EP3916225B1 - Vacuum pump - Google Patents

Description

The present invention relates to a vacuum pump with a pump chamber and an inlet connected to the pump chamber and an outlet connected to the pump chamber. In this case, a gas to be pumped can be pumped from the inlet to the outlet in the pump chamber, in particular by means of a pump body. A chamber to be evacuated can be connected to the inlet. In addition, the vacuum pump is designed to supply gas ballast into the pump chamber.

A vacuum pump according to the preamble of claim 1 is from DE 102 55 792 A1 known. Vacuum pumps that allow the supply of gas ballast are in the EP 2 071 186 A2 , the DE 702 480 C , EP 2 821 650 A1 and DE 10 2007 043 350 B3 disclosed.

When operating vacuum pumps, a chamber connected to the inlet of the vacuum pump is usually evacuated. The vacuum pump sucks in gas present in the chamber at the inlet and pumps this gas to be pumped through the outlet, whereby the chamber is evacuated. The gas initially present in the chamber is further compressed within the vacuum pump as it approaches the outlet, so that any moisture contained in the gas to be pumped condenses and precipitates in the area of the outlet. It is undesirable for (condensed) water to remain in the pump room.

In order to remove the moisture or water from the pump room again, it is known to use a gas ballast, that is to say to pump a ballast gas through the pump room of the vacuum pump, so that the ballast gas or gas ballast removes the water from the pump room.

The problem with conventional methods can be that it is not guaranteed that there is actually no more moisture in the pump chamber of the vacuum pump.

It is therefore the object underlying the invention to provide a vacuum pump which prevents water or moisture from remaining in the pump chamber.

This task is solved by a vacuum pump according to claim 1.

The vacuum pump according to the invention comprises a control device which is designed to calculate a ballast pumping duration, which indicates how long gas ballast must be pumped in order to pump out water present or suspected in the pumping chamber, wherein the control device is further designed to supply the gas ballast for a supply duration effect, whereby the feeding time depends on the calculated ballast pumping time.

The invention is based on the knowledge that the ballast pumping duration can be calculated (or at least estimated using reasonable assumptions), so that a ballast pumping duration can be specified for the respective operating parameters or the respective operating state, which ensures that water present or suspected in the pumping room is within the ballast pumping time can be completely pumped out. The calculation can also be based on assumptions so that an assumed amount of water can be calculated. The calculated amount of water can preferably be chosen so that the calculated amount of water usually exceeds the amount of water actually present in the pumping room. The ballast pumping duration calculated from the calculated amount of water can then be used to introduce gas ballast into the pumping room for the supply duration.

The calculations and/or determinations of quantities (e.g. the amount of water) described herein may also be estimates, as the calculations are based at least in part on assumptions and/or measurements (with inaccuracies).

The feeding time can in particular correspond to the ballast pumping time or can also differ from it, as will be explained later.

It is understood that the vacuum pump is in operation during the supply period, conveys the supplied gas ballast towards the outlet and releases it through the outlet.

The gas ballast (also called ballast gas or additional gas load) creates a flushing effect that allows the water present in the pump chamber to be pumped out of the pump through the outlet.

The gas ballast can be a different gas than the gas to be conveyed, for example the gas ballast can come from a different source (not from the chamber to be evacuated), have a different temperature and/or a different humidity, and the like. An inert gas or, for example, air can be provided as gas ballast. The gas ballast can in particular have a low relative humidity (of, for example, less than 40% or less than 30% or 20%). In particular, the gas ballast can also be, for example, dry nitrogen. Gases with low humidity can easily absorb water present in the pump room and lead to the water being discharged from the pump room.

The control device can in particular be designed to automatically effect the supply of the gas ballast, as will be explained in more detail later. Alternatively The control device can also output a signal, which then instructs an operator to manually open a valve or the like.

Advantageous developments of the invention can be found in the description, the drawings and the subclaims.

According to the invention, the control device is designed to calculate the amount of water present in the pump room. When calculating the amount of water available, the potential amount of water that is currently in the pump room can be determined. The amount of water can in principle include evaporated and/or condensed water. Accordingly, instead of the amount of water, one could also speak of the amount of moisture.

