Flowserve 1888 Parallel Slide Gate Valve - Manual (Page 11)

9.3 Lapping Procedure
After the valve has been disassembled, a visual inspection of the seating
surfaces of the Discs (004) and Seat Rings (013) can be made to determine
if lapping is necessary to remove any minor scratches on these parts prior
to assembling the valve. The following procedure should be followed:
(a) The disc should be lapped on a flat grooved lapping plate, or if
available, a lapping machine may be used. A "medium" grade
lapping compound should be used for the first and successive
applications and a "fine" grade compound similar to "Clover A Grit
No. 280" should be used for the final lapping process.
(b) If it is necessary to lap the face of the seat ring, a standard lapping
plate can be used of approximately the same diameter as the disc.
9.4 Trouble Shooting
A. EXCESSIVE TEE HANDLE (175) EFFORT OR BINDING
Excessive tee handle effort or binding would indicate that the Stem
(025) either needs to be lubricated; or the Gland Flange (133) is too
tight as a result of the Gland Stud Nuts (234) being tightened
unevenly. Lubrication (Para. 7.3) should be checked at regular
intervals of 6-months. To tighten the Gland Stud Nuts evenly, they
should be loosened and retightened in an alternating fashion.
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 CAUSE PERMANENT
DAMAGE TO THE SEATING SURFACES IF THE FOREIGN
MATTER IS SECURELY LODGED IN PLACE. Instead,
disassemble the valve and remove the sources 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 lapped
until no visible defects remain. (Refer to Para. 9.3)
C. LEAKAGE AROUND STEM (025) AND THRU THE STUFFING BOX
Worn Packing (110, 112). Replace the packing following the
instructions set forth in Para. 9.2.