WO1995013473A1

WO1995013473A1 - Liquid-metering pump

Info

Publication number: WO1995013473A1
Application number: PCT/EP1993/003156
Authority: WO
Inventors: Michael Wally; Christian Arnold
Original assignee: Prominent Dosiertechnik Gmbh
Priority date: 1992-06-16
Filing date: 1993-11-10
Publication date: 1995-05-18
Also published as: JPH08506162A; DE4219663A1; DE4219663C2

Abstract

Described is a liquid-metering pump with a pump chamber (2) whose volume increases during the aspiration stroke and decreases during the compression stroke and at whose upper end an air-vent valve assembly (15) is fitted. The aim of the invention is to improve the vent valve assembly in such a pump, in particular to design it so that it vents according to requirements. To this end, the valve assembly (15) has a flow-actuated valve (16) whose response behaviour is determined by the state of aggregation of the liquid flowing through it.

Description

Liquid dosing pump

The invention relates to a liquid metering pump with a pump chamber, the volume of which increases during a suction stroke and decreases during a pressure stroke, and a vent valve device is arranged at the upper end thereof.

Metering pumps of this type are designed, for example, as piston pumps, but in particular as membrane pumps. If such a pump is to pump liquid into a system under higher pressure, the performance of the pump will be reduced or it will fail completely as soon as gas enters the pump chamber. In contrast to liquids, gas is compressible. In this case, the movement of the piston or the membrane does not push liquid out of the pump chamber into the system, but rather the gas volume is reduced. The gas reaches the pen chamber, for example, when changing the storage container from which the liquid is drawn off, or in the case of outgassing liquids. In particular in the case of higher concentrated liquids which are to be metered with the metering pump,

ORIGINAL DOCUMENTS the problem of self-outgassing is becoming increasingly important.

A venting device for a liquid piston pump is known from DE 28 03 470 C3, in which a vent switching valve, a throttle and a check valve are arranged side by side. The check valve opens into a return line to the tank. The throttle should be set so that it allows gases to pass through, while practically completely throttling liquids. However, extensive experience and appropriately qualified specialist personnel are required to set such a choke. Particularly when the pressure fluctuates, it cannot be avoided that significant quantities of liquid escape through the throttle. If, on the other hand, the throttle gap is set too small, the desired venting effect does not occur. The venting effect is sufficient in normal operation. If, however, larger amounts of gas have entered the pump chamber, as can be the case, for example, when changing the container, manual venting must be carried out via the vent valve. This commissioning is cumbersome. Not all users can be expected to have the skills to properly perform such venting.

EP 0 354 484 B1 shows a further metering pump with a vent valve and a membrane acting as a piston. After a predetermined number of piston strokes, this vent valve is opened for a further predetermined number of piston strokes via a gear mechanism or an electromagnet and then closed again. Although this has the advantage that complete venting can be carried out in the pump chamber even with large amounts of gas, without external intervention being necessary. In operation, however, such a vent is extremely unsatisfactory. enough. Since the ratio of opening times to closing times is fixed, on the one hand it can happen that liquid escapes through the vent valve when all gas has already been displaced from the pump chamber. Conversely, it can also happen that the opening times of the vent valve device are too short to allow all gas to escape.

The invention is therefore based on the object of specifying a liquid metering pump with an improved venting possibility.

This object is achieved in the case of a liquid metering pump of the type mentioned at the outset in that the vent valve device has a flow-actuated valve, the response of which is determined by the state of aggregate of the fluid flowing through.

The physical state of the flowing fluid can be that of a liquid or that of a gas. As long as gas flows through the valve, it remains open. Only when liquid flows through the valve does it respond and close. As a result, the pump chamber is actually vented as required. The venting only takes effect when there is gas in the pump chamber. If the pump chamber is completely filled with liquid, liquid will already flow through the valve at the beginning of the pressure stroke, which closes it immediately and prevents further liquid leakage. The reverse remains

Valve opened for the required time, ie the required number of pressure strokes, until all of the gas has been displaced from the pump chamber. In practically all cases, the metering pump thus vented itself in the fastest possible way, regardless of whether the pump chamber is completely filled with gas, as is the case, for example, with an initial start-up may be the case, or whether only small amounts of gas have escaped from the liquid, as can occasionally occur during operation.