According to the invention, the amount of water present in the pump room is determined based on the volume of a chamber connected to the inlet. According to the invention, the volume of the chamber is determined based on a previous pump-out time, the pumping speed of the pump and/or a pressure difference over the pump-out time.

In principle, the amount of water present in the pump room can be determined based on the volume of the chamber, assuming that all water from the volume of the chamber remains in the pump room. The volume of the chamber can, for example, be a maximum volume of a chamber to be connected specified by the manufacturer. This maximum volume can also be used if a smaller chamber is connected if necessary. The volume of the chamber can, for example, be permanently stored in the control device. This ensures that the amount of water in the pump room is not too low.

berechnen, wobei t_A die Auspumpzeit, S das Saugvermögen der Vakuumpumpe, p₁ der Druck in der Kammer (oder am Einlass) beim Beginn der Auspumpzeit und p₂ der Druck am Ende der Auspumpzeit ist. Zur Bestimmung des Kammervolumens kann das Steuergerät die bisherige Auspumpzeit erfassen. Das Saugvermögen der Pumpe (Einheit m³/h) ist der Pumpe inhärent und kann dementsprechend ebenfalls im Steuergerät hinterlegt sein. Alternativ oder zusätzlich kann das Saugvermögen der Pumpe auch über eine Leistungsmessung der von der Vakuumpumpe aufgenommenen Leistung ermittelt werden. Auf diese Weise können unterschiedlich große Kammern erkannt werden und es kann unterschiedlichen Auspumpzeiten Rechnung getragen werden. Wird ein größeres Kammervolumen berechnet als das fest im Steuergerät hinterlegte Kammervolumen, so kann das größere Kammervolumen verwendet werden.Alternatively or additionally, the control unit can also determine the chamber volume V _K using the formula $$v_K=\frac{t_A\ast S}{\mathit{ln}\frac{p_1}{p_2}}$$

calculate, where t _A is the pump-out time, S is the pumping speed of the vacuum pump, p ₁ is the pressure in the chamber (or at the inlet) at the start of the pump-out time and p ₂ is the pressure at the end of the pump-out time. To determine the chamber volume, the control unit can record the previous pump-out time. The pumping speed of the pump (unit m ³ /h) is inherent to the pump and can therefore also be stored in the control unit. Alternatively or additionally, the pumping speed of the pump can also be determined by measuring the power consumed by the vacuum pump. In this way, chambers of different sizes can be recognized and different pump-out times can be taken into account. If a larger chamber volume is calculated than the chamber volume stored in the control unit, the larger chamber volume can be used.

According to a further embodiment, in order to determine the amount of water present in the pump room, it is assumed that the gas to be pumped in the connected chamber has the maximum permitted temperature for the vacuum pump and/or the maximum permitted humidity for the vacuum pump. It is also preferably assumed that all moisture in the gas to be pumped or in the (already) pumped gas remains as water in the pump room.

The fact that all moisture in the gas to be pumped or already pumped remains as water in the pump chamber can be assumed as the basis for all embodiments described herein.

The maximum temperature and the maximum (relative) humidity of the gas in the chamber are also fixed for a respective vacuum pump and are therefore known. In order to ensure that the water is completely pumped out of the pump chamber, it can be assumed that the gas in the chamber actually has the maximum humidity and temperature permitted for the vacuum pump.

For example, the maximum temperature may be 40°C and the maximum relative humidity may be 80% for the gas to be conveyed. At 40°C, air can absorb a maximum of 50 g/m ³ of water. If it is now assumed that the chamber has a volume of 200 liters, these 200 liters contain 8 g of water. The amount of water in the pump room after evacuating such a chamber is therefore assumed to be 8 g.

