Pumps – Successive stages – With interstage intake or additional inlet to latter stage
Patent
1999-07-26
2000-09-26
Freay, Charles G.
Pumps
Successive stages
With interstage intake or additional inlet to latter stage
417267, 418 8, F04B 300
Patent
active
061235164
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a vacuum pump, comprising at least one pump chamber and at least one chamber for a motor, drive, gear, crankshaft or the like, adjoining said pump chamber.
In many branches of industry, vacuum pumps of the kind affected here need to pump etching and/or toxic gases. These gases may enter into chambers adjoining the pump chambers, said chambers being generally separated by seals (shaft seals, labyrinth boxes etc.) from the pump chambers. Etching gases give rise to corrosion or abrasions in these chambers, resulting in premature wear of the bearings or damage to other components located therein. Moreover, etching or toxic gases may pass through the chambers adjoining the pump chamber into the atmosphere. In the semiconductor industry, the demand for dry vacuum pumps, i.e. vacuum pumps which are free of oil at least with respect to their pump chamber, is ever increasing. The reason for this is, that the processes which are performed in vacuum chambers to which the vacuum pumps are connected, need to be protected against interfering hydrocarbons. The gases forming or employed in the semiconductor industry pumped by the vacuum pump often have the property of forming solids while they are being compressed to atmospheric pressure. Also deposits of this kind may cause harm in the chambers adjoining the pump chamber.
SUMMARY OF THE INVENTION
It is the task of the present invention to design a vacuum pump of the aforementioned kind so that the risk of damage in the chambers adjoining the pump chamber as well as escaping of etching or toxic gases from the vacuum pump is mostly reduced.
This task is solved through the present invention by equipping the vacuum pump with a gas ballast device and by feeding the ballast gas through the chambers adjoining the pump chamber. A vacuum pump designed according to the present invention has an outer gas ballast or purge gas inlet, and a gas inlet located directly at the casing of the pump chamber. Located between outer gas inlet and gas inlet are one or several chambers in need of being purged adjoining the pump chamber. In a pump designed as detailed, the gas entering through the gas ballast inlet has the effect of purging the chamber or chambers adjoining the pump chamber. If etching or toxic gases enter in to the chamber adjoining the pump chamber through seals which are not, or no longer completely fulfilling their sealing task, then these gases are pumped back together with the ballast or purge gas into the pump before being able to cause damage or escaping into the atmosphere. A further advantage of the present invention is, that the design engineer has more options at his disposal regarding the choice for the location of the inlet for the gas ballast or purge gas. Finally, the gas inlet at the casing of the pump chamber may be held open all the time, so that a low pressure forms in the chamber adjoining the pump chamber. The risk of toxic or etching gases escaping through leaks in the outer casing is thus further reduced.
BRIEF DESCRIPTION OF THE DRAWINGS
Further advantages and details of the present invention shall be explained by reference to the design examples depicted schematically in drawing FIGS. 1 and 2. Depicted in
drawing FIG. 1 is a two-stage rotary vane vacuum pump and
drawing FIG. 2 a four-stage piston vacuum pump.
DESCRIPTION OF THE INVENTION
The rotary vane vacuum pump depicted in drawing FIG. 1 comprises pump chamber casing 1 and drive motor 2. The pump chamber casing 1 is located within pump chamber 3 formed by outer casing 4, the motor in motor chamber 5 formed by motor casing 6 which is flanged to the outer pump casing 4. Located in pump chamber casing 1 are the pump chambers 7 and 8 with their rotors 9 and 10. The rotors 9 and 10 are fitted to motor shaft 11 which is supported by multiple bearings in pump chamber casing 2 and which is sealed. The larger stage 7, 9 of the pump is the inlet stage and it is linked to inlet 12. The outlet 13 is linked to outlet stage 8, 10. Inlet stage 7,
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Patent Abstracts of Japan, vol. 012, No. 346 (M-742)Sep. 16, 1988 & JP 63 105294A (Hitachi Ltd; others: 01), May 10, 1988.
Wutz et al., "Theorie und Praxis der Vakuumtchnik," Verlag Friedr., Vieweg & Sohn, Braunschweig/Wiesbaden, 3. uberarb. Aufl., 1986, S. 134-139 No Translation.
Fussel, "Trockenlaudfende Vakuumpumpen in der chemischen Industrie", In: Vakuum in der Praxis, 1994, Nr. 2, S.85-88; No Translation.
Bahnen Rudolf
Burghard Hans Josef
Giebmanns Wolfgang
Evora Robert Z.
Freay Charles G.
Leybold Vakuum GmbH
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