Flowserve 1888 Double-Disc Gate Valve - Manual (Page 16)

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9.0 MAINTENANCE INSTRUCTIONS (Continued)
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. Abide by the following procedure:
(a) The disc should be lapped on a flat, grooved lapping plate or, if available, a lapping machine can 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 Troubleshooting
A. EXCESSIVE TEE HANDLE (175) EFFORT OR BINDING
Excessive tee handle effort or binding indicates that the stem (025) either needs to be lubricated or
the flange gland (133) is too tight as a result of the gland nuts being tightened unevenly. Lubrication
(Paragraph 7.3) should be checked at regular intervals of six months. To evenly tighten the gland nuts,they
should be loosened and retightened in an alternating fashion.
B. LEAKAGE BETWEEN THE DISC (004) AND SEAT RING (013)
Leakage between the disc (004) and seat ring (013) could be an indication that foreign matter is on
the seating surfaces, in which case the valve should be opened and closed ONE TIME in an attempt
to dislodge any matter that might have inadvertently lodged there. DO NOT OPEN AND CLOSE THE VALVE
MORE THAN ONCE, SINCE THIS COULD 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 Paragraph 9.3.)
C. LEAKAGE AROUND STEM (025) AND THROUGH THE STUFFING BOX
Worn packing (110, 112). Replace the packing following the instructions set forth in Paragraph 9.2
in this section.
1888-lb. Double-Disc Gate Valve FCD ADENIM0001-00