stroke.

[0052] The connecting rod 180 is articulated at one end on a point fixed with respect to the piston 16, while the other end of the connecting rod can move in a vertical window of the valve holder 181 and come to bear against one of the two ends of this window, in one of the two stable positions of the distribution member. The elastic means 18 is integral, at each of its ends, with an articulation member received respectively in a housing provided on the connecting rod and on the pusher 185. Each housing is open in a direction substantially opposite to the direction of the force exerted by the elastic means 18 in the wall of the housing in question. This elastic means 18 can advantageously be constituted by a convex spring blade.

[0053] The inlet of the hydraulic machine for the main liquid is located at the first pipe 10, and the outlet for the mixture is located at the second pipe 11.

[0054] According to the cycle associated with this configuration, the pressurised main liquid, generally water, enters the lower chamber 12 via the pipe 10. The upper valves are closed while the lower valves are open, allowing the discharge of the liquid from the upper chamber 13 to the mixing chamber 14 and then the emptying of the mixture to the outlet via the pipe 11. Indeed, under the action of the pressure of the main liquid on the lower face of the upper crown of the piston, the latter begins an upward stroke, which tends to reduce the volume of the upper chamber and therefore to drive the contents thereof towards the mixing chamber, since the communication is open.

[0055] At the end of the upward stroke, the pusher 185 comes to bear against a stop connected to the cover 191, which causes, under the action of the elastic means 18, the tilting of the connecting rod 180 towards the other lower stable position, with movement of the valve holder towards the base of the piston. The lower valves close while the upper valves open. The pressurised liquid can pass from the lower chamber 12 to the upper chamber 13, whose communication with the mixing chamber 14 is now cut off, and the movement of the piston is reversed. This movement is reversed because of the pressure which the main liquid admitted into the upper chamber exerts on the upper face of the upper crown. At the end of the downward stroke, the pusher 185 by its lower end meets a stop 184 integral with the casing 190, which causes a further tilting of the connecting rod towards the raised position and a movement of the valve holder 181 causing the closure of the upper valves and the opening of the lower valves. The movement of the piston 16 is reversed again and the piston returns along an upward stroke.

[0056] At the same time, the reciprocating movement of the piston during the supplying of the hydraulic machine with liquid, makes it possible to alternately generate suction through the sleeve 15 into the mixing chamber 14 or else at the outlet 11 of the hydraulic machine. The sleeve 15 is connected to the suction device 2, also called metering mechanism 2 by means of a nozzle.

[0057] As depicted in FIG. 2, this metering mechanism 2, provided with a suction nozzle equipped with a suction valve, therefore communicates at one of its ends, by means of the sleeve 15, also called an access pipe, with a cavity inside the hydraulic machine and at the other of its ends with a reservoir of product which is to be metered.

[0058] The reciprocating movement of the piston 16 during the supplying of the hydraulic machine with main liquid, generates an aspiration of the additive which is injected into the mixing chamber. Generally, the suction device includes at least one suction valve which opens when the piston moves away from the sleeve (i.e. in an upward stroke) and then an expulsion at the outlet via the pipe 11 with closure of the first suction valve when the piston moves towards the sleeve (i.e. in a downward stroke).

[0059] As depicted in FIGS. 2 and 3, the proportional metering pump according to the invention also includes a device 3 for controlling the pressure losses of the pump, which is adjustable as a function of the flow at the inlet of the pump.

[0060] This device 3 is provided with a first venturi 30 connected, in parallel with the hydraulic machine, to the inlet E and to the outlet of the pump S.

[0061] A venturi means a tube including a converging section located upstream of a narrowing or neck, and a diverging section downstream of the neck. A narrowing or neck means a zone of the venturi, the axial extent of which can be relatively long, which has a reduced diameter relative to the inlet and outlet diameter. It is at the neck that a depression is formed with acceleration of the liquid.

