Patent Application
20170045051
The present invention relates to a pumping method making it possible to reduce the consumption of electrical energy as well as improve the performance in terms of flow rate and final vacuum in a pumping system in which the main pump is a lubricated rotary vane vacuum pump. The invention likewise relates to a pumping system which can be used to achieve the method according to the present invention.
The general tendencies to increase the performance of vacuum pumps, to reduce the costs of installations and the consumption of energy in industries have brought significant developments in terms of performance, energy economy, bulkiness, in the drives, etc.
The state of the art shows that to improve the final vacuum and to reduce the consumption of energy supplementary stages must be added in vacuum pumps of the multi-stage Roots or multi-stage claw type. For screw vacuum pumps there must be additional turns of the screw and/or the rate of internal compression must be increased. For lubricated rotary vane vacuum pumps one or more supplementary stages must also be added in series and the rate of internal compression increased.
The state of the art concerning the pumping systems which aim to improve the final vacuum and to increase the flow rate show booster pumps of Roots type arranged upstream from primary lubricated rotary vane pumps. This type of systems is bulky, operates either with by-pass valves presenting problems of reliability or by employing means of measurement, control, adjustment or servo-control. However, these means of control, adjustment or servo-control must be controlled in an active way, which necessarily results in an increase in the number of components of the system, its complexity and its cost.
The present invention has as object to propose a pumping method in a pumping system making it possible to reduce the electrical energy necessary for putting a chamber under vacuum and for maintaining the vacuum in this chamber, as well as to achieve a decrease in the temperature of the exit gas.
The present invention also has as object to propose a pumping method in a pumping system making it possible to obtain a higher flow rate at low pressure than that which can be obtained with the aid of a single lubricated rotary vane vacuum pump during the pumping of a vacuum chamber.
The present invention likewise has as object to propose a pumping method in a pumping system making it possible to obtain a better vacuum than that which can be obtained with the aid of a single lubricated rotary vane vacuum pump in a vacuum chamber.
These objects of the present invention are attained with the aid of a pumping method which is achieved within the framework of a pumping system, the configuration of which consists essentially of a primary lubricated rotary vane vacuum pump equipped with a gas inlet port connected to a vacuum chamber and with a gas outlet port leading into a conduit which is equipped with a non-return valve before coming out into the atmosphere or into other apparatuses. The suction end of an ejector is connected in parallel to this non-return valve, its exit going into the atmosphere or rejoining the conduit of the primary pump after the non-return valve.
Such a pumping method is in particular the subject matter of the independent claim 1. Different preferred embodiments of the invention are moreover the subject matter of the dependent claims.
The method consists essentially of feeding the ejector with working fluid and making it operate continuously all the while that the primary lubricated rotary vane vacuum pump pumps the gases contained in the vacuum chamber through the gas inlet port, but also all the while that the primary lubricated rotary vane vacuum pump maintains a defined pressure (for example the final vacuum) in the chamber by discharging the gases rising through its outlet.
According to a first aspect, the invention resides in the fact that the coupling of the primary lubricated rotary vane vacuum pump and of the ejector does not require measurements and specific devices (for example sensors for pressure, temperature, current, etc.), servo-controls or data management and calculation. Consequently, the pumping system suitable for implementing the pumping method according to the present invention comprises a minimal number of components, has great simplicity and is far less expensive than the existing systems.
By its nature, the ejector integrated in the pumping system can always operate without damage according to the present pumping method. Its dimensioning is determined by a minimal consumption of working fluid for the operation of the device. It is normally single-staged. Its nominal flow rate is selected depending upon the volume of the exit conduit of the primary lubricated rotary vane vacuum pump, limited by the non-return valve. This flow rate can be 1/500 to 1/20 of the nominal flow rate of the primary lubricated rotary vane vacuum pump, but can also be less or greater than these values. The working fluid for the ejector can be compressed air, but also other gases, for example nitrogen.
The non-return valve, placed in the conduit at the outlet of the primary lubricated rotary vane vacuum pump can be a commercially available standard element. It is dimensioned according to the nominal flow rate of the primary lubricated rotary vane vacuum pump. In particular, it is foreseen that the non-return valve closes when the pressure at the suction end of the primary lubricated rotary vane vacuum pump is between 500 mbar absolute and the final vacuum (for example 100 mbar).
According to another variant, the ejector is multi-staged.
According to still another variant, the ejector can be made of material having chemical resistance to substances and gases commonly used in the chemical industry and the semi-conductor industry, just as well in the single-staged ejector variant as in that of the multi-staged ejector.
The ejector is preferably of small size.
According to another variant, the ejector is integrated in a cartridge which incorporates the non-return valve.
According to still another variant, the ejector is integrated in a cartridge which incorporates the non-return valve and this cartridge itself is accommodated in the oil separator of the primary lubricated rotary vane vacuum pump.
According to still another variant of the method of the present invention, to meet specific requirements, the flow rate of gas at the pressure necessary for the operation of the ejector is controlled in an “all or nothing” way. In effect, the controlling consists in measuring one or more parameters and in putting the ejector into operation or stopping it, depending upon certain predefined rules. The parameters, provided by suitable sensors, are, for example, the motor current of the lubricated rotary vane vacuum pump, the temperature or the pressure of the gases in the space of the exit conduit of the primary lubricated rotary vane vacuum pump, limited by the non-return valve, or a combination of these parameters.
