METHOD AND PUMP FOR PROPORTIONAL DOSING WITH LOW FLOW

Description

[0001] The present invention relates to a method and a proportional dosing pump for introducing a liquid additive into a main liquid stream, flowing in a pipe, the pump being of the reciprocating differential piston type for drawing the additive from a container and dosing it, this pump having a first inlet to receive a main liquid flow which ensures the drive of the pump, a second inlet to draw the additive and an outlet for the mixture of additive and liquid.

[0002] Typically, and as described in document EP 3440353 B1, the differential piston performs a reciprocating motion and drives a plunger piston to draw the additive to be metered during an upward stroke and to inject this additive into the main fluid or engine fluid during a downward stroke. Another metering pump known in the prior art is disclosed by document FR 2 681 646 A1; however, the pump in this document does not include a positive displacement pump with a rotating shaft, and a motion converter designed to transform the reciprocating translational motion of the hydraulic machine into a rotary motion transmitted to the rotating shaft of the positive displacement pump.

[0003] However, when the objective is to obtain low dosages, i.e. less than 300 ppm, or even on the order of a few tens of ppm, the proportional dosing pump can no longer provide such a dosage.

[0004] Indeed, conventional suction devices do not allow for sizing that can extract a sufficiently small quantity of additive in each cycle.

[0005] The proportional dosing pump then provides a dosage much higher than what is required.

[0006] Therefore, the invention aims, above all, to propose a method and a proportional dosing pump which no longer present, or present to a lesser degree, the disadvantages mentioned previously and which allow the optimization of the operation of proportional dosing pumps, in particular in the case where the targeted dosages are low.

[0007] The invention is based in particular on replacing previous dosing mechanisms with positive displacement pumps, that is, pumps in which the fluid transfer occurs by means of a volume displacement with each cycle. The flow rate of a positive displacement pump is then proportional to the actuation speed of its moving parts and depends very little on the discharge pressure.

[0008] The invention is based, according to a preferred embodiment, on the replacement of previous dosing mechanisms by peristaltic type pumps, that is to say, pumps capable of drawing in and expelling a liquid when operating at low speed, i.e., at speeds of less than a few revolutions per hour.

[0009] The invention relates in particular to a proportional dosing pump comprising a hydraulic machine having an inlet and an outlet, the hydraulic machine extending along a longitudinal axis (x) and containing a component adapted to perform a reciprocating motion along this axis, the supply of the main fluid to the hydraulic machine at the inlet triggering a reciprocating translational motion of the component along the longitudinal axis (x), the proportional dosing pump comprising: a volumetric pump, having a rotation axis, an inlet intended to be made in fluid communication with an additive tank and an outlet in fluid communication with the outlet of the hydraulic machine, a motion converter intended to transform the reciprocating translational motion of the component into a rotational motion, said rotational motion being transmitted directly or indirectly to the rotation axis of the volumetric pump, so that the supply to the hydraulic machine drives the volumetric pump which thus supplies the outlet of the hydraulic machine with additive, the additive mixing with the main fluid at the outlet of the hydraulic machine. Optional features of the invention, complementary or alternative, are listed below

[0010] According to a preferred embodiment, the volumetric pump can be a peristaltic pump.

[0011] According to another preferred embodiment, the pump may further include a variator for adjusting the speed of the rotation from the motion converter.

[0012] According to an embodiment relating to the motion converter, the motion converter may include a rotor having at least one helical rail and an actuator, each extending longitudinally along the longitudinal axis (x), the actuator being linked at one of its ends with the hydraulic machine element and cooperating with the helical rail of the rotor, as well as an output linked in rotation with the rotor and preferably in the form of a pinion, the raising and then lowering of the element inducing the rotation of the rotor in the same direction.

[0013] According to a certain particularity of the aforementioned embodiment, the actuator may comprise a shaft connected to the hydraulic machine organ, a first axis mounted perpendicularly on the shaft of the actuator, the first axis being provided to slide at one end in a first straight rail arranged in the body of the motion converter, while the second axis is provided to slide at one end in a first helical rail arranged on the rotor.