[0062] The device 3 also includes a means 32 for closing off the neck 301 of the first venturi, which is mounted slidingly in said neck to control the passage cross-section thereof.

[0063] The device 3 also includes means 31, 33, 35, 36 that are sensitive to the pressure loss in the pump and that are capable of controlling the sliding of the closing-off means to reduce the passage cross-section when the pressure loss in the pump increases and / or the flow decreases, and to increase the passage cross-section when the pressure loss in the pump decreases and / or the flow increases.

[0064] According to a particular and advantageous embodiment depicted in FIGS. 1 and 3, the means sensitive to the pressure loss in the pump include a second venturi 31 installed on a first pipe 39 connecting the inlet E of the pump to the inlet of the hydraulic machine, and comparison means 33, 35, 36 between the pressure at the neck 301 of the first venturi 30, and the pressure at the neck 311 of the second venturi 31.

[0065] In this configuration, the first venturi, provided with a converging section 300, a neck 301 and a diverging section 302, is in fluid communication upstream of its neck 301 with the second venturi 31, by means of the first pipe 39.

[0066] The second venturi 31 is provided with a converging section 310, a neck 311 and a diverging section 312, and is connected to the inlet 10 of the hydraulic machine.

[0067] According to a particular and equally advantageous embodiment depicted in FIGS. 1 and 3, the pressure comparison means 33, 35, 36 include a first chamber 36 and a second chamber 35, the first chamber being in fluid communication with the neck 301 of the first venturi, and separated in a sealed manner from the second chamber 35 by movable separation means 33, said second chamber 35 being in fluid communication with the neck 311 of the second venturi.

[0068] The first chamber 36 is in fluid communication with the neck 301 of the first venturi by means, for example, of a conduit 360.

[0069] The second chamber 35 is in fluid communication with the neck 311 of the second venturi by means, for example, of a conduit 350.

[0070] The closing-off means 32 is integral with said movable separation means, so that their deformation causes said closing-off means to slide over a stroke making it possible to enlarge or decrease the passage cross-section of the neck of the first venturi.

[0071] The movable separation means 33 are advantageously a membrane.

[0072] The stroke for bringing the closing-off means 32 into abutment is defined by the distance between the closed-off position (when the means is pressed into the neck of the first venturi) and the position in abutment of the closing-off means against a shoulder 380 of the housing 38 of the device 3, this position in abutment being obtained when the pressure in the chamber 36 presses the membrane 33 away from the neck of the first venturi.

[0073] According to the principle of the invention and as depicted in FIGS. 3, 8 to 11, the closing-off means 32 extends inside the neck 301 of the first venturi while defining a first surface 322 referred to as “downstream” and delimited by its free end 320, said first surface being substantially perpendicular to the geometric axis (y) of the first venturi. The closing-off means 32 extends inside the neck 301 of the first venturi while also defining a second surface 321 referred to as “upstream” and a third surface 323 connecting the first and second surfaces.

[0074] “Substantially perpendicular” means the fact that the first surface forms an angle with the geometric axis (y) of the first venturi, of the order of 90 degrees with a deviation of up to plus or minus 10%, but generally between plus or minus 0 and 5%.

[0075] Thus, the portion of the closing-off means intended to adjust the constriction of the neck of the first venturi is a volume delimited by:

[0076] the downstream surface 322, i.e. the surface in contact with the liquid present in the neck downstream of the closing-off means, taking account of the direction of circulation of the liquid.

[0077] This downstream surface 322 is vertical and extends along the axis (z) of the hydraulic machine, when the first venturi extends along its geometric axis (y) in a horizontal plane.

[0078] the upstream surface 321, i.e. the surface in contact with the liquid present in the neck upstream of the closing-off means, taking account of the direction of circulation of the liquid.

[0079] and the connecting surface 323 which depicts the zone where the constriction occurs.