Starting with a cycle of evacuation of the chamber, the pressure there is elevated, for example equal to the atmospheric pressure. Given the compression in the primary lubricated rotary vane vacuum pump, the pressure of the gases discharged at its outlet is higher than the atmospheric pressure (if the gases at the outlet of the primary pump are discharged directly into the atmosphere) or higher than the pressure at the inlet of another apparatus connected downstream. This causes the opening of the non-return valve.
When this non-return valve is open, the action of the ejector is felt very slightly as the pressure at its inlet is close to equal that at its outlet. In contrast, when the non-return valve closes at a certain pressure (because the pressure in the chamber has dropped in the meantime), the action of the ejector brings about a progressive reduction of the difference in pressure between the chamber and the conduit after the non-return valve. The pressure at the outlet of the primary lubricated rotary vane vacuum pump becomes that at the inlet of the ejector, that at its outlet being always the pressure in the conduit after the non-return valve. The more the ejector pumps, the more the pressure drops at the outlet of the primary lubricated rotary vane vacuum pump, in the closed space (limited by the non-return valve), and consequently the difference in pressure between the chamber and the outlet of the primary lubricated rotary vane vacuum pump decreases. This slight difference reduces the internal leaks in the primary lubricated rotary vane vacuum pump and causes at the same time a reduction of the pressure in the chamber, which makes it possible to improve the final vacuum. In addition, the primary lubricated rotary vane vacuum pump consumes less and less energy for the compression and produces less and less compression heat.
In the case of controlling of the ejector, there exists an initial position for start-up of the pumping system when the sensors are in a defined state or give initial values. As the primary lubricated rotary vane vacuum pump pumps the gases of the vacuum chamber, the parameters such as the current of its motor, the temperature and the pressure of the gases in the space of the exit conduit begin to change and reach threshold values detected by the sensors. This causes the switching on of the ejector. When these parameters return to the initial ranges (outside the set values) with a time lag, the ejector is stopped.
According to still another variant of the present invention, the flow of gas at the pressure necessary for the operation of the ejector is provided by a compressor. In a noteworthy way, this compressor can be driven by the primary lubricated rotary vane pump or, alternatively or in addition, in an autonomous way, independently of the primary lubricated rotary vane pump. This compressor can suction the atmospheric air or gases in the gas exit conduit after the non-return valve. The presence of such a compressor renders the lubricated rotary vane vacuum pump systems independent of a compressed gas source, which can meet the demands of certain industrial environments. The compressor can provide the flow of gas at the pressure necessary for the operation of a plurality of ejectors, respectively forming part of a plurality of vacuum pump systems having as primary pumps lubricated rotary vane pumps. The compressor forms part of the system also in the case of continuous operation of the ejector as well as in the case of its controlling according to the parameters, controlled by suitable sensors.
On the other hand, it is also evident that the study of the mechanical concept seeks to reduce the space between the gas outlet port of the primary lubricated rotary vane vacuum pump and the non-return valve with the aim of lowering the pressure there more quickly.
The features and the advantages of the present invention will appear with more details within the context of the description which follows with example embodiments given by way of illustration and in a non-limiting way with reference to the attached drawings:
This pumping system SP comprises a chamber 1, which is connected to a suction port 2 of a primary lubricated rotary vane vacuum pump 3. The gas outlet port of the primary lubricated rotary vane vacuum pump 3 is connected to a conduit 5. A non-return discharge valve 6 is placed in the conduit 5, which after this non-return valve 6 continues into a gas exit conduit 8. The non-return valve 6, when it is closed, allows the formation of a space 4, contained between the gas outlet port of the primary vacuum pump 3 and itself. The pumping system SP also comprises an ejector 7, connected in parallel to the non-return valve 6. The suction port of the ejector is connected to the space 4 of the conduit 5, and its discharge port is connected to the conduit 8. The feed conduit 9 provides the working fluid for the ejector 7.
From the start of the primary lubricated rotary vane vacuum pump 3, the working fluid for the ejector 7 is injected through the feed conduit 9. Then the primary lubricated rotary vane vacuum pump 3 suctions the gases in the chamber 1 through the port 2 connected at its inlet and compresses them to discharge them afterwards at its outlet in the conduit 5 through the non-return valve 6. When the closure pressure for the non-return valve 6 is reached, it closes. Starting from this moment the pumping of the ejector 7 makes the pressure in the space 4 decrease progressively to the value of its limit pressure. In parallel, the power consumed by the primary lubricated rotary vane vacuum pump 3 decreases progressively. This takes place in a short time period, for example for a certain cycle in 5 to 10 seconds.
With a clever adjustment of the flow rate of the ejector 7 and of the closure pressure of the non-return valve 6 as a function of the flow rate of the primary lubricated rotary vane vacuum pump 3 and the space of the chamber 1, it is moreover possible to reduce the time before the closure of the non-return valve 6 with respect to the duration of the evacuation cycle and thus reduce the losses in working fluid during this time of operation of the ejector 7 without effect on the pumping. Furthermore, these “losses”, which are minute, are taken into account in the evaluation of the energy consumption. On the other hand, the advantage of simplicity gives an excellent reliability to the system as well as a lower price in comparison with similar pumps equipped with programmable automatic control and/or speed controller, controlled valves, sensors, etc.
With respect to the system represented in
With respect to the systems shown in
Certainly the present invention is subject to numerous variations regarding its implementation. Although diverse embodiments have been described, it is well understood that it is not conceivable to identify in an exhaustive way all the possible embodiments. Of course replacing a described means with an equivalent means can be envisaged without departing from the scope of the present invention. All these modifications form part of the common knowledge of one skilled in the art in the field of vacuum technology.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2014/058948 | 5/1/2014 | WO | 00 |