Preferably, the valve is normally open and generates a state-dependent pressure drop in the outflowing fluid which acts on the valve in the closing direction and which is only large enough in the case of liquid to close the valve. Here, the fact is used that, with otherwise identical flow paths, liquids bring about a higher pressure drop than gases. As long as gas flows through the valve, it remains open. In the case of liquid, however, a closing force is generated via the valve which is large enough to close the valve, that is to say to prevent or interrupt the flow of liquid. The force necessary to close the valve is basically generated by the piston or diaphragm, which reduces the size of the pump chamber during a pressure stroke. However, the power required to close the valve is negligibly small compared to the pump power, so that this additional load on the diaphragm or the piston is negligible.

In this case, the valve advantageously closes against a predetermined opening force, the pressure drop for gas producing a smaller force and for liquid a greater force than the opening force. With the help of this opening force, on the one hand, the state of rest of the valve is defined. On the other hand, this creates a threshold value that allows a distinction to be made between gases and liquids. So the valve has a built-in pressure or force measurement function. Only when the opening force is exceeded, which is by definition only the case with the flow of liquids the valve closes. Otherwise it remains open for ventilation.

The valve in the flow path of the fluid preferably has a throttle, which forms an outlet of a pressure chamber, in which an actuating element, which is connected to a closing body and can be moved against a valve seat, and to which the pressure in the pressure chamber acts. The fluid creates a pressure drop across the throttle. This pressure drop is smaller for gases than for liquids. In the case of liquids, it is large enough to increase the pressure in the pressure chamber so that it can move the closing body against the valve seat via the actuating element. In the event of a corresponding drop in pressure, which can be caused by a liquid flow, but not by a gas flow, the closing body is moved against the valve seat and prevents further leakage of liquid. Conversely, it can be achieved with such a construction that gas can easily pass through at the flow speeds for which the pump is designed.

It is preferred here that the closing body forms the actuating element, the throttle between

Closing body and valve seat or is formed in the closing body. In the rest position there is only a narrow gap between the closing body and the valve seat, through which gas can flow without any appreciable drop in pressure. However, a fluid flow causes a pressure drop, which in turn leads to an increase in pressure in the pressure chamber. This pressure presses the closing body against the valve seat while reducing the size of the gap. This creates a kind of self-increasing effect, because with a narrowing gap, i.e. a more throttling throttle, the pressure drop across the valve very quickly increases and leads to a correspondingly rapid increase in pressure in the pressure chamber. This rapid increase in pressure in turn leads to a very rapid closing of the valve, ie to a very rapid movement of the closing body onto the valve seat.

The closing body is preferably designed as a membrane made of elastic material which, when installed, has a prestress. The preload serves to generate the opening force. The pretension defines a rest position of the membrane. The preload can be caused by the shape of the membrane. However, it can also only be generated by tensioning the membrane during installation.

The membrane preferably has an opening approximately in the middle, at least one outlet channel opening eccentrically into the valve seat. The membrane can therefore be clamped in its entire edge area, which leads to high mechanical stability of the valve and convenient manufacturing options. Furthermore, such a configuration allows a relatively large opening of the valve. In the middle area of the membrane, in which the distance to the edge clamping is greatest, the membrane also permits the greatest deflection.

The opening is advantageously surrounded by an annular bead which, in the closed position, bears against an essentially flat surface of the valve seat. With such a configuration, the opening is sealed immediately.

The valve seat and / or the closing body advantageously has a structure on its closing surface which limits the contact between the closing body and the valve seat to relatively narrow or small surface areas. This prevents the closing body from being sticks to the seat, which could possibly be caused by suppressing it after closing. Such sticking is prevented with a high degree of reliability by the relatively narrow surface areas, which may well approximate a line contact.

The surface areas are preferably designed as concentric rings or knobs. These surround the opening in the middle and lead to a graduated sealing of the closing body on the valve seat to the outside.

