Proportioning pump for introducing an additive in a fluid stream

Abstract

The invention concerns a device for varying the dosage of an additive (A) in a main flow (P) of liquid, the proportioning being provided by a pump (1) driven by the main flow, the pump comprising a first intake (2) for the main flow, a second intake (3) for the additive and an outlet for the dosed mixture. A branch pipe (5) of the main flow is provided between a zone (6) located upstream of the first intake (2) and a zone (7) located downstream of the outlet (4), so as to enable a parallel flow not comprising the additive. Periodic control means (C) for the branch pipe (5) and the first intake (2) of the pump are also provided so that each control period comprises at least a phase (Ud1) for which the branch pipe (5) is open and the first intake (2) is closed, and another phase (Ud2) for which the branch pipe (5) is closed while the first intake (2) is open.

Description

[0001] The invention relates to a device for varying the metering of an additive into a main flow of liquid, the metering being carried out by a pump driven by the main flow of liquid, the pump comprising a first inlet for the main flow of liquid, a second inlet for the additive, and an outlet for the metered mixture of additive.

[0002] Systems entailing control of the flow of one or more different products are commonplace. In all cases, the aim is to keep the ratio of these flows to a constant value or one suited to a process.

[0003] These systems generally comprise, when gravity is insufficient, a means of pressurizing or of forcing the flow of at least one of the products by way of an additive. It is therefore necessary to have an auxiliary source of energy. This is the case with centrifugal or positive-displacement pumps, electrical or thermal for example. Furthermore, it is necessary to have means monitoring and adjusting the various flow rates to match their ratio to a desired value. These means also, for the most part, demand a source of energy, which is often electrical, but which draws less power.

[0004] U.S. Pat. No. 5,957,153 discloses a system involving several solenoid valves for injecting an additive. In the absence of electrical energy for operating the solenoid valves, the additive cannot be injected.

[0005] Proportional metering devices are known, for example from FR-2602282, FR-2681645 or FR-2681646, and these have the advantage of being autonomous from the energy point of view. What happens is that they are both a pump driven by the main flow of liquid and a means of controlling the flow, because they are volumetric on account of their design.

[0006] However, the market trend towards management and monitoring of the various operations and the increase in the complexity of the processes means there is now a demand for means for altering the metering proportions that can be automatically controlled.

[0007] Metering devices of the type of FR 2 681 645 or FR 2 681 646 offer the possibility of manually adjusting the metering. When the metering is to be adjusted, the metering stroke needs to be varied so as to alter the amount of additive injected or taken in. It is conceivable for this manual adjustment to be automated or controlled automatically using mechanical means. Such a solution does not appear to be very satisfactory because the parts are generally designed to be operated by hand and are therefore not suited to automatic operation by mechanical or electromechanical means. Furthermore, the precision of the metering generally varies with the stroke length of a piston, and decreases for small metered amounts corresponding to short strokes.

[0008] There are also fixed metering devices in which the metered quantity remains fixed for a given piston stroke. It is desirable to be able also to vary the metering of such fixed metering devices.

[0009] The object of the invention is therefore, above all, to provide a device making it possible to vary the metering of an additive in a main flow of liquid which is of simple and effective design and which can be fitted immediately to a metering device, particularly a fixed metering device, while at the same time giving good metering precision and good homogeneity of the metered mixture.

[0010] According to the invention, a device for varying the metering of an additive to a main flow of liquid, the metering being carried out by a pump driven by the main flow of liquid, the pump comprising a first inlet for the main flow with a branch leading from a region lying upstream of the inlet and control means on this branch, a second inlet for the additive, and an outlet for the metered mixture, is characterized in that:

[0011] the branching-off of the main flow is performed between the region lying upstream of the first inlet and a region lying downstream of the outlet on a length of pipe that can be connected to the outlet so as to allow a parallel flow that does not contain the additive;

[0012] and the control means on the branch are means of periodically controlling the branch of the first inlet of the pump, these control means being designed so that each control period comprises at least one phase for which the branch is open and the first inlet is closed, and another phase for which the branch is closed while the first inlet is open.

[0013] Advantageously, the periodic control means are designed to allow the duration of each phase to be adjusted.

[0014] As a preference, the periodic control frequency is chosen to be high enough to ensure homogeneous mixing of the additive at the outlet.

