Turbine pump with a stator stage integrated with a spacer ring

Abstract: A turbine pump has a transition chamber (9), which separates a low-pressure section (1B) from a high-pressure section (1A) and into which an additional inlet port (5) opens. The chamber (9) is defined by a stator stage (10) consisting of a disc (11) with a peripheral edge (12), integral with said disc (11) and forming a spacer ring integrated into the stator stage, and with radial blades (17) joined with the disc (11) at both ends.

Description: The present invention refers to high-vacuum pumps, and more particularly it concerns a turbine pump, in particular a turbomolecular pump, of the kind comprising an intermediate inlet for a gas flowing in counter-current flow to the operating direction of the pump. Pumps with such an intermediate inlet are employed e.g. in leak detectors, where a test gas, usually helium, which enters a vessel to be tested or escapes therefrom because of leaks, is led to the intermediate inlet of the pump, wherefrom it flows in counter-current flow towards a gas detector, usually a mass spectrometer, connected to the low-pressure side of the pump. Examples of such pumps are disclosed in US-A 4,472,962, US-A 6, 030,189, US-A 4,550,593 and US-A 5,585,548. US-A 4,472,962 discloses a pump in which the intermediate inlet opens into an annular channel, formed in the pump housing and surrounding the rotor of an intermediate pumping stage. That pump requires a relatively high vacuum in the area where the test gas enters, e. g. a vacuum of the order of 10-5 mbar (1 mPa). US-A 6,030,189 discloses a pump with an intermediate inlet for a test gas opening into an annular channel surrounding a group of co-operating stator and rotor stages. The stator stages are clamped between spacer rings and spacer rings located in correspondence with the annular channel have high-conductance openings connecting the intermediate inlet to the pumping chamber. US-A 4,550,593 discloses a pump where the intermediate inlet opens into a transition chamber separating a group of low-pressure stages and a group of high-pressure stages. The intermediate chamber is defined by two rotor stages. The stator stages are clamped between spacer rings, and the spacer rings located in correspondence of the intermediate inlet have high conductance openings for admitting the test gas. US-A 5,585,548, upon which the preamble of claim 1 is based, discloses a pump in which the intermediate inlet opens into a transition chamber separating a group of low-pressure stages and a group of high-pressure stages. The chamber is limited upwards (low-pressure side) by a rotor impeller and downwards by a stator stage comprising a stationary disc, defining with the rotor shaft a constriction intended for providing a high detection sensitivity without any danger of the pressure in the test gas detector increasing to inadmissible levels. In an embodiment, the disc has a set of axially projecting strips. This pump does not require a relatively high vacuum in the inlet area of the test gas, where it tolerates pressures of the order of 0.1 mbar (10 Pa). DE-A 179 37 393 discloses a stator stage integrated with a spacer ring for a turbine pumps. The stator blades extend between the spacer ring and an internal ring, allowing mounting the stator around a rotor shaft, and are integrally formed therewith. The blades are so arranged that gaps exist between adjacent blades. DE-A 39 22 782 discloses another molecular pump with stator stages captured between adjacent spacer rings. The aim of the invention is to provide a pump, in particular with an intermediate inlet, exhibiting improved performance in terms of pumping efficiency, compression ratio and conductance of the test gas, such as helium, in order to increase the maximum pressure that can be tolerated at the intermediate port through which the test gas enters. This aim is achieved in that at least the stator stage defining the transition chamber has radial blades that are arranged at an acute angle relative to the surface of disc such that adjacent radial blades overlap with the interposition of separation channels that pass through the whole thickness of disc, so as to make the stage optically opaque in axial direction. The above and other aims of the invention will become apparent from the following description of a preferred embodiment, given by way of non limiting example and shown in the accompanying drawings, in which: Fig. 1 is a schematical cross-sectional view of a pump with an intermediate inlet, according to the invention; Fig. 2 is a perspective view of the stator stage located in correspondence with the intermediate inlet; Fig. 3 is a plan view of the stator stage shown in Fig. 2; Fig. 4 is a plan view showing the stator stage divided into two halves for allowing mounting on the rotor; Fig. 5 is a cross-sectional view according to a plane passing through line A-A in Fig. 2; and Fig. 6 is a cross-sectional view according to a plane passing through line B-B in Fig. 2. In Fig. 1, the turbomolecular pump in accordance with the invention, generally designated 1, has a housing 2 into which open: a low-pressure inlet that, in the application of the pump to a leak detector, is connected to the test gas detector, not shown; a high-pressure outlet 4, communicating with the atmosphere or a fore pump; and an intermediate inlet 5 for the test gas, intended to flow in counter-current flow towards the detector. The pump has multiple stages, each associated with a rotor impeller 6, carried by a shaft 7. Rotor impellers 6 cooperate with stator stages 8 arranged along the walls of housing 2. Intermediate inlet 5 opens into a transition chamber 9, separating a high-pressure pump section (the lower section), from a low-pressure pump section (the upper one). The two sections are designated 1A and 1B, respectively. Section 1B is the section operating in counter-current flow in the application to a leak detector. No rotor impeller is provided in correspondence with transition chamber 9 (hence the pump has one pumping stage less than conventional pumps), and the chamber is limited upwards by a stator stage 10 forming one of the novel features of the present invention. The remaining stator stages 8, as well as rotor impellers 6, are of conventional type. Referring to Figs. 2 to 6, stator stage 10 is a substantially cup-like member, comprising a disc 11 with a central bore 16 where rotor shaft 7 passes, and a side wall 12, integral with disc 11 and acting as a spacer ring. Such a structure allows a precise location of stator stage 10 within chamber 9. As shown in Fig. 4, stator stage 10 in effect comprises two identical portions 10', 10" that can be separated to allow mounting the stator about rotor shaft 7. The two portions are obtained by cutting stator stage 10 along a diameter at the end of the manufacture. In Fig. 4, the elements in the two portions are designated by reference numerals with a prime or a double prime, respectively. Side wall 12 axially projects from disc 11 at both sides thereof and, as shown in Fig. 1, its total height substantially corresponds with the spacing between the last stator stage 8 of low pressure section 1B and the first stator stage 8 of high pressure section 1A. Portion 12A that, when the stator is mounted, is located on the side of high pressure pump section 1A, is higher than the other portion and has a high-conductance opening 13 formed therein, which communicates with intermediate inlet 5. Portion 12B located on the low pressure side has instead an annular groove 14 housing a resilient ring 15 arranged to keep the two halves 10', 10" of stator stage 10 in contact. A plurality of radial blades 17 is arranged along a peripheral portion of disc 11. Said blades are regularly spaced along the circumference of disc 11 and are separated by channels 18 passing through the whole thickness of disc 11. Blades 17 are joined with disc 11 not only at their radially inner edges, but also at their radially outer edges, where they end in correspondence of spacer ring 12. Also the corresponding separation channels 18 are thus closed at both ends. As clearly shown in Fig. 6, blades 17 form a very narrow angle with the plane of disc 11, and adjacent blades 17 overlap, leaving very narrow channels therebetween, so that the stage is made optically opaque in axial direction. In the embodiment shown, with eighteen blades, the angle is of about 10° and the separation channels have a constant thickness s of about 1 mm in radial direction. Those values allow attaining, at stator stage 10, a compression ratio of 2 for nitrogen and maintaining a molecular gas flow in the direction from inlet 3 to outlet 4 up to pressures as high as about 100 mtorr (13,33 Pa) - that is the pump can tolerate a pressure of 13,33 Pa in the transition chamber - without losing the compression capacity of the upper stages. It is evident that the above description is given only by way of non limiting example and that changes and modifications are possible without departing from the scope of the claims. In particular, the pump could include a plurality of stator stages made like stage 10.

