EP0689647B1 - Pressurisation/partial vacuum pump for delivering predetermined amounts of a product - Google Patents

Abstract

A pump including a sealed chamber (10) which can suck in a product feed through a first inlet (16) by means of an air pump (32) forming a partial air vacuum therein via a port (19). The product is received in an inner vessel (20) supported on a weight sensor (30) which outputs an electrical signal representative of the product weight. The signal is fed to an electronic air pump control unit (50). Once the product has reached the desired weight, it is discharged by the air pump pressurising said chamber, the product exiting through a vertical outlet (18) with its lower end at the bottom of the vessel.

Description

The present invention relates to a pump using an air vacuum to suck from a supply duct a predetermined quantity of product, such as a liquid, a viscous, granulated or lumpy material, then an air pressure for return this quantity to a discharge pipe.

Such a pump is advantageously used, for example, in the transfer of exact amounts of corrosive products, such as salts in an electrolysis bath used for surface treatment, or in the supply of industrial washing machines in powdered form. washing, or dosing of liquid in water treatment.

A known pump of this type for transferring battery acid is described in document SU 626 251. This pump comprises a sealed chamber provided at its bottom with a butterfly drainage valve and at its upper face with a valve float. An adjacent vacuum pump establishes a partial vacuum in this chamber, which draws the liquid from an associated reservoir. When the liquid level has reached a pre-established threshold, the float opens the upper valve which restores atmospheric pressure within the chamber then stopping the arrival of the liquid. On the other hand, the weight of the liquid is sufficient to open the drainage valve allowing the evacuation of the liquid from below. Once the float is lowered and the upper valve closed, the suction pump begins to establish a new vacuum for the next cycle. Another pump operating on a similar mechanism is described in document SU 676,761.

However, the accuracy based on the lifting of a float may prove to be insufficient for precise dosing, especially if the pump is incorporated in a machine undergoing vibrations. Furthermore, the upward movement of the float can be hampered by the friction forces along its guide rod, in particular when transferring viscous or granular products.

Document EP-A-0 303 376 describes a marine brine vacuum pump for fish fishing comprising an imposing hermetic chamber in which the brine can be sucked by a first lower duct when an air vacuum is applied through a pneumatic line connected to an air pump. The brine can then be discharged into a second upper evacuation duct, the lower end of which is close to the bottom of the chamber, when an air pressure is then applied in the chamber. Each duct is controlled by a throttled bladder valve. A weighing sensor interposed between the hoist and the external support cables of the chamber measures the increase in the weight of the chamber as it is filled, and its signal is applied to an electronic control unit for the valves and the air pump.

However, in this configuration, the sensor first measures the weight of the cables, the chamber, the valves, the pneumatic lines and the entire lower duct before starting to measure the change in the weight of product introduced. It is practically impossible to measure precisely small quantities of product, the offset and calibration gain values of the sensor then being extreme.

The object of the present invention is a metering pump operating by vacuum then overpressure, which ensures better precision in the quantity of product transferred, and this with increased reliability thanks to a simplification of the constituent parts.

These aims are achieved by a pump comprising a hermetic chamber into which a product arriving by a first conduit can be sucked when an air depression is applied through a mouthpiece. by an air pump, because the product is received in an internal tank held by a weighing sensor delivering an electrical signal representative of the weight of the product, this signal being applied to an electronic unit for controlling the air pump, the product being discharged, when an air overpressure is then applied in the chamber by the air pump, in a second vertical discharge conduit whose lower end is located at the bottom of the tank.

Advantageously, the chamber and the tank can be two nested coaxial cylindrical elements. Preferably, the bottom of the tank is concave conical.

Usefully, the tank is made of a material inert to corrosion such as glass or polyvinyl chloride. Its upper edge may advantageously have a collar oriented inwardly to significantly reduce the risk of product overflowing.

The hermetic chamber can be made of any waterproof and mechanically resistant material, in particular of molded and / or assembled plastic elements. This chamber may include a removable top cover for possible cleaning. So the first supply lines and the second discharge duct may be integral with this cover which they pass through.

