EP3167191B1 - Diaphragm pump with reduced leak extension in the event of overload - Google Patents

Description

The present invention relates to a diaphragm pump with a leak-relief valve.

Diaphragm pumps generally have a delivery chamber which is separated from a hydraulic chamber by a membrane, wherein the delivery chamber is connected both to a suction connection and to a pressure connection. The filled with working fluid hydraulic chamber can then be acted upon with a pulsating working fluid pressure. Due to the pulsating working fluid pressure, a pulsating movement of the diaphragm between a pressure position, in which the volume of the delivery chamber is smaller, and a suction position, in which the volume of the delivery chamber is greater, reciprocated. This makes it possible, via the suction port, which is connected to a corresponding check valve with the pumping chamber to suck the fluid when the volume of the pumping chamber is increased, and via the pressure port, which is also connected to a corresponding check valve with the pumping chamber, under Relieve pressure when the volume of the pumping chamber is reduced.

As a working fluid usually a hydraulic oil is used. In principle, however, other suitable liquids can be used.

Through the membrane, the medium to be pumped is separated from the drive, whereby on the one hand the drive is shielded from harmful influences of the pumped medium and on the other hand, the fluid from harmful influences of the drive, for example impurities, is shielded.

The pulsating working fluid pressure is often provided by means of a movable piston in contact with the working fluid. The piston is reciprocated, for example, in a hollow cylindrical element, whereby the volume of the hydraulic space is reduced and increased, which leads to an increase and decrease of the pressure in the hydraulic chamber and in consequence to a movement of the membrane. Despite various measures to prevent flow around the piston with the working fluid, can not be ruled out in practice that each stroke a small amount of the working fluid is lost through the narrow remaining gap between the piston and hollow cylindrical element, which gradually the working fluid in the Hydraulic room is reduced.

Furthermore, gas can penetrate into the hydraulic space, which must be removed therefrom to allow full lifting movement of the membrane. For this purpose, a vent valve is often connected to the hydraulic chamber, via which a certain amount of gas and possibly a small amount of working fluid is discharged during the pressure stroke. This also gradually reduces the amount of working fluid in the hydraulic chamber.

This has the consequence that the pressure stroke is no longer completely carried out by the membrane, since not enough working fluid for Druckhubbewegung the membrane is available.

Therefore, for example, in the DE 1 034 030 has already been proposed to connect the hydraulic chamber with the interposition of a valve, a so-called leak-relief valve, with a working fluid reservoir.

If necessary, working fluid can be added to the hydraulic chamber through this leak-relief valve. However, it is important to ensure that not too much working fluid is placed in the hydraulic chamber, since then the membrane moves in the compression stroke too far into the pumping chamber and possibly gets into contact with valve channels or the inner contour of the dosing in contact and is damaged.

In normal operation, the leak relief valve is designed so that exactly the amount of working fluid that has been lost during the pressure stroke, at the end of the suction stroke, i. essentially in the suction position, is refilled.

The metering pump described is typically used in a corresponding process plant, i. It is connected to a corresponding suction line and a pressure line. Although not generally desired, it may happen that in the process plant, the pressure line is accidentally closed, so that the metering pumps against a closed volume, which can lead to an unacceptably high pressure development, causing damage to the membrane or drive parts of the pump can lead.

To prevent this, therefore, the hydraulic chamber is often equipped with an outlet channel which is closed by a pressure relief valve which is designed such that when the pressure in the hydraulic chamber above a predetermined maximum value p _max increases, the pressure relief valve opens, so that working fluid through the outlet channel leave the hydraulic room and is generally fed back into the working fluid reservoir.

As a result, a further increase in pressure can be prevented.

Due to the oil return, however, there is a significant heating of the entire hydraulic system, in particular the pressure relief valve and the hydraulic oil.

In particular, when the blockage of the pressure line for a long time interval continues, the temperature of the pump can increase significantly, as with each pressure stroke again hydraulic fluid must be discharged through the pressure relief valve and is fed back through the leak-relief valve.

Depending on the application area of the dosing pump, however, certain temperature classes must be observed in accordance with the ATEX guidelines of the European Union. Heating of the pump is therefore only allowed to a certain extent.

In order to meet the requirements of the ATEX guidelines, various measures are known in the prior art. For example, the stroke frequency and, as a consequence, the dosing output can be limited, so that even if the pressure line is blocked, the limit temperature is not exceeded at any point within the pump. However, this measure leads to a significantly limited dosing, since the pump, even if there is no blockage of the pressure line is operated at a limited stroke frequency. In addition, the pump-specific limit power must be determined accordingly consuming.

