EP0688954A1 - Controlled replenishment device for high pressure membrane pumps - Google Patents

Abstract

An obstruction is formed by an oscillating piston (8), which acts upon a pump membrane (1) by hydraulic fluid. A spring loaded relief valve prevents excessive suction, by permitting hydraulic fluid to flow from the supply volume (9) to the pressurised volume (7). The piston acts as a control slide, releasing the connection to the relief valve only after at least part of the suction stroke has been completed. The connection may be released if the piston has completed approximately half of its stroke, or may be kept closed for at least the start of the stroke. <IMAGE>

Description

The invention relates to a hydraulically driven diaphragm pump according to the preamble of claim 1.

In known diaphragm pumps of the generic type, a leakage supplement device, a so-called sniffing device, is usually provided, which has a sniffing connection in the form of a connecting channel between the pressure chamber and the storage chamber. This connection channel is normally closed by a vacuum-controlled, spring-loaded sniffer valve. The snifting valve then responds or opens the connection between the pressure chamber and the storage chamber when the piston generates an excessive vacuum in the hydraulic system caused by a lack of hydraulic fluid during the suction stroke. This negative pressure in the work space is detected by the sniffer valve, so that the missing hydraulic fluid in the pressure space can then be supplemented via the connecting channel coming from the storage space.

With such a leak supplement, the problem arises that vacuum peaks that occur in the hydraulic system at the beginning of Suction stroke of the piston occur, lead to a premature response of the sniffer valve. Such a pronounced vacuum peak, the so-called Joukowsky shock, occurs preferably in the case of large high-pressure diaphragm pumps at the beginning of the suction phase when the liquid column in the suction line is accelerated suddenly when the suction valve is opened. The resultant premature response of the snifting valve results in the pressure chamber being overfilled with hydraulic fluid, which in turn causes the diaphragm to be deflected or stressed excessively during the pressure stroke.

In order to avoid such a premature response of the snifting valve due to the occurring vacuum peaks - and the resulting overfilling of the hydraulic pressure chamber with hydraulic fluid - it is already known to influence the leakage supplementation by means of a so-called membrane system control. Here, the membrane itself takes over the actuation of a control valve, a control slide controlled by the membrane sensing the membrane in the area of the suction stroke end position and in this suction stroke end position of the membrane opening the connection from the storage space to the pressure space. The leak is only supplemented when the membrane has reached a predetermined limit position at the end of the suction stroke.

Furthermore, a modified membrane system control is also known, by means of which premature leakage supplementation can also be prevented. Here, a control system influenced by the respective membrane system is also provided, which works with spring-loaded control pins. These normally keep the leakage valve closed mechanically. However, if a movably guided perforated plate is moved accordingly against the force of springs through the membrane in the suction stroke end position, the control pins are also displaced thereby, so that the leakage supplement valve is released.

Known membrane control systems of this type, however, have the disadvantage that they are structurally complex. In addition, they have to be set very precisely in order to function precisely in the case of small diaphragm strokes, which occur particularly in high-pressure diaphragm pumps with metal diaphragms.

The invention is therefore based on the object of designing the diaphragm pump of the generic type in order to eliminate the disadvantages described in such a way that a premature response of the snifting valve, in particular during the occurrence of the coupling vacuum peak, is prevented with little design effort and thus prevents such vacuum peaks from already occurring trigger the sniffer valve at the beginning of the suction stroke.

The features of the invention created to achieve this object result from claim 1. Advantageous refinements thereof are described in the further claims.

The invention is based on the essential idea of controlling the sniffer connection between the pressure chamber and the storage chamber not by the membrane system but by the position of the displacement piston itself. This is done in such a way that the piston serves as a control element, in particular as a control slide, which at least at the beginning of the suction stroke interrupts the sniffer connection between the pressure chamber and the storage chamber and only releases this connection when it has covered part of its suction stroke. In this case, the piston preferably releases the sniffer connection when it has covered approximately half of its stroke.

Overall, this effectively prevents the vacuum peak occurring at the beginning of the suction stroke Sniffer valve triggers prematurely, because at this point the sniffer connection between the pressure chamber and the storage chamber is still inevitably closed by the piston.

Such a sniffing obstruction, controlled by means of the respective piston position, can be achieved with simple constructive means, at the same time ensuring that it works effectively.

