EP0148069B1 - Vacuum pump installations supplied by a cooling liquid under constant pressure - Google Patents

Abstract

1. Installation for obtaining a reduced pressure in an enclosure, comprising at least one liquid ring vacuum pump (1), whose intake chamber (12) is provided with a gas intake conduit (16), whose delivery chamber (13) is provided with a delivery conduit (17) for the drawn-in gas conveying the entrained cooling liquid, and whose cylindrical case (2), which encloses the bladed wheel (3), is provided with a cooling liquid inlet (18) disposed on the intake side of the pump case (2) characterized in that the gas intake conduit (16) is connected by at least one first communication means (19) to the said enclosure, the cooling liquid inlet (18) co-operates with a circuit (21 - 26 ; 21, 27 - 30) for supplying cooling liquid at a constant pressure, and a head loss generating means (31) is disposed in the gas intake conduit (16) or in the said first communication means (19), the head loss generating means (31) being formed by a diaphragm (31) with an invariable aperture cross section which is selected to create almost instantaneously upon starting the pump a reduced pressure in the intake chamber (12) of the said pump (1) and consequently, upon starting the pump (1), to instantaneously form the liquid ring in the pump (1) and almost immediately compensate for the cooling liquid expelled by the delivery conduit (17).

Description

The present invention relates to an installation for producing a reduced pressure in an enclosure, which comprises at least one liquid ring vacuum pump, the suction chamber of which is provided with a gas suction duct, the chamber of which discharge is provided with a suction gas discharge conduit conveying driven coolant and whose cylindrical body containing the impeller is provided with a coolant inlet disposed on the suction side of the pump body.

For ease of presentation of the prior art, it will be considered that the coolant is constituted by water, it being understood that it can in fact be made up of any low-volatility liquid of low viscosity .

Known installations of this type, described for example in UA-A-3 108 738, have essentially two drawbacks, namely on the one hand, that of a difficult priming of the vacuum pump especially when the constant inlet pressure cooling water is weak and on the other hand, that of an irregular vacuum rise.

The first drawback is due to the absence of vacuum at start-up in the suction compartment of the vacuum pump, a vacuum which contributes to the admission of cooling water into the pump body. There is in fact at start-up a delay in the suction of the cooling water forming the liquid ring, compared to the normal rejection of this water accompanying the discharge of the gas sucked from the enclosure to be evacuated, this delay being particularly accentuated in the case where the vacuum pump is supplied with cooling water by means of a tank whose constant level of water is low, that is to say is in a horizontal plane located at or well below the pump axis.

To overcome this first drawback, an attempt has been made to raise the constant water level, but this way of proceeding gives rise to a sudden start-up of the additional power absorbed and a risk of rupture of the impeller blades as a result of the engorgement of water between the blades taking part or all of the place of the gas to be discharged. Since this increase in the constant level must therefore necessarily be limited, it cannot satisfactorily resolve the problems mentioned above. In addition, when the water level is too low in said constant level tank, the introduction of cooling water into the pump body cannot be carried out at the most favorable point with good efficiency and in particular in the part upper said body and this, due to the difficulty of priming the pump.

The second drawback is due to the significant variation, during the rise in vacuum, of the flow of cooling water sucked into the body of the pump, flow which tends towards zero at the start of the rise in vacuum and gradually increases to stabilize at final vacuum, this progressive increase in the flow rate being linked to the increase in the vacuum prevailing in the enclosure during the rise in vacuum.

Furthermore, US-A-2 044 867 describes a rotary vacuum pump such as a vane pump, the gas suction conduit of which includes means for reducing the power absorbed at start-up.

The object of the present invention is to remedy the drawbacks mentioned above and to do this, it proposes an installation of the type defined in the first paragraph of this description, which is characterized in that the gas suction pipe is connected by at least a first means of communication to said enclosure, the coolant supply cooperates with a coolant coolant supply circuit at constant pressure and a means generating a pressure drop is arranged in the conduit gas suction or in said first communication means, the means generating a pressure drop being constituted by a diaphragm with constant opening section chosen to create almost instantaneously at pump start-up a reduced pressure in the pressure chamber aspiration of said pump, and therefore, to obtain, when the pump is started, the instantaneous formation of the liquid ring in the pump and the almost immediate compensation of the liquid refrigeration rejected by the discharge pipe.