Advantageously, several outlet channels open radially offset between individual rings. Several outlet channels have a corresponding flow capacity, so that ventilation can take place relatively quickly. On the other hand, the concentric rings or knobs ensure, when a liquid flow occurs, that the valve can be closed very quickly. Any gas remaining between the membrane and the valve seat can still escape through outlet channels located further outside, while the membrane is already beginning to close from the inside to the outside.

The pump chamber is preferably provided with an outlet valve which only opens at a predetermined minimum pressure. This minimum pressure can then be used to ensure ventilation. Even if only small gas residues remain in the pump chamber, which due to their small volume can only be compressed to a small extent, blocking the pump chamber outlet means that these small gas residues can also be reliably removed from the pump chamber.

The flow-actuated valve is advantageously arranged in series with a check valve. This Check valve prevents gas from being sucked into the pump chamber via the flow-actuated valve during a suction stroke.

The check valve is preferably arranged in the flow direction behind the flow-actuated valve. The check valve then does not cause a pressure drop which could have a disruptive effect on the function of the flow-operated valve.

The membrane is advantageously formed from metal, in particular stainless steel or Hastelloy, an elastomer or a plastic, PVDF or PTFE or a composite of these materials. With such materials it can be assumed with a high degree of reliability that the fluid does not stick and leads to a malfunction of the valve function.

The invention is described below on the basis of preferred exemplary embodiments in conjunction with the drawing. Show here:

1 shows a first embodiment of a liquid metering pump,

2 shows a detailed view of a vent valve arrangement and

3 shows a second embodiment of a liquid metering pump.

A liquid metering pump 1 has a pump chamber 2 which is delimited by a housing 3 and a membrane 4. Instead of the membrane 4, a piston can also be used. The membrane 4 is moved back and forth via an actuating rod 5 by a drive (not shown in more detail). When moving to the left the volume of the pump chamber 2 decreases. Such a movement is referred to below as the pressure stroke. When the diaphragm 4 moves to the right, the volume of the pump chamber 2 increases. Such a movement is referred to below as the suction stroke. An inlet connection 6 opens into the pump chamber 2 and can be connected to a feed line (not shown in more detail) via a screw connection 7. An inlet valve 8, which is designed as a gravity-operated check valve, is arranged between the pump chamber 2 and the inlet connection 6. During a suction stroke, the valve body shown as a ball is lifted from its seat and clears the way from the inlet connection 6 into the pump chamber 2. During a pressure stroke, the ball is pressed onto the valve seat and prevents the fluid in the pump chamber 2 from escaping into the inlet connection 6. The pump chamber is also connected to an outlet connection 9, which is not connected to a screw connection 10 by a screw connection 10 Dosing line shown in more detail can be connected. An outlet valve 11 is arranged between the outlet connection 9 and the pump chamber 2 and opens against the force of a spring 12 in the outlet direction. The spring 12 defines an opening pressure. The outlet valve 11 opens only when the opening pressure is exceeded. When the opening pressure falls below this in the pump chamber 2, it closes again.

At its uppermost point, a ventilation channel 13 leaves the pump chamber 2. The ventilation channel 13 opens into a pressure chamber 14 of a ventilation valve device 15. The ventilation valve device 15 consists of a series connection of a ventilation valve 16 and a check valve 17 and will be explained in more detail with reference to FIG. 2 . Fig. 2a shows the vent valve 16 in the open position. Fig. 2b shows it in the closed position. The vent valve 16 has a spring membrane 18 made of metal, for example stainless steel, plastic, elastomer, metal-elastomer composite or plastic-elastomer composite. In particular, PVDF or PTFE can be used as the material. The advantage of these materials is that nothing can adhere to them, so that even escaping liquid cannot lead to sticking or clogging of the valve.

Approximately in the middle of the spring membrane 18 there is an opening 19 which is surrounded by an annular bead 20 which, in the closed state, lies against an essentially flat surface 21. The spring membrane 18 cooperates with a valve seat 22, of which the surface 21 forms a part. Several outlet channels 23 open into the valve seat 22. These can, for example, as shown, be arranged radially offset from one another. A plurality of output channels 23 can also be arranged distributed in the circumferential direction.

