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XIV. Maintenance Instructions (Cont.)
squarely on the flat surface and avoid rocking the lap, which
will cause rounding of the seat.
D. Lapped Nozzle Seat Widths
A wide nozzle seat will induce leakage, especially in the
smaller-orifice, lower-pressure valves. For this reason, the
seat of valves other than O-Ring valves should be as narrow
as practical. Since the seat must be wide enough to carry
the bearing load imposed upon it by the pressure force, the
higher pressure valves must have wider seats than the lower
pressure valves. The nozzle seat width should conform to the
measurements in Table 3 and Table 4.
To measure the seat width, use a Model S1-34-35-37 Bausch
and Lomb Optical Co. measuring magnifier or an equivalent
seven-power glass with a 3/4" (19.05 mm) scale showing
graduations of 0.005" (0.13 mm). Figure 19a and 19b illustrate
the use of this tool in measuring the nozzle seat width. If
additional lighting is required for measuring, use a gooseneck
flashlight similar to the Type A Lamp Assembly (Standard
Molding Corp.), or equivalent.
E. Lapping Disc Seats
Use a ring lap or lapping plate to lap the disc in a circular
motion, applying uniform pressure and slowly rotating the disc
or lap.
•
Apply 1000 lapping compound (see Table 17 in Lapping
Figure 19a: Measuring Magnifier
32 | BHGE
Tools Section (Section XXIII.C). Lap disc to a polish finish.
•
Remove lapping compound completely from Disc and Disc
Holder.
Measuring
Magni er
Nozzle
Figure 19: Measuring Magnifier
Figure 19b: Magnifier Details
© 2019 Baker Hughes, a GE company. All Rights Reserved.
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