[0015] The periodic control means may comprise:

[0016] a first valve means for closing or opening the branch;

[0017] a second valve means for closing or opening the first inlet of the pump;

[0018] and control means for, on the one hand, opening the first valve means and at the same time closing the second valve means and, on the other hand, closing the first valve means and at the same time opening the second valve means using pulses, the frequency and duration of which are adjustable.

[0019] Advantageously, each valve means consists of a solenoid valve and the control means comprise an electric pulse generator controlling the solenoid valves.

[0020] The first and second valve means may be combined into a single three-way valve, particularly a three-way solenoid valve.

[0021] The pump may be a metering device with a fixed setting. The regulating device makes it possible to vary the metering between a maximum value corresponding to the value of the fixed setting and a practically zero value.

[0022] The precision of the metering is maintained for all the setting values.

[0023] The invention also relates to a metering pump equipped with a device for varying the metered proportions as defined hereinabove, and to a metering installation comprising a pump and such a device.

[0024] The solenoid valve device according to the invention consumes very little energy and the solenoid valves can be operated using a cell or a battery, which means that the assembly can easily be moved around and carried.

[0025] The invention consists, apart from the provision explained hereinabove, in a certain number of other provisions which will be dealt with more fully hereinbelow with regard to an exemplary embodiment which is described with reference to the attached drawing, but which is not in any way limiting.

[0026] FIG. 1 of these drawings is a diagram of a device for varying the metering of an additive according to the invention.

[0027] FIG. 2 is a diagram with a three-way valve.

[0028] FIG. 3, finally, is a diagram illustrating, as a function of time along the x-axis, the distribution of the injection of additive.

[0029] Referring to FIG. 1, it is possible to see a device R for varying the metering of an additive A in the main flow P of liquid.

[0030] Metering is carried out by a pump 1, of vertical axis, driven by the main flow of liquid. The pump has a first inlet 2 for the main flow, a second inlet 3 for the additive A and an outlet 4 for the metered mixture. The pump 1 is autonomous from the energy point of view and requires no electrical power supply in order to work.

[0031] The pump 1 may be, for example, of the type taught by FR 2 681 646 which allows the metering to be adjusted manually, or of the fixed metering type where there is no possibility of manual adjustment of the metering.

[0032] The actual pump proper is situated in the smaller-diameter lower part 1a of a casing and is operated by a hydraulic motor situated inside the larger-diameter upper part 1b of the casing. This hydraulic motor (not visible in the drawing) comprises a differential piston moving in a vertical reciprocating motion inside the part 1b, the reversals of the movement of which are controlled mechanically and/or hydraulically, without involving any electrical control, or particularly, solenoid valves. The actual pump proper comprises a plunger piston which can move in vertical reciprocating translation and is connected mechanically to the differential piston of the motor. Such an assembly is known in particular from patent FR 2 602 282, the description of which is incorporated by a reference into this description, and to which reference may be made for fuller details.

[0033] The device R comprises a branch 5 of the main flow between a region 6 lying upstream of the first inlet 2 and a region 7 lying downstream of the outlet 4. The branch 5 is formed of a single pipe forming a bypass between the region 6 and the region 7.

[0034] The device R may comprise a length of pipe 8 which can be connected between the inlet 2 and a pipe 9 of the main flow, the region 6 lying on this length 8. The downstream region 7 lies on a length 10 of pipe that can be connected to the outlet 4 and to another pipe 11 for removing the metered mixture.

[0035] Means C for periodically controlling the branch 5 and the first inlet 2 are provided.

[0036] According to the exemplary embodiment, the control means C comprise a first solenoid valve 12 mounted on the branch 5 downstream of the region 6 and a second solenoid valve 13 mounted on the length 8 to control the inlet 2 of the pump 1. A pulse generator 14 comprises two outputs connected by respective electric wires 15, 16 to the solenoid valves 12, 13.

[0037] The control signals from the generator 14 are periodic and designed so that, during one phase, the branch 5 is open and the first inlet 2 is closed and, during another phase, the branch 5 is closed and the inlet 2 is open.

[0038] The phase for which the branch 5 is open (and the inlet 2 is closed) corresponds to a square-wave control signal Ud1 represented by rectangular square wave in FIG. 1, and the other phase for which the inlet 2 is open (and 5 is closed) corresponds to a signal Ud2 also represented by a square wave in FIG. 1.

