Rotary expansible chamber devices – With plural working fluid inlet or outlet passages
Patent
1996-02-15
1997-12-16
Vrablik, John J.
Rotary expansible chamber devices
With plural working fluid inlet or outlet passages
418 87, 418 97, 418DIG1, F04C 2502, F04C 2702
Patent
active
056977719
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a vacuum pump and in particular, to a vacuum pump with a gas ballast facility.
Supplying the gas ballast means the admission of gases into the pump chamber of a vacuum pump at a point of time when the pump chamber is sealed off towards the intake side. By supplying gas ballast it is possible to prevent damaging condensation of vapours which are taken in. In the case of a two-stage vacuum pump the gas ballast is commonly supplied into the fore-vacuum stage. But it is also known to supply the gas ballast to the high vacuum stage.
SUMMARY OF THE INVENTION
Oil sealed pumps pump together with the gas flow an oil flow which enters from the oil reservoir into the pump during each turn. The pumped oil is returned to the oil reservoir. Gases with entrained oil vapours are delivered to the pump's outlet. Thus generally an internally or externally connected oil separator or gas filter is connected downstream of the outlet of such pumps, where in this oil separator the by far greater part of the entrained oil vapours are separated from the gas flow.
DESCRIPTION OF THE INVENTION
It is known to return the oil which is separated in the gas filter back through the inlet of the pump. The oil returned back to the suction side of the pump impairs the ultimate pressure; moreover, there exists the danger of unwanted backstreaming of oil into the connected recipient, which may lead to faults in the processes being run in the recipient.
In another solution, the oil separated in the gas filter is returned directly to the oil sump of the pump. This kind of oil return is only possible if an auxiliary pump is present, or--which is generally not the case--the gas filter is arranged so far above the pump chamber that the oil flows--owing to its gravitational force--back into the oil sump.
From DE-B-10 98 150 a rotary piston pump vacuum pump is known where an oil separator follows at its outlet. The oil separator is designed as a cyclone. Moreover, the known vacuum pump has a gas ballast facility which comprises a gas channel with a valve. A side channel which leads to the oil separator opens into said gas channel. The side channel has the effect that the oil mist contained in the chamber of the oil separator is partly sucked in as gas ballast into the work space of the pump. If aggressive gases are pumped with this pump, then there exists the disadvantage that these enter the pump chamber of the pump once more. Moreover, the side channel does not serve the purpose of returning the oil which has been separated in the oil separating chamber.
Also the contents of GB-A-863 162 belong to the state-of-the-art. This document lays open a gas compressor. An oil separator from which oil might be returned is not present.
It is the task of the present invention to create a vacuum pump having the aforementioned characteristics in which the danger of returning aggressive gases back to the pump chamber no longer exists and in which the means for returning the oil from the oil separator are designed to be especially simple.
In the case of this solution according to the present invention, only the oil from the oil separator returns via the gas ballast facility back into the pump chamber of the vacuum pump. Aggressive gases which are pumped into the oil separator are not again returned to the pump chamber of the vacuum pump.
A different solution to the task of the present invention, which may only be implemented in the case of two-stage vacuum pumps, is that the duct which serves the purpose of returning the separated oil opens into an intermediate channel which links the outlet of the high vacuum stage to the inlet of the fore-vacuum stage.
In the case of both proposed solutions the duct which serves the purpose of returning the oil opens at a point in the vacuum pump, where during operation of the vacuum pump a low pressure prevails which ensures pumping of the oil from the oil separator to the pump. The influence on the ultimate pressure characteristic is negligible. The danger of oil backs
REFERENCES:
patent: 4204815 (1980-05-01), LeBlanc
patent: 4268230 (1981-05-01), Bassan
Arndt Lutz
Kaiser Winfried
Muller Peter
Leybold Aktiengesellschaft
Vrablik John J.
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