WO2002070896A1

WO2002070896A1 - Continuous-flow fluid dosing device

Info

Publication number: WO2002070896A1
Application number: PCT/BE2002/000023
Authority: WO
Inventors: François-Mathieu Winandy
Original assignee: Cofido S.A.; Fmsw Consulting S.P.R.L.
Priority date: 2001-02-28
Filing date: 2002-02-28
Publication date: 2002-09-12
Also published as: EP1236893A1

Abstract

The invention relates to a flow compensation device for a positive-displacement pump (2) of a dosing device, comprising a first (4) and a second actuation means (18), in which the second actuation means (18) comprises a variable-volume chamber (14) which is connected downstream of said positive-displacement pump and in series with the latter. The first (4) and second actuation means (18) are independent and controlled by a mechanical or electronic regulator (20). Said regulator is connected to a pressure and/or flow sensor (22) that controls the operation of the positive-displacement pump (2) and of the variable-volume chamber (14) so that the flow of the latter is in opposite phase to the irregularities in the dosing curve of the positive-displacement pump (2) using a time delay (E). In this way, the fluid is delivered in a continuous flow at the outlet of said device with a view to increasing the flow-rate range of the pump.

Description

CONTINUOUS FLOW FLUID DOSING DEVICE

Subject of the invention

The present invention relates to a dosing device for liquids in continuous flow in a wide flow range and in particular to a device for compensating for metering irregularities encountered on these devices.

Technological background and state of the art

A conventional positive displacement pump is generally dimensioned as a function of the maximum flow rate that it will have to supply in an installation. This flow is called nominal flow. If the flow required by the installation is lower than the maximum flow of the pump, it is necessary to operate this pump discontinuously or at reduced speed.

Such a solution is however not applicable to all installations, in particular in chemical production installations, in treatment installations or in medical equipment, where it is necessary to be able to precisely dose the quantity of fluid delivered per unit of time, without hiatus. The problem can be solved by choosing a pump working at a speed calculated exactly on that required by the installation, which implies that manufacturers have a range of pumps of infinite variety, economically difficult to manage. In addition, it is extremely rare that an installation works at an unchanging regime: it is therefore mandatory to design pumps whose flow rate can be modulated over a very wide range of use. We can play on the frequency of the volumetric pump cycles or on its rotation speed. In the case of a piston pump, the stroke of the piston can be limited. However, we come up against a technical limit as soon as we try to pass below the barrier of about 20% of the value of the nominal flow rate: problems of precision, friction, relatively large clearance in the mechanism of va back and forth, defusing, degassing of the fluid, relatively large internal leaks in the case of eccentric rotor pumps, etc.

Another problem linked to the use of positive displacement pumps results from the existence of dead times when going from a suction phase to a delivery phase and vice versa in the case of piston pumps / membrane, and generally when the sequences of successive dosing phases occur. This phenomenon can only be partially masked by using pumps arranged in parallel with alternating phases: whatever the number of pumps used, there are invariably jolts in the flow curve. In addition to its cost, this solution notably leads to an increase in the number of valves involved and therefore a significant increase in the sources of possible breakdowns. To cover a flow range from 0.1 liter / hour to 2000 liters / hour, we are currently forced to use 20 to 30 different pumps.

Document US-P 4,810,168 discloses a low pulsation metering system comprising two pistons in phase opposition or simply phase shifted, actuated by a camshaft and a drive motor. In this document, we try to minimize the pulsations by acting on the phase shift of the cams and by regulating the pulsations of the motor. The disadvantage of this system is that it operates according to a fixed and predetermined phase relationship which must be optimized for a given flow rate. This alleviates dosage irregularities without making them disappear completely. The two cams are moreover linked together by a shaft which is itself driven by a single motor. The predetermined phase relationship makes optimized operation impossible in a flow range wide enough for industrial applications. The relative precision of the dosage cannot therefore be maintained over the entire operating range.

Kiwao Seki also offers in patent application EP-A2-0303220 a method of regulation for the pulse motor of such a configuration. Furthermore, it offers a second configuration with two motors and ball valves having the drawback of the lack of tightness. This system is equipped with a whole series of detectors such as piston position detectors or limit switches. This system is again very complex and can only be envisaged for laboratory applications.

Document EP-A2-0367099 discloses a similar system with a circular cam offset from the axis and a second cam whose shape depends on the first and in particular on its offset. The author of this document establishes a complex mathematical relationship determining the exact shape of the second cam with respect to the first, thus establishing the exact phase difference between the two cams for a given flow rate. Here the relationship between the two cams connected together and moved again by a single motor is again fixed and therefore has the same type of drawback as that encountered in the previous document. Abdel-Rahman Mahmoud proposes in EP-A1- 0471930A1 a method of real-time compensation of the compressibility of supercritical fluids for chromatographic analysis applications in the laboratory. Such complex regulations on very low flow rate and very high pressure pumps can only be taken into account for very high technical applications in a laboratory context and are not suitable for dosing of liquids in industrial applications with wide flow range.