In an embodiment of the invention, it is possible to have the piston act directly or indirectly as a control slide, but in any case the design effort associated with a diaphragm control system is avoided. In addition, it is possible to provide the control on the high-pressure side or on the low-pressure side, so that either a pressure-chamber-side channel of the sniffer connection or a reservoir-side channel is kept closed or controlled by the piston.

If the piston keeps the pressure chamber side channel of the sniffer connection closed - at least at the beginning of its suction stroke - the arrangement is preferably such that this pressure chamber side channel of the sniffer connection opens into the cylinder bore for the piston. This pressure chamber-side channel of the sniffing connection is therefore only released by the piston for the purpose of supplementing the leak when the latter has covered a certain distance of its suction stroke, so that the vacuum peak which occurred at the beginning of the suction stroke has remained ineffective.

If, on the other hand, the piston keeps a reservoir-side channel of the sniffer connection closed for a certain time at the beginning of its suction stroke, the configuration can be such that the reservoir-side channel of the sniffer connection opens into the cylinder bore for the piston. This canal-side canal then connected to a piston channel, which opens into the storage space, when the piston has covered part of its suction stroke.

In a modification of this, it is also possible for the piston to act indirectly as a control element, for example by connecting the piston at its rear end to a parallel auxiliary control slide. This is displaceable in a part of the channel of the sniffer connection on the storage space side and can, because it is hollow or as a sleeve, interrupt or release the connection to the storage space depending on the stroke position of the displacement piston.

Overall, the invention prevents with simple means that the vacuum peak occurring in the hydraulic system at the start of the suction stroke causes the snifting valve to respond prematurely, which would result in the pressure chamber being overfilled with hydraulic fluid.

Fig. 1

schematisch im Schnitt eine hydraulisch angetriebene Membranpumpe mit einer durch den Kolben bewirkten hochdruckseitigen Steuerung der Schnüffelbehinderung;

Fig. 2

schematisch in Form zweier Diagramme (1. Druck über Hubweg = Indikatordiagramm und 2. Druck über Zeit) den Kurvenverlauf charakteristischer Daten beim Druckhub sowie Saughub der Membranpumpe zur Darstellung der beim Beginn des Saughubes auftretenden Unterdruckspitze;

Fig. 3

eine abgewandelte Ausführungsform mit einer niederdruckseitigen Steuerung der Schnüffelbehinderung;

Fig. 4

eine gegenüber Fig. 3 abgewandelte Ausführungsform mit niederdruckseitiger Steuerung und

Fig. 5

eine weiterhin abgewandelte Ausführungsform mit einer einen zusätzlichen Steuerkolben (Hilfssteuerschieber) verwendenden niederdruckseitigen Steuerung.

The invention is explained below with reference to the drawing. This shows in:

Fig. 1

schematically in section a hydraulically driven diaphragm pump with a high-pressure control of the sniffing obstruction caused by the piston;

Fig. 2

schematically in the form of two diagrams (1st pressure over stroke = indicator diagram and 2nd pressure over time) the curve of characteristic data during the pressure stroke and suction stroke of the diaphragm pump to show the vacuum peak occurring at the start of the suction stroke;

Fig. 3

a modified embodiment with a low-pressure control of the sniffing disability;

Fig. 4

an alternative to FIG. 3 embodiment with low-pressure control and

Fig. 5

a further modified embodiment with an additional control piston (auxiliary control slide) using low-pressure control.

The hydraulically driven diaphragm pump shown in FIG. 1 is a high-pressure diaphragm pump in which a metal diaphragm 1 is used. This is clamped between two perforated plates 2, 3 - a perforated plate 2 with a flat inner surface and a perforated plate 3 with a concave inner surface. These, in turn, are clamped between a pump housing 4 and a pump cover 5, which is detachably attached to the front of the latter.

The membrane 1 separates a delivery chamber 6 from a pressure chamber 7 filled with hydraulic fluid.

The diaphragm pump shown has a hydraulic diaphragm drive in the form of an oscillating displacement piston 8, which can be displaced in a sealed manner in the pump housing 4 between the pressure chamber 7 and a storage chamber 9 for the hydraulic fluid. In the illustrated embodiment, the piston 8 is sealed by means of a so-called ground-in seal.