Claims: Turbine pump with a transition chamber (9) at an intermediate pressure separating a low-pressure section (1B) from a high-pressure section (1A) and with an additional inlet (5) opening into said chamber (9), said sections comprising multiple rotor stages (6) carried by a shaft (7) and multiple stator stages (8, 10) comprising each a bladed disc (11) surrounding the rotor shaft (7), said transition chamber (9) being defined on one side by a stator stage (10), characterised in that at least the stator stage (10) defining said transition chamber (9) has radial blades (17) that are arranged at an acute angle relative to the surface of the disc (11) such that adjacent radial blades (17) overlap so as to make the stage optically opaque in axial direction, and are separated by separation channels (18) that pass through the whole thickness of the disc (11). A pump according to claim 1, characterised in that said acute angle is of the order of 10°. A pump according to claim 1 or 2, characterised in that said separation channels (18) have a radially constant and defined thickness (s). A pump according to claim 3, characterised in that said thickness (s) is in the range 0.5 to 2 mm, and preferably is of the order of 1 mm. A pump according to any of claims 1 to 9, characterised in that said radial blades ( 17) of said stator stage (10) are joined at a radially outer edge with a spacer ring (12) of the disc (11) and are joined at a radially inner edge of the disc (11). A pump according to claim 5, characterised in that said spacer ring (12) axially projects from said disc (11) in opposite directions and to different extents in both directions, and has, in a portion (12A) projecting to a greater extent, a high-conductance opening (13) communicating with said additional inlet (5). A pump according to claim 6, characterised in that said portion (12A) projecting to a greater extent is the portion located on the side of the high pressure section (1A). A pump according to claims 6 or 7, characterised in that it comprises at least a further stator stage integrated with a spacer ring. A pump according to any preceding claim, characterised in that said stator stage(s) (10) integrated with a spacer ring (12) is divided into two identical portions (10', 10") along a diametrical line, to allow mounting the stage (10) about the rotor shaft (7), and said spacer ring (12) has, in a portion (12B) projecting to a lesser extent, an annular groove (14) housing a resilient ring (15) arranged to keep the two halves (10', 10") of stator stage (10) in contact.

Inventors: CARBONERI ROBERTO, GIORS SILVIO, CARBONERI, ROBERTO, GIORS, SILVIO
Applicants: VARIAN SPA, VARIAN S.P.A.
Application year: 2001
Main classification: F04D19
IPC codes: F04D19, F04D29