GB2128693A - Labyrinth seal - Google Patents

Abstract

In order to reduce the destabilising effects resulting from a non-uniform pressure distribution in the circumferential seal cavities (3) of a labyrinth seal (2), each cavity (3) is divided circumferentially into compartments (4) by a series of radial impeding walls (5). The compartments (4) of each cavity (3) are all connected by radial ducts (6) to an outer circumferential manifold (7). <IMAGE>

Description

SPECIFICATION Labyrinth seal This invention relates to a labyrinth seal in which, by the maintenance of a uniform pressure distribution in each circumferential seal cavity of the seal, there is achieved a reduction in the destabilising effects which can compromise the proper operation of, for example, high-performance turbo machines.

A labyrinth seal for a rotary shaft is known to comprise a succession of circumferential teeth which face the shaft so as to define, between them and the shaft, circumferential cavities which trap the fluid in such a manner as to limittothe maximum extent the flow offluid between the upstream side and the downstream side ofthe seal. However, rotation ofthe shaft also causes rotation of the fluid located in each circumferential cavity of the labyrinth seal, thereby creating eccentricity between the rotating part and the seal, especially if the shaft becomes displaced for any reason.The circumferential motion ofthefluid in the cavity leads to a non-uniform circumferential distribution ofthe pressure in each labyrinth cavity, which tends to amplify the shaft displacement and give rise to gradually increasing shaft vibrations. The result is therefore a self-exciting destabilising effect which car.

influence the stability of the rotary shaft to a determining extent.

According to the present invention, there is provided a labyrinth seal for a rotary shaft, comprising a succession of circumferential teeth facing the shaft and defining between them and the shaft, circumferential cavities arranged to trap fluid in such a mannerasto limittheflowoffluid between the upstream side and the downstream side of the seal, there being disposed in each of the circumferential cavities ofthe seal a plurality of radial impeding walls which circumferentially divide the cavity into compartments.

In accordance with the invention, there is present, in each circumferential cavity of the labyrinth seal, a plurality of radial impeding walls which circumferentially divide the cavity into compartments. By this means, the circumferential velocity ofthefluid in each compartment is on the average very low, and therefore in practice there can be an almost symmetrical circumferential distribution ofthe circumferential velocity ofthe fluid in each seal cavity, this resulting in an analogous pressure distribution.

In orderto ensure that the pressure distribution in each labyrinth cavity is effectively circumferentially symmetrical so that no destabilising effect occurs, whatever the position of the shaft relative to the seal, according to a preferred embodiment of the invention the individual compartments of each circumferential cavity ofthe labyrinth seal are connected by radial ducts to an outer circumferential manifold.

In this respect, by connecting together all the compartments of a labyrinth seal cavity and thus balancing the pressure in the compartments, the circumferential manifold eliminates any tendency for a non-uniform pressure distribution to arise in the individual seal cavities as a result of any shaft displacement, and thus makes itimpossiblefor large-amplitude damaging vibrations to be induced in the shaft by the labyrinth seal.

For a better understanding of the invention, referpence will now be made, byway of example, to the drawings in which: Figure lisa partly-sectional side view of a labyrinth seal for a rotary shaft, in accordance with the invention; Figure 2 is a section through the seal along the line AAofFigure 1; and Figure 3 is a section through the seal along the line BB of Figure 1.

The Figures show a rotary shaft 1 and a labyrinth seal 2, which seal comprises a succession of circumferential cavities 3i (i= 1 n) facing the shaft 1.

Each seal cavity 3i is divided circumferentially into a numberofcompartments4i(i=1 n) by . .. n) by radial impeding walls 5i (i=l ...... n), and all the compartments 4i of each cavity are connected by correspondingradialducts6i(i=l n) to a single outer circumferential manifold 7i (i= 1 n) (see specifically Figure 3).

1. A labyrinth seal for a rotary shaft, comprising a succession of circumferential teeth facing the shaft and defining between them and the shaft, circumferential cavities arranged to trap fluid in such a manner asto limitthe flow of fluid between the upstream side and the downstream side of the seal, there being disposed in each of the circumferential cavities of the seal a plurality of radial impeding walls which circumferentially divide the cavity into compartments.

