MAINTENANCE

LAPPING PROCEDURE

1. Mount the valve body in a vise with seat ring installed and facing upward.
   
   
2. Apply a small amount of 240 grit or finer abrasive lapping compound to the radius of the disc.
   
   
3. Carefully lower the disc into its seating position on the seat ring. (It may be helpful to thread a spare connector into the back end of the disc to get a better grip for lapping.) Allow the weight of the disc to hold it in contact with the seat ring as you use a light back and forth twisting motion (see illustration).
   
   
4. Continue this oscillating motion while also allowing the disc to gradually rotate at least 360 degrees.
   
   
5. On discs with a spherical radius (all except 3/4” valves), the disc should be rotated at various angles off the main axis of the valve. This preserves the radius while letting all points of the disc contact all points around the seat ring angle.
   
   
6. Most 3/4” valves have discs with an angle rather than the spherical radius of the larger sizes. To lap these valves, it is necessary to guide the disc and keep it in line with the bore of the body. This can be done by making a brass bushing that will fit the disc and body and will guide the disc during lapping.
   
   
7. Occasionally lift the disc to allow new compound to find it’s way onto the seating area. Never let the compound dry out, as this can cause galling. If the compound has broken down or dried out, pull out the disc, clean, and apply more compound. Repeat the lapping and cleaning until you see a solid light gray area all around both parts, indicating that they are in complete contact with each other. As you approach completion, let the compound break down into a finer grit for final lapping. As usual with any skill, lapping will get easier and faster each time you do it.
   
   
8. On repairs done in our shop, we also go one step further by checking with “Prussian Blue” for complete contact of the two parts. Remember, the better the contact between these parts, the better the valve will shut off, and the longer it will give trouble free performance.
   
   
9. Once the lapping is complete, thoroughly clean all parts of excess abrasive compound and flush out the body as much as possible. Set aside the clean disc in preparation for reassembly. Remember that even though the seat and disc are made of very hard materials, accidentally bumping with a harder material can damage the seating area, spoiling your freshly lapped surfaces.
   
   
10. Proceed with reassembly per previous instructions.