DIAPHRAGM PUMP WITH REDUCED LEAK EXTENSION IN THE EVENT OF OVERLOAD

Abstract

The present invention concerns a diaphragm pump comprising a delivery chamber separated from a hydraulic chamber 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. In that arrangement the hydraulic chamber is connected to a working fluid supply by way of a leak replenishment valve, 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.sub.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 rises above a predetermined maximum value p.sub.Max the pressure limiting valve opens and working fluid can leave the hydraulic chamber by way of the outlet valve. To provide a corresponding diaphragm pump which automatically reduces the metering power in the overpressure situation without the use of additional sensors being necessary it is proposed according to the invention that the working fluid supply is arranged in a first and in a second chamber, the two chambers being connected together by way of a first connecting passage.

Claims

1. A diaphragm pump comprising a delivery chamber separated from a hydraulic chamber 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 is connected to a working fluid supply by way of a leak replenishment valve, 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 pMin 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 rises above a predetermined maximum value pMax the pressure limiting valve opens so that working fluid can leave the hydraulic chamber by way of the outlet passage, characterised in that the working fluid supply is arranged in a first and in a second chamber, the two chambers being connected together by way of a first connecting passage.

2. A diaphragm pump as set forth in claim 1 characterised in that the connecting passage is closable.

3. A diaphragm pump as set forth in claim 1 characterised in that the outlet passage is connected to the second chamber.

4. A diaphragm pump as set forth in claim 1 characterised in that the leak replenishment valve 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 pMin the closing member moves in the direction of the open position.

5. A diaphragm pump as set forth in claim 1 characterised in that the first connecting passage is arranged lower than the leak replenishment valve.

6. A diaphragm pump as set forth in claim 5 characterised in that there is provided a second connecting passage between the first chamber and the second chamber, wherein the second connecting passage is arranged above the first connecting passage.

7. A diaphragm pump as set forth in claim 6 characterised in that the first chamber is so designed that working fluid can pass from the second chamber into the first chamber only by way of the first connecting passage.

8. A diaphragm pump as set forth in claim 7 characterised in that the second connecting passage 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.

9. A diaphragm pump as set forth in one of claims claim 1 characterised in that there is provided a valve for closing the first connecting passage.

10. A diaphragm pump as set forth in claim 1 characterised in that the flow through the connecting passage is throttled so that in an overpressure situation, 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.

11. A diaphragm pump as set forth in claim 1 characterised in that the flow through the connecting passage can be throttled so that in an overpressure situation, 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.

12. A diaphragm pump as set forth in claim 5 characterised in that there is provided a second connecting passage between the first chamber and the second chamber, wherein the second connecting passage is arranged above the first connecting passage and above the leak replenishment valve.

13. A diaphragm pump as set forth in claim 5 characterised in that there is provided a second connecting passage between the first chamber and the second chamber, wherein the second connecting passage is arranged above the first connecting passage and above the leak replenishment valve, wherein the second connecting passage is arranged above the level of working fluid in the second chamber.

Description

[0052] FIG. 1 shows a partial sectional view of a first embodiment of the invention. The diaphragm (not shown) is disposed at the left outside the view in FIG. 1 and is connected to a leak replenishment valve 5 which is resiliently prestressed 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 together by way of a first connecting passage 4 which here is in the form of a nozzle.

[0053] The nozzle cross-section is so dimensioned that in the overpressure situation more working fluid is discharged into the hydraulic chamber 6 by way of the leak replenishment valve 5 than can be added by way of the nozzle 4. In addition an opening 3 which functions as a second connecting passage is arranged between the first chamber 1 and the second chamber 2. The leak replenishment valve 5 is of such a design that, when too little working fluid is in the hydraulic chamber 6 in particular at the end of the suction stroke, that is to say in the suction position, the leak replenishment valve 5 opens so that working fluid can flow from the first chamber into the hydraulic chamber 6. In normal operation the amount of working fluid which has to be replaced by way of the leak replenishment valve is very small. In the overpressure situation, that is to say for example upon a blockage of the pressure line, the pressure in the hydraulic chamber 6 rises rapidly so that, for safety reasons, working fluid is discharged from the hydraulic chamber 6 by way of a pressure limiting valve (not shown) and is delivered for example into the second chamber 2 of the working fluid supply. In the overpressure situation the leak replenishment valve 5 must pass a markedly larger amount of working fluid out of the first chamber.

[0054] The mode of operation of the metering pump according to the invention will be apparent from the diagrammatic views in FIGS. 2 and 3.

[0055] FIG. 2 shows the condition in the normal mode of operation. It is possible to see the working fluid supply comprising the first chamber 1 and the second chamber 2, being connected together by a nozzle 4 which is arranged beneath the fluid level and which functions as a first connecting passage. The second connecting passage is implemented by the opening 3 disposed above the level of working fluid. Upon opening of the leak replenishment valve 5 working fluid flows out of the first chamber into the hydraulic chamber adjoining same to the left in FIG. 2.

[0056] At the moment at which the leak replenishment valve 5 is opened working fluid flows out of the first chamber 1 and the level of fluid in the first chamber falls. As soon as the leak replenishment valve 5 is closed again the level of working fluid in the first chamber 1 rises again as working fluid can flow from the second chamber 2 into the first chamber 1 by way of the nozzle 4.

[0057] In the normal mode of operation the loss of working fluid in the hydraulic chamber is so slight that, during a complete stroke, the amount of working fluid supplied can be easily supplied through the first connecting passage 4 from the second chamber into the first chamber.

