EP0072275B1 - Diaphragm pump for a vacuum free of oil - Google Patents

Abstract

Dry vacuum diaphragm pump, for pumping between an inlet port (2) and an exhaust port (3), and comprising a tubular diaphragm (12) retained by its resilience on a central body (11) in the biconical interior volume of a body (1), in such manner as to form a pumping chamber (15) into which debouch inlet and exhaust ports, and a control chamber (16). Port (3) communicates through a valve (7) with a capacity (9) maintained under partial vacuum by an auxiliary vacuum pump (23). The distribution mechanism (20, 21, 27) places the chamber (16) in communication alternatively with atmosphere and with the intake of the auxiliary pump (23).

Description

The present invention relates to a dry membrane vacuum pump, more particularly intended to constitute at least one stage of a vacuum pump for obtaining a vacuum free of oil contamination.

For many applications of the vacuum technique, obtaining a "clean" vacuum, without oil contamination, is an essential need. Oil diffusion pumps are therefore more and more often replaced by ionic, cryogenic, etc. pumps.

Unfortunately, these modern pumps can only be used if a "primary" pressure of the order of 1 Pascal or less has already been obtained. This primary vacuum must of course be clean too. In the current state of the art, this result can only be obtained by sorption pumps, cooled with liquid nitrogen, with all the disadvantages that this entails.

The only "clean" mechanical pumps in use are diaphragm pumps.

A diaphragm pump, whether used as a vacuum pump or as a compressor, has a tight elastic membrane stretched between two rigid bodies. There is thus formed, on either side of the membrane, on the one hand a pumping chamber into which open orifices provided with valves for suction and discharge, and on the other hand a control chamber where the the pressure is varied cyclically to generate the pumping movement of the membrane. French patent 581223 for example describes such a pump. However, the limit vacuum obtained by such pumps in single-stage systems is of the order of at least 10 ⁴ Pascals. This relatively high limit is due, among other things, to the use of valves. In particular, the conductance of an intake valve decreases with the pressure of the vacuum system and tends towards zero. The valves are also generating what is called a "dead volume"; at the end of each cycle, a small volume of pumped gas is trapped at the discharge pressure and returns to the emptied enclosure. Finally, the movement of the membrane is obtained by rigid coupling with a mechanical device. The flexibility of the membrane is thus considerably reduced, which further increases the dead volume. But above all the discharge conductance for the parts remote from the discharge valve becomes very low. A certain quantity of gas is then trapped at high pressure, deforming the membrane and considerably increasing the dead volume.

The subject of the present invention is a means of obtaining a "clean" primary vacuum with a diaphragm pump, corresponding to a much lower limit pressure than that obtained with existing devices.

• a) un mouvement de refoulement en plaquant la membrane progressivement contre le premier corps rigide, obturant ainsi d'abord les orifices d'admission et refoulant ensuite le gaz vers les orifices de refoulement,
• b) un mouvement d'aspiration en ramenant la membrane vers le deuxième corps rigide, entrainant d'abord la fermeture des soupapes de refoulement et dégageant ensuite les orifices d'admission.

The invention therefore relates to a dry membrane vacuum pump for transferring a gas from at least one suction orifice to at least one discharge orifice, constituted by an elastic membrane stretched between a first and a second rigid body, such so that the volume between the membrane and the first rigid body constitutes a pumping chamber into which open the suction orifices and the discharge orifices, and that the volume on the other side of the membrane constitutes a control chamber for maneuvering the membrane by varying the pressure cyclically to generate alternately:

• a) a discharge movement by pressing the membrane progressively against the first rigid body, thereby first blocking the intake orifices and then discharging the gas towards the discharge orifices,
• b) a suction movement by bringing the membrane towards the second rigid body, first causing the closing of the discharge valves and then releasing the intake orifices.

According to the invention, the discharge orifices communicate via valves with a capacity maintained at a pressure below atmospheric pressure by an auxiliary vacuum pump; on the other hand it includes a distribution mechanism for alternately communicating the control chamber with the atmosphere and with the suction of an auxiliary vacuum pump.

