Flowserve 800 Piston Lift Check Valve - Manual (Page 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 800 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)