Usefully, the second discharge pipe is fitted with a non-return valve to prevent part of the product from returning to the pump when the overpressure disappears. Also usefully, the supply pipe can be connected to a plurality of valves mounted in parallel to control the supply of different products, and the discharge pipe can also be connected to a plurality of valves controlling the outlet of the product dosed to different destinations.

For example, the weighing sensor consists of a parallelepipedal block of metal partially hollowed out in its center, and on the upper and / or lower face of which a stress gauge has been stuck, one end being fixed at a fixed point of the hermetic chamber, the other end supporting the tank. Alternatively, the weighing sensor can be based on a piezoelectric crystal with two opposite electrodes.

The invention will be better understood from the study of an embodiment taken by way of nonlimiting example and illustrated in schematic section in the appended figure.

As illustrated, the metering pump comprises an external chamber 10 hermetically closed by a cover 12 tightening a seal 14. In this chamber is installed a tank 20 supported by a weighing sensor 30. A first supply conduit 16 of product crosses the cover 12 and stops in the upper part of the tank 20. Conversely, a second product discharge conduit 18 crosses the same cover 12 and extends to the bottom of the same tank 20. By elsewhere, the sealed chamber 10 can be put under overpressure and then under vacuum by an air pump 32 connected to a mouth 19 of the chamber 10 either by two separate lines P and D or the same common line.

In the embodiment illustrated in this figure, the chamber 10 and the tank 20 are cylindrical, the tank 20 being arranged in the chamber 10 coaxially. This tank has a concave conical bottom 22, the lower end of the discharge conduit 18 then being located at its lowest level. If desired, the tank 20 can be partially closed at its upper edge by a flange 24 extending radially inward.

Since the tank 20 can be made to receive corrosive products, it is preferred to make it from a chemically inert material such as glass. However, for considerations of lightness and strength, certain polyvinyl chlorides prove to be preferable. The external chamber, on the other hand, must be sealed and mechanically solid to resist variations in internal pressure as well as vibrations that may potentially exist in the machines in which the pump is intended to be installed. We can consider, to achieve this room, a molded or stamped metal. However, certain thermosetting plastics or synthetic resin can prove to be sufficiently solid while being lighter and less expensive to produce.

So that the sensor 30 can effectively measure the weight of the tank, it is important that it does not come into frictional contact with the internal walls of the chamber 10. In addition, so that the weighing is insensitive to variations in internal pressure of chamber 10, it is necessary that these variations can have repercussions as much on the upper face as on the lower face of this tank. It is therefore necessary to provide a sufficient passage for the air between the external walls of the tank and the internal walls of the chamber, and to provide air access over practically the entire bottom of this tank.

By way of example, the chamber 10 can have an external diameter of 160 mm for a height of 190 mm cover included, while the tank is reduced to a diameter of 100 mm for a height of 110 mm.

As illustrated, the weighing sensor 30 is produced from a substantially parallelepipedal metal block and hollowed out longitudinally in its center, the ends of the recess being rounded. This horizontal sensor is then fixed at one of its ends to the bottom of the chamber 10 while its other end supports the tank 20. One or more strain gauges are bonded to the upper and / or lower face of the metal block. These strain gauges are connected to an electronic unit 50 controlling the function of the air pump 32.

Furthermore, the inlet duct 16 is connected to at least one solenoid valve making it possible to close this duct at will, and this by remote control of the control circuit 50. Better still, this duct 16 can be connected to a plurality of connected solenoid valves 34 in parallel then allowing the transfer of different products from several neighboring tanks.

On the other hand, the discharge conduit 18 is firstly provided with a non-return valve 38. This valve can be housed in the lower part of the conduit 18 near the concave bottom 22 of the tank 20. The outlet of this discharge conduit is also controlled by one or more solenoid valves 36 allowing, always under the control of the circuit 50, to modify the destination of the transferred product.

As described, the metering pump according to the invention operates in the following manner.