According to a particular embodiment of the invention,

• - le deuxième corps est coaxial au premier,
• - la membrane élastique est de forme tubulaire de diamètre naturel inférieur au diamètre extérieur du deuxième corps, et est fixée de façon étanche par ses extrémités aux extrémités du premier corps.

the internal surface of the first rigid body has the shape of two trunks of cones joined by their bases, the delivery orifices being arranged in the middle zone of larger diameter and the suction orifices in the end zones of smaller diameter,

• - the second body is coaxial with the first,
• - The elastic membrane is of tubular shape with a natural diameter less than the outside diameter of the second body, and is fixed in leaktight manner at its ends to the ends of the first body.

According to an alternative embodiment, the same auxiliary vacuum pump is used both to maintain a vacuum downstream of the discharge valve, and to create the vacuum applied cyclically to the control chamber.

According to a simple variant of the invention, the auxiliary pump, intended to create a vacuum in the control chamber, is integrated into the main pump. It is essentially constituted by a second thick elastic membrane, stretched between the second rigid body and the first membrane. A distribution mechanism allows on the one hand to communicate alternately the space between the second rigid body and the second membrane with a source of compressed air and the atmosphere, and on the other hand, to put the control chamber , that is to say here the space between the two menbranes, at the atmospheric pressure or isolate it. The admission of atmospheric air into the control chamber coincides with the admission of compressed air under the second membrane: during this simultaneous admission, the first membrane is pressed against the first rigid body: the main pump delivers. At the same time, the second membrane is pressed against the first. In the next phase, the control chamber is isolated while the compressed air under the second membrane escapes, the second membrane retracts, creating a vacuum under the first which also retracts: the main pump sucks.

The invention will be better understood by referring to particular embodiments, given by way of example and represented by the accompanying drawings.

Figures 1 and 2 show in simplified manner, and in longitudinal section, a pump produced according to the invention provided with an external auxiliary vacuum pump. Figure 1 shows the pump at the end of the suction phase; Figure 2 at the end of the delivery phase.

Figures 3 and 4 show an alternative embodiment of the dispensing mechanism, applied to the pump of Figures 1 and 2, respectively in the suction and discharge control position.

Figures 5 and 8 show in the same conditions as in Figures 1 and 2, respectively at the end of suction and at the end of delivery, an alternative embodiment with an auxiliary control pump integrated.

By first referring to Figures 1 and 2 we will see that the pump is constituted by a first hollow rigid body 1 whose inner wall is in the form of two trunks of cones joined by their bases. The body 1 has a suction orifice 2 in an end region with a small internal diameter, while the discharge orifice 3 is located in the central part with a large internal diameter. The suction port 2 is connected by a tube 4 to the enclosure 5 in which we want to create a vacuum. The discharge orifice 3 is provided with a valve 7 constituted by a simple elastic sheet, one end of which is fixed at 8 to the body 1, while its other end is free to press against the body or to move away from it according to pressure variations on either side of the body. The valve 7 is inside a small delivery chamber 9 provided with a nozzle 10.

The center of the hollow body 1 is occupied by a cylindrical body 11 covered with a waterproof tubular elastic membrane 12, for example in a product sold under the trademark "NEOPRENE". The natural internal diameter of the membrane 12 is less than the external diameter of the body 11, so that it is applied under tension against the body 11.

The membrane 12 is distended at each end to enclose an outer flange 13; each flange 13, by tightening the screws 14 engaged on the body 11, tightly blocks each end of the membrane 12 on the end faces of the body 1. This gives two interior chambers. The chamber 15 between the membrane 12 and the body 1 constitutes the actual pumping chamber, where both the suction and discharge orifices 2 and 3 open. The chamber 16 between the membrane 12 and the body 11 constitutes the control chamber under the action of a distribution system to which it is connected by the conduit 17. When, as in FIG. 1. the membrane 12 is pressed against the body 11, the chamber 16 is in fact cut into two parts , each at one end of the body 11, but connected by the balancing duct 18.

The conduit 17, via the T-conduit 19, is connected to two two-way solenoid valves 20 and 21. The other path of the solenoid valve 20 communicates directly with the atmosphere. The other path of the solenoid valve 21 is connected by the conduit 22 to an auxiliary vacuum pump 23. A tube 24 connects the nozzle 10 of the discharge chamber 9 to a nozzle 25 on the conduit 22, in the vicinity of the solenoid valve 21.