The surface of the spring membrane 18 facing the valve seat 22 is structured, i.e. it has a number of annular projections 24 which concentrically surround the opening 19 and have the effect that the contact between the spring membrane 18 and the valve seat 22 is limited to relatively narrow surface areas. One can almost speak of a line contact.

The spring membrane 18 has a certain preload, which can be generated by installing the spring membrane in the housing 3. It is also conceivable that the spring membrane is already designed as a molded part with a certain preload. In the idle state shown in FIG. 2a, a small gap 25 is formed between the spring diaphragm 18 and the valve seat 22, which forms an outflow fluid against a throttle resistance. The throttle resistance leads to a pressure drop in the outflowing fluid. This pressure drop depends, among other things, on the physical state of the fluid flowing out, whether it is a gas or a liquid.

Alternatively, the throttle can also be formed through the opening 19.

During a pressure stroke of the membrane 4, gas that has collected in the ventilation channel 13 can easily escape through the gap 25 between the spring membrane 18 and the valve seat 22 and can reach a ventilation bore 26 in the housing 3 via the outlet channels 23 and the check valve 17 . The outflowing gas is not compressed. A pressure increase in the pressure chamber 14 therefore does not take place or does not take place to any appreciable extent. When starting up for the first time or after changing a storage container with the liquid to be dosed, it may well happen that the pump chamber 2 is completely filled with gas and several strokes of the membrane 4 are therefore necessary to get all the gas into the ventilation channel 13 to promote. After a smaller or larger number of pump clearances or strokes, however, the pump chamber 2 and also the ventilation channel 13 are completely filled with liquid, which thus also reaches the pressure chamber 14. The liquid now also flows through the gap 25 between the spring membrane 18 and the valve seat 22. However, the throttling effect of this gap 25 is different for liquids than for gases. In other words, the throttle formed by the gap 25 or the opening 19 produces a greater pressure drop in the case of liquid than with gases. The pressure drop leads to an increase in pressure in the pressure chamber 14. The pressure drop is of course also dependent on the viscosity of the liquid and on the flow rate. However, since both parameters are generally known, the gap 25 or the opening 19 can be dimensioned accordingly, that is to say that for the given or desired delivery capacity of the metering pump 1 it is correspondingly low in the case of gases, but correspondingly high in the case of liquids Pressure drop causes.

The increased pressure in the pressure chamber 14 is now so great for liquids that it overcomes the prestress of the spring membrane 18 and presses it against the valve seat 22. Since the gap 25 becomes smaller and smaller during this movement, the pressure drop across the gap 25 also rises faster and faster, so that the valve 16 is quasi-suddenly closed. The closing takes place from the inside to the outside, i.e. the annular bead surrounding the opening 19 first comes to rest against the flat surface 21. This ensures that the valve 16 closes immediately on the one hand when liquid occurs, but on the other hand still gas through the outlet channels lying further out, insofar as it already reaches them has to be dissipated.

If a small amount of liquid escapes, it can flow back through a return channel 27 to the storage container.

As long as gas can still flow through the vent valve 16, no appreciable pressure can build up in the pump chamber 2. No liquid, which may still contain gas, is therefore pumped through the outlet valve 11 against the force of the spring 12. Rather, the entire pump output is used to drive the gas out of the pump chamber 2. Only when that Breather valve 16 is closed by the liquid present or flowing through, a pressure builds up in the pump chamber 2. However, this then takes place very quickly, so that after the opening pressure of the outlet valve 11 has been overcome, the corresponding one

Amount of liquid can be dispensed into the outlet port 9.

In the case of a suction stroke, the inlet valve 8 opens. The check valve 17 closes, so that no gas can be drawn into the pump chamber 2 via the vent valve 16. Due to the pretensioning of the spring membrane 18, the vent valve 16 opens in order to be able to perform its venting function again on the next pump stroke for any gas that may arise or be sucked in.

3 shows a further embodiment of a liquid metering pump, in which the same parts are provided with the same, corresponding parts with reference numerals increased by 100.