[0014] According to another feature of the aforementioned embodiment, the actuator may include a shaft connected to the hydraulic machine component, a first axis and a second axis mounted perpendicularly on the actuator shaft, the first axis being provided to slide at a first end and a second end respectively in a first straight rail and a second straight rail arranged in the body of the motion converter, while the second axis is provided to slide at a first end and a second end respectively in a first helical rail and a second helical rail arranged on the rotor.

[0015] Advantageously, the shaft can be connected to the hydraulic machine component by means of a pivot joint.

[0016] According to an embodiment relating to the variator, the variator may include an output shaft, a toothed cone, the axis of revolution of which is inclined with respect to the output shaft, such that one of its profile edges extends parallel to the output shaft, a roller fixed in rotation to the output shaft and capable of translating along the output shaft, the output pinion of the converter engaging the toothed wheel of the cone, the toothed cone driving the roller in rotation by friction as well as the output shaft, itself driving the shaft of the volumetric pump.

[0017] According to a certain particularity of the aforementioned embodiment, the variator may further include means for adjusting the position of the roller on the output shaft of the variator, these means comprising a roller fixing support, further attached to a cable gland mounted on the rotor body and whose tightening / loosening on the rotor body allows the roller to move along the output shaft of the variator.

[0018] According to another feature of the aforementioned embodiment, the variator may include disengagement means allowing the surface of the cone to be moved away from the roller, so as to prevent the roller from being driven by adhesion.

[0019] Advantageously, the disengagement means may consist of a pull rod passing through a support attached to the body of the motion converter and anchored in the toothed cone, and a spring mounted compressed on said pull rod to press the cone against the roller, a pull on said pull rod further compressing the spring and allowing the cone to be moved away from the roller.

[0020] Advantageously, the proportional dosing pump can include an injection T supplied by the output of the hydraulic machine and by the output of the volumetric pump.

[0021] In this case, preferably, the injection T can be fitted with a first check valve and a second check valve intended respectively to prevent reflux towards the hydraulic machine and towards the volumetric pump.

[0022] The invention also relates to a proportional dosing method employing a proportional dosing pump according to the invention, and in which the following steps are carried out: The inlet of the volumetric pump is connected to a container filled with the additive to be dosed. The inlet of the hydraulic machine is connected to a source of main liquid. The variator is adjusted to adjust the rotation speed resulting from the motion converter, according to the expected dosage. The inlet of the hydraulic machine is supplied with main liquid at a predetermined flow rate, so that the supply to the hydraulic machine drives the volumetric pump which thus supplies the additive to the outlet of the hydraulic machine, or to the injection T if the pump outlet is equipped with an injection T, the additive mixing with the main liquid.

[0023] Other advantages and particularities of the invention will appear on reading the detailed description of implementations and embodiments which are in no way limiting, and the following appended drawings: [ Fig.1 This figure represents a schematic view of a hydraulic machine usable in the invention. Fig.2 This figure represents a schematic profile view of a proportional dosing pump according to the invention. Fig.3 This figure represents a detail of the converter of a proportional dosing pump according to one embodiment of the invention. Fig.4 This figure represents a detail of the variator of a proportional dosing pump according to an embodiment of the invention.

[0024] Referring to the [ Fig.1 ], we can see a hydraulic machine 1 of the type used in the proportional dosing pump according to the invention.