Another way to comply with the ATEX guidelines is to use an appropriate temperature sensor that senses the temperature of the pump, preferably near the pressure relief valve, and outputs a signal when the limit temperature is exceeded, which then shuts down the pump. By this measure, however, a temperature sensor must be maintained. In addition, the signal emitted by the temperature sensor must be prepared and processed accordingly.

Another solution is to use a flow switch in the outlet channel, which detects the hydraulic oil flow via the pressure relief valve in case of overpressure and ensures that the pump is switched off.

Again, there are additional costs for the flow monitor and the associated signal conditioning electronics.

Based on the described prior art, it is therefore an object of the present invention to provide a diaphragm pump, which automatically reduces the dosing in the overpressure case, without the use of additional sensors is necessary.

According to the invention, this object is achieved in that the outlet channel is connected to the second chamber, and that the connecting channel either closable or the flow through the connecting channel throttled or at least throttled, so that in an overpressure case, i. when hydraulic oil has left the hydraulic chamber via the pressure relief valve, more hydraulic oil from the first chamber is tracked into the hydraulic chamber than can flow during a stroke of the second chamber in the first chamber.

Also, the working fluid flowing past the piston can be returned to one of the two chambers.

Depending on the embodiment, therefore, the overpressure causes the pressure in the first chamber and / or the filling level in the first chamber to drop, since less working fluid can flow from the second chamber into the first chamber than via the leak-relief valve from the first chamber into the first chamber Hydraulic room is discharged.

But as soon as the filling level or the pressure in the first chamber drops below a certain value, gas is introduced into the hydraulic chamber via the leak-relief valve. However, if gas is in the hydraulic space, due to the compressibility of the gas, this results in reduced movement of the membrane, thus reducing the metering efficiency and thus preventing the metering pump from being heated above a predetermined maximum temperature.

The measure according to the invention therefore ensures that, in the overpressure case, gas penetrates into the hydraulic chamber and thereby prevents further heating of the pump.

In one embodiment, the connecting channel can be closed by means of a valve.

During operation of the pump, the valve is usually closed. About the leak-relief valve is the working fluid through the piston or the vent valve escaped, refilled. However, this amount is very small, so that the working fluid level in the first chamber drops only very slowly. The first chamber can be sized so that the pump can be operated in this state for several days or even weeks, without the level or the working fluid pressure drops so far that gas penetrates through the leak-relief valve in the hydraulic chamber.

Also, it is possible to recirculate the working fluid flowing past the piston into the first chamber, thereby slowing down the lowering of the liquid level.

In the overpressure case, however, the amount of working fluid to be supplied via the leak-relief valve sharply increases, so that the level or the working fluid pressure rapidly decreases and gas enters the hydraulic space.

As soon as gas has penetrated into the hydraulic chamber, the function of the pump is disturbed and further heating is excluded.

In order to put the pump back into operation, the valve of the connecting channel must be opened, so that the first chamber is filled again with sufficient working fluid. Since a certain gas volume is conveyed out of the hydraulic chamber with each pressure stroke, when gas is in the hydraulic chamber, and now no more gas is supplied via the leak-relief valve, the pump can work normally again.

The valve of the connection channel can be regularly opened for a short time, either manually - e.g. in the event of an error or during regular checks - or automatically, e.g. Timed every 24 hours to increase the working fluid level in the first chamber.

In a further particularly preferred embodiment, a second connection channel between the first and second chamber is provided.

In this case, the second connecting channel can be arranged above the first connecting channel and preferably above the leak-relief valve, wherein the second connecting channel is particularly preferably arranged above the working-fluid level in the second chamber.

When the second communication passage is located above the working fluid levels in the two chambers, it provides pressure equalization between the first and second chambers. The second communication passage may have a large cross section, so that the pressure in the first and second chambers is always the same. However, the first connection channel is dimensioned in such a way that in the overpressure case, as already described above, more working fluid can be discharged from the first chamber into the hydraulic chamber than can flow from the second chamber via the first connecting channel into the first chamber.

This will cause the working fluid level in the first chamber to drop. As soon as the working fluid level in the first chamber is at the level of the leak-relief valve, less working fluid and, in addition, gas in the hydraulic space is tracked. However, if gas is in the hydraulic space, due to the compressibility of the gas, this results in reduced movement of the membrane, thus reducing the metering efficiency and thus preventing the metering pump from being heated above a predetermined maximum temperature. As soon as the blockage in the pressure line has been rectified, no working fluid will escape from the hydraulic chamber via the pressure relief valve. The existing gas in the hydraulic chamber is then discharged successively via the vent valve. As now less hydraulic fluid is needed in the hydraulic chamber, the working fluid level in the first room will increase again and the dosing will increase again.