The type and connection of electrical supply to the coils of the solenoid valves 20 and 21 are such that they operate in opposition, that is to say that one is necessarily open while the other is closed, and vice versa. In the example shown in FIGS. 1 and 2, the solenoid valve 20 is normally closed and the solenoid valve 21 normally open, and the two coils are supplied in parallel from a line 26, by means of an oscillating relay 27 which cyclically energizes and cuts power to both coils.

The first phase of evacuating the enclosure 5 can be ensured by the conventional auxiliary pump 23. The solenoid valves 20 and 21 are de-energized with the oscillating relay 27 in the rest position as shown in FIG. 1. The pump 23 sucks then directly into the enclosure 5 through the tube 4, the orifice 2, the chamber 15, the orifice 3, the valve 7 open, and the tube 24; at the same time it maintains the chamber 18 in depression, which allows the membrane 12 to remain pressed against the body 11 by its own elasticity.

When the vacuum reaches the practical limit of 1 to 2.10 ⁴ Pascals, the pump according to the invention is actuated by activating the relay 27. When the relay switches to take the position shown in FIG. 2 the coils of the solenoid valves 20 and 21 are powered; 21 is closed and 20 open. The atmospheric pressure is then established in the chamber 16 and the membrane 12 is inflated from the inside to come to be pressed against the internal biconical face of the body 1. In this movement the membrane firstly closes the suction orifice 2 , then the progressive reduction in volume of the chamber 18 flushes out by compressing the gas it contained towards the discharge orifice 3. The combined action of the compression upstream of the valve 7 and of the vacuum maintained continuously in downstream by the auxiliary pump 23 is sufficient to lift the valve and expel the gas towards the pipe 24.

When the relay 27 returns to the position of FIG. 1, the chamber 16 is again placed under vacuum and the elasticity of the membrane brings it back into contact with the central body 11. This movement firstly causes the valve to close. discharge 7, then a very high vacuum in the pumping chamber 15 because the suction pipe remains closed by the membrane until the last part of the withdrawal movement thereof. When the orifice 2 is discovered, part of the gas remaining in the enclosure is sucked into the chamber 15 and a new delivery phase can begin with a new position reversal of the relay 21 and of the solenoid valves 20 and 21.

It will be noted that in the system described, the valve 7, although constituted by a simple elastic sheet, functions in fact like a complex valve with pneumatic control: at the start of the intake phase the solenoid valve 21 opens and the air return solenoid valve 20 closes. The air accumulated in the chamber 18 under the membrane 12 spreads in the auxiliary circuit 22-24 and the pressure downstream of the discharge valve 7 rises suddenly. This valve is thus pressed energetically on its seat and the "return flow" is practically canceled in the critical intake phase. The downstream pressure, continuously pumped by the auxiliary pump 23 will then decrease continuously. At the start of the compression phase, the air re-entry valve 20 opens while the valve 21 closes to isolate the auxiliary pumping circuit downstream from the valve. The pressure in the discharge chamber 9 therefore continues to decrease during compression in the chamber 15 and the gas can be easily evacuated through the valve 7 made soft by a minimum plating force. This optimization of the operation of the discharge valve eliminates the drawbacks of "stiff" discharge valves as they exist in conventional devices.

To facilitate the action of the return flow to forcefully press the valve 7 onto its seat at the start of the intake phase, we will seek to create a strong conductance between the chamber 9 downstream of the valve 7 and the orifice. suction 17 of the control chamber 18. This will be achieved if the tap 25 on the duct 22 is close to the solenoid valve 21.

To further improve the operation, the membrane 12 may have a smaller thickness at the ends. The inlet 2 is closed off at an earlier point in the compression phase.

The choice of this geometry is dictated by the following considerations: the tubular membrane 12 with a diameter less than the outside diameter of the cylinder 11 is here still taut. It therefore retracts for a reasonable vacuum between it and the cylinder 11, even if the vacuum between it and the body 1 is already very high. Furthermore, the symmetrical shape of 1, with the delivery port in the center, ensures that at the end of compression the residual delivery cavity is exactly opposite the corresponding port 3. The real "dead volume" is thus reduced to a minimum.

The rate of pressure increase in the chamber 15, between the suction position of Figure 1 and the discharge position of Figure 2 is of the order of at least 500. The new pump could thus play the role of a "boost pump". Its coupling with existing coarse vacuum dry pumps transforms them into high performance pumps and divides the limit vacuum by a factor of at least 500.