2. A labyrinth seal as claimed in claim 1, wherein the individual compartments of each circumferential seal cavity are connected by radial ducts to an outer circumferential manifold.

3. A labyrinth seal substantially as herein before described with reference to, and as shown in, the drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (3)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Labyrinth seal This invention relates to a labyrinth seal in which, by the maintenance of a uniform pressure distribution in each circumferential seal cavity of the seal, there is achieved a reduction in the destabilising effects which can compromise the proper operation of, for example, high-performance turbo machines. A labyrinth seal for a rotary shaft is known to comprise a succession of circumferential teeth which face the shaft so as to define, between them and the shaft, circumferential cavities which trap the fluid in such a manner as to limittothe maximum extent the flow offluid between the upstream side and the downstream side ofthe seal. However, rotation ofthe shaft also causes rotation of the fluid located in each circumferential cavity of the labyrinth seal, thereby creating eccentricity between the rotating part and the seal, especially if the shaft becomes displaced for any reason.The circumferential motion ofthefluid in the cavity leads to a non-uniform circumferential distribution ofthe pressure in each labyrinth cavity, which tends to amplify the shaft displacement and give rise to gradually increasing shaft vibrations. The result is therefore a self-exciting destabilising effect which car. influence the stability of the rotary shaft to a determining extent. According to the present invention, there is provided a labyrinth seal for a rotary shaft, comprising a succession of circumferential teeth facing the shaft and defining between them and the shaft, circumferential cavities arranged to trap fluid in such a mannerasto limittheflowoffluid between the upstream side and the downstream side of the seal, there being disposed in each of the circumferential cavities ofthe seal a plurality of radial impeding walls which circumferentially divide the cavity into compartments. In accordance with the invention, there is present, in each circumferential cavity of the labyrinth seal, a plurality of radial impeding walls which circumferentially divide the cavity into compartments. By this means, the circumferential velocity ofthefluid in each compartment is on the average very low, and therefore in practice there can be an almost symmetrical circumferential distribution ofthe circumferential velocity ofthe fluid in each seal cavity, this resulting in an analogous pressure distribution. In orderto ensure that the pressure distribution in each labyrinth cavity is effectively circumferentially symmetrical so that no destabilising effect occurs, whatever the position of the shaft relative to the seal, according to a preferred embodiment of the invention the individual compartments of each circumferential cavity ofthe labyrinth seal are connected by radial ducts to an outer circumferential manifold. In this respect, by connecting together all the compartments of a labyrinth seal cavity and thus balancing the pressure in the compartments, the circumferential manifold eliminates any tendency for a non-uniform pressure distribution to arise in the individual seal cavities as a result of any shaft displacement, and thus makes itimpossiblefor large-amplitude damaging vibrations to be induced in the shaft by the labyrinth seal. For a better understanding of the invention, referpence will now be made, byway of example, to the drawings in which: Figure lisa partly-sectional side view of a labyrinth seal for a rotary shaft, in accordance with the invention; Figure 2 is a section through the seal along the line AAofFigure 1; and Figure 3 is a section through the seal along the line BB of Figure 1. The Figures show a rotary shaft 1 and a labyrinth seal 2, which seal comprises a succession of circumferential cavities 3i (i= 1 n) facing the shaft 1. Each seal cavity 3i is divided circumferentially into a numberofcompartments4i(i=1 n) by . .. n) by radial impeding walls 5i (i=l ...... n), and all the compartments 4i of each cavity are connected by correspondingradialducts6i(i=l n) to a single outer circumferential manifold 7i (i= 1 n) (see specifically Figure 3). CLAIMS

1. A labyrinth seal for a rotary shaft, comprising a succession of circumferential teeth facing the shaft and defining between them and the shaft, circumferential cavities arranged to trap fluid in such a manner asto limitthe flow of fluid between the upstream side and the downstream side of the seal, there being disposed in each of the circumferential cavities of the seal a plurality of radial impeding walls which circumferentially divide the cavity into compartments.

2. A labyrinth seal as claimed in claim 1, wherein the individual compartments of each circumferential seal cavity are connected by radial ducts to an outer circumferential manifold.

3. A labyrinth seal substantially as herein before described with reference to, and as shown in, the drawings.