[0025] The hydraulic machine 1 comprises a reciprocating differential hydraulic piston 16 contained within a housing 190 consisting of a cylindrical body extending along an axis (x) and surmounted by a cover 191 assembled to the body in a removable manner, notably by screwing. The component, also called the differential piston 16, is arranged within the housing 190 to slide in reciprocating motion along the axis (x). The component 16 has, in its upper part, a large-section upper ring 160, the periphery of which bears in a sealed manner against the inner wall of the housing. The shaft of the differential piston, coaxial with the housing and of smaller diameter than the upper ring 160, is integral with this ring and extends downwards. The lower part of the piston shaft slides in a sealed manner within a cylindrical housing 17 coaxial with the housing. The shaft is closed at its lower part by a lower base 161.The differential piston 16 and the cylindrical housing 17 compartmentalize the interior of the casing according to a so-called "mixing" chamber 14 delimited by the cylindrical housing 17 and the lower base of the differential piston 161, a so-called "upper" chamber 13 delimited by the upper ring 160 and the cover 191 of the casing, and a so-called "lower" chamber 12, of substantially annular shape, delimited by the part below the upper ring 160, by the casing and by the cylindrical housing 17.

[0026] The hydraulic machine comprises a first pipe 10 connecting the lower chamber 12 to the outside, and a second pipe 11 connecting the mixing chamber 14 to the outside. A cylindrical sleeve 15 coaxial with the casing extends downwards from the mixing chamber to allow connection of the mixing chamber to an injection device 2. This injection device is actuated by the hydraulic machine by means of a piston rod 162, itself connected to an additive pumping means (not shown in the figures). For further details concerning this type of device, see documents EP0255791 and EP1151196.

[0027] Hydraulic switching means are provided for supplying and emptying the chambers 12, 13, and 14 separated by the piston. These switching means are controlled by the piston's movements and include a connecting rod 180 acting on a distribution element capable of assuming two stable positions. More specifically, the distribution element comprises at least one valve carrier 181 including at least one first valve, referred to as the "upper" valve 182, cooperating with a seat 163 formed in the upper ring of the piston, and at least one second valve, referred to as the "lower" valve 183, cooperating with a seat 164 formed in the lower base of the piston.

[0028] The hydraulic machine also includes triggering means comprising a pusher 185 designed to cause, at the end of the piston's stroke, by bearing against a stop, an abrupt change in the position of the switching means under the action of an elastic means 18, thus reversing the piston's stroke. The bearing against a stop (not shown in the figures) occurs near the cover 191 to allow the piston to change from an upward stroke to a downward stroke. Bearing against a stop 184 also occurs near the lower part of the casing to allow the piston to change from a downward stroke to an upward stroke.

[0029] The connecting rod 180 is articulated at one end to a fixed point relative to the piston 16, while the other end of the connecting rod can move within a vertical window of the valve carrier 181 and abut against one of the two ends of this window, in one of the two stable positions of the distribution element. The elastic means 18 is fixed, at each of its ends, to a pivoting member received respectively in a housing provided on the connecting rod and on the tappet 185. Each housing is open in a direction substantially opposite to the direction of the force exerted by the elastic means 18 on the wall of the housing in question. This elastic means 18 can advantageously be made of a convex leaf spring.

[0030] The hydraulic machine's inlet for the main fluid is located at the first pipe 10, and the outlet for the mixture is located at the second pipe 11.

[0031] According to the cycle associated with this configuration, the main pressurized liquid, generally water, enters the lower chamber 12 through the tube 10. The upper valves are closed while the lower valves are open, allowing the liquid to be pumped from the upper chamber 13 to the mixing chamber 14 and then the mixture to be discharged to the outlet via the tube 11. Indeed, under the action of the pressure of the main liquid on the lower face of the upper ring of the piston, the latter begins an upward stroke, which tends to decrease the volume of the upper chamber and therefore to expel its contents towards the mixing chamber, since the communication is open.