It will be readily understood that, due to the almost instantaneous creation of this stable reduced pressure for a predetermined time and independent of the pressure prevailing in the chamber to be evacuated, there is a significant suction as soon as the pump is started. coolant in the pump body which allows almost immediate compensation of the rejected coolant; it follows the instantaneous and irreversible formation of the liquid ring and consequently priming of the pump.

Furthermore, during a first phase of evacuation, the flow rate of the suctioned refrigerating liquid is constant until the pressure in the enclosure to be evacuated reaches the predetermined reduced pressure existing downstream of the means for creating the pressure drop. This results in a perfectly regular vacuum rise during this first phase.

The rise in vacuum of the predetermined reduced pressure to the desired final vacuum is not further disturbed, because during this second phase of vacuum rise, there is only a small variation in the flow rate of refrigeration liquid drawn in.

The means for creating the pressure drop can be of any design. Thus, for example, it could be a diaphragm whose opening is suitably sized to create the desired predetermined reduced pressure almost instantaneously. It could also be a valve with two opening positions, a position of small opening suitable for the almost instantaneous creation of said reduced pressure and a position of greatest opening; this valve will preferably be of the automatic servo-controlled valve type so that it is brought from the position of small opening to the position of largest opening when the pressure in the enclosure changes from a value greater than said reduced pressure predetermined value equal to or less than the latter. This type of valve and its mode of slaving to the pressure prevailing in the chamber to be evacuated, are perfectly known to those skilled in the art and a more detailed description of these means is unnecessary. It is also possible that the automatic valve is slaved to the power absorbed by the pump, the transition from the position of small opening to the position of largest opening being obtained when the power absorbed by the pump increases at the time of the passage of the first vacuum phase to the second vacuum phase.

It will also be understood that the higher the opening section of the diaphragm or of the valve in the low opening position, the faster the vacuum rise; conversely, the smaller this section, the greater the ease of priming and the stability of vacuum rise.

When the constant pressure coolant supply circuit includes a constant level coolant tank connected by a second communication means to said coolant inlet, the coolant in the tank may, in accordance with invention, to be in a horizontal plane located indifferently at the height of the longitudinal axis of the pump, below or even above this axis.

According to another characteristic of the invention, the discharge chamber of the pump is provided at its base with an outlet for refrigeration liquid discharged by said pump. This outlet, through which all or part of the rejected refrigerant can be evacuated, makes it possible to increase the pressure of the refrigerant in the refrigerant supply circuit without disadvantage, and in particular to raise the level of the refrigerant in the constant level tank.

Advantageously, said outlet cooperates with a means for creating between this outlet and the atmosphere a column of liquid of variable height, this means can for example be constituted by a U-shaped tube, one of the branches of which is connected to the liquid outlet. refrigeration rejected and the other branch of which is open to the atmosphere and of variable height. Thanks to this means, it is possible to adjust the water level in the cylindrical body of the stopped pump in order to prime the pump more easily and safely.

Advantageously, the outlet of the rejected coolant or the means for creating a column of liquid is provided with a diaphragm for metering the flow rate of the coolant released by the pump, so that the latter is free of gas. repressed.

According to yet another characteristic of the invention, the supply of coolant is in a horizontal plane located above the longitudinal axis of the cylindrical body containing the impeller, that is to say at a level desirable for good performance, this being made possible by the characteristics of the invention, even if for example the water level in the coolant tank is in a horizontal plane located below this axis.

Finally, the suction gas discharge pipe can cooperate via a third means of communication with the coolant supply circuit at constant pressure with a view to recycling all or part of the coolant carried by the gas sucked.

• - la figure 1 est une coupe longitudinale schématique d'une pompe à anneau liquide, effectuée suivant la ligne I-I de la figure 2,
• - la figure 2 est une coupe schématique suivant la ligne II-II de la figure 1,
• - la figure 3 est la représentation schématique d'un premier mode de réalisation de l'invention, le circuit d'alimentation en liquide de refrigération à pression constante comprenant un bac à niveau constant, ce niveau étant dans un plan horizontal situé au-dessus de l'axe longitudinal de la pompe à anneau liquide, et
• - la figure 4 est la représentation schématique d'un second mode de réalisation de l'invention, le circuit d'alimentation en liquide de réfrigération à pression constante comprenant un bac à niveau constant, ce niveau étant dans un plan horizontal situé nettement au-dessous de l'axe longitudinal de la pompe à anneau liquide.