The pump cover 5 has a spring-loaded inlet valve 10 and a spring-loaded outlet valve 11 in the usual way. These two valves 10, 11 are connected via an inlet channel 12 and an outlet channel 13 to the delivery chamber 6 in such a way that the conveying medium during the suction stroke of the displacer 8 and thus the diaphragm 1 to the right according to FIG the inlet valve 10 and the inlet channel 12 is sucked into the delivery chamber 6. In contrast, the pumped medium is then metered out of the delivery chamber 6 in the direction of the arrow during the pressure stroke of the piston 8 and thus of the membrane 1 via the outlet channel 13 and the outlet valve 11.

In order to prevent the pressure chamber 7 from being overfilled with hydraulic fluid and thus to protect the membrane 1 from excessive deflection or stress during the pressure stroke, a pressure limiting valve 14 is provided which communicates with the pressure chamber 7 and the storage chamber 9 via corresponding channels 15, 16 communicates; it is set such that it opens when an undesirably large excess pressure in the pressure chamber 7 occurs at the end of the pressure stroke of the piston 8, so that the excess hydraulic fluid is then discharged into the reservoir 9 via the channels 15, 16.

In order to prevent the occurrence of cavitation in a corresponding manner at the end of the membrane suction stroke and to ensure the leakage supplementation required due to the leakage losses, a leakage supplementation device 17 is provided. This has a conventional spring-loaded, vacuum-controlled sniffer valve 18, which is connected to the storage space 9 via a channel 19. The leak supplement device 17 or the sniffer valve 18 is connected to the pressure chamber 7 via a further channel 20 which, as can be clearly seen in FIG. 1, leads from the sniffer valve 18 directly into the cylinder bore 21 for the piston 8 or opens there. In the exemplary embodiment shown, this pressure chamber-side channel 20 opens into the piston cylinder bore 21 at a point which is approximately half the stroke h of the piston 8, i.e. in the middle between its front and rear dead center.

As can be seen, the piston 8 holds the pressure chamber side Channel 20 of the leakage supplement device 17 is closed at the beginning of its suction stroke, so that the sniffer connection between the pressure chamber 7 and the storage chamber 9 is thereby interrupted. This connection is only released by the piston 8 when it has covered part of its suction stroke. Only then is the leakage replenishment device 17 or the sniffer valve 18 able to replenish hydraulic fluid from the reservoir 9 when an excessively high vacuum caused by leakage losses occurs.

The arrangement shown, in which the controlled sniffing hindrance occurs on the high pressure side, is particularly suitable for stroke-controllable diaphragm pumps with a constant piston center position. As already explained, the piston 8 is used as a control slide for temporarily blocking the leakage supplement device 17 in order to prevent its premature response at the beginning of the piston suction stroke. At the beginning of the suction stroke, the piston 8 is in the position according to FIG. 1, in which its front end surface is approximately flush with the corresponding wall of the pressure chamber 7. In this piston position, which corresponds to position 3 of the two diagrams according to FIG. 2, the channel 20 of the leakage supplement device 17 on the pressure chamber side is closed by the piston 8. After the piston 8 has moved to position 4 in the respective diagrams according to FIG. 2 in the course of its suction stroke, the suction pressure ps generated is sufficient to open the inlet valve 10. Then the liquid column in the inlet line 12, the inlet valve 10 and the membrane 1 must be accelerated, whereby a vacuum peak with the amplitude Δp is generated, as can be seen at position 4 in the respective diagrams according to FIG. 2. This vacuum peak, referred to as Joukowsky shock, would normally cause the snifting valve 18 to respond prematurely and thus undesirably overfill the pressure chamber 7 with hydraulic fluid from the storage chamber 9. While At this time, however, the channel 20 on the pressure chamber side is still closed by the piston 8, so that, owing to this purely piston-controlled sniffer, the sniffer valve 18 cannot respond to the vacuum peak mentioned. Only towards the end of the suction stroke, after the piston 8 has covered the distance h (= suction stroke) shown in FIG. 1, does the end face of the piston 8 pass through the opening of the channel 20 on the pressure chamber side and release it. Thus, it is now possible to add hydraulic fluid from the storage space 9 via the channels 19, 20 to the pressure space 7 during a remaining short piston travel distance.

In the modified embodiment shown in FIG. 3, in contrast to the control of the sniffing obstruction on the high-pressure side according to FIG. 1, control of the sniffing obstruction on the low-pressure side is provided. This is particularly suitable for diaphragm pumps with a constant stroke length, the sealing of the piston 8 within its cylinder bore 21 likewise being formed by means of a single-joint seal, just as in the previously described embodiment according to FIG. 1.

