Rotary kinetic fluid motors or pumps – Smooth runner surface for working fluid frictional contact
Reexamination Certificate
2000-11-09
2002-04-23
Ryznic, John E. (Department: 3745)
Rotary kinetic fluid motors or pumps
Smooth runner surface for working fluid frictional contact
C415S073000
Reexamination Certificate
active
06375413
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to vacuum pumps and, more particularly, to pumps employing molecular drag mode of operation, preferably in conjunction with a regenerative mode of operation.
BACKGROUND OF THE INVENTION
Vacuum pumps and/or compressors are known which operate in a regenerative mode and in which a rotor spins at high speed, for example ten thousand revolutions/min (10,000 rpm), within a stator body and in which the rotor has a series of blades positioned in an annular array either on a peripheral edge of the rotor or alternatively on a side of the rotor at its periphery, and the stator has an annular channel within which the blades rotate having a cross sectional area greater than that of the individual blades except for a small part of the channel known as a “stripper” which has a reduced cross section providing a close clearance for the blades.
In use of such a pump, gas to be pumped enters the annular channel via an inlet positioned adjacent one end of the stripper and the gas is urged by means of the blades on the rotating rotor along the channel until it strikes the other end of the stripper and the gas is then urged through an outlet situated on that other end of the stripper. It is known that pumps/compressors employing such a mode of operation can provide a high compression ratio at relatively low flow rates. However, these pumps are best suited to pumping in continuum flow conditions and with such pumps it can be difficult to obtain a sufficiently high ultimate vacuum and pumping speed without resort to the use of an additional vacuum pump in tandem which is suited to transitional and/or molecular flow.
In our earlier European Patent Application No. 0 805 275 A, we described a vacuum pump in which a substantially higher compression could be obtained through the use of a multi-stage pumping action associated with the rotor in particular. In our earlier European Application, there was disclosed a vacuum pump of the regenerative type comprising a rotor and a stator body in which the rotor was adapted for rotation and in which the rotor had a series of blades positioned in an annular array on a side of the rotor and the stator had an annular channel within which the blades could rotate having a cross-sectional area greater than that of the individual blades except for a small part of the channel which had a reduced cross-section providing a close clearance for the blades and wherein the rotor had at least two series of blades positioned in concentric annular arrays on a side of the rotor and the stator had a corresponding number of channels within which the blades of the arrays could rotate and means were provided to link the channels to form a continuous passageway through which gas being evacuated by the pump could pass.
It was further disclosed that the pumps of the earlier European application may be employed:
i) as individual vacuum pumps in their own right,
ii) in conjunction with other vacuum pumps such as turbo molecular pumps or molecular drag pumps,
iii) as a component part of larger hybrid vacuum pumps also comprising stages of different type, for example molecular drag stages.
In particular, it was disclosed that hybrid pumps comprising a regenerative stage according to the earlier European Application together with a type of molecular drag stage, for example are known as a “Holweck” stage, were particularly beneficial.
In a Holweck stage, there is provided alternate stationary and rotating concentric hollow cylinders with a threaded upstanding flange to form a helical structure substantially extending across the gap between adjacent cylinders, the flange being attached either to a surface of a rotating or of a stationary cylinder.
It was found that such pumps, especially the regenerative/molecular drag compound pumps, were generally able to provide a higher ultimate vacuum together with a relatively higher compression ratio than that available with comparable vacuum pumps.
Nevertheless, the pumps of our prior European application can in some circumstances suffer from the disadvantage that a sufficiently higher pumping capacity cannot always be attained.
This invention is concerned with a modified design of vacuum pump in which this and other disadvantages are removed.
SUMMARY OF THE INVENTION
In accordance with the invention, there is provided a vacuum pump for pumping gas from a pump inlet to a pump outlet, comprising a rotor and a stator body in which the rotor is adapted for rotation and including at least two molecular drag stages each comprising adjacent stationary and rotating Holweck cylinders attached to the stator body and the rotor respectively and with a threaded upstanding helical flange positioned therebetween which is attached either to the stationary or to the rotating cylinder wherein the molecular drag stage closest to the pump inlet has the threaded flange on its rotating cylinder and the subsequent molecular drag stage or stages has the threaded flange on the stationary cylinder
A central feature of the invention is the presence of a threaded flange on the rotating Holweck cylinder of the first Holweck stage, ie the Holweck stage closest to the pump inlet. It is this feature—coupled with the reverse positioning of the flange in the subsequent Holweck stage—which allows the pump overall to exhibit generally superior properties with particular reference to the high pumping capacity and compression and low power consumption at higher (inlet) pressures.
In addition, it is extremely advantageous for the Holweck stages to be arranged in a radial configuration, in particular adapted so that the gas being pumped flows radially outwards from the first Holweck cylinder to a subsequent, radially arrayed Holweck cylinder or cylinders. The additional benefits of such pumps include:
i) a lower power consumption in continuum flow than with axially arranged Holweck cylinders of comparable outside diameter
ii) an ability to assemble and dis-assemble the rotor from the pump body
iii) compactness of the pump overall
The pumps of the inventions preferably also include a regenerative stage towards the outlet end of the pump such that gas being pumped enters the regenerative stage following its exhaustion for the molecular drag stages. Preferably, the regenerative stage comprises a series of blades positioned in an annular array on one or both faces of the rotor or on an edge of the rotor.
In preferred embodiments, the rotor has at least two series of blades positioned in concentric annular arrays on a face of the rotor and the stator has a corresponding number of channels in which the arrays of blade can rotate.
In such embodiments, the blades advantageously extend in a substantially axial direction. The rotor is preferably shaped such that the side on which the arrays of blades are positioned presents a substantially flat surface for receiving the arrays; usually, the flat surface will be radially orientated relative to the main axis of the rotor. Generally, the flat surface between the arrays will cooperate with corresponding annular flat surfaces on the stator to provide a face seal between the arrays.
If appropriate, the invention also incorporates the possibility of there being at least two arrays of blades on each side of the rotor, each side preferably presenting a substantially flat surface for receiving the arrays.
In preferred embodiments, the rotor has at least five or six arrays on one or both sides thereof.
The individual blades of each array will generally be arranged radially in relation to the rotor. Each blade may be substantially flat or, at least in part, may be arcuate with the concave side pointing in the direction of travel of the rotor; the latter is preferred to assist in pumping efficiency.
It is preferred for the blade edges which co-operate with the stripper to have a flat surface rather than pointed or radiused ends to improve the “sealing” between the blades and the stripper.
Typically, each array may comprise at least about ten, preferably at least fifty blades. Generally, there may usefully be up to abo
Ryznic John E.
The BOC Group plc
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