During the initialization phase, the control circuit 50 reads the initial weight of the tank 20 as seen by the gauge 30. Then, the circuit 50 opens one of the valves 34 and starts the air pump 32 to create a depression of the order of 100 to 200 mm of water. This has the effect of sucking the product which, emerging through the conduit 16, accumulates in the tank 10. The increase in the weight of this tank is monitored by the control circuit 50 constantly reading the electrical signal from the sensor 30.

When a predetermined weight of product is measured in the tank 10, the circuit 50 closes the solenoid valve 34, stops the air pump 32 and restores the atmospheric pressure inside the chamber 10. Then, this same circuit opens the 'one of the outlet solenoid valves 36 and switches on the same air pump 32 to create an overpressure in the chamber 10. This overpressure is applied on top of the product present in the tank 10, and forces it to be evacuated by the second conduit 18. In view of the position of the end of this conduit in the concave bottom 22 of the tank, this product is entirely removed. Indeed, shortly before the end, the overpressure begins to escape through this same conduit 18 which then functions as a vacuum cleaner for the final quantities of product. The non-return valve 38 then prevents any backtracking when the control circuit 50 stops the pump 32 and restores atmospheric pressure. A new dosing product transfer cycle can then start again.

Alternatively, the tank 20 could be held by a plurality of weighing sensors installed between its upper edge and the cover 12. The advantage of this metering pump according to the invention is the use of electronic weighing sensors ensuring precision of remarkable measure. Indeed, whatever the electronic sensor used, it can be calibrated by first carrying out a no-load measurement, giving the initial weight of the tank, then by measuring a predetermined quantity of a reference material of known weight . The electronic circuit 50 can then calculate an offset value and a gain value to be applied to the electrical signal to obtain the rigorous measurement of the weight of the only product subsequently transferred. In the event of vibrations, the circuit establishes an average of the values recorded during a unit of time, and decides based on this average. Many variations and improvements can be made to this dosing pump.

Claims (9)

1. Pump comprising a hermetically sealed chamber (10) into which a product arriving by a first conduit (16) can be sucked when a negative air pressure is applied through a mouthpiece (19) by an air-pump (32), the said product being discharged into a second, evacuation conduit (18) when a positive air pressure is then applied in the chamber (10) by the air-pump, and also a weighing sensor (30) delivering an electrical signal which is representative of the weight of product introduced into the chamber, the said signal being applied to an electronic control unit (50) for the air-pump, characterised in that the sensor is internal to the chamber and holds an internal tank receiving the product, and in that the lower end of the second, vertical, evacuation conduit (18) is located at the bottom of the tank.
2. Pump according to claim 1, characterised in that the chamber (10) and the tank (20) are two nested, coaxial, cylindrical elements.
3. Pump according to claim 1, characterised in that the bottom (22) of the tank (20) is concavely conical.
4. Pump according to claim 1, characterised in that the tank (20) is produced from a material which is inert in respect of corrosion, and in that the hermetically sealed chamber (10) is produced from moulded and/or assembled plastic elements.
5. Pump according to claim 1, characterised in that the upper edge of the tank (20) has a flange which is orientated towards the inside.
6. Pump according to claim 1, characterised in that the chamber (10) comprises a demountable upper lid (12), and in that the first, admission conduit (16) and the second, evacuation conduit (18) are integral with the said lid, through which they pass.
7. Pump according to claim 1, characterised in that the second, evacuation conduit (18) is equipped with a non-return valve (38) .
8. Pump according to claim 1, characterised in that the admission conduit (16) is connected to a plurality of valves (34) mounted in parallel in order to control the supply of different products, and/or the evacuation conduit (18) is connected to a plurality of valves (36) in order to control the departure of the metered product to various destinations.
9. Pump according to claim 1, characterised in that the weighing sensor (30) is made up of a parallelepipedal metal block which is partially hollowed-out in its centre and onto the upper and/or lower face of which there has been glued a strain gauge, one end being fixed at a fixed point on the hermetically sealed chamber (10) and the other end supporting the tank (20).

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