The pumping speed depends essentially on the frequency of the intake cycle, that is to say on the pumping speed of the auxiliary pump. The vacuum required for operation is of the order of 2.10 ⁴ Pascals or more, and corresponds to a pressure range where the pumping speed of conventional diaphragm pumps is high.

The "boost pump" not only considerably improves the limit pressure, but allows the conventional pump to be used under optimum pressure conditions for pumping speed.

It is clear that the solenoid valves controlled by an oscillating relay constitute only one embodiment among others of the distribution device for alternately communicating the control chamber 18 with the atmosphere and with the auxiliary pump 23. FIGS. 3 and 4 show in a simplified manner another device operating purely pneumatically and performing the same functions as the combination of two solenoid valves 20 and 21. The device, which constitutes a vacuum dynamometer with piston and return spring, comprises a tubular body in bronze 30, closed by two bottoms 31 and 32. A piston 33 slides freely in the bore of the body 30, which it seals in two chambers 34 and 35. The piston 33 is returned by a tension spring 36 until 'in a position in abutment on a shoulder 37. The conduit 17 of the chamber 16 is connected by a U-shaped conduit 39 to the inner chamber 34 of the body 30. In the chamber 34 and facing a branch of the corrugated 39, also opens a conduit 40 connected to the conduit 22 for connection with the auxiliary pump 23. An orifice 41 also opens facing the other branch of the conduit 39 to communicate the chamber 34 with the outside. The bottom 31 has an exhaust valve 43 and a calibrated orifice 44 between the chamber 35 and the outside. Finally, the internal bent conduit 45 opens onto the lateral face of the piston 33, a usual guide not shown being provided to prevent the latter from rotating during its longitudinal stroke, so that the lateral outlet of the conduit 45 passes in front of the branches of the conduit 39.

In the position shown in Figure 3, the device is equivalent to the two solenoid valves 20 and 21 in their positions in FIG. 1. In fact, the chamber 16 communicates with the auxiliary pump via 17, 39, 34 40 and 22, while the communication with the atmosphere is cut off by the piston 33 which closes the orifice 41. The vacuum generated in the chamber 34 causes the suction of the piston 33 to the left, against the return action of the spring 36. But this movement is slowed down by the calibrated orifice 44 which does not lets air in very gradually into chamber 35.

When the piston approaches its end of stroke, it closes both the conduit 40 and the left branch of the conduit 39, which stops the suction in the chamber 16, equivalent to the closing of the solenoid valve 21 of the electrical solution. Under the effect of the time delay, the piston continues its stroke slightly to the left although the rest of the chamber 34, still under vacuum, is isolated. The piston then discovers the orifice 41 and the right branch of the conduit 39, which suddenly puts the chamber 16 in communication with the atmosphere via 17, 39, 35 and 41 equivalent to the opening of the solenoid valve 20. Under the action this time more brutal of the atmospheric pressure in the chamber 35, the piston 33 ends its course to the left until the conduit 45 is presented in front of the left branch of 39 (Figure 4). The atmospheric pressure is then established on the two faces of the piston 33, which is brought quickly to the right by the spring 36, without pneumatic braking because the air in the chamber 35 freely escapes through the valve 43.

In this recoil movement, the piston cuts the communication with the atmosphere of the chamber 16 and re-establishes the vacuum therein of the pump 23, which corresponds to a new suction cycle.

Reference will now be made to FIGS. 5 and 6 for an alternative embodiment with an integrated control auxiliary pump. Here the general geometry is the same, but the central cylindrical body 11 is surrounded by another thick waterproof elastic membrane 50, of tubular shape and hermetically tightened by its ends on the body 11 by means of collars 51.

• - la chambre de pompage proprement dite 15, où débouchent comme dans la première variante les orifices d'aspiration 2 et de refoulement 3,
• - la chambre de commande 16 qui ne communique ici par le conduit 17 qu'avec une seule électrovanne 20 normalement fermée, et dont l'autre sortie est à l'atmosphère,
• - une chambre interne 52 qui constitue la chambre de manoeuvre de la pompe auxiliaire intégrée. La chambre 52 communique, par le conduit 53 intérieur au corps 11, puis par le conduit 54 qui le prolonge en traversant le flasque 13, avec la voie centrale d'un distributeur constitué ici par exemple par une électrovanne à trois voies 55.