[0032] At the end of its upward stroke, the pusher 185 comes to rest against a stop attached to the cover 191. This, under the action of the spring blade, causes the connecting rod 180 to pivot to the other stable lower position, with the valve carrier moving towards the base of the piston. The lower valves close while the upper valves open. The pressurized fluid can then flow from the lower chamber 12 to the upper chamber 13, whose communication with the mixing chamber 14 is now severed, and the piston's movement is reversed. This movement is reversed due to the pressure exerted by the main fluid admitted into the upper chamber on the upper face of the upper ring.At the end of its downward stroke, the pusher 185, at its lower end, encounters a stop 184 attached to the housing 190. This causes the connecting rod to pivot again towards the raised position and the valve carrier 181 to move, resulting in the closure of the upper valves and the opening of the lower valves. The movement of the piston 16 is then reversed, and the piston begins its upward stroke.

[0033] Simultaneously, the reciprocating motion of the piston during the supply of liquid to the hydraulic machine allows for the alternative generation of suction up to the outlet 11, the latter being connected to an injection device 2, also called the dosing mechanism 2.

[0034] The hydraulic machine can also be of the type described in document EP1971776 A1 and on the [ Fig.1 ].

[0035] This hydraulic machine comprises a casing with a body and a lid, and a separating means for performing an alternating movement within the casing between the body and the lid, this separating means defining two chambers. The hydraulic machine also includes hydraulic switching means for supplying liquid to and draining the aforementioned chambers. These switching means include a distribution element capable of assuming two stable positions and controlled by the movements of the separating means. The casing body further contains a compartment connected to a pressurized liquid inlet, in which the switching means are housed, as well as triggering means comprising a pusher linked to the separating means, designed to cause, at the end of its stroke, an abrupt change in the position of the switching means, under the action of an elastic means, to reverse the stroke.The distribution unit comprises a distribution spool mounted against a fixed flat plate relative to the casing body. The distribution spool slides in a sealed manner, without a gasket, against the plate, which has orifices connected respectively to the casing chambers and to a liquid outlet. Depending on its position, the spool is designed to close some of the orifices or connect them to the fluid inlet or the exhaust.

[0036] As described in the [ Fig.2 The proportional dosing pump according to the invention comprises a hydraulic machine 1 such as those described above. This machine is therefore provided with an inlet 10 and an outlet 11, the hydraulic machine extending along a longitudinal axis x and containing a member 16 adapted to perform a reciprocating motion, the supply of liquid to the pump at the inlet triggering a reciprocating translational motion along the longitudinal axis x of the member 16.

[0037] The proportional dosing pump includes a volumetric type pump 4, having a shaft 42, an inlet 40 intended to be connected by fluid to a reservoir, and an outlet 41 in fluid communication 51 with the outlet 11 of the hydraulic machine.

[0038] A positive displacement pump is a pump in which a certain quantity of "trapped" fluid is forced to move to the outlet.

[0039] The flow rate of a positive displacement pump is proportional to the speed of actuation of its moving parts and depends very little on the discharge pressure; however, the energy consumed by the pump is proportional to the pressure difference between the outlet and the inlet of the pump.

[0040] Advantageously, the volumetric pump is a peristaltic pump.

[0041] A peristaltic pump is a pump used to produce a flow of fluids, either liquids or gases. The fluid, liquid or gas, is contained in a flexible tube and is propelled by a system that compresses the tube inside the pump. The peristaltic pump generally consists of a head, most often circular in shape, inside which is a flexible tube through which the fluid to be pumped travels.

[0042] This tube is deformed by a rotor equipped with rollers, which compress it against the circular head. The rollers, which block sections of the tube during their rotation, displace the retained fluid in the same direction. The fluid is drawn into the pump inlet due to the tube's elasticity.

[0043] At no point does the fluid come into contact with the rotor. It is only in contact with the inside of the tube, which prevents any risk of contamination from the pump's movement, or even corrosion or abrasion of the tube by aggressive or contaminated fluids. The fluid discharge is subject to pulsations due to the passage of the rollers.

[0044] Of course, any other pump that can operate at low speeds (i.e., at speeds below a few revolutions per hour) could also be used.

