standards / manuals / guidelines for small hydro development - AHEC

C. Gland SealsNormally two types of shaft gland seals are in use in different power stations:i) Carbon or ferrobestos segment.ii) Rubber flap type.1. Carbon or Ferrobestos Segment TypeThe seal segment s are housed in the stuffing box. Stuffing box being always in touchwith the shaft is subjected to excessive wear and tear. The overhauling of the stuffing boxbecomes necessary when it is observed that consumption of cooling water has considerablyincreased or excessive water in top cover appears to be coming. In general maintenance of theseal is required to be done annually.In the event of breakage or damage to a carbon segment it is advisable to replace thewhole set of carbon segments. In very rare case only the damaged segment is replaced caremust be taken to ensure that the axial thickness of the new segments falls within the limit sizeto ±0.002” of the existing ring to which it is to be fitted.All carbon segments and spacers are fitted to place and match marked on assembly.Whenever any part is replaced it should be ensured that match marking after final assembly isdone. Whenever reassembly of the gland seal with existing gland ring or new ring is done itis importance to ensure:b) All carbon / ferrobestos segments are carefully examined for any chipping or damage.c) All stainless steel facings are flat and square with the gland sleeve and there are notsteps at the facing joints.d) Stainless steel facing and sleeve are completely free from grease.e) Ensure proper bedding of segments with shaft sleeve.f) All segment to segment and segment to stainless steel mating surfaces are perfect.g) All garter springs are assembled to obtain even tension all around.h) Alignment of segments in the lower assembly is carefully checked with a hard woodpeg for similar device before fitting retaining pins.2. Rubber flap typeMaintenance of rubber flap type gland seal is comparatively simpler and easier. Onlyprecaution during assembly of rubber gland is jointing of the rubber seal in the proper way.The quality of rubber used plays a very important role for satisfactory performance of therubber gland. In one of the recently commissioned power stations rubber gland seal used tofail very frequently. The cause of frequent failure was discussed and analysed to be lying inthe quality of rubber. The problem after selection and use of proper quality of rubber is nowover.D. Guide vane servomotorNormally main source of trouble is rubber cup seals which need to be replaced after a fewyears. Rubber seals should be replaced during annual maintenance. It is important that all theparts are match marked before dismantling so that reassembly is correctly done.AHEC/MNRE/SHP Standards/ E&M Works – Guidelines for Operation and Maintenance of Small Hydropower Station 25