CA1249616A - Labyrinth seal - Google Patents

Abstract

IMPROVED LABYRINTH SEAL
ABSTRACT OF THE DISCLOSURE
An improved labyrinth seal for reducing the destabilising effects determined by non-uniform pressure distribution in the circumferential seal cavities, in which each cavity is divided circumferentially into compartments by a series of radial impeding walls. Said compartments of each cavity are all connected by radial ducts to an outer circumferential manifold.

Description

124~i16 This invention relates to improvements in a labyrinth seal which by maintaining uniform pressure distribution in each circumferential seal cavity considerably reduces the destabilising effects which can compromise proper operation of high-performance turbo machines.

A labyrinth seal for a rotary shaft is known to comprise a succession of circumferential teeth which face the shaft to define, between them and the shaft, circumferential cavities which trap the fluid in such a manner as to limit to a maximum the flow of fluid between the upstream side and the downstream side of the seal.

However, the shaft rotation also causes rotation of the fluid located in each circumferential cavity of the labyrinth seal, and, especially if the shaft becomes displaced for any reason, so creating eccentricity between the rotating part and the seal, the circumferential motion of the fluid in the cavity leads to non-uniform circumferen-tial distribution of the 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 can influence the stability of the rotary shaft to a determining extent.

The object of the present invention is to obviate the aforesaid drawback, and to provide a labyrinth seal in which the destabilising effect typical of a conventional labyrinth seal does not occur.

In meeting this and other objects, the present invention provides a labyrinth seal for a rotary shaft, comprising a succession of circumferential teeth facing the shaft and 1i~4~3616 - la -defining, between them and the shaft, circumferential cavities arranged to trap fluid in such a manner as to limit the flow of fluid between the upstream side and the down-stream side of the seal, there being disposed in each circumferential cavity a plurality of radial impeding walls which circumferentially divide the cavity into compartments, and the individual compartments of each circumferential cavity being connected by radial ducts to an outer circum-ferential manifold.
As noted, one characteristic of the present invention is the disposition, in each circumferential cavity of the labyrinth seal of a sufficient number of radial impeding '3616 walls which circumferentially divide said cavity into ~ompartments.
By this means, the c;rcum~erential velocity of the fluid in each compartment is on the average very iow, and there is therefore in practice a]m~st sy~metrica] circumferential distribution of the circumferential velocity of the fluid in each seal cavity, this resulting in analo~ous pressure distribution.
In order to ensure that the pressure distribution in each lab)rrinth cavity is e~feotively always circumferentially syr~netrical so that no destabilising effect ever occurs, whatever the positioll of the sha~ rela~ive to the seal, accordin~ to a furtller charaeteris~ic of the invention the individual compartments of each circumferential cavity of the labyrinth seal are connected by radial ducts to an où~er c;rcumferential manifold.
~n this respect, by connecting together all the compartmerts of a labyrinth seal cavity and thus balancing the pressure in said compartments, said circumferential rnanifold eliminates any tendency for non-uniform pressure distribution to arise in the individual seal cavities as a result of any shaft displacement, and thus makes it impossible for large-arnplitude damagin~ vibrations to be induced in the shaft by the labyrinth seal.
The inven~ion is described in detail hereinafter with reference to the accompanying drawin~ which illustrate a preferred embodiment by way of non-limiting ex~mple only, in that technical or construct-ional mlodifications can be made thereto without leaving the scope of the present invention.
In said drawin~s:
Fi~ure l is a partly sectional side view of a labyrinth seal for 1~4~61.6 a rotary shaft constructed in accord~nce with the inventioni Figure 2 is a seccion through the seal on the line AA of Figure l;
Figure 3 is a section through the séal on the line ~3B of Figure ].
In the figures, the refcrence numeral 1 indicates a rotary shaft and 2 the labyrinth seal, l~hich comprises a succession of circun~-ferential ~vities 3i (i = ~,.. .....n) facing the shaft 1.
Each seal cavity 3i is divided circu1nferentially into a r.umber of comp2rtments 4i (i = l......... n) by radial impeding walls 5i t i -l...... n~, ~nd all the cGsnpartment~ ~i of ~ach ca~ity are comle~tcd 10 by corresponding radial ducts 6i ~i = l........ .n) to a single outer circ~lferential s.~nifold 7i (i = l..... n), (see specifically Figure 3).

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A labyrinth seal for a rotary shaft, comprising a succession of circumferential teeth facing the shaft and defining, between them and the shaft, cir-cumferential cavities arranged to trap fluid in such a manner as to limit the flow of fluid between the upstream side and the downstream side of the seal, there being dis-posed in each circumferential cavity a plurality of radial impeding walls which circumferentially divide the cavity into compartments, and the individual compartments of each circumferential cavity being connected by radial ducts to an outer circumferential manifold.