In contrast to the embodiment according to FIGS. 1 and 2, in which the actuating element and the closing body have been embodied together by the spring membrane 18 and the throttle was formed by the gap 25, in the embodiment according to FIG. 3 all functions are separated Realized components. The vent valve 116 thus has a pressure chamber 114, the output of which is formed by a throttle 125 which leads to the check valve 17. The pressure chamber 114 is in turn delimited by an actuating membrane 28 which can be displaced against the force of a spring 29. A closure element 31 is fastened to the membrane 29 via an actuating rod, which comes into contact with a valve seat 122 when the membrane is appropriately deflected. Fluid, which is pressed into the pressure chamber 114 with the aid of the membrane 4, flows through the throttle 125 and the check valve 17 into the return line 27 or the venting bore 26. A pressure drop which is dependent on the state of the aggregate arises at the throttle 125 and is associated with gases leads to a slight pressure increase in the pressure chamber 114, but to a significant pressure increase in the case of liquids. The pressure arising in the pressure chamber 114 is then so great that it overcomes the force of the springs 29 and moves the actuating membrane 28 against the force of the spring 29. The actuating membrane 28 simultaneously moves the closure element 31, which blocks the liquid path as soon as it comes into contact with the valve seat 122. Otherwise, the function is the same as for the liquid metering pump according to FIGS. 1 and 2.

There may be deviations from the illustrated embodiments in many respects. In particular, the pump can also work with a piston instead of the membrane 4.

Claims

claims

Liquid dosing pump with a pump chamber, the volume of which increases during a suction stroke and decreases during a pressure stroke, and a vent valve device is arranged at the upper end thereof, characterized in that the vent valve device (15) has a flow-actuated valve (16), whose response is determined by the physical state of the flowing fluid.

2. Pump according to claim 1, characterized in that the valve (16, 116) is normally open and generates an aggregate-dependent pressure drop in the outflowing fluid, which acts in the closing direction on the valve (16, 116) and which only Liquid is large enough to close the valve (16, 116).

3. Pump according to claim 2, characterized in that the valve (16, 116) closes against a predetermined opening force, the pressure drop in gas producing a smaller force and in liquid a greater force than the opening force.

4. Pump according to one of claims 1 to 3, characterized in that the valve (16, 116) in the flow path of the fluid has a throttle (25, 125) which forms an outlet of a pressure chamber (14, 114) , in which one with a closing body (18,

31), which is movable against a valve seat (22, 122), is connected to an actuating element (18, 28) which acts on the pressure in the pressure chamber (14, 114).

5. Pump according to claim 4, characterized in that the closing body (18) the actuating element bil¬ det, the throttle (25) between the closing body (18) and valve seat (22) or in the closing body (18) is formed.

6. Pump according to claim 5, characterized in that the closing body (18) is designed as a membrane made of elastic material, which has a pre-tension installed.

7. Pump according to claim 6, characterized in that the membrane (18) has an opening (19) approximately in the middle and at least one outlet channel (23) opens off-center in the valve seat (22).

8. Pump according to claim 7, characterized in that the opening (19) is surrounded by an annular bead (20) which, in the closed position, lies against an essentially flat surface (21) of the valve seat (22).

9. Pump according to one of claims 4 to 8, characterized in that the valve seat (22, 122) and / - or the closing body (18, 31) on its closing surface has a structure (24, 124) which is in contact between the closing body (18, 31) and the tilsitz (22, 122) limited to relatively narrow areas.

10. Pump according to claim 9, characterized in that surface areas as concentric rings or as

Knobs are formed.

11. Pump according to claim 9 or 10, characterized gekennzeich¬ net that several outlet channels (23) open radially offset between individual rings.

12. Pump according to one of claims 1 to 11, characterized in that the pump chamber (2) is provided with an outlet valve (11) which only opens at a predetermined minimum pressure.

13. Pump according to one of claims 1 to 12, characterized in that the flow-actuated valve (16, 116) is arranged in series with a check valve (17).

14. Pump according to claim 13, characterized in that the check valve (17) is arranged in the flow direction behind the flow-actuated valve (16, 116).

15. Pump according to one of claims 6 to 14, characterized in that the membrane (18) is formed from metal, in particular stainless steel or Hastelloy, from elastomer or plastic, in particular PVDF or PTFE, or a composite of these materials.