The invention will be illustrated below with reference to the accompanying drawings in which:

• FIG. 1 is a schematic longitudinal section of a liquid ring pump, taken along line II of FIG. 2,
• FIG. 2 is a diagrammatic section along line II-II of FIG. 1,
• - Figure 3 is a schematic representation of a first embodiment of the invention, the circuit for supplying refrigeration liquid at constant pressure comprising a constant level tank, this level being in a horizontal plane located above the longitudinal axis of the liquid ring pump, and
• FIG. 4 is the schematic representation of a second embodiment of the invention, the circuit for supplying refrigeration liquid at constant pressure comprising a tank with constant level, this level being in a horizontal plane located clearly at below the longitudinal axis of the liquid ring pump.

The liquid ring vacuum pump 1 represented by FIGS. 1 and 2 comprises, in a manner known per se, a cylindrical body 2 partially filled with water and in which rotates a paddle wheel 3 whose hub 4 is wedged on a eccentric shaft 5 and rotated by a motor 6. This water, set in motion by the impeller 3 is projected against the body 2 and forms a water ring 7 which determines a cell 8 with the hub 4.

The rotating vanes move in this cell 8 by delimiting spaces whose volume increases in the zone situated to the right of the vertical plane of symmetry of FIG. 2 and decreases in the zone situated to the left of said vertical plane of symmetry.

The pump 1 also furthermore comprises, in a manner known per se, an enclosure 9 adjoining the front wall 10 of the body 2, this enclosure being divided by a partition 11 into a suction chamber 12 and a discharge chamber 13. The chamber suction 12 communicates with the cell 8 through an opening 14 and the delivery chamber 13 communicates with this same cell through an opening 15 smaller than the opening 14, the openings 14 and 15 being formed in the wall 10.

Furthermore, the chamber 12 is provided on its cylindrical wall with a gas suction duct 16 and the chamber 13 is provided on its cylindrical wall with a duct 17 for discharging the sucked gas and the discharged refrigeration water by the pump 1. Finally, the cylindrical body 2 is provided with an inlet 18 for cooling water disposed on the suction side of the pump body 2 and situated in a horizontal plane extending above the longitudinal axis of the pump.

The gas to be conveyed is sucked in through line 16 and discharged through line 17.

At each rotation of a blade of the wheel 3, there is thus a suction followed by a discharge and the set of blades allows a virtually continuous suction and discharge.

As shown in Figures 3 and 4, the suction duct 16 is connected to the enclosure where it is desired to create the vacuum (not shown) by a tube 19 equipped with a check valve 20 which allows to isolate the pump enclosure when the pump stops. These same figures also show that the pump 1 is coupled with a tank 21 with a constant level of water.

In the case of Figure 3, where the tank 21 is equipped with a float valve 22 (allowing the maintenance of a constant level in said tank) supplied with water by a conduit 23 carrying a valve 24 and a too -full 25 located above the float in its high position, the constant level determined by said float valve being in a horizontal plane located above the axis of the pump 1, this coupling is more precisely achieved by connecting by a tube 26, the inlet 18 for cooling water to tank 21, below the constant level and in particular at the bottom of said tank 21.

In the case of FIG. 4, where a constant level is maintained in the tank 21 by an overflow 27, this constant level being in a horizontal plane situated below the axis of the pump 1, the coupling between the latter and the tank 21 is produced by connecting, via a pipe 28, the inlet 18 to the base of said tank 21, in this pipe 28 opening an inlet 29 for cooling water, on which a valve 30 is mounted.

In accordance with the invention, the installations which are the subject of FIGS. 3 and 4 each comprise means 31 generating a pressure drop arranged in the tube 19, this means being constituted in the present case by a diaphragm whose opening is dimensioned for instantly create, when the pump 1 starts, a reduced pressure in the suction chamber 12, in the body of the pump 2 (suction side) and in the tube 19 downstream of said diaphragm 31 and, consequently, an instant suction of the cooling water from the tank 21 through the inlet 18 and therefore compensation for the rejected water carried by the pumped gas.

Still in accordance with the invention, the discharge chamber 13 of the pump 1 is provided at its base with an outlet 32 through which all or part of the said discharged water carried by the discharged gas can be discharged. In the case of the installation in FIG. 3, the possible balance of this rejected water is evacuated with the gas discharged through the discharge pipe 17 extended by a pipe 33 ending in a three-way valve 34 allowing said pipe 33 to be put in connection either with a pipe 35 ending for example in a tank (not shown) for receiving the discharged water, or with a pipe 36 opening into the tank 21 above the constant level, in which case there is recycling of the balance of rejected refrigeration water.

