FIELD OF INVENTION
The present invention relates to an improved vapour seal for hydro generators. More particularly, the invention relates to an improved vapour seal which has high abrasion resistance, dimensional stability and is compatible with various grades of oil used in hydro generator.
BACKGROUND AND PRIOR ART OF THE INVENTION
In hydro generators, the bearings are fully immersed in oil in the bearing housing. During continuous operation, friction and churning cause increase in temperature of the oil. This in turn causes the oil to evaporate which can escape through the bearing clearances and condense on the other rotating and static parts like pole, field winding and insulation, Stator winding and insulation etc. This condensed oil along with the dust, grit etc. is detrimental to the various components actively reducing their life and may cause failures.
This assembly called the oil vapour seal has been designed and developed to arrest the escape of the oil vapours from the bearing housing during machine operation.

Early designs of oil vapour seals were of fabricated steel or cast Aluminium. Labyrinth is made by machining in the cast aluminium vapour seal. Fabricated Vapour Seals have been discontinued due to inherent problems of distortion, wear and handling. Aluminium casting Vapour Seals which were being used, have the following disadvantages:
(1) Wear and tear of labyrinth surface, thus reducing effectivity of the seal
(2) Heavy in weight (difficult to handle in limited space)
(3) If once damaged rectification process is cumbersome.
(4) Machining required
(5) Poor adjustability
OBJECTS OF THE INVENTION
Therefore it is an object of the invention to propose an improved vapour seal for hydro generators which is capable of arresting escape of oil vapours.
Another object of the invention is to propose an improved vapour seal for hydro generators which is capable of maintaining dimensional stability.

Yet another object of the invention is to propose an improved vapour seal for hydro generators which is compatible with various grades of oil used in hydro generator bearings.
A further object of the invention is to propose an improved vapour seal for hydro generators which is light in weight and can be handled easily in restricted space.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig.l - 3-dimensional- Top view of FRP oil vapour seal according to the
invention.
Fig.2 - 3-dimensional- view of reverse side of Fiber reinforced polymer
(FRP) oil vapour seal according to the invention.
Fig.3 - Isometric view of a segment of FRP oil vapour seal from inner
side according to the invention.
Fig.4 - Isometric view of another segment of FRP oil vapour seal from
outer side according to the invention.
Fig.5 - shows nitrile rubber serrations according to the invention.
Fig.6 - shows casted aluminium oil vapour seal according to prior art.
Fig.7 - shows FRP vapour seal segment assembly according to the
invention.

Fig.8 - shows sectional view of FRP vapour seal with clamping of nitrile rubber labyrinth on to the segments according to the invention.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION
In the present invention, the new oil vapour seal is made of low density material, which is light in weight and can be handled easily in restricted space. It has also a replaceable nitrile rubber labyrinth (D) which can be replaced easily in situ. The material has excellent dimensional stability and is compatible with various grades of oil used in hydro generator bearings.
As shown in Fig.l and 2, this new oil vapour seal (A) is made of fiber reinforced polymer (FRP). Since these vapour seal assemblies are very large in size, these are essentially made in segments (B) as shown in Fig. 3 and 4. To overcome the problems like heavy weight, adjustment of oil vapour seal in limited space and replacement of the serrations due to wear and tear, the FRP oil vapour seal has been designed and developed.
Fibre Reinforced Polymer Composite is a material system which consists of glass fibre reinforced in polymer resin with or without

additives and processed for final products. FRP composites have been tested and established for their excellent physical, mechanical, electrical, chemical, thermal and corrosion resistant properties. As shown in fig.5, nitrile rubber labyrinth serration (C) is used. Nitrile rubber is also of replaceable nature and can be replaced easily as and when required.
The present invented FRP oil vapour has following advantages:
1. Excellent physical, mechanical, electrical, chemical and thermal properties.
2. Other properties like corrosion resistance, easy processing, economic feasibility makes them user friendly.
3. Nitrile Rubber rings used in FRP Vapour seals have following advantages:

• Low Cost
• Excellent abrasion resistance
• High level of uniformity and dimensional stability
• Resistance to lubricating oils
• Easily replaceable

4. Light in weight
5. Highly flexible
6. Better surface finish

As shown in Fig.7, the segments (B) are joined together by bolts (1). Metallic inserts (2) have been provided in the FRP segments for this purpose. Nitrile rubber gaskets (3) are also provided in the joints for sealing. Serrations (C) are provided on the nitrile rubber ring (D) to form a labyrinth with the purpose of sealing. The rubber used for this item has been especially developed. The nitrile rubber labyrinth is fixed on to the segments by clamp plates and screws (E,F) as shown in

WE CLAIM
1. An improved vapour seal (A) for hydro generators comprising:
a plurality of segments (B) of a oil vapour seal (A) having metallic inserts (2) along with nitrile rubber gasket (3) provided in between two segments (B) for sealing and joining together by a plurality of bolts (1);
characterised in that a plurality of nitrile rubber rings (D) are fixed on to each segment (B) wherein the said nitrile rubber rings (D) are provided with serrations (C) to form a labyrinth for sealing when the segments are assembled to a oil vapour seal.
2. An improved vapour seal as claimed in claim 1, wherein the oil
vapour seal is made of glass fibre reinforced polymer.
3. An improved vapour seal as claimed in claim 1, wherein the
nitrile rubber labyrinth (D) is fixed on to the segments by clamp
and screws (E,F).

An improved vapour seal (A) for hydro generators consists of a plurality of segments of a oil vapour seal (A) having metallic inserts (2) along with nitrile rubber gasket (3) provided in between two segments (B) for sealing and joining together by a plurality of bolts. The nitrile rubber rings (D) are fixed on to each segment (B) and are provided with serrations (C) to form a labyrinth for sealing. The segments (B) are assembled to an oil vapour seal (A).