Evacuation of a film chamber

Abstract

A device for evacuating a film chamber using a pump system that comprises at least two vacuum pumps, designed to evacuate the film chamber alternately. A suction capacity of the first vacuum pump is greater than that of the second vacuum pump and the final pressure achievable by the first vacuum pump is less than that of the second vacuum pump.

Claims

1. A device for evacuating a film chamber, the film chamber having flexible walls, the device comprising: a pump system that comprises at least two vacuum pumps comprising a first vacuum pump and a second vacuum pump configured to evacuate the film chamber alternatingly, wherein a volume flow rate of the first vacuum pump is greater than a volume flow rate of the second vacuum pump, wherein a final pressure achievable by the second vacuum pump is less than a final pressure of the first vacuum pump, wherein the film chamber is evacuated by the second vacuum pump through a pipeline which connects the film chamber to the second vacuum pump, wherein the pipeline is connected with a buffer chamber, and wherein the pump system is configured to evacuate the buffer chamber with the second vacuum pump while evacuating the film chamber with the first vacuum pump.

2. The device of claim 1, wherein each of the two vacuum pumps is connected with the film chamber via a separate pipeline.

3. The device of claim 1, wherein the two vacuum pumps are connected with the film chamber via a common pipeline.

4. The device of claim 1, wherein the pump system has a valve with at least three ports, of which a first port is connected with the first vacuum pump, a second port is connected with the second vacuum pump, and a third port is connected with the film chamber, wherein a first switching position of the valve connects the first port with the third port, and a second switching position of the valve connects the second port with the third port.

5. The device of claim 4, wherein the valve is a 3/2-way valve.

6. The device of claim 1, wherein the buffer chamber has a volume in the range of six to fifteen times the volume of the film chamber.

7. The device of claim 1, wherein a suction capacity of the first vacuum pump is higher than an initial volume of the film chamber, and the final pressure achievable by the first vacuum pump is higher than 50 mbar and less than 200 mbar.

8. The device of claim 1, wherein a suction capacity of the second vacuum pump is less than a pre-evacuated residual volume of the film chamber, and the final pressure achievable by the second vacuum pump is less than 50 mbar.

9. The device of claim 1, wherein the first vacuum pump comprises one or a plurality of jet pumps.

10. The device of claim 1, wherein at least one of the two vacuum pumps comprises a pipeline connecting the pump with the film chamber and comprising a stop valve.

11. A method for evacuating a film chamber, the film chamber having flexible walls, the method comprising: alternatingly evacuating the film chamber by a first vacuum pump and a second vacuum pump, wherein a volume flow rate of the first vacuum pump is greater than a volume flow rate of the second vacuum pump, wherein a final pressure achievable by the second vacuum pump is less than a final pressure of the first vacuum pump, and wherein the film chamber is evacuated by the second vacuum pump through a pipeline which connects the film chamber to the second vacuum pump, wherein the pipeline is connected with a buffer chamber; and prior to the evacuation of the film chamber by the second vacuum pump, evacuating by the second vacuum pump the buffer chamber while evacuating the film chamber by the first vacuum pump.

12. The method of claim 11, wherein a first port of a valve is connected with the first vacuum pump, wherein a second port of the valve is connected with the second vacuum pump, and wherein a third port of the valve is connected with the film chamber, wherein a first switching position of the valve connects the first port with the third port, and wherein a second switching position of the valve connects the second port with the third port, the method further comprising: prior to the evacuation of the film chamber by the first vacuum pump, switching the valve to the first switching position, wherein the valve is switched to the second switching position prior to the evacuation of the film chamber by the second vacuum pump.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic illustration of a device in a first operational state,

(2) FIG. 2 shows the illustration in FIG. 1 in a second operational state, and

(3) FIG. 3 shows the arrangement of FIG. 1 in a third operational state.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(4) A central core element of a device according to the example embodiments is a 3/2-way valve 12 having three ports 14, 16, 18 and two operating paths. A first vacuum pump 20 in the form of a Venturi pump is connected with the first port 14. A second vacuum pump 22 in form of a displacement pump is connected with the second port 16. The pipeline 24 connecting the second port 16 with the second vacuum pump 22 is connected with a buffer chamber 26 in a gas-conveying manner. The third port 18 is connected with the film chamber 28 via a pipeline 25. A stop valve 30 is arranged in the pipeline 25 between the film chamber 28 and the third port 18. As an alternative, it is conceivable that each of the two vacuum pumps 20, 22 is connected with the film chamber 28 via an own separate pipeline.

(5) The film chamber 28 includes or consists of two film layers 32, 34 between which the specimen 36 is arranged.

(6) The Venturi pump 20 is connected with a valve 38 so as to be able to control the operation of the pump 20.

(7) The device can be based on the idea to combine a pump having a high suction capacity, but also a high end pressure, with a pump having a low end pressure, but a low suction capacity. These two pumps 20, 22 are selectively and alternately connected with the film chamber 28 via the 3/2-way valve 12 so as to evacuate the film chamber.

(8) At the beginning, as illustrated in FIG. 1, first, the second vacuum pump 22 is operated so as to evacuate the buffer chamber 26. The 3/2-way valve 12 is in its first switching position, in which the first port is connected with the third port. However, the first vacuum pump 20 does not yet evacuate the film chamber 28, since the stop valve 30 is blocked (shown in black). In the Figures, open valve paths are shown in white and blocked valve paths are shown in black.

(9) As shown in FIG. 1, the second vacuum pump 22 already evacuates the buffer chamber 26 to a low pressure and possibly to the end pressure to be reached in the film chamber 28, while the film chamber 28 is still being prepared or equipped with the specimen 36.

(10) Thereafter, as illustrated in FIG. 2, the control valve 38 for the first vacuum pump 20 is opened in order to activate the same. The 3/2-way valve 12 remains in the first switching position and the stop valve 30 is opened so that the first vacuum pump 20 now evacuates the film chamber 28 with its high suction capacity. During evacuation with the high suction capacity, the film tightly clings to the specimen 36 and the surrounding free volume inside the film chamber 28 is reduced to a few cm.sup.3.

(11) In order to bring the film chamber 28 to the desired end pressure to be reached, the operational state of the device of the present invention as illustrated in FIG. 3 is used. Here, the 3/2-way valve is moved to the second switching position in which the second port 16 is connected with the third port 18. The second vacuum pump 22 and the buffer chamber 26 are thus connected with the film chamber 28 in a gas-conveying manner, since the stop valve 30 stays open. The control valve 38 for the first vacuum pump 20 is closed in order to deactivate the first vacuum pump. When the 3/2-way valve is switched from the first into the second operational state, the film chamber 28 is abruptly evacuated into the buffer chamber 26. Using the second vacuum pump 22, the desired end pressure to be reached by the second vacuum pump 22 can then be reached within a short period.

(12) While the first vacuum pump 20 (Venturi pump) can only reach an end pressure of 200 mbar, the second vacuum pump 22 can reach an end pressure of only 20 mbar. During the second operational state illustrated in FIG. 2, the first vacuum pump 20 evacuates the film chamber 28 to a free volume of 50 cm.sup.3. The buffer chamber 26 has a buffer volume of 500 cm.sup.3. After evacuation with the second vacuum pump 22 illustrated in FIG. 3, this results in an end pressure in the film chamber of:
p=(200 mbar.Math.50 cm.sup.3+20 mbar.Math.500 cm.sup.3)/(550 cm.sup.3)=36 mbar.