[0080] As depicted in FIGS. 4 to 7, it is understood that the verticality of the downstream surface 322 makes it possible to limit the lifting surface of the closing-off means downstream of the constriction zone.

[0081] This makes it possible to avoid the depression of the closing-off means due to the pressure P322 made lower than the pressure P321 because of the pressure loss generated by the constriction.

[0082] This depression would indeed be detrimental since it would lead to an over-metering of the additive.

[0083] Advantageously, the third surface 323 connects the first and second surfaces in a beveled manner so as to form with said geometric axis an acute angle A, the vertex of which is at the free end 320 of the first surface. This angle is therefore defined between the horizontal plane passing through the geometric axis (y) of the first venturi and the bevel plane in which the third surface 323 extends.

[0084] This connecting surface, which connects the first surface to the second surface, is inclined with respect to the geometric axis (y) of the first venturi, so that it forms a bevel pointing towards the end 320 of the first surface referred to as “downstream” at an acute angle A. This angle is defined between the horizontal plane passing through the geometric axis (y) of the first venturi and the plane in which the third surface 323 extends.

[0085] It is therefore understood that the bevel formed by the connecting surface 323 makes it possible to reduce the length of the constriction zone.

[0086] This makes it possible to contain the Venturi effect at the free end 320 of the downstream surface.

[0087] Since the passage cross-section is reduced at the free end 320 of the downstream surface with respect to the neck, the speed increases and the pressure decreases. This reduction in pressure must be as local as possible in order not to unbalance the closing-off means and thus increase the over-metering at low flow.

[0088] According to an embodiment, the closing-off means comprises a base 325 from which the first and second surfaces extend.

[0089] This base can accommodate, for example, a threaded end to allow the fixing of the closing-off means to the membrane 33.

[0090] The assembly of the base and the membrane can also be achieved by overmoulding.

[0091] According to a first alternative depicted in FIGS. 8 and 9, the first 322 and second 321 surfaces are planar so as to form a blade.

[0092] The blade can be beveled or not, in the sense that the third surface 323 can be substantially parallel to the geometric axis of the first venturi or else connect the first and second surfaces in a beveled manner so as to form with said geometric axis an acute angle A, the vertex of which is at the free end 320 of the first surface.

[0093] In order to stiffen the blade, reinforcing means are advantageously provided on at least one of the first and second surfaces.

[0094] These reinforcing means can comprise or consist of a rib 326 extending over all or part of the length of the second surface.

[0095] According to a second alternative, all of the first, second and third surfaces together form a bevelled cylinder.

[0096] According to a third alternative depicted in FIGS. 10 and 11, all of the first, second and third surfaces form a bevelled half-tube, the convexity of which is oriented downstream. This bevelled half-tube is notched at the base 325, so that the restriction is as sharp as possible in order to reduce the length of the restriction (in the direction of flow).

[0097] Preferably, the acute angle a is between 25 and 75 degrees.

[0098] So as to limit the turbulence and cavitation phenomena, at least one of the first, second or third surfaces has one or more recesses 327.

[0099] Preferably, it is the first surface that has one or more recesses 327.

[0100] In summary, the design of the closing-off means, and more generally of the device for controlling the pressure losses according to the invention, makes it possible to divide by 10 the front surface of the closing-off means subjected to pressures lower than the upstream pressure. This makes it possible to reduce very strongly the parasitic forces on the closing-off means, which can then be controlled by the membrane in a much more reactive manner, thus improving the precision of the division at low flow.

[0101] In terms of manufacturing, the components of the device 3 can be produced by plastic moulding and fitted in a compact manner in a housing 38.

[0102] The sealing of the device is ensured by a set of seals 37.

[0103] Advantageously, the first and second venturi extend substantially parallel to one another, thus allowing a good compactness of the device 3.

[0104] Even more advantageously, the first and second venturi extend substantially parallel to one another in the direction (y) perpendicular to the longitudinal axis (z) of the hydraulic machine.