[0039] FIG. 3 again shows the square waves Ud1 and Ud2 along the x-axis (time), while the y-axis carries the proportion or percentage f% of additive introduced by the pump 1 into the main flow P for each step of operation corresponding to each square wave Ud2.

[0040] FIG. 2 shows an alternative form of embodiment whereby the two solenoid valves 12, 13 are replaced by a three-way solenoid valve 12a controlled by the generator 14 with a wire 15a. The solenoid valve 12a performs the same functions as those described earlier in the case of the two valves 12 and 13.

[0041] Downstream of the regions 7 there is a flow regulator 17, advantageously adjustable, for the metered mixture.

[0042] The durations of the square waves Ud1 and Ud2 can be adjusted with great precision by virtue, for example, of quartz clocks and/or timers so that there is no need to envisage slaving the outlet value of the metering to a setpoint value.

[0043] The frequency of the square waves Ud1 and Ud2 is chosen to be as high as possible according to the solenoid valve 12, 13 whose vibration is to be avoided. The frequency is preferably higher than 10 Hz, particularly of the order of 50 Hz.

[0044] Tests have shown, quite surprisingly, that the fact of chopping the main flow of liquid P (which is the fluid that drives the pump 1) gives rise to neither vibrations nor disturbances in the operation of the pump 1. This pump generally comprises a piston moved in a reciprocating rectilinear motion. The frequency of the square waves Ud1, Ud2 is advantageously chosen to be at least equal to 10 times the mean frequency of the reciprocating movement of the piston of the pump 1.

[0045] A homogeneous mixture of the additive and of the main liquid is obtained in the outlet pipe 11.

[0046] The way in which the device and the installation work is described in greater detail hereinbelow.

[0047] The flow of liquid into which the additive is injected is denoted Qm; this flow Qm is that of the stream passing through the pump when the solenoid valve 13 is open and the solenoid valve 12 is closed. The flow of liquid branched off and into which no additive is injected when the solenoid valve 12 is open while 13 is closed is denoted Qb.

[0048] Because the pressure drops are not necessarily identical depending on the path from region 6 to region 7 which passes via the pump 1, and the path passing via the branch 5, the flows Qm and Qb are not generally identical.

[0049] Qb/Qm ratio is denoted Rq, i.e. Rq=Qb/Qm.

[0050] Rd is also set as being equal to Ud1/Ud2.

[0051] By denoting the frequency of the square waves UD1, Ud2 as N, there will be N square waves Ud2 and therefore N injections per unit time, for example per second.

[0052] Upon each square wave Ud2, the volume of liquid leaving the pump contains a percentage of additive A corresponding to the percentage f% defined by the pump 1.

[0053] The actual percentage R% of the mixture will have a value of at most f% where Ud1 is zero and lower than f% when Ud1 is not zero.

[0054] The flow Qp of the mixture at the outlet, in the pipe 11, is equal to the sum of the treated volumes and of the untreated volumes per unit time.

[0055] In one time unit, the total duration of the injections is equal to N.Ud2; the treated volume is therefore Qm.N.Ud2.

[0056] A similar line of argument reveals that the untreated volume per unit time is equal to Qb.N.Ud1.

[0057] The actual percentage R% of additive is equal to the ratio of the amount of additive contained in the treated volume to the total volume.

[0058] The amount of additive contained in the treated volume is equal to f%.Qm.N.Ud2.

[0059] The total volume per unit time is equal to: Qb.NUd1+Qm.N.Ud2=N(Qb.Ud1+Qm.Ud2).

[0060] Hence:

R%=(f%.Qm.N.Ud2)/N(Qb.Ud1+Qm.Ud2)

[0061] and simplifying:

R%=(f%.Qm.Ud2)/(Qb.Ud1+Qm.Ud2)

[0062] and simplifying again:

R%=f%/[(Qb.Ud1/Qm.Ud2)+1]

[0063] now: Qb.Ud1/Qm.Ud2=(Qb/Qm).(Ud1/Ud2)=Rq.Rd=Rd.Rq

[0064] With the result that: R%=f%/(1+Rd.Rq)

[0065] According to the invention, by varying Rd=Ud1/Ud2 from zero to infinity, it is possible to vary the metering R% from a maximum value corresponding to f% to a zero value, while at the same time maintaining a distribution of the injection that is uniform over time, something which is not the case when the stroke of a piston is varied.