berechnet werden, wobei q_{m, Wasser} die Wasserdampfkapazität, p_w die Wasserdampfverträglichkeit der Vakuumpumpe am Einlass, S das Saugvermögen der Vakuumpumpe am Einlass, M die molare Masse von Wasser, R die allgemeine Gaskonstante und T die absolute Temperatur ist.According to a further embodiment, the control device is designed to calculate the ballast pumping duration from the water vapor capacity of the vacuum pump and the amount of water in the pump chamber. The water vapor capacity is the largest amount of water that a vacuum pump can continuously suck in and pump in the form of water vapor per unit of time under ambient conditions of 20°C and 1,013 hPa. The water vapor capacity can be specified, for example, in g/h. The water vapor capacity is a quantity for a water vapor mass flow. The water vapor capacity can be determined in particular according to the formula $$q_{m,\mathit{Water}}=p_W\cdot S\cdot M\cdot {\left(\mathit{RT}\right)}^{-1}$$

can be calculated, where q _{m, water} is the water vapor capacity, p _w is the water vapor compatibility of the vacuum pump at the inlet, S is the pumping speed of the vacuum pump at the inlet, M is the molar mass of water, R is the general gas constant and T is the absolute temperature.

The water vapor capacity indicates the highest water vapor pressure at which a vacuum pump can continuously suck in and pump pure water vapor under normal ambient conditions (20°C, 1,013 hPa).

berechnet werden. Dabei ist q_pV,Ballast der Gasballaststrom, S das Saugvermögen der Vakuumpumpe, p_s der Sättigungsdampfdruck des Wasserdampfs bei Abgastemperatur (d.h. am Auslass), p_A der Partialdruck des Wasserdampfs beim Zuführen des Gasballasts, p₀ der Atmosphärendruck der Umgebung und α ein dimensionsloser Korrekturfaktor, der der Tatsache Rechnung trägt, dass zum Öffnen eines gegebenenfalls vorhandenen Auslassventils ein Druck größer als der Atmosphärendruck erforderlich ist. α kann beispielsweise einen Wert von 1,1 annehmen. Die Wasserdampfverträglichkeit hat die Dimension eines Drucks und wird üblicherweise in hPa angegeben. Falls die vorstehend genannten Drücke p nicht gemessen werden, so können jeweils solche Maximalwerte angenommen werden, die für die Vakuumpumpe gerade noch zulässig sind und die zu einer maximal großen Wassermenge oder Ballastpumpdauer oder zu einer niedrigen Wasserdampfverträglichkeit führen.The water vapor tolerance p _w can be determined using the formula $$p_W=\frac{q_{\mathit{pV},\mathit{ballast}}\ast \left(p_S-p_a\right)}{S\ast \left(\alpha \ast p_0-p_a\right)}$$

be calculated. Where q _pV,Ballast is the gas ballast flow, S is the pumping speed of the vacuum pump, p _s is the saturation vapor pressure of the water vapor at the exhaust gas temperature (ie at the outlet), p _A is the partial pressure of the water vapor when the gas ballast is supplied, p ₀ is the atmospheric pressure of the environment and α is a dimensionless one Correction factor that takes into account the fact that a pressure greater than atmospheric pressure is required to open an exhaust valve, if present. For example, α can take a value of 1.1. The water vapor compatibility has the dimension of a pressure and is usually given in hPa. If the above-mentioned pressures p are not measured, maximum values can be assumed that are just permissible for the vacuum pump and that lead to a maximum amount of water or ballast pumping time or to a low water vapor compatibility.

The water vapor capacity increases as the partial pressure of the water vapor in the gas ballast decreases and also increases at a higher temperature at the outlet, since the saturation vapor pressure of the water vapor then increases at the exhaust gas temperature.

Accordingly, the control device can be designed to determine the water vapor capacity of the vacuum pump based on the moisture of the gas ballast and/or based on the partial pressure of the water vapor in the gas ballast and/or based on the temperature at the outlet. For a low humidity or a low partial pressure of the water vapor in the gas ballast or a high temperature at the outlet, a higher water vapor capacity can be determined accordingly. The humidity of the gas ballast, the partial pressure of the water vapor in the gas ballast and/or the temperature at the outlet can each be determined by measurement or by specifying set values.

An exemplary vacuum pump can have a water vapor capacity of, for example, 44.7 g/h. If it is now assumed (especially in a worst-case scenario) that there is a quantity of 8 g of water in the pumping room, this results in a ballast pumping time of 11 min (8 g / 44.7 g/h = 11 min). Since this is a worst-case scenario, it is ensured that the entire amount of water has actually been removed from the pumping room after the ballast pumping period has expired.