In an alternative embodiment, it is provided that the first chamber is designed such that working fluid can only reach the first chamber via the first connecting channel. In this case, therefore, no pressure compensation via a second connection channel is possible. In overpressure, this means that more working fluid is transferred via the leak-relief valve from the first chamber into the hydraulic chamber as working fluid from the second chamber can flow into the first chamber, that the pressure of the working fluid in the first chamber is significantly reduced. By lowering the pressure, the hydraulic oil cavitates, thus introducing gas into the hydraulic space. As a result, the hydraulic displacement process of the pump is disturbed so much that the power consumption of the drive drops sharply and consequently an excessive heating of the hydraulic fails.

Also in this embodiment, a second connection channel may be helpful if it is closed by a check valve, wherein the flow direction of the check valve is arranged in the direction of the second chamber. The check valve ensures that the second connection channel remains closed in all the previously described functional states of the pump.

However, it may be required for some applications that, if the membrane layer does not match the desired position, a safety valve or a specially designed leak-relief valve returns at least a portion of the working fluid back to the first chamber to protect the membrane. This is the case, for example, in the case of a blockage of the suction line, if the membrane does not move back into the suction position and therefore too much Working fluid flows into the hydraulic chamber. During the pressure stroke, the membrane then moves beyond the pressure position, which can lead to damage to the membrane. Therefore, a safety valve or a specially designed leak-relief valve can be provided, which opens in the event that the membrane moves beyond the printing position.

If the safety valve or the leak-relief valve are designed such that the escaping working fluid is returned to the first chamber, the use of the check valve in the second connecting channel is advantageous, which then possibly give overpressure occurring in the first chamber via the check valve in the second chamber can be.

The leak-relief valve is advantageously designed such that it has a between a closed position, in which the valve passage is closed, and an open position in which the valve passage is open, a reciprocating closing body, which held by means of a pressure element in the closed position is, wherein the pressure element is designed such that when the pressure in the hydraulic chamber is less than a set pressure p _min , the closing body moves in the direction of the open position.

In an alternative embodiment, the first connection channel is arranged lower than the leak-relief valve. Thereby, the second chamber can be dimensioned relatively compact, since it is only necessary that the connecting channel is always below the working fluid level in the second chamber.

The device according to the invention has the advantage that no external power supply is necessary. In addition, no signal processing and evaluation is required, which makes the inventive measure maintenance and wear. There are no additional components needed.

Figur 1

eine Teilschnittansicht einer ersten erfindungsgemäßen Ausführungsform,

Figur 2

eine schematische Darstellung der Funktionsweise der Ausführungsform von Figur 1 im Normalbetrieb,

Figur 3

eine schematische Darstellung der Funktionsweise der Ausführungsform von Figur 1 im Überdruckbetrieb,

Figur 4

eine Teilschnittansicht einer zweiten Ausführungsform der Erfindung und

Figur 5

eine schematische Darstellung der Funktionsweise der zweiten Ausführungsform gemäß Figur 4.

Further advantages, features and possible applications will become apparent from the following description of two preferred embodiments and the accompanying figures. Show it:

FIG. 1

a partial sectional view of a first embodiment of the invention,

FIG. 2

a schematic representation of the operation of the embodiment of FIG. 1 in normal operation,

FIG. 3

a schematic representation of the operation of the embodiment of FIG. 1 in overpressure mode,

FIG. 4

a partial sectional view of a second embodiment of the invention and

FIG. 5

a schematic representation of the operation of the second embodiment according to FIG. 4 ,

In FIG. 1 a partial sectional view of a first embodiment of the invention is shown. The membrane (not shown) is on the left outside the representation of FIG. 1 and is connected to the leak-relief valve 5, which is resiliently biased within the hydraulic chamber 6 and closes the connection between the hydraulic chamber 6 and the first chamber 1 of the working fluid supply. The working fluid is arranged in the first chamber 1 and in the second chamber 2. The first chamber 1 and the second chamber 2 are connected to each other via a first connecting channel 4, which is designed here as a nozzle.

The nozzle cross-section is dimensioned such that in the overpressure case, more working fluid will be discharged via the leak-relief valve 5 into the hydraulic chamber 6 than can be tracked via the nozzle 4. Furthermore, an opening 3, which functions as a second connection channel, is arranged between the first chamber 1 and the second chamber 2. The leak-relief valve 5 is designed such that, in particular when at the end of the suction stroke, i. is in the suction position too little working fluid in the hydraulic chamber 6, the leak-relief valve 5 opens so that working fluid from the first chamber can flow into the hydraulic chamber 6. In normal operation, the amount of working fluid that needs to be replaced via the leak-relief valve is very low. In the overpressure case, i. For example, in a blockage of the pressure line, the pressure in the hydraulic chamber 6 increases rapidly, so for safety reasons working fluid via a pressure relief valve (not shown) discharged from the hydraulic chamber 6 and discharged, for example, in the second chamber 2 of the working fluid reservoir. In the overpressure case, the leak-relief valve 5 must track a significantly larger amount of working fluid from the first chamber.