Aims of the invention

The present invention aims to provide a device capable of compensating for metering irregularities encountered in many pumping systems to allow metering of liquids in a very wide flow range without significant losses in the relative metering accuracy. This is how the present invention sets itself the objective of replacing the 20 to 30 pumps currently required to cover a flow rate of 0.1 to 2000 liters / hour by 2 to 4 pumps provided with the device according to

1 invention.

Summary and characteristic elements of the invention The present invention aims to provide a flow compensation device for a positive displacement pump 2 of a metering device, comprising a first 4 and a second actuating means 18 , characterized in that said second means 18 comprises a variable volume chamber 14 connected downstream of said positive displacement pump and in series therewith, said first 4 and second actuating means 18 being independent and controlled by a mechanical or electronic regulator 20 which can be connected to a pressure sensor and / or flow 22 which controls the actuation of the positive displacement pump 2 and the variable volume chamber 14 in such a way that the flow thereof is in phase opposition with the irregularities of the dosing curve of the pump volumetric 2 using a time shift E such that the fluid is delivered in a continuous flow at the outlet of said device.

A key element of the present invention shows that the flow rate of said device can be ensured in a ratio of 1/200, and even up to 1/2000 compared to the nominal flow rate without significant loss of relative precision on the dosage of the liquid.

In a preferred embodiment of the present invention the positive displacement pump 2 is a piston or diaphragm pump with sealed inlet 8 and outlet 10 valves of the membrane type or ball valve while the volume chamber variable 14 is not fitted with an outlet valve. In another preferred embodiment, the positive displacement pump 2 is a peristaltic pump or a sparrow pump.

One of the essential advantages of the present invention is that the positive displacement pump 2 and the rest of the device may or may not form two separate entities. Finally, the invention shows the use of the device according to any one of the preceding claims for the continuous flow metering of liquids in flow ranges up to 1/2000 of the flow nominal without significant loss of relative metering accuracy.

Other features and advantages of the invention will emerge from the description of particular embodiments of the invention which are illustrated in the figures.

Brief description of the figures

- Figure 1 is a schematic cross-sectional view of a metering and compensation device according to the invention.

Figure 2 is an operating diagram of the invention in the case of a piston pump. Figure 3 shows the operating diagrams of the invention in the case of various other positive displacement pumps.

Detailed description of the invention The object of the invention is a continuous flow fluid metering device comprising a positive displacement pump, provided with an actuating means, an inlet valve and a an outlet valve, in which a variable volume chamber provided with a second actuation means is connected downstream of the positive displacement pump and in series with it, the first and second actuation means being controlled by a regulator electronic or mechanical that can be connected to a pressure or flow sensor controlling the actuation of the positive displacement pump and the variable volume chamber with offset of suction and discharge phase, generating a time offset E such that the liquid is debited in a continuous flow.

By time shift E, as shown in Figure 2, we mean the crossing sequence allowing 'to make the relative dosing error negligible, when one of the pistons reaches a critical point such as a neutral point for example.

This system can find its application in positive displacement piston or diaphragm pumps, or with a peristaltic pump or a sparrow pump. It allows the flow range of the same pump to be very broadly widened while making no concessions on the relative dosing precision. The positive displacement pump and the rest of the device can form two separate entities or be in the same entity according to the preferred embodiment.

Essentially, 3 pumps fitted with the device according to the present invention will cover a flow range ranging for the first from 0.1 to 20 1 / h approximately, for the second from 10 to 200 1 / h approximately and for the third from 100 to 2000 1 / h. It is obvious that we are talking here about nominal flow requiring an operation of 10 to 100% of each of the values determined within the ranges mentioned above. These values are given by way of example and can in no way be regarded as restrictive for the present invention.

Description of a preferred embodiment of the invention

Figure 1 shows, schematically, a positive displacement pump 2, shown here as a piston pump, provided with an actuating means 4, a piston 6, inlet valves 8 and outlet 10, and a chamber 12. Downstream of the pump 2 is disposed a variable volume chamber 14, provided with a piston 16 set in motion by a second actuating means 18. The first and the second actuating means 4, 18 are independent and are controlled by an electrical or mechanical regulator.

The operation of the device will be described with particular reference to Figure 2. The curves a, b and c respectively representing the flow of the positive displacement pump 2, the flow of the chamber 14 and the resulting flow.

At time To, the pump 2 having sucked fluid through the inlet valve 8, the volume of its chamber 12 is filled to the maximum. The actuating means 4 of the pump 2 forces the piston 6 to start its inward stroke. The valve 10 opens and the fluid begins to flow in the outlet circuit.

Almost simultaneously, the regulator 20 controls the second actuating means 18 to withdraw the piston 16 from the volumetric chamber 14. Part of the fluid delivered by the pump 2 is therefore temporarily stored in the chamber 14.