According to a further embodiment, the supply time corresponds to between 70% and 110%, preferably between 80% and 100%, particularly preferably between 90% and 100% of the ballast pumping time. The supply duration is in particular the period in which gas ballast is actually supplied and pumped through the outlet by the vacuum pump in order to discharge the amount of water from the pump room. The feeding time can correspond exactly to the calculated ballast pumping time. However, it is also possible for the feeding time to be chosen to be longer or shorter than the ballast pumping time. Using the worst-case assumptions, it can be assumed, for example, that all water can be removed from the pump room during the supply period, even if the time is shortened to 70%. A gas ballast valve of the vacuum pump can be open during the supply period. While the gas ballast valve is open, the gas to be evacuated can Chamber must be separated in particular in order to avoid a subsequent increase in pressure in the chamber.

According to a further embodiment, the control device is designed to cause the opening of a gas ballast valve and thus the supply of the gas ballast, the gas ballast valve preferably being opened when the pressure falls below a predetermined pressure at the inlet. The gas ballast valve can therefore be opened automatically by the control unit. Alternatively, the control unit can also instruct an operator to open the gas ballast valve using a signal. The gas ballast valve can in particular be opened or the supply period can begin when the chamber has been sufficiently evacuated and the pressure at the inlet falls below 10 mbar or 1 mbar, for example.

For the supply of the gas ballast, a worst-case assumption can again be made, namely that the gas ballast is ambient air, with the ambient air having the maximum temperature and/or humidity permitted for the (environment of the) vacuum pump (e.g. 40° C and 30% relative humidity).

According to a further embodiment, the control device is designed to close the inlet while supplying the gas ballast or to fundamentally separate the chamber from the pump space. As already stated above, by closing the inlet while supplying the gas ballast, only a small change in the minimum pressure in the chamber can be achieved. Such operation can also be referred to as clocked operation.

Alternatively, the inlet can be open while simultaneously supplying gas ballast (gas ballast valve open). In this case, it can then be continuously calculated how much new moisture was introduced from the chamber into the pump room and what amount of water was pumped out. The calculated one Ballast pumping time can then be extended during operation, so that the delivery time can also be extended.

According to a further embodiment, a channel for supplying the gas ballast opens into the pump chamber, the channel preferably opening between the inlet and the outlet in the pump chamber and in particular being arranged closer to the outlet than to the inlet. The channel is therefore a separate access to the pump room for the inlet and outlet. In particular, the channel can be located closer to the outlet because the moisture precipitates or condenses there due to the higher pressure.

According to a further embodiment, the vacuum pump is a scroll pump. Accordingly, the vacuum pump can have two parallel chambers that compress the gas to be pumped towards the interior or towards the outlet of the vacuum pump. The vacuum pump can have two interlocking spirals, which compress and convey the gas to be pumped and also the supplied gas ballast in the direction of the outlet by moving in opposite directions. The pump body can accordingly comprise one or more of the spirals. A gas ballast bore connected to the gas ballast valve can be positioned so that at least one of the two parallel chambers or both chambers can be supplied with the gas ballast at a time.

Alternatively, the vacuum pump can also be a rotary vane vacuum pump, preferably an oil-lubricated rotary vane vacuum pump. In particular, the pump body can be formed by a rotor shaft and at least one rotary valve.

In principle, the vacuum pump can be designed in one or more stages, for example in two stages.

A further subject of the invention is a method for operating a vacuum pump according to claim 10.

Finally, the invention also relates to a vacuum pumping system with a vacuum pump as described herein, the vacuum pumping system comprising a chamber to be evacuated, which is coupled to the inlet of the vacuum pump.

The statements regarding the vacuum pump according to the invention apply accordingly to the method according to the invention and the vacuum pump system according to the invention. This applies in particular to advantages and embodiments.

It goes without saying that all of the developments and embodiments mentioned herein can be combined with one another, unless something to the contrary is explicitly stated.