The operation of the dosing pump according to the invention will become apparent with reference to the schematic representations of Figures 2 and 3 ,

In FIG. 2 the state is shown in normal operation. One recognizes the working fluid reservoir, which consists of the first chamber 1 and the second chamber 2, which is connected to each other by a below the liquid level nozzle 4, which acts as a first connecting channel. The second connection channel is realized through the opening 3, which is above the working fluid level. When opening the leak-relief valve 5 working fluid flows from the first chamber in the in FIG. 2 left adjoining hydraulic room.

At the moment when the leak-relief valve 5 is opened, working fluid flows out of the first chamber 1 and the fluid level in the first chamber drops. As soon as the leak-relief valve 5 is closed again, the working fluid level in the first chamber 1 rises again, since working fluid can flow via the nozzle 4 from the second chamber 2 into the first chamber 1.

In normal operation, the loss of working fluid in the hydraulic chamber is so small that during a complete stroke the tracked working fluid can easily be tracked through the first connecting channel 4 from the second chamber to the first chamber.

In the overpressure case, however, a larger amount of hydraulic fluid is discharged abruptly from the hydraulic chamber and fed back via a corresponding pressure relief valve and the supply 7 of the second chamber 2 of the working fluid. In the overpressure case, an undesired heating not only of the recirculated hydraulic oil, but also the pressure relief valve (not shown).

Due to the inventive division of the working fluid in two chambers connected by a narrow first connecting channel chambers is achieved in the overpressure operation that during a stroke not enough working fluid can flow from the second chamber into the first chamber to compensate for the working fluid loss through the pressure relief valve.

As a result, this causes, as in FIG. 3 shown schematically, the working fluid level in the first chamber 1 gradually decreases. At some point, however, the working fluid level in the first chamber 1 will be in the region of the opening to the leak-relief valve 5, so that when the leak-relief valve 5 opens, gas is also conducted into the hydraulic chamber. However, as soon as there is gas in the hydraulic chamber, the metering performance is significantly reduced due to the compressibility of the gas, whereby less energy is introduced into the pump and there is no further heating.

As soon as the overpressure operation has ended, ie any blockage in the pressure line has been eliminated, the pressure relief valve will no longer open and therefore no larger amount of hydraulic oil will leave the hydraulic chamber. In this situation, more working fluid will again flow from the second chamber into the first chamber via the nozzle 4 as working fluid from the first chamber 1 is fed into the hydraulic chamber via the leak-relief valve 5, so that the working fluid level in the first chamber 1 will increase again. Once the level has risen so far that the leak-relief valve is again completely below the working fluid level, no gas is in the hydraulic chamber fed and the dosing increases again. The gas contained in the hydraulic chamber can be discharged via a vent valve.

In FIG. 4 a partial sectional view of a second embodiment of the invention is shown. This differs essentially from the first embodiment in that there is no pressure equalization, the second connecting channel is present and the connection of the first and second chamber is closed by a check valve 9, which prevents a working fluid flow from the second chamber 2 into the first chamber 1 and a bypass 10, which has a small cross-section, so that working fluid can flow from the second chamber 2 into the first chamber 1 to a lesser extent.

In Fig. 4a the check valve 9 with bypass 10 is shown enlarged. It can be seen that the bypass line 10 provides a direct connection between the first chamber 1 and second chamber 2.

Fig. 5 is a schematic diagram illustrating the operation of the embodiment of FIG FIG. 4 clarified.

In normal operation, the loss of working fluid in the hydraulic chamber is so small that during a complete stroke the supplied via the leak-relief valve 5 working fluid can be easily tracked through the bypass 10 from the second chamber into the first chamber.

In the overpressure case, however, a larger amount of hydraulic fluid is discharged abruptly from the hydraulic chamber and fed back via a corresponding pressure relief valve and the supply 7 of the second chamber 2 of the working fluid. In the overpressure case, an undesired heating not only of the recirculated hydraulic oil, but also the pressure relief valve (not shown).

Due to the inventive division of the working fluid in two chambers connected by a narrow first connecting channel chambers is achieved in the overpressure operation that during a stroke not enough working fluid can flow from the second chamber into the first chamber to compensate for the working fluid loss through the pressure relief valve.