[0045] The proportional dosing pump also includes a motion converter 2 designed to transform the reciprocating translational motion of the hydraulic machine component 16 into a rotary motion. This rotary motion is intended to be transmitted to the rotation axis 42 of the positive displacement pump 4, preferably peristaltic, so as to drive said pump.

[0046] Regarding the motion converter, and according to a particular embodiment represented in [ Fig.3 The motion converter 2 comprises a body 22, a rotor 23 housed within another body and equipped with at least one helical rail, and an actuator 21 extending longitudinally along the longitudinal axis x of the hydraulic machine. The body 22 is fixed relative to the hydraulic machine, while the rotor 23 rotates relative to the hydraulic machine, and the actuator 21 translates relative to the hydraulic machine.

[0047] The actuator 21 is linked at one of its ends with the component 16 of the hydraulic machine and cooperates with the helical rail of the rotor 23.

[0048] Advantageously, a pinion 24 is also provided, linked in rotation with the rotor 23, which constitutes an output of the converter according to a rotational movement, which is therefore initially induced by the translation of the actuator 21.

[0049] According to a first embodiment, the actuator 21 comprises a shaft 29 connected to the component 16 of the hydraulic machine, a first axis 25 and a second axis 26 each mounted perpendicularly on the shaft 29 of the actuator.

[0050] Furthermore, the first axis 25 is designed to slide at a first end 25a in a first straight rail 27a fitted in the body 22 of the motion converter 2 to prevent the shaft 29 from rotating and to guide it only in translation.

[0051] The second axis 26 is designed to slide at a first end 26a in a first helical rail 28a fitted on the rotor 23, so as to drive the rotor in rotation, without the shaft 29 rotating.

[0052] According to a second embodiment which this time presents a double guide, the first axis is provided to slide at a first end 25a and at a second end 25b respectively in a first straight rail 27a and in a second straight rail 27b arranged in the body 22 of the motion converter 2.

[0053] Similarly, the second axis 26 is designed to slide at a first end 26a and at a second end 26b respectively in a first helical rail 28a and in a second helical rail 28b fitted on the rotor 23, so as to drive the rotor into rotation without the shaft 29 rotating.

[0054] By doubling the rails, the translational guidance and rotational locking of shaft 29 are thus improved.

[0055] Furthermore, the raising and lowering of component 16 induces the rotation of rotor 23 in the same direction.

[0056] According to one variant, the shaft 29 of the actuator 21 can be provided with one or more longitudinal grooves each capable of receiving a rib formed on the body 22 of the motion converter 2.

[0057] In this way, the cooperation of the grooves of the shaft 29 with the corresponding ribs of the body 22 of the motion converter 2, prevents the shaft 29 from rotating and allows it to be guided only in translation.

[0058] Preferably, the shaft 29 is connected to the hydraulic machine component 16 by means of a pivot joint 20. This is because the component 16 has a natural tendency to rotate during operation. The pivot joint allows this movement to be free, thus preventing the shaft 29 from loosening and / or uneven wear of the component 16.

[0059] According to a preferred mode, the proportional dosing pump includes a variator 3 designed to adjust the speed of the rotation coming from the motion converter 2.

[0060] According to a particular embodiment represented in [ Fig.4 ], the variator 3 comprises an output shaft 32 substantially parallel to the axis (x) of the hydraulic machine, a toothed cone 30, whose axis of revolution is inclined such that one of its longitudinal edges extends parallel to the output shaft 32.

[0061] A roller 33 is mounted on the output shaft 32 so as to be rotationally fixed to the output shaft 32. The roller remains in contact with the toothed cone on its longitudinal edge.

[0062] The output pinion 24 of the converter drives the toothed wheel of the cone 30, while the toothed cone 30 drives the roller 33 in rotation by friction.

[0063] Thus, the roller 33 drives the output shaft 32, which in turn drives the shaft 42 of the volumetric pump.

[0064] This variator includes means 34, 340 for adjusting the position of the roller 33 along the output shaft 32 of the variator.