As can be seen from FIG. 3, in this embodiment, the pressure chamber-side channel 20a starting from the snifting valve 18 of the treat device 17 is arranged in such a way that it does not open into the cylinder bore 21 of the displacer 8, but rather runs to the pressure chamber 7 and opens out at its end wall.

The channel 19 on the storage room side, which, starting from the sniffer valve 18, runs in the direction of the storage room, is also provided. However, its end facing away from the snifting valve 18 does not open directly into the storage space 9, but, as it were, only indirectly. For this purpose, the channel 19 on the storage room side opens with its end facing away from the snifting valve 18 into an additional channel 19a, which - transversely extending to the axis of the displacer 8 - runs in a bush-like insert 22 which displaceably guides the piston 8 and in turn opens into the storage space 9.

The piston 8 has an annular groove 23 at a specific point on its longitudinal extent, this point being selected such that it is at a distance h (piston stroke path) from the additional duct 19a when the piston 8 is at its front dead center position (pressure stroke end shown in FIG. 3) ) having. This means that the piston 8 in the position shown, which also marks the start of the suction stroke - corresponding to position 3 in the two diagrams according to FIG. 2 - keeps the additional channel 19a closed and thus also the sniffer connection between the supply chamber 9 and the pressure chamber 7 interrupts. If the piston 8 then moves from left to right in the course of its suction stroke according to FIG. 3 and thereby passes through position 4 in the two diagrams according to FIG. 2, the vacuum peak which occurs cannot lead to a premature response of the snifting valve 18 since the annular groove 23 of the piston 8 is still at a distance from the additional channel 19a, so that the sniffer connection to the storage space is interrupted.

When the piston 8 has arrived at the end of its suction stroke and, in accordance with position 1 in the two diagrams according to FIG. 2, assumes the position shown in broken lines according to FIG. 3, the annular groove 23 of the piston 8 is at the level of the additional channel 19a. As a result, the sniffer connection between the reservoir 9 and the pressure chamber 7 is established via the channels 19a, 19 and 20a, so that when an excessive vacuum is created in the hydraulic system due to a lack of hydraulic fluid, the sniffer valve 18 responds and automatically the missing hydraulic fluid from the Storage room 9 added. Then when the piston 8 starts again with the pressure stroke and moves from position 1 to position 2 according to the two diagrams according to FIG. 2, the annular groove 23 of the piston 8 immediately shifts out of alignment with the additional channel 19, so that the latter is closed immediately and the sniffer connection is interrupted.

In the further modified embodiment according to FIG. 4, the configuration is similar to the embodiment according to FIG. What is different, however, is that the piston 8 is sealed in your bore 21 not by means of a single-joint seal, but by means of piston rings 24, which are fixed on the piston 8 in the usual way.

In addition, the piston 8 instead of an annular groove 23 is provided with a reduced-diameter piston part 8a, so that an annular space 23a is formed between this reduced-diameter piston part 8a and the associated cylinder bore 21, which function corresponds to that of the annular groove 23.

As can be seen, the additional channel 19a connected to the storage chamber-side channel 19 is designed in such a way that it does not pass through the entire insert 22, transverse to the axis of the piston 8, but only opens into the cylinder bore 21 of the piston 8. The connection between the additional channel 19a and the storage space 9 is made, with a corresponding piston position, in that a further channel 19b is provided in the insert part 22, which extends from the storage space 9 to the cylinder bore 21 of the piston 8 and there at a point which displaces to the mouth of the additional channel 19a, opens out.

As is clearly evident from FIG. 4, in the position of the piston 8 shown, which corresponds to the position at the end of the pressure stroke or at the beginning of the suction stroke corresponding to position 3 in the two diagrams according to FIG. 2, the sniffer connection between the storage space 9 and the pressure space 7 is interrupted. The same also applies if the piston 8 passes over the position 4 in the two diagrams according to FIG. 2 in the course of its suction stroke, since here the two channels 19a, 19b are still closed by the piston 8, so that the in this position occurring vacuum peak can not lead to a premature response of the sniffer valve 18. Only when the piston 8 approaches or reaches position 1 in the two diagrams according to FIG. 2 in the course of its further suction stroke, does the piston 8 with its reduced-diameter piston part 8a reach the region of the two mouths of the channels 19a, 19b. As a result, the connection between these two channels 19a, 19b is then established via the annular space 23a, so that the sniffing connection between the storage space 9 and the pressure space 7 is hereby also released and any necessary leakage addition via the snifting valve 18 is made possible.

