Flowserve Cast Flex Wedge Gate Valve - Manual (Page 17)

Cast Flex Wedge Gate Valves FCD ADENIM0010-02
17
5.0 VALVE MAINTENANCE
(Continued)
5.6 Refinishing Sealing Surfaces
Minor discontinuities in both the disc and seat sealing surfaces, which may cause leakage, can, in many cases, be
removed by lapping. Major defects such as cracks or deep gouges will generally require replacement of the part.
NOTE: Lapping is a polishing process in which a sealing surface is ground with an abrasive held in place by a special
fixture. The abrasive is commonly found in paste form or bonded to a paper backing. Detailed instructions on the use
of lapping abrasives and fixtures, normally supplied with such equipment, should be adhered to. In addition to
following lapping materials manufacturers' recommendations, the following precautions should be observed when
refinishing sealing surfaces in Anchor/Darling flex-wedge valves:
1. Both seat and disc sealing surface angles must be maintained with a great degree of accuracy. Extreme care must
be taken to lap these surfaces evenly and assure their flatness.
2. Anchor/Darling flex-wedge valves are supplied with a crowned sealing surface on the seat in order to provide
precise seat width and tight sealing. Lapping of the seat will cause the sealing band width to be significantly
increased. Subsequent to all seat refinishing operations, the seat width must be checked against the dimensions
supplied in Table 2 and reduced if necessary. Failure to do so may create leakage problems, particularly at lower
pressures.
Table 2