[0066] By varying the duration Ud2 during which the pump or metering device 1 is operating, the main flow Qp is sampled into treated flow pulses Qm and untreated flow pulses Qb. Starting out with a fixed metering device 1, it is possible to vary the metering.

[0067] The ratio of the flows Qb/Qm may be either defined as being constant by control means of the valve or nozzle type or any other regulating means, or alternatively may vary, something which then requires compensation for these variations by adjusting the ratio of the durations using conventional automatic control theory.

[0068] The force that drives the pump 1 is the water flow. Only the electronic or digital control by the pulse generator 14 needs to be electrically powered, and this can easily be done using a battery. The device can be readily built into or loaded onto a mobile installation.

[0069] The pump 1 may be chosen to have a fixed metered setting of satisfactory precision. The precision of the fixed metered setting is not degraded by the device according to the invention and this makes it possible to obtain high precisions.

[0070] Numerous applications are possible.

[0071] One advantageous application relates to the metering of an additive or of a colorant into the water used for preparing concrete on a building site, in the building industry.

[0072] Other nonlimiting exemplary applications relate in particular to the injection of detergents into washing or disinfection liquids, to the injection of liquid fertilizers in agriculture, and to the injection into drinking troughs of liquid medicinal products for animals.

Claims

1. A device for varying the metering of an additive (A) to a main flow (P) of liquid, the metering being carried out by a pump (1) driven by the main flow of liquid, the pump comprising a first inlet (2) for the main flow with a branch leading from a region (6) lying upstream of the inlet (2) and control means on this branch, a second inlet (3) for the additive, and an outlet (4) for the metered mixture, characterized in that:

the branching-off (5) of the main flow is performed between the region (6) lying upstream of the first inlet (2) and a region (7) lying downstream of the outlet (4) on a length (10) of pipe that can be connected to the outlet (4) so as to allow a parallel flow that does not contain the additive;

and the control means on the branch are means (C) of periodically controlling the branch (5) of the first inlet (2) of the pump, these control means (C) being designed so that each control period comprises at least one phase (Ud1) for which the branch (5) is open and the first inlet (2) is closed, and another phase (Ud2) for which the branch (5) is closed while the first inlet (2) is open.

2. The device as claimed in claim 1, characterized in that the periodic control means (C) are designed to allow the duration of each phase (Ud1, Ud2) to be adjusted.

3. The device as claimed in claim 1 or 2, characterized in that the periodic control frequency (N) is chosen to be high enough to ensure homogeneous mixing of the additive at the outlet.

4. The device as claimed in claim 1 or 2, characterized in that the periodic control frequency (N) is at least 10 Hz, particularly of the order of 50 Hz.

5. The device as claimed in one of the preceding claims, characterized in that the periodic control means (C) comprise:

a first valve means (12) for closing or opening the branch (5);

a second valve means (13) for closing or opening the first inlet (2) of the pump;

and control means (14) for, on the one hand, opening the first valve means (12) and at the same time closing the second valve means (13) and, on the other hand, closing the first valve means (12) and at the same time opening the second valve means (13) using pulses, the frequency (N) and duration (Ud1, Ud2) of which are adjustable.

6. The device as claimed in claim 5, characterized in that each valve means (12, 13) consists of a solenoid valve and the control means comprise an electric pulse generator (14) controlling the solenoid valves.

7. The device as claimed in claim 6, characterized in that the first and second valve means are combined into a single three-way solenoid valve (12a).

8. The device as claimed in one of the preceding claims, characterized in that it comprises, downstream of the region (7) lying downstream of the outlet (4), a flow regulator (17), possibly adjustable.

9. A metering pump, particularly with a fixed metering setting, for metering an additive (A) into a main flow (P) of liquid, the pump (1) being driven by the main flow of liquid and comprising a first inlet (2) for the main flow, a second inlet (3) for the additive and an outlet (4) for the metered mixture, which pump is equipped with a device as claimed in one of claims 1 to 8 for varying the metered proportions.

10. An installation for metering an additive (A) into a main flow (P) of liquid, comprising a metering pump, particularly with a fixed metering setting, the pump (1) being driven by the main flow of liquid and comprising a first inlet (2) for the main flow, a second inlet (3) for the additive and an outlet (4) for the metered mixture, which pump is equipped with a device as claimed in one of claims 1 to 8 for varying the metered proportions.