When the piston 6 reaches the end of the stroke, the regulator 20 controls the second actuating means 18 to initiate the re-entrant stroke of the piston 16 of the volumetric chamber 14. The valve 10 closes and the pump 2 can start a filling cycle while the volumetric chamber continues to ensure a constant fluid flow in the outlet circuit.

The presence of the regulator 20 makes it possible to remove any irregularity in the flow curve, in particular by anticipating E of the top and bottom dead centers in the travel of the two pistons which allows a considerable widening of the flow range which can be provided by the same pump, which is the main objective of the present invention.

The possible presence of a flow sensor 22 and / or pressure in the output circuit allows In addition, rectify in real time any actual variation in the flow curve.

The advantages of the device described are manifold. A first advantage is that it is possible to increase the ratio of the effective / nominal flow rate of the pump by one to two orders of magnitude (1/200 to 1/2000) while keeping the same continuity and above all the same precision. relative dosage. We can therefore simultaneously expand the range of possibilities of existing metering pumps while reducing the number of models, resulting in a reduction in storage costs, spare parts etc. Furthermore, although one has shown in FIG. 1 a monobloc device, it is perfectly possible to dissociate the positive displacement pump 2 from the rest of the device, which means that one can put on the market conversion “kits” adaptable to all types of standard positive displacement pumps.

This conversion kit can be adapted to a wide variety of positive displacement pumps of various types: rotary pumps, eccentric rotor pumps, sparrow pumps

(so-called pigtail), piston or diaphragm pumps, gear pumps, peristaltic pumps, lobe pumps,

, etc. If the pump .2 is driven by a symmetrical movement, we can set a volume ratio of 2/1 for the two chambers 12 and 14. However, we can provide an asymmetrical movement (faster movement of the piston to the 'suction), which allows the volume of chamber 14 to be reduced accordingly.

Another decisive advantage of the device of the invention is that it is possible to work at low flow rates with a pump whose volume of the chamber is comparable to that of a pump with a higher flow rate and that there is therefore no need to fear the known problem of degassing of the transported fluid.

It will be noted that the device comprises a limited number of parts in contact with the transported fluid and that consequently the risks of malfunction, fouling and reciprocal pollution are reduced accordingly.

The concept of suction and delivery is of course not present on each type of positive displacement pump. Fig. 3 illustrates other intended applications of the device of the invention. This figure shows the flow curves of various cyclic flow pumps. The suction and discharge phases of the variable volume chamber are here in opposition to the irregularities of the metering curve of these different positive displacement pumps. Curve K is that of a diaphragm pump with magnetic impulse; curve L is a piston and diaphragm pump with mechanical connecting rod-crank drive; curve M is that of a tube pump (or peristaltic pump); curve N is that of a Moineau pump. The hatched areas represent the flow compensations made by the volumetric chamber 14.

Claims

1. A flow compensation device for a positive displacement pump (2) of a metering device, comprising a first (4) and a second actuating means (18), characterized in that said second means (18) comprises a variable volume chamber (14) connected downstream of said positive displacement pump and in series therewith, said first (4) and second actuating means (18) being independent and controlled by a mechanical or electronic regulator (20) capable of be connected to a pressure and / or flow sensor (22) which controls the actuation of the positive displacement pump (2) and of the variable volume chamber (14) so that the flow thereof is in opposition phase with irregularities in the metering curve of the positive displacement pump (2) using a time offset (E) such that the fluid is delivered in a continuous flow at the outlet of said device.

2. Device according to claim 1 characterized in that the flow rate of said device can be ensured in a ratio of 1/200 with respect to the nominal flow rate without significant loss of relative precision on the dosage of the liquid.

3. Device according to claim 1 characterized in that the flow rate of said device can be ensured in a ratio of 1/2000 with respect to the nominal flow rate without significant loss of relative precision on the dosing of the liquid.

4. Device according to claims 1 characterized in that the positive displacement pump (2) is a piston or diaphragm pump with inlet (8) and outlet (10) leaktight diaphragm or ball valve type valves.

5. Device according to any one of the preceding claims, characterized in that the variable volume chamber (14) is not provided with an outlet valve.

6. Device according to any one of the preceding claims, characterized in that the positive displacement pump (2) is a peristaltic pump.

7. Device according to any one of claims 1 to 5 characterized in that the positive displacement pump (2) is a sparrow pump.

8. Device according to any one of the preceding claims, characterized in that the positive displacement pump (2) and the rest of the device form two separate entities.

9. Metering device according to any one of claims 1 to 7 characterized in that the positive displacement pump _ (2) and the rest of the device form the same entity.

10. Use of the device according to any one of the preceding claims for the continuous flow metering of liquids in flow ranges up to 1/2000 of the nominal flow without significant losses in the relative metering accuracy.