[0065] These means include a roller fixing support 340, which support is integral with a stuffing box 34 mounted on the rotor body 23 and whose tightening / loosening on the rotor body 23 allows the roller to move along the output shaft 32.

[0066] Advantageously, the variator includes disengagement means 31 allowing the cone 30 to be moved away from the roller 33, so that the cone no longer drives the roller by adhesion.

[0067] The toothed wheel of cone 30 remains in contact with the output of the converter (which is preferentially pinion 24).

[0068] According to a preferred embodiment, the disengagement means 31 consist of a pull rod passing through a support 35 attached to the body 22 of the motion converter 2 and anchored in the toothed cone, and a spring mounted compressed on said pull rod to press the cone against the roller, a pull on said pull rod further compressing the spring and allowing the cone to be moved away from the roller.

[0069] When the pulling force on the pull tab ceases, the spring returns to its original position and again presses the cone against the roller.

[0070] In order to optimize the mixing between the main liquid (generally water which arrives at the outlet 11 of the hydraulic machine, and the additive which arrives from the volumetric pump, preferably peristaltic, the proportional dosing pump includes an injection T 5 which is therefore supplied by the outlet 11 of the hydraulic machine and by the outlet 41 of the peristaltic pump.

[0071] Advantageously, the injection T is equipped with a first check valve and a second check valve provided respectively downstream of the outlet 11 of the hydraulic machine and downstream of the outlet 41 of the peristaltic pump to prevent the reflux of the mixture respectively towards the hydraulic machine and towards the peristaltic pump.

[0072] Regarding the proportional dosing process, the following steps are carried out: The inlet 40 of the volumetric pump 4, preferably peristaltic, is connected to a container filled with the additive to be dosed. The inlet 10 of the hydraulic machine 1 is connected to a source of main liquid. The inlet of the hydraulic machine is supplied with main liquid at a predetermined flow rate.

[0073] When the proportional dosing pump is equipped with a variator 3, the variator 3 is adjusted (for example by adjusting the position of the roller on the output shaft 32), according to the expected dosing, before supplying the inlet of the hydraulic machine with the main liquid at a predetermined flow rate.

Claims

1. A proportional metering pump comprising a hydraulic machine (1) equipped with an inlet (10) and an outlet (11), the hydraulic machine extending along a longitudinal axis (x) and enclosing a member (16) capable of performing a reciprocating movement along this axis, the supply of main liquid to the inlet of the hydraulic machine triggering a reciprocating translational movement of the member (16) along the longitudinal axis (x), the proportional metering pump comprising: - a displacement pump (4), equipped with an axis of rotation (42), an inlet (40) intended to be placed in fluid communication with an additive reservoir and an outlet (41) in fluid communication (51) with the outlet (11) of the hydraulic machine, - a movement converter (2) designed to transform the reciprocating translational movement of the hydraulic machine member (16) into a rotational movement, said rotational movement being transmitted directly or indirectly to the axis of rotation of the displacement pump (4), such that the supply to the hydraulic machine actuates the displacement pump which thus supplies additive to the outlet (11) of the hydraulic machine, the additive mixing with the main liquid at the outlet of the hydraulic machine.

2. The proportional metering pump according to claim 1, wherein the displacement pump (4) is a peristaltic pump.

3. The proportional metering pump according to claim 1 or 2, the proportional metering pump further comprising a variable speed drive (3) designed to adjust the speed of rotation derived from the movement converter (2).

4. The proportional metering pump according to any one of the preceding claims, wherein the movement converter (2) comprises a rotor (23) equipped with at least one helical rail (28a, 28b) and an actuator (21) which each extend longitudinally along the longitudinal axis (x) of the hydraulic machine, the actuator being connected at one of its ends to the hydraulic machine member (16) and cooperating with the helical rail of the rotor (23), as well as an outlet rotationally connected to the rotor (23) and being preferably in the form of a pinion (24), the raising and then lowering of the hydraulic machine member (16) inducing rotation of the rotor (23) in the same direction.

