Flowserve 800 Globe Valve - Manual (Page 11)

800 Globe Valves FCD ADENIM0008-00
11
9.0 Maintenance Instructions
(Continued)
9.3 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 surface may be removed by re-machining the surface to remove
a few thousandths of material. Major defects will generally require replacement of the disc.
(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 globe valves, the sealing surface angles on both the disc and seat ring
must be kept within close tolerance (30
°
[+½
°
] for the seat - 29
°
[-½
°
] for the disc) it is important when lapping
to use fixtures that will maintain these angles. 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.
9.4 Troubleshooting
A. Excessive Handwheel (136) Effort or Binding
Excessive handwheel effort or binding would indicate that the stem threads (024) or yoke bushing
(016) needs to be lubricated; or the flange gland (133) is too tight as a result of the gland nuts being
tightened unevenly. Lubrication (Para. 7.3) should be checked at regular intervals of 6-months. To
tighten the gland nuts evenly, they should be loosened and retightened in even increments while
checking concentricity between the stem and gland bore.
B. Leakage Between the Disc (004) and Seat (013)
This could be an indication that there is foreign matter on the seating surfaces in which case the valve
should be opened and closed ONE TIME in an attempt to dislodge any matter that may have
inadvertently lodged there. DO NOT OPEN AND CLOSE THE VALVE MORE THAN ONCE AS THIS
MAY TEND TO CAUSE PERMANENT DAMAGE TO THE SEATING SURFACES IF THE FOREIGN
MATTER IS SECURELY LODGED IN PLACE. Instead, disassemble the valve and remove the source
of the trouble. If no foreign matter is found, inspect the seating surfaces of the valve for signs of a
scarred or damaged seat - in which case the seating surfaces of the disc (004) and seat ring (013)
should be refinished until no visible defects remain. (Refer to Para. 9.3)
C. Leakage Around Stem (024) and thru the Stuffing Box
Worn packing (110, 112). Replace following the instructions set forth in Para. 9.2.