In the further modified embodiment according to FIG. 5, low-pressure control of the sniffing obstruction is also provided. For this purpose, the piston 8 has a parallel auxiliary control slide in the form of an additional control piston 25 at its storage chamber end. This is arranged on a flange 26 attached to the piston 8 in the vicinity of its circumference and extends in such a way that it plunges into a correspondingly extending channel 27 of the housing 4. As shown, this housing channel 27 is connected, on the one hand, to the channel 19 of the leakage supplement device 17 on the storage room side and, on the other hand, opens out into the storage room 9.

The additional control piston 25 is hollow or a sleeve with ends open on both sides. In this way, on the one hand, in the position of the piston 8 shown, which corresponds to the end of the pressure stroke or the beginning of the suction stroke according to FIG Position 3 in the two diagrams according to FIG. 2 corresponds to the sniffer connection between the storage chamber 9 and the pressure chamber 7 being interrupted, since the control piston 25 is largely completely immersed in the housing channel 27 and thus closes the channel 19 on the storage chamber side. On the other hand, the additional control piston 25, when the piston 8 is near or in its suction stroke end position - corresponding to position 1 in the two diagrams according to FIG. 2 - together with the piston 8 has shifted accordingly, so that the connection between the storage chamber side channel 19 and the housing channel 27 is released. Thus, the sniffer connection between the storage chamber 9 and the pressure chamber 7 - via the hollow control piston 25, the housing channel 27, the storage chamber-side channel 19 and the pressure chamber-side channel 20a - is made, so that with a corresponding negative pressure in the pressure chamber 7, the sniffer valve 18 responds and for an automatic leak replenishment from the storage room 9 ensures.

When the piston 8 then begins the pressure stroke again and moves from position 1 to position 2 according to the two diagrams according to FIG. 2, the control piston 25, which moves synchronously with the piston 8, plunges again into the housing channel 27 and closes again the canal 19.

Claims (8)

Hydraulically driven diaphragm pump, in particular high-pressure diaphragm pump, with a diaphragm (1) clamped in between the pump housing (4) and the pump cover (5), in particular a metal diaphragm, which separates a delivery chamber (6) from a hydraulic pressure chamber (7),
a hydraulic diaphragm drive in the form of an oscillating displacement piston (8) which can be displaced in a cylinder bore (21) of the pump body (4) between the pressure chamber (7) and a storage chamber (9) for the hydraulic fluid,
and a leakage supplement device (17), which has a sniffer connection in the form of a connecting channel (19, 20) between the pressure chamber and the storage chamber, which is normally closed by a vacuum-controlled, spring-loaded sniffer valve (18),
characterized,
that the position of the piston (8) controls the sniffer connection between the pressure chamber (7) and the reservoir (9), such that the piston (8) serves as a control slide which interrupts the sniffer connection between the pressure chamber and the reservoir at least at the beginning of the suction stroke and only then releases when he has covered part of his suction stroke. Diaphragm pump according to claim 1, characterized in that the piston (8) releases the sniffer connection between the pressure chamber (7) and the storage chamber (9) after approximately half of its suction stroke. Diaphragm pump according to claim 1 or 2, characterized in that the piston (8) keeps the channel (19) of the sniffer connection on the storage chamber side closed at least at the beginning of its suction stroke. Diaphragm pump according to Claim 3, characterized in that the duct (19) of the sniffer connection on the storage chamber side opens into the cylinder bore (21) for the piston (8) and can be connected to a piston duct (23; 23a) which leads to the storage chamber, when the piston (8) has covered part of its suction stroke. Diaphragm pump according to claim 3, characterized in that the piston (8) is connected at its storage chamber end to a parallel auxiliary control slide (25) which is displaceable in part (27) of the storage chamber channel (19) of the sniffer connection and its connection to the storage chamber (9) interrupts or releases depending on the stroke position of the displacer (8). Diaphragm pump according to claim 5, characterized in that the auxiliary control slide (25) is hollow or a sleeve. Diaphragm pump according to Claim 1 or 2, characterized in that the piston (8) keeps the channel (20) of the sniffer connection on the pressure chamber side closed at least at the beginning of its suction stroke. Diaphragm pump according to claim 7, characterized in that the pressure chamber-side channel (20) of the sniffer connection opens into the cylinder bore (21) for the piston (8).

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