[0105] The method for proportional metering of an additive into a main liquid flow using a pump in accordance with the invention will now be described.

[0106] When the pump is at rest, i.e. when it is not in operation, the closing-off means 32 closes off the neck 301 of the venturi 30, so that the passage cross-section s1 of the neck 301 is less than 5 mm2 , or even zero.

[0107] When one begins to supply the hydraulic machine with main liquid, the main liquid stream arrives at the inlet E of the pump and does not flow or flows only slightly through the neck 301 of the first venturi.

[0108] The main liquid, which flows mainly through the second venturi 31, operates the hydraulic machine 1 by actuating the differential piston 16 with the aid of almost all of the main stream derived by the second venturi 31 and the first pipe 39.

[0109] The metering mechanism 2 driven by the reciprocating movements of the differential piston 16 takes doses of additive from the container and the metered mixture is injected downstream of the neck of the venturi 302 through the conduit 11 in the direction of the outlet S of the pump.

[0110] When the flow of the main liquid arriving at the inlet E of the pump increases, the pressure in the chamber 35 decreases and deforms the membrane 33 which rises and reduces the volume of the chamber 35.

[0111] This causes the translation of the closing-off means 32. The latter no longer closes off the neck 301 of the venturi 30 and the main liquid can then flow through the neck 301 of the first venturi.

[0112] The main liquid can then flow through the conduit 360.

[0113] At the neck 301 of the venturi 30, the flow speed of the fluid increases and its static pressure decreases.

[0114] At the neck 311 of the venturi 31, the flow speed of the fluid decreases and its static pressure increases.

[0115] When the pump is supplied with a determined flow at the inlet E, the differential piston 16 operates with the aid of a fraction of the main stream derived by the second venturi 31 and the first pipe 39.

[0116] The metering mechanism 2 driven by the reciprocating movements of the differential piston 16 takes doses of additive from the container and the metered mixture is injected downstream of the neck of the venturi 302 through the conduit 11 in the direction of the outlet S of the pump.

[0117] During the rise of the differential piston 16 and of the plunger piston of the metering mechanism 2, the pressure loss between the inlet 10 and the outlet 11 of the hydraulic machine is greater than at the fall.

[0118] The increase in the pressure loss when rising causes a decrease in the flow passing through the hydraulic machine, and therefore into the neck 311 of the venturi 31, which results in an increase in pressure at the neck 311.

[0119] The pressure at the neck 311 of the second venturi 31 therefore increases with respect to that prevailing at the neck of the first venturi 301.

[0120] In these conditions, the pressure in the chamber 35 becomes greater than that prevailing in the chamber 36 and the membrane 33 deforms to allow the closing-off means 32 to slide and enter further into the neck of the venturi 301. This results in an increase in the pressure loss between the inlet (converging section 300) and the outlet (diverging section 302) of the venturi 30, which makes it possible to equalize the pressure loss at the neck of the venturi 30 and the pressure loss between the inlet 10 and the outlet 11 of the hydraulic machine 1, or at least to minimize the difference between these pressure losses, which contributes to improving the metering accuracy.

[0121] During the fall of the differential piston 16 and of the plunger piston of the metering mechanism 2, the pressure loss between the inlet 10 and the outlet 11 of the hydraulic machine 1 is smaller, so that the closing-off means 32 rises into the chamber 36 and decreases the constriction of the neck of the venturi 301 and therefore the pressure loss between the inlet (converging section 300) and the outlet (diverging section 302) of the venturi 30.

[0122] Thus, for high flows, the closing-off means 32 and the membrane 33 will oscillate at the speed of the differential piston 16 to ensure a better match between the pressure loss at the neck of the venturi 30 and the total pressure loss in the hydraulic machine 1.

[0123] For small flows, the working range of the device is made reliable with a precise metering and a good operating efficiency, insofar as the Venturi effect is controlled at the neck 301 of the first venturi 30.