Fig. 1

eine Vakuumpumpe mit einer angeschlossenen zu evakuierenden Kammer in schematischer Ansicht; und

Fig. 2

ein Ablaufdiagramm für das Auspumpen von Wasser aus einem Pumpraum.

The invention is described below purely by way of example with reference to the drawings. Show it:

Fig. 1

a schematic view of a vacuum pump with a connected chamber to be evacuated; and

Fig. 2

a flow chart for pumping out water from a pump room.

Fig. 1 shows a vacuum pump 10, which is designed as a scroll pump. A pump chamber 12 is arranged in the vacuum pump 10, in which a gas to be pumped is pumped or conveyed from an inlet 16 to an outlet 18 by means of a spiral-shaped pump body 14 (not explicitly shown). A chamber 20 to be evacuated is connected to the inlet 16, in which in the present example there are 200 liters of air at 40 ° C and 80% humidity.

At the inlet 16 of the vacuum pump 10, a pressure sensor 22 is arranged, which determines the pressure of the air flowing in from the chamber 20 via the inlet 16. The pressure sensor 22 is coupled to a control device 24 of the vacuum pump 10 and transmits its measurement results to the control device 24. The control device 24 also receives measurement results from a temperature sensor 26, which is arranged at the outlet 18.

A gas ballast valve 28 is also arranged on the vacuum pump 10, which can introduce ambient air 30 between the inlet 16 and the outlet 18 into the pump chamber 12. The control device 24 is coupled to the gas ballast valve 28 in order to be able to open the gas ballast valve 28.

In addition, the control device 24 is connected to a power measurement 32, the power measurement 32 recording the power currently required by the vacuum pump 10, so that the control device 24 can draw conclusions about the respective pumping speed and the pumping time/pump-out time of the vacuum pump 10.

The operation of the vacuum pump 10 will now be described with reference to the flowchart of Fig. 2 explained. In step 100 the pump-out time begins. Here, the initial pressure at the inlet 16 or in the chamber 20 is first determined via the pressure sensor 22 and the vacuum pump 10 begins pumping the gas to be pumped out of the chamber 20. During a pump-out time 110, the chamber 20 is further evacuated, with the gas ballast valve 28 is closed. By evacuating the chamber, water condenses from the chamber 20 in the pumping chamber 12. If a predetermined minimum pressure is now fallen below in the chamber 20 or at the inlet 16, the pumping out time ends with step 120. The pressure then present at the inlet is measured via the pressure sensor 22 determined. In addition, the temperature of the pump at the outlet 18 can be measured via the temperature sensor 26. Based on the performance measurement 32, the control unit 24 can also determine at what suction speed the vacuum pump 10 was operated and for how long. In this way, the control device 24 can determine the volume of the chamber 20 connected to the inlet 16 or the volume pumped out. The pressure difference between steps 100 and 120 is also used for this determination.

From the pumped out volume of the chamber 20 and a worst-case assumption for the temperature and humidity of the gas in the chamber 20, the control device 24 calculates in step 130 the amount of water potentially present (in particular suspected) in the pump chamber 12.

The ballast pumping duration is then calculated from the amount of water in step 140 using the water vapor capacity of the vacuum pump. If the water vapor capacity of the vacuum pump 10 is, for example, 44.7 g/h and the amount of water was calculated as 8 g, the ballast pumping time is 11 minutes.

In the subsequent step 150, the control device 24 then opens the gas ballast valve 28 and closes the inlet 16. In step 150, gas ballast (in this Example ambient air) is pumped to remove the amount of water from the pump room 12. The duration of the pumping of gas ballast, i.e. the supply time, can be selected according to the ballast pumping time of 11 minutes, so that the pumping of gas ballast is stopped after 11 minutes. At this point it can be assumed that all water or moisture has been removed from the pump room 12. You can then start again at step 100.

According to the invention, worst-case assumptions ensure that practically all water is removed from the pump room during the supply period of the gas ballast.

