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Body-Bonnet Assembly
a) Inspect the bonnet bolts to ensure that it is not damaged. Any damaged bolts should be replaced.
b) Place the entire bonnet assembly onto the valve body, taking care not to damage the disc.
c) Tighten the bolts in the crossover method like a shown in Fig. 1.
d) Test the valve as required, and place the valve back into service.
8.3 Metal to Metal Sealing
If the seat examination shows only small defects, it is possible to renew seat sealing surface lapping the seat with the
special tool and immediate action is necessary.
To repair the disc seat or body seat, the valve must be removed from pipe line, then use the following procedure:
a) Using a thick polishing paste, alternately turn clockwise and counterclockwise about 90°, softly pressing. Lift up often
and turn the tool, changing its contact position with seat. Go on with lapping until any defect disappears, adding, polishing
paste if necessary. And then clean the seat and repeat treatment using a thinner polishing paste.
b) Remove lapping tool and clean carefully the seat, using a washing agent.
c) After lapping, it is recommended that the surface of the seat and disc be checked for proper contact using marking
blue. Coat the body seats with marking blue, and tightly press the disc into the body seats by hand. Remove the disc,
and examine to make sure there is continuous contact between the sealing surfaces of the disc and body seat.
d) If such contact is not homogen, repeat steps a, b and c until excellent contact is obtained. If disk defect is greater, a
trial to repair it can be performed metal cutting the sealing surface of disk on a lathe. After metal cutting perform lapping
as indicated above.
Doc. No: FRM.65
Rev. No: 00 Rev. Date: 01.06.2015
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