As a result, this leads to the fact that aufgurnd the lack of pressure equalization in the overpressure case more working fluid from the chamber 1 is discharged into the hydraulic chamber 6 as can flow via the bypass 10 from the second chamber 2 into the first chamber 1, so that the Pressure in the first chamber drops rapidly. This has the consequence that cavitation occurs, ie the working fluid from guest and the resulting gas is transported via the leak-relief valve in the hydraulic chamber, which also leads to an incomplete stroke, which reduces the energy introduced into the pump and the temperature is lowered.

Once the overpressure operation is completed, i. any blockage in the pressure line has been eliminated, the pressure relief valve will not open and therefore no larger amount of hydraulic oil leave the hydraulic chamber. In this situation, more working fluid will again flow from the second chamber into the first chamber via the bypass 10 as working fluid from the first chamber 1 is fed into the hydraulic chamber via the leak-relief valve 5, so that the pressure in the first chamber 1 will increase again. As soon as the pressure has risen again accordingly, cavitation will no longer occur and the dosing capacity will rise again. The gas contained in the hydraulic chamber can be discharged via a vent valve.

In fault operation of the membrane layer, for example in a blockage of the suction line, the leak-relief valve opens and the excessive hydraulic oil volume can flow via the first chamber 1 and the opening check valve 9 with slight overpressure in the second chamber 2, without the membrane being damaged.

LIST OF REFERENCE NUMBERS

1

first chamber

2

second chamber

3

second connection channel

4

Nozzle / first connection channel

5

Leakage compensation valve

6

hydraulic chamber

7

feed

9

check valve

10

bypass

Claims (7)

1. A diaphragm pump comprising a delivery chamber separated from a hydraulic chamber (6) by way of a diaphragm, wherein the delivery chamber is respectively connected to a suction connection and a pressure connection and the hydraulic chamber which can be filled with a working fluid can be acted upon with a pulsating working fluid pressure and the diaphragm can be reciprocated between a pressure position in which the volume of the delivery chamber is smaller and a suction position in which the volume of the delivery chamber is larger, wherein the hydraulic chamber (6) is connected to a working fluid supply by way of a leak replenishment valve (5), wherein the leak replenishment valve is so designed that when the pressure in the hydraulic chamber in the suction position of the diaphragm is less than a predetermined minimum value (p_min) the leak replenishment valve opens and the hydraulic chamber has an outlet passage which is closed by a pressure limiting valve which is so designed that if the pressure in the hydraulic chamber (6) rises above a predetermined maximum value (p_max) the pressure limiting valve opens so that working fluid can leave the hydraulic chamber by way of the outlet passage, wherein the working fluid supply is arranged in a first (1) and in a second chamber (2), the two chambers being connected together by way of a first connecting passage (4), characterised in that the outlet passage is connected to the second chamber (2), and in that the connecting passage is either closable or the flow through the connecting passage is throttled or at least can be throttled so that in an overpressure situation, that is to say when hydraulic oil has left the hydraulic chamber by way of the pressure limiting valve, more hydraulic oil is passed out of the first chamber into the hydraulic chamber than can flow during a stroke from the second chamber into the first chamber.
2. A diaphragm pump as set forth in claim 1 characterised in that the leak replenishment valve (5) has a closing member which is reciprocable between a closed position in which the valve passage is closed and an open position in which the valve passage is opened and which is held in the closed position by means of a pressure element, wherein the pressure element is so designed that when the pressure in the hydraulic chamber is less than a setting pressure (p_min) the closing member moves in the direction of the open position.
3. A diaphragm pump as set forth in one of claims 1 or 2 characterised in that the first connecting passage (4) is arranged lower than the leak replenishment valve (5).
4. A diaphragm pump as set forth in claim 3 characterised in that there is provided a second connecting passage (3) between the first chamber (1) and the second chamber (2), wherein the second connecting passage (3) is arranged above the first connecting passage (4) and preferably above the leak replenishment valve (5), wherein particularly preferably the second connecting passage (3) is arranged above the level of working fluid in the second chamber (2).
5. A diaphragm pump as set forth in claim 4 characterised in that the first chamber (1) is so designed that working fluid can pass from the second chamber (2) into the first chamber (1) only by way of the first connecting passage (4).
6. A diaphragm pump as set forth in claim 5 characterised in that the second connecting passage (3) is closed by a non-return valve, the through-flow direction of the non-return valve being arranged in the direction of the second chamber (2).
7. A diaphragm pump as set forth in one of claims 1 through 6 characterised in that there is provided a valve (9) for closing the first connecting passage (4).

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