Reference symbol list

10

vacuum pump

12

Pump room

14

pump body

16

inlet

18

outlet

20

chamber

22

Pressure sensor

24

Control unit

26

Temperature sensor

28

Gas ballast valve

30

Ambient air

32

Performance measurement

100

Start of pumping out time

110

Pump out time

120

End of pumping out time

130

Calculation of water quantity

140

Calculation of ballast pumping time

150

Pumping gas ballast for the delivery period

Claims (11)

1. A vacuum pump (10) comprising a pump space (12), an inlet (16) connected to the pump space (12) and an outlet (18) connected to the pump space (12), wherein a gas to be conveyed can be conveyed in the pump space (12) from the inlet (16) to the outlet (18), wherein a chamber (20) to be evacuated can be connected to the inlet (16),

   wherein the vacuum pump (10) is configured for supplying a gas ballast into the pump space (12),

   characterized in that

   the vacuum pump (10) comprises a control device (24) which is configured to calculate a ballast pumping duration that indicates how long gas ballast has to be pumped in order to pump out water present or presumed to be present in the pump space (12), with the control device (24) further being configured to bring about a supply of the gas ballast for a supply duration, with the supply duration depending on the calculated ballast pumping duration,

   wherein the control device (24) is configured to calculate the amount of water present in the pump space (12),

   wherein the amount of water present in the pump space (12) is determined based on the volume of a chamber (20) connected to the inlet (16) and the volume of the chamber (20) is determined based on a previous pump-out time, the suction capacity of the pump and/or a pressure difference over the pump-out time.
2. A vacuum pump (10) according to claim 1,
   wherein it is assumed for the determination of the amount of water present in the pump space (12) that, in the connected chamber (20), the gas to be conveyed has the maximum permitted temperature for the vacuum pump (10) and/or the maximum permitted moisture for the vacuum pump (10), wherein it is preferably likewise assumed that all the moisture of the gas to be conveyed or of the conveyed gas remains as water in the pump space (12).
3. A vacuum pump (10) according to one of the claims 1 to 2,
   wherein the control device (24) is configured to calculate the ballast pumping duration from the water vapor capacity of the vacuum pump (10) and from the amount of water.
4. A vacuum pump (10) according to claim 3,
   wherein the control device (24) is configured to determine the water vapor capacity of the vacuum pump (10) based on the moisture of the gas ballast and/or based on the partial pressure of the water vapor in the gas ballast and/or based on the temperature at the outlet (18).
5. A vacuum pump (10) according to any one of the preceding claims,
   wherein the supply duration corresponds to between 70% and 110%, preferably between 80% and 100%, particularly preferably between 90% and 100%, of the ballast pumping duration.
6. A vacuum pump (10) according to any one of the preceding claims,
   wherein the control device (24) is configured to bring about the opening of a gas ballast valve (28) and thus the supply of the gas ballast, wherein the gas ballast valve (28) is preferably opened when a predetermined pressure is fallen below at the inlet (16).
7. A vacuum pump (10) according to any one of the preceding claims,
   wherein the control device (24) is configured to close the inlet (16) and/or to separate the chamber (20) from the pump space (12) during the supply of the gas ballast.
8. A vacuum pump (10) according to any one of the preceding claims,
   wherein a channel for supplying the gas ballast leads into the pump space (12), wherein the channel preferably leads into the pump space (12) between the inlet (16) and the outlet (18) and is in particular arranged closer to the outlet (18) than to the inlet (16).
9. A vacuum pump (10) according to any one of the preceding claims,
   wherein the vacuum pump (10) is a scroll pump.
10. A method of operating a vacuum pump (10) comprising a pump space (12), in which
    a ballast pumping duration is calculated that indicates how long gas ballast has to be pumped to pump out water present or presumed to be present in the pump space (12) and a supply of the gas ballast is brought about for a supply duration, wherein the supply duration depends on the calculated ballast pumping duration,
    wherein the amount of water present in the pump space (12) is calculated, wherein the amount of water present in the pump space (12) is determined based on the volume of a chamber (20) connected to an inlet (16) and the volume of the chamber (20) is determined based on a previous pump-out time, the suction capacity of the pump and/or a pressure difference over the pump-out time.
11. A vacuum pump system comprising a vacuum pump (10) according to any one of the claims 1 to 9, wherein the vacuum pump system comprises a chamber (20) to be evacuated that is coupled to the inlet (16) of the vacuum pump (10).

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