In the case of the installation of FIG. 4, the water rejected and not evacuated by the outlet 32, is discharged with the gas sucked, by the discharge conduit 17 extended by a conduit 37 opening into the tank 21 above constant level.

Furthermore, the outlet 32 can cooperate with a means creating a water column between said outlet 32 and the atmosphere. As shown in Figures 3 and 4, this means is constituted by a U-shaped tube 38, one 39 of the branches 39, 40 is connected to the outlet 32 and the other branch 40 is open to the atmosphere, the branches 39, 40 being connected together by a horizontal branch 41 and the branch 40 opening into the tank 21 above the constant level in the case of the installation in FIG. 4. On the other hand, according to the invention, can vary the height of the water column in the means 38, for example by pivoting of the branch 40 around the branch 41 and in a vertical plane, means 42 allowing this pivoting being provided for this purpose between the branch 40 and the branch 41. In the installation of FIG. 3, the free end of the branch 40 in the high position is situated in the horizontal plane passing through the longitudinal axis of the pump and in the installation of FIG. 4, the free end of this branch 40 in the high position is located in the horizontal plane passing through l hub axis 4.

According to another characteristic of the invention, a diaphragm 43 is disposed in the outlet 32 or in the U-shaped tube 38, with a diaphragm allowing the quantity of water evacuated by this channel to be measured so that there is no gases escaping simultaneously via this same route.

Finally, a diaphragm 44 can be placed on the tubing 26, 28 the latter having the function of regulating the quantity of water admitted into the pump body 2.

It is essential in any liquid ring vacuum pump that at start-up the water level in the pump body does not exceed a threshold value beyond which there is a risk of rupture of the pump vanes. This implies that, for known installations, the water level in the cooling water tank is not not too high but, as we saw previously, this condition is, for known installations, very often incompatible with easy priming of the pump due to the low pressure of admission of the cooling water in the body pump. In the installations according to the invention which have just been described, it is on the contrary possible to have, as soon as the pump 1 is started, a flow rate of flow of cooling water through the inlet 18 suitable for priming instantaneous of the pump, whether the water level in the tank 21 is very high or very low, and without stopping, the water level exceeds a dangerous threshold in the pump body.

In fact, in the installation object of FIG. 3, the valve 24 being in the open position, the water in the tank 21 is located at level I. This water flows by gravity into the pump body 2 via from the tubing 26 and is immediately evacuated from the pump by the outlet 32 and the U-shaped tube 38. When the pump stops, the water in the pump body 2 is located between the level II (which is located in the horizontal plane passing through the base of the openings 14, 15) and level IV (which is in the horizontal plane passing through the longitudinal axis of the pump 1) according to the pivoting position of the branch 40, this is that is to say always at a level not likely to cause damage to the blades when the pump starts. If the valve 24 is in the closed position when stopped, the water level in the body 2 is established in the same manner as above between position II and position IV, the water in the tank 21 stabilizing at level III located in the horizontal plane passing through the arrival 18.

Furthermore, in the installation object of FIG. 4, the valve 30 being in the open or closed position, the water is situated at level V (outlet level of the overflow 27). When the pump 1 stops, the water stabilizes in the pump body 2 at level VI located in the horizontal plane passing through the axis of the hub 4, this level being as previously adjustable as a function of the pivoting position of branch 40, the lowest level being level II. Here again at standstill, the water stabilizes in the body 2 at a level which presents no danger for the pump 1. Furthermore, despite the fact that the level of the water in the tank 21 is located in a horizontal plane passing far below the longitudinal axis of the pump, the cooling water is, as soon as this pump is started, sucked into the body 2, the valve 30 being in the open position, thanks to the presence of the diaphragm 31.

It is therefore clear that these installations are capable of restarting safely with instant priming of the pump and a steady rise in vacuum.

dans l'enceinte à mettre sous vide. Le fait que le vide maximum atteint dans l'enceinte soit inférieur à celui pouvant normalement être atteint compte tenu des caractéristiques de la pompe, est la preuve de l'existence d'une fuite de gaz au niveau de ladite enceinte. Cette fuite peut être symbolisée et remplacée par une ouverture pratiquée sur l'enceinte, ayant par exemple un diamètre de 5 mm. Le taux de compression de la pompe est, dans les conditions définies ci-dessus, de 188 = 7,6, le débit de gaz aspiré en amont de ladite ouverture étant de IN = 13 m²/h mesuré à la pression atmosphérique.As an example, suppose that pump 1 establishes a flow rate of aspirated gas of approximately 100 m ³ / h under a vacuum of

in the enclosure to be evacuated. The fact that the maximum vacuum reached in the enclosure is lower than that which can normally be achieved taking into account the characteristics of the pump, is proof of the existence of a gas leak at the level of said enclosure. This leak can be symbolized and replaced by an opening made on the enclosure, for example having a diameter of 5 mm. The compression ratio of the pump is, under the conditions defined above, of 188 = 7.6, the flow rate of gas sucked upstream of said opening being IN = 13 m ² / h measured at atmospheric pressure.