There is thus obtained, between the internal biconical surface of the body 1 and the central body 11, successively:

• the actual pumping chamber 15, where, as in the first variant, the suction 2 and discharge 3 ports open,
• the control chamber 16 which here communicates via the conduit 17 only with a single solenoid valve 20 normally closed, and the other outlet of which is in the atmosphere,
• - An internal chamber 52 which constitutes the operating chamber of the integrated auxiliary pump. The chamber 52 communicates, by the conduit 53 inside the body 11, then by the conduit 54 which extends it by crossing the flange 13, with the central channel of a distributor constituted here for example by a three-way solenoid valve 55.

At rest when the solenoid valve coil is not supplied, as shown in Figure 5, the conduit 54 is in communication with the atmosphere. When the coil is energized, the solenoid valve communicates the conduit 54 with the conduit 57 connected to a compressed air distribution 58, autonomous compressor or distribution network.

The electrical supply connection of the solenoid valves 20 and 55 is such that when the valve 20 is closed the valve 55 puts the conduit 54 into the atmosphere, and when the valve 20 is open the valve 55 supplies the conduit 54 and the chamber 52 in compressed air. The coils of the solenoid valves 20 and 55 are supplied in parallel from a line 26, by means of an oscillating relay 27 which cyclically energizes and cuts the supply of the two coils.

As in the variant of FIGS. 1 and 2, the delivery chamber 9 downstream from the valve 7 is maintained in permanent vacuum; this is achieved here by connecting its nozzle 10 to a compressed air ejector 60.

In the position represented in FIG. 6, corresponding to the end of the delivery phase, the atmospheric pressure established by the opening of the valve 20 in the chamber-16 drives the membrane 12 on the internal face of the body 1. At the same time time, the compressed air brought into the chamber 52 by the valve 55 inflates the membrane 50 which comes into contact with the membrane 12 and minimizes the volume of the chamber 16. The switching of the relay 27 then cuts the supply of the coils of the two solenoid valves 20 and 55 which take the positions represented in FIG. 5. The setting in the atmosphere of the chamber 52 lets the membrane 50 return to its normal position to come to be pressed against the body 11. By its removal the membrane 50 creates a strong vacuum in the chamber 16 under the membrane 12 because the closed valve 20 prevents air from entering it. The depression in the chamber 16 in turn allows the membrane 12 to retract towards the membrane 50 and the body 11, which causes a strong depression in the pumping chamber 15 and the suction as soon as the orifice 2 is uncovered .

It can be seen that the internal membrane 50 and its inflating operation with compressed air or deflating plays the same role as the auxiliary pump 23 of the first variant to create the vacuum under the main membrane 12 during the suction phase. However, here the vacuum chamber 9 is kept under vacuum by the independent ejector 60.

In this compressed air version, the pumping speed depends essentially on the flow rate of the supply circuit used. The intake volume is much larger than in mechanically coupled diaphragm pumps and the pumping speed may be increased by death.

These new pumps are therefore all naturally intended for applications where a clean primary vacuum of much less than 10 Pa must be obtained with practical and simple means, for example for priming ionic, cryogenic or turbomolecular pumps, widely used in research laboratories and the electronic industry .

Claims (10)

1. Dry vacuum diaphragm pump for transferring a gas from at least one inlet port (2) to at least one exhaust port (3), constituted by a resilient diaphragm (12) retained between a first and second rigid body, in such manner that the volume between the diaphragm (12) and the first rigid body (1) constitutes a pumping chamber (15) into which open the inlet ports and the exhaust ports, and that the volume on the other side of the diaphragm (12) constitutes a control chamber (16) for actuating the diaphragm to cause it to vary the pressure cyclically so as to generate alternatively:

(a) an exhaust movement in which the diaphragm (12) is forced progressively against the first rigid body (1), thereby first blocking the inlet ports, and then exhausting the gas in the direction of the exhaust ports,

(b) an intake movement in which the diaphragm (12) is returned toward the second rigid body (11), causing first the closure of the exhaust valves and then clearing the inlet ports,

wherein the exhaust ports (3) communicate via the valves (7) with a capacity (9) maintained at a pressure lower than atmospheric pressure by an auxiliary vacuum pump (23), and by the fact that the same comprises a distribution mechanism (21, 22) for placing the control chamber (16) alternatively in communication with atmosphere and with the intake of an auxiliary vacuum pump.