5. The proportional metering pump according to the preceding claim, wherein the actuator (21) comprises a shaft (29) connected to the hydraulic machine member (16), a first axis (25) and a second axis (26) mounted perpendicularly on the actuator shaft (29), the first axis being designed to slide at a first end (25a, 25b) in a first rectilinear rail (27a, 27b) arranged in the body (22) of the movement converter (2), while the second axis is designed to slide at a first end (26a, 26b) in the helical rail (28a, 28b) arranged on the rotor (23).

6. The proportional metering pump according to claim 4, wherein the actuator (21) comprises a shaft (29) connected to the member (16), a first axis (25) and a second axis (26) mounted perpendicularly on the actuator shaft (29), the first axis being designed to slide at a first end and at a second end (25a, 25b) respectively in a first rectilinear rail and in a second rectilinear rail (27a, 27b) arranged in the body (22) of the movement converter (2), while the second axis is designed to slide at a first end and at a second end (26a, 26b) respectively in a first helical rail and in a second helical rail (28a, 28b) arranged on the rotor (23).

7. The proportional metering pump according to one of claims 5 or 6, wherein the shaft (29) is connected to the hydraulic machine member (16) by means of a pivot link (20).

8. The proportional metering pump according to any one of claims 3 to 7, wherein the variable speed drive (3) comprises an output axis (32), a toothed cone (30), the axis of revolution of which is inclined relative to the output axis (32), such that one of its profile ridges extends in parallel to the output axis (32), a roller (33) rotationally integral with the output axis (32) and capable of traversing along the output axis (32), the converter output pinion (24) meshing with the toothed wheel of the cone (30), the toothed cone (30) rotationally driving, by adhesion, the roller (33) as well as the output axis (32), itself driving the displacement pump axis (42).

9. The proportional metering pump according to the preceding claim, wherein the variable speed drive (3) comprises means (34, 340) for adjusting the position of the roller (33) on the output axis (32) of the variable speed drive, these means including a roller fastening support (340), furthermore integral with a stuffing box (34) mounted on the body of the rotor and the tightening / loosening of which on the body of the rotor (23) makes it possible to move the roller along the output axis (32) of the variable speed drive.

10. The proportional metering pump according to claim 8 or 9, wherein the variable speed drive includes decouplers (31) making it possible to move the surface of the cone (30) away from the roller (33), so as to prevent driving of the roller by adhesion.

11. The proportional metering pump according the preceding claim, wherein the decouplers (31) consist in a pull rod passing through a support (35) integral with the body (22) of the movement converter (2) and anchored in the toothed cone, and in a compressed spring mounted on said pull rod to press the cone against the roller, traction on said pull rod further compressing the spring and making it possible to move the cone away from the roller.

12. The proportional metering pump according to any one of the preceding claims, the proportional metering pump comprising an injection T (5) supplied by the hydraulic machine outlet (11) and by the displacement pump outlet (41).

13. The proportional metering pump according to the preceding claim, wherein the injection T is provided with a first non-return valve and a second non-return valve designed respectively to prevent backflow towards the hydraulic machine and towards the displacement pump.

14. A proportional metering method employing a proportional metering pump in accordance with any of claims 3 to 13, the method comprising the following steps: - connecting the inlet (40) of the displacement pump (4) to a container filled with the additive to be metered, - connecting the inlet (10) of the hydraulic machine (1) to a source of main liquid, - performing setting of the variable speed drive (3) designed so as to adjust the rotation speed resulting from the movement converter (2) to the expected metering, - supplying the hydraulic machine inlet with the main liquid in accordance with a predetermined flow rate, such that the supply to the hydraulic machine actuates the displacement pump which thus supplies additive to the hydraulic machine outlet (11), or an injection T supplied by the hydraulic machine outlet (11) and by the displacement pump outlet (41) if the pump outlet is equipped with an injection T, the additive mixing with the main liquid.