By placing in the duct 16 or the tubing 19 a diaphragm 31 having an opening with a diameter of 15 mm (corresponding to an area 9 times larger than that of the opening with a diameter of 5 mm), one instantly creates in the suction chamber 12 or in the suction part of the body 2, a reduced pressure of the order of IV Pa corresponding to a theoretical flow rate of aspirated gas of 50 m ³ / h (80 m3 / h in practice).

Pa. Ensuite, la montée en vide dans l'ensemble chambre d'aspiration 12 (corps 2) - tubulure 19 - enceinte se fait normalement jusqu'à

Pa sans perturbation notable.This reduced pressure remains unchanged until the pressure in the enclosure upstream of the diaphragm 31 reaches this same reduced pressure of

Pa. Then, the vacuum rise in the suction chamber 12 (body 2) - tubing 19 - enclosure assembly is normally done until

Pa without notable disturbance.

If we want to increase the ease of priming the pump, it will be necessary to reduce the diameter of the diaphragm opening 31 and to raise the water level IV (or VI) when stopped by acting on the branch 40. Conversely, if we want to accelerate the vacuum rise in the enclosure, it will be necessary to increase this diameter and to remain for safety within a fair limit in raising the level IV (or VI) when stopped.

Claims (8)

1. Installation for obtaining a reduced pressure in an enclosure, comprising at least one liquid ring vacuum pump (1), whose intake chamber (12) is provided with a gas intake conduit (16), whose delivery chamber (13) is provided with a delivery conduit (17) for the drawn-in gas conveying the entrained cooling liquid, and whose cylindrical case (2), which encloses the bladed wheel (3), is provided with a cooling liquid inlet (18) disposed on the intake side of the pump case (2), characterised in that the gas intake conduit (16) is connected by at least one first communication means (19) to the said enclosure, the cooling liquid inlet (18) co-operates with a circuit (21 - 26; 21, 27 - 30) for supplying cooling liquid at a constant pressure, and a head loss generating means (31) is disposed in the gas intake conduit (16) or in the said first communication means (19), the head loss generating means (31) being formed by a diaphragm (31) with an invariable aperture cross section which is selected to create almost instantaneously upon starting the pump a reduced pressure in the intake chamber (12) of the said pump (1) and consequently, upon starting the pump (1), to instantaneously form the liquid ring in the pump (1) and almost immediately compensate for the cooling liquid expelled by the delivery conduit (17).

2. Installation according to claim 1, in which the circuit for supplying cooling liquid at a constant pressure comprises a tank (21) which has a constant level of cooling liquid and is connected by a second communication means (26; 28) to the said cooling liquid inlet (18), the cooling liquid in the said tank being in a horizontal plane disposed substantially at the level of the longitudinal axis of the pump (1) or above this axis.

3. Installation according to claim 1 or 2, characterised in that the delivery chamber (13) of the pump (1) is provided at its bottom with an outlet (32) for cooling liquid expelled by the said pump.

4. Installation according to claim 3, characterised in that the said outlet (32) cooperates with a means for creating a liquid column of a variable height between this outlet and the atmosphere.

5. Installation according to claim 4, characterised in that the means for creating a liquid column is formed by a U-tube (38), one (39) of whose branches (39, 40) is connected to the expelled cooling liquid outlet (32) and the other (40) of whose branches is open to the atmosphere and of a variable height.

6. Installation according to any one of claims 3 to 5, characterised in that the expelled cooling liquid outlet (32) or the means (38) for creating a liquid column is provided with a diaphragm (43) for metering the flow rate of the cooling liquid expelled by the pump.

7. Installation according to any one of the preceding claims, characterised in that the delivery conduit (17) for the drawn-in gas co- operates via a third communication means (33, 34, 36; 37) with the circuit for supplying cooling liquid at a constant pressure for the purpose of recycling all or some of the cooling liquid conveyed by the drawn-in gas.

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