2. Dry vacuum diaphragm pump for transferring a gas from at least one inlet port (2) to at least one exhaust port (3) constituted by a resilient diaphragm (12) retained between a first an a second rigid body, in such manner that the volume between the diaphragm (12) and the first rigid body (1) constitutes a pumping chamber (15) into which open the inlet ports and the exhaust ports, and that the volume on the other side of the diaphragms (12) constitutes a control chamber (16) for actuating the diaphragm by varying the pressure in this chamber cyclically so -as to generate alternatively:

(a) an exhaust movement in which the diaphragm (12) is forced progressively against the first rigid body (1), thereby first blocking the inlet ports and then exhausting the gas in the direction of the exhaust ports.

(b) an intake movement in which the diaphragm (12) is returned toward the second rigid body (11), causing first the closure of the exhaust valves and then clearing the inlet ports

. characterized by the fact that the exhaust ports (3) communicate via the valves (7) with a capacity (9) maintained at a pressure lower than the atmospheric pressure by an auxiliary vacuum pump (60); by the fact that the control chamber is limited by the diaphragm (12) and by a second thick resilient diaphragm (50) surrounding the second rigid body (11); by the fact that the pump is fitted with a distribution mechanism (20-55) for placing the space (52) between the second body (11) and the second diaphragm (50) in alternative communication with atmosphere and with a compressed air distribution (58) and for alternatively insulating the control chamber (16) placing it in communication with the atmosphere, this phase coinciding with the admission of compressed air in the space (52); by the fact that during the admission of air at atmospheric pressure in the control chamber and of compressed air in the space (52), the diaphragm (12) is forced against the first rigid body (1) by the atmospheric pressure (exhaust phasis). Meanwhile, the second thick diaphragm (5) is forced against the first diaphragm (12) by the compressed air, thus reducing the volume of the control chamber (16) to a minimum; by the fact that, in the next phasis, the control chamber (16) is insulated and the space (52) beneath the second thick diaphragm is connected with the atmosphere: the compressed air is evacuated and the second thick diaphragm (50) shrinks and causes a depression beneath the first diaphragm (12) which shrinks also (inlet phasis). The thick diaphragm plays the role of an auxiliary pump directly located under the diaphragm (12).

3. Pump according to claim 1 or 2, wherein

(a) the internal surface of the first rigid body (1) has the shape of two truncated cones joined at their bases, the exhaust ports (3) being located in the larger diameter central zone, and the inlet ports (2) in the smaller diameter end zones;

(b) the second body (11) is coaxial with the first;

(c) the resilient diaphragm (12) is of tubular shape, with a natural diameter less than the outer diameter of the second body (11), and is tightly attached by its ends to the ends of the first body (1).

4. Pump according to claim 1, wherein the same auxiliary vacuum pump (23) is used for creating a partial vacuum downstream of the exhaust valve (7) and for creating the cyclically applied partial vacuum in the control chamber (16).

5. Pump according to claim 4, wherein the intake conduit of the auxiliary vacuum pump (23) comprises a strong conductance branch (22, 24) between the downstream side of the exhaust valve (7) and the intake conduit (17) in the control chamber (16).

6. Pump according to claim 1, wherein said distribution mechanism is constituted by two two-path electromagnetic sluice gates (20, 21) connected in parallel by one of their paths to the conduit (17) for actuating the control chamber, and by their other path respectively to atmosphere and to the intake of the auxiliary pump (23), the two sluice gates being controlled in opposition by means of an oscillating relay (27).

7. Pump according to claim 1 wherein said distribution mechanism is constituted by a partial vacuum dynamometer (30), with piston (33) and return spring (36).

8. Pump according to claim 2, wherein said distribution mechanism relative to the space between the second body and the second diaphragm is an electrically controlled distributor (55) controlled by the same oscillating relay (27) which also controls the placement of the control chamber (16) in communication with atmosphere.

9. Pump according to claim 1, 2,3,4, 5, 6, 7 or 8, wherein said first diaphragm (12) has a reduced diameter in the area of the inlet ports (2).

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