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 18
in Lapping Tools Section XXIII.C. Lap disc to a
polish finish.
• Remove lapping compound completely from Disc
and Disc Holder.
F. Precautions and Hints for
Lapping Seats
To ensure a quality lapping process, observe the
following precautions and guidelines:
Keep work materials clean. Always use a fresh
lap. If signs of wear (out of flatness) are evident,
recondition the lap.
Apply a very thin layer of lapping compound to the
lap to prevent rounding off the edges of the seat.
Keep the lap squarely on the flat surface, and avoid
rocking the lap, which causes rounding of the seat.
When lapping, keep a firm grip on the lapped part to
prevent dropping it and damaging the seat.
Lap in a circular motion while applying a uniform
pressure. Slowly rotate the lap to evenly distribute
the lapping compound. Wipe off the old compound
and replace it with new compound frequently. Apply
more pressure to speed the cutting action of the
compound. To check the seating surfaces, remove
all compound from the seat and the lap. Then, shine
the seat with the same lap using the lapping method
as described above. Low sections on the seating
surface show up as shadow in contrast to the shiny
portion. If shadows are present, further lapping is
necessary. Only laps known to be flat can be used.
It should take only a few minutes to remove the
shadows.
When lapping is complete, any lines appearing
as cross-scratches can be removed by rotating
the lap on its axis (which has been wiped clean of
compound) on the seat. Thoroughly clean the lapped
seat using lint free cloth and a cleansing fluid.
ATTENTION!
Before assembly, grind the contact surfaces of the
nozzle and O-Ring retainer to provide metal-to-
metal seat tightness in the event of O-Ring failure.
G. Reconditioning of Laps
Ring laps are reconditioned by lapping them on a flat
lapping plate in a figure-eight motion (Figure 37). To
ensure the best results, recondition the ring laps after
each use. Use an optical flat to check the quality of
the lap.
Nozzle laps must be re-machined to recondition the
lapping surfaces. Place the nozzle lap in a lathe
between centers (Figure 38). The surfaces marked
A and B must be running concentric.
Lapping Plate
Ring Lap
Figure 37: Lapping Pattern
Lathe Center
Lathe Center
A
C
D
B
85°
90°
Figure 38: Nozzle Lap in a Lathe
XIV. Maintenance Instructions (Cont.)
44 |
Baker Hughes
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