Rotary expansible chamber devices – Shaft or trunnion lubrication or sealing by diverted working...
Patent
1995-06-14
1997-06-24
Gluck, Richard E.
Rotary expansible chamber devices
Shaft or trunnion lubrication or sealing by diverted working...
F04C 1816, F04C 2700, F16C 3380, F16J 1540
Patent
active
056412800
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a rotary screw compressor for oil-free air provided with inlet channel means and outlet channel means and having at least one compression stage, each stage including at least one rotor with at least one shaft journal mounted in oil-lubricated bearing means, which shaft journal is provided with seal means between the rotor and the bearing means, which seal means include at least three frictionless seal means surrounding the shaft journal and a plurality of annular chambers surrounding the shaft journal, which frictionless seal means and annular chambers are arranged in an alternating sequence along the shaft journal.
In such compressors handling oil-free air an effective seal between the working space and the bearings is necessary in order to avoid that oil-contaminated air from the bearing housing mixes with the compressed air which can be dry or contain water. The use of direct contact mechanical seals for that purpose results in high friction losses. This is avoided with the type of seal arrangement mentioned above where frictionless seals are used together with a blocking gas, e.g. air.
Seals of this type are disclosed in U.S. Pat. No. 3,975,123 and FR-A-2 569 780.
In U.S. 3,975,123 the seal arrangement has four frictionless seals with three annular chambers between them. Blocking air is supplied to the intermediate annular chamber of the seal and flows outward towards the outermost annular chamber, from which it is withdrawn together with oil leaking from oil-lubricated bearing means. The innermost annular chamber is inactive at full load and connected to inlet pressure at part load for supply of air.
In FR-A-2 569 780 a similar seal device is applied to a two stage air compressor, but in this case only two annular chambers are present. Also in this disclosure the supply and withdrawal of blocking air is such that the blocking air flows in the outward direction.
The relative localisation of the supply and withdrawal of the blocking air in the known devices has the consequence that oil-contaminated air from the roller bearings leaks to the withdrawal channel where it is mixed with the blocking air and leaking air from the compression stage. This causes a problem in that the withdrawn air has to be purified if it is led to the compressor inlet or to the ambient atmosphere.
The object of the present invention is to attain a seal arrangement of the kind in question in which the above described problem is overcome.
SUMMARY OF THE INVENTION
According to the invention this has been achieved in that the outermost annular chamber is connected via a supply channel to a source of pressurized air, and a withdrawal channel is connected to another of the annular chambers positioned between said outermost annular chamber. Outermost means being most remote from the rotor.
By supplying the blocking air to the outermost annular chamber, the oil-contaminated air in the bearing housing is prevented from leaking along the shaft journal to the withdrawal channel. The air withdrawn from the seal means thus is free from oil.
The invention is particularly, but not exclusively intended for a multistage compressor, in which case each of the withdrawal channel means are connected to a common collecting channel communicating with the compressor inlet channel downstream variable throttling means in the inlet channel.
In an alternative embodiment when applied to a multistage compressor the withdrawal channel means at the high pressure end of the end stage are directly connected to atmosphere, whereas all the other withdrawal channel means are selectively connected to atmospheric air via shut-off valve means.
Further advantageous embodiments of the invention are specified in the dependent claims.
The invention will be further explained through the following detailed description of preferred embodiments thereof and with reference to the accompanying drawings.
FIG. 1 is a schematic section through a part of a compressor according to the invention.
FIG. 2 is a diagrammatic
REFERENCES:
patent: 1188189 (1916-06-01), Little
patent: 2331641 (1943-10-01), Walker
patent: 3265293 (1966-08-01), Schibbye
patent: 3975123 (1976-08-01), Schibbye
patent: 4329126 (1982-05-01), Nishimura
patent: 4477223 (1984-10-01), Giroux
patent: 5228298 (1993-07-01), Kun et al.
Gluck Richard E.
Svenska Rotor Maskiner AB
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