[0058] In the overpressure situation however a larger amount of hydraulic fluid is abruptly let out of the hydraulic chamber and is fed to the second chamber 2 of the working fluid supply again by way of a corresponding pressure limiting valve and by way of the feed 7. In the overpressure situation there is an unwanted rise in temperature not only of the recycled hydraulic oil but also of the pressure limiting valve (not shown).

[0059] The fact that the working fluid supply is divided according to the invention into two chambers connected by a narrow first connecting passage provides however in the overpressure mode of operation that during a stroke it is no longer possible for sufficient working fluid to flow from the second chamber into the first chamber in order to compensate for the loss of working fluid by way of the pressure limiting valve.

[0060] As a result this means that, as diagrammatically shown in FIG. 3, the level of working fluid in the first chamber 1 gradually falls. Sometime the level of working fluid in the first chamber 1 will however be in the region of the opening to the leak replenishment valve 5 so that, when the leak replenishment valve 5 opens, gas is also passed into the hydraulic chamber. As soon as gas is in the hydraulic chamber however the metering power is markedly reduced due to the compressibility of the gas whereby less energy is introduced into the pump and a further rise in temperature fails to occur.

[0061] As soon as the overpressure mode of operation is concluded, that is to say a blockage which is possibly present in the pressure line has been removed, the pressure limiting valve will no longer open and therefore a larger amount of hydraulic oil will not leave the hydraulic chamber. In that situation once again more working fluid will flow from the second chamber into the first chamber by way of the nozzle 4 than working fluid is caused to flow from the first chamber 1 into the hydraulic chamber by way of the leak replenishment valve 5 so that the level of working fluid in the first chamber 1 will rise again. As soon as the level has risen to such an extent that the leak replenishment valve is again completely beneath the level of the working fluid then no more gas is passed into the hydraulic chamber and the metering power rises again. The gas contained in the hydraulic chamber can be discharged by way of a venting valve.

[0062] FIG. 4 shows a partial sectional view of a second embodiment according to the invention. This differs from the first embodiment substantially in that there is no second connecting passage functioning as a pressure equalization means and the connection of the first and second chambers is closed by a non-return valve 9 which prevents a flow of working fluid from the second chamber 2 into the first chamber 1 and has a by-pass 10 which is of a small cross-section so that working fluid can flow to a slight extent from the second chamber 2 into the first chamber 1.

[0063] FIG. 4a shows the non-return valve 9 with by-pass 10 on an enlarged scale. It will be seen that the by-pass line 10 provides a direct communication between the first chamber 1 and the second chamber 2.

[0064] FIG. 5 is a diagrammatic view showing the mode of operation of the embodiment of FIG. 4.

[0065] In normal operation the loss of working fluid in the hydraulic chamber is so slight that, during a complete stroke, the amount of working fluid added by way of the leak replenishment valve 5 can easily be passed through the by-pass 10 from the second chamber into the first chamber.

[0066] In the overpressure situation however a larger amount of hydraulic fluid is abruptly let out of the hydraulic chamber and fed to the second chamber 2 of the working fluid supply again by way of a suitable pressure limiting valve and by way of the feed means 7. In the overpressure situation there is an unwanted rise in temperature not only of the recycled hydraulic oil but also of the pressure limiting valve (not shown).

[0067] The fact that the working fluid supply is divided according to the invention into two chambers connected by a narrow first connecting passage provides however in the overpressure mode of operation that during a stroke it is no longer possible for sufficient working fluid to flow from the second chamber into the first chamber in order to compensate for the loss of working fluid by way of the pressure replenishment valve.

[0068] As a consequence the result of this is that, by virtue of the lack of pressure equalization in the overpressure situation, more working fluid is discharged from the chamber 1 into the hydraulic chamber 6 than can flow by way of the by-pass 10 from the second chamber 2 into the first chamber 1 so that the pressure in the first chamber rapidly falls. This has the consequence that cavitation occurs, that is to say the working fluid outgases and the resulting gas is transported by way of the leak replenishment valve into the hydraulic chamber, which likewise leads to an incomplete stroke whereby the energy introduced into the pump is reduced and the temperature is reduced.

[0069] As soon as the overpressure mode of operation is concluded, that is to say a blockage which is possibly present in the pressure line, has been removed, the pressure limiting valve will no longer open and therefore a relatively large amount of hydraulic oil will not leave the hydraulic chamber. In that situation once again more working fluid will flow from the second chamber into the first chamber by way of the by-pass 10, than working fluid is passed from the first chamber 1 into the hydraulic chamber by way of the leak replenishment valve 5 so that the pressure in the first chamber 1 will rise again. As soon as the pressure has correspondingly risen again no further cavitation will occur and the metering power rises again. The gas contained in the hydraulic chamber can be discharged by way of a venting valve.

[0070] In the disturbance mode of operation in respect of the diaphragm position, for example upon a blockage in the suction line, the leak replenishment valve opens and the excessively large volume of hydraulic oil can flow by way of the first chamber 1 and the opening non-return valve 9 at a slightly increased pressure into the second chamber 2 without the diaphragm suffering damage.

LIST OF REFERENCES

[0071] 1 first chamber [0072] 2 second chamber [0073] 3 second connecting passage [0074] 4 nozzle/first connecting passage [0075] 5 leak replenishment valve [0076] 6 hydraulic chamber [0077] 7 feed means [0078] 9 non-return valve [0079] 10 by-pass