Flowserve 1878 Piston Check Valve - Manual (Page 9)

1878 Piston Check Valves FCD ADENIM0005-00
9
9.0 Maintenance Instructions
(Continued)
9.2 Refinishing Sealing Surfaces
Minor discontinuities in the seat sealing surface, 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.
Minor discontinuities on the valve disc sealing surfaces may be removed by remachining the surface to
remove a few thousandths of material. Major defects will generally require replacement of the part.
(NOTE: Lapping is a polishing process where 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 order to maintain seat tightness in piston check valves, the sealing surfaces on both the disc and seat ring
must be kept within close tolerances. Flowserve does not recommend lapping the disc directly to the seat.
A good seal is dependent on line contact. Direct contact lapping will result in excessive seat widths.
Lapping equipment for the series 1878 piston lift check valve seat is available through Flowserve. Contact
your nearest Flowserve representative for information.
9.3 Reassembly
9.3.1 First, all dirt, scale and foreign matter should be removed from inside the valve body and bonnet.
9.3.2 Before reassembling the valve, check the seating surfaces to determine that no scratches or minor
imperfections are on the disc or seat ring. If any are evident - lap these surfaces until none are
visible. (Reference Para. 9.2)