[0124] In other words, since at low flow the pressure losses are not negligible, the final metering would be much too high if all the driving liquid passed into the metering device due to the complete closing-off by the means 32, which would be due to a very marked Venturi effect.

[0125] In summary, the total pressure loss in the hydraulic machine 1 is compensated by the pressure loss at the neck of the venturi 30 with precision both for high flows and for low flows.

[0126] In conclusion, the design of the closing-off means, and more generally of the device for controlling the pressure losses according to the invention, makes it possible to divide by 10 the front surface of the closing-off means subjected to pressures lower than the upstream pressure. This makes it possible to reduce very strongly the parasitic forces on the closing-off means, which can then be controlled by the membrane in a much more reactive manner, thus improving the precision of the division at low flow.

[0127] The embodiments described below being by no means limiting, one may consider in particular variants of the invention comprising only a selection of features described, isolated from the other features described (even if this selection is isolated within a sentence comprising these other features), if this selection of features is sufficient to confer a technical advantage or to differentiate the invention with respect to the prior art. This selection comprises at least one feature, preferably functional without structural details, or with only a part of the structural details if this part is only sufficient to confer a technical advantage or to differentiate the invention with respect to the prior art.

[0128] It should be noted that the various features, forms, variants and embodiments of the invention may be associated with one another, in various combinations insofar as they are not incompatible or exclusive of one another.

Claims

1. A proportional metering pump for proportional metering of an additive into a main liquid, provided with an inlet and an outlet, and comprising;a metering mechanism configured to draw an additive stored in a reservoir;a hydraulic machine with an inlet and an outlet connected to both the inlet of the hydraulic machine and the outlet of the pump, wherein the hydraulic machine includes a reciprocating of performing a reciprocating movement, wherein the reciprocating movement is triggered by the main liquid being supplied to the inlet of the hydraulic machine and the reciprocating movement alternately causing an aspiration of the additive into the hydraulic machine and an expulsion of a mixture of the main liquid and the additive at the outlet of the hydraulic machine; anda device for controlling pressure losses of the pump, as a function of flow at the inlet of the pump, said device being provided with a first venturi connected, in parallel with the hydraulic machine, to the inlet of the pump and to the outlet of the pump, and said device including:a close-off mechanism for closing off a neck of the first venturi, the close-off mechanism being mounted slidingly in said neck to control a cross-sectional size of the neck, wherein a portion of the close-off mechanism that extends inside the neck defines: (a) a downstream first surface substantially perpendicular to a geometric axis of the first venturi, (b) an upstream second surface, and (c) a third surface connecting the downstream first surface and the upstream second surface in a beveled manner so as to form an acute angle with said geometric axis, a vertex of which is at a free end of the downstream first surface; anda control mechanism configured to control the close-off mechanism to reduce the cross-sectional size of the neck when pressure loss in the pump increases and / or the flow decreases, and to increase the cross-sectional size of the neck when the pressure loss in the pump decreases and / or the flow increases.

2. The proportional metering pump according to claim 1, characterised in that the control mechanism includes:a second venturi installed on a first pipe connecting the inlet of the pump to the inlet of the hydraulic machine, wherein a second neck of the second venturi is connected the neck of the first venturi so that pressure at the neck can be compared with pressure in the second neck of the second venturi.

3. The proportional metering pump according to claim 2, characterised in that a connection between the neck and the second neck includes:a first chamber in fluid communication with the neck of the first venturi; anda second chamber in fluid communication with the second neck of the second venturi, where the first chamber is separated in a sealed manner from the second chamber by movable separation element, and wherein the close-off mechanism is integral with said movable separation element, so that deformation of the movable separation element causes said close-off mechanism to enlarge or decrease the cross-sectional size of the neck of the first venturi.

4. The proportional metering pump according to claim 3, characterised in that the movable separation element comprises a membrane.

5. The proportional metering pump according to claim 1, characterised in that the close-off mechanism comprises a base from which the downstream first surface and the upstream second surface extend.

6. The proportional metering pump according to claim 1, characterised in that the downstream first surface and the upstream second surface are planar so as to form a blade.

7. The proportional metering pump according to claim 1, wherein at least one of the downstream first surface and the upstream second surface is or includes reinforcement.

8. The proportional metering pump according to claim 7, characterised in that reinforcement comprise a rib extending over all or a part of a length of the upstream second surface.

9. The proportional metering pump according to claim 1, characterised in that the downstream first surface, the upstream second surface, and the third surface form a bevelled cylinder.

10. The proportional metering pump according to claim 1, characterised in that the downstream first surface, the upstream second surface, and the third surface form a bevelled half-tube.

11. The proportional metering pump according to claim 1, characterised in that the acute angle is between 25 and 75 degrees.

12. The proportional metering pump according to claim 1, characterised in that at least one of the downstream first surface, the upstream second surface, and the third surface has one or more recesses.

13. The proportional metering pump according to claim 12, characterised in that the downstream first surface has the one or more recesses.

14. The proportional metering pump according to claim 3, characterised in that the first venturi and the second venturi extend substantially parallel to one another.

15. (canceled)16. A method for metering an additive into a main liquid flow using a proportional metering pump that includes a hydraulic machine with an inlet and an outlet connected to both the inlet of the hydraulic machine and an outlet of the pump, wherein the hydraulic machine includes a reciprocating member capable of performing a reciprocating movement, the method comprising:drawing an additive stored in a reservoir with a metering mechanism;in response to main liquid being supplied to the inlet of the hydraulic machine, triggering the reciprocating movement of the reciprocating member to alternately cause an aspiration of the additive into the hydraulic machine and an expulsion of a mixture of the main liquid and the additive at the outlet of the hydraulic machine; andcontrolling pressure losses of the pump, as a function of flow at an inlet of the pump with a device that includes a first venturi connected, in parallel with the hydraulic machine, to the inlet of the pump and to the outlet of the pump, wherein the device includes a close-off mechanism for closing off a neck of the first venturi, the close-off mechanism being mounted slidingly in said neck to control a cross-sectional size of the neck, wherein a portion of the close-off mechanism that extends inside the neck defines: (a) a downstream first surface substantially perpendicular to a geometric axis of the first venturi, (b) an upstream second surface, and (c) a third surface connecting the downstream first surface and the upstream second surface in a beveled manner so as to form an acute angle with said geometric axis, a vertex of which is at a free end of the downstream first surface; andcontrolling the close-off mechanism to reduce the cross-sectional size of the neck when pressure loss in the pump increases and / or the flow decreases, and to increase the cross-sectional size of the neck when the pressure loss in the pump decreases and / or the flow increases.

17. The method of claim 16, wherein the controlling is effectuated by a control mechanism that includes a second venturi installed on a first pipe connecting the inlet of the pump to the inlet of the hydraulic machine, wherein a second neck of the second venturi is connected the neck of the first venturi, and the method further comprises:comparing pressure at the neck with pressure in the second neck of the second venturi.

18. The method of claim 16, wherein a connection between the neck and the second neck includes: (a) a first chamber in fluid communication with the neck of the first venturi; and(b) a second chamber in fluid communication with the second neck of the second venturi, where the first chamber is separated in a sealed manner from the second chamber by movable separation element, and wherein the close-off mechanism is integral with said movable separation element, and the method further comprises:causing said close-off mechanism to enlarge or decrease the cross-sectional size of the neck of the first venturi based on deformation of the movable separation element.

19. The method of claim 18, characterised in that the movable separation element comprises a membrane.

20. The method of claim 16, characterised in that the close-off mechanism comprises a base from which the downstream first surface and the upstream second surface extend.

21. The method of claim 16, characterised in that the downstream first surface and